Re: CJ5 misfires at high RPM/hard acceleration
 

On Sun, 15 Jul 2007 11:42:53 -0700, matthew.nye@gmail.com wrote:

>The initial timing is 6 degrees BTDC & the dwell angle is about 31. I
>get about 16hg of steady vacuum at idle & about 7psi of fuel pressure
>at idle. The idle & even light acceleration is perfect, which makes
>me think it's not a timing chain issue, but I don't know enough about
>what the symptoms of a slipped chain would be to make that call. When
>the engine is at TDC of piston 1's compression stroke, the rotor lines
>up perfectly with cylinder 1's plug wire, which also makes me thing
>it's not necessarily a timing chain issue. Since I have changed the
>plugs & tried to further diagnose the problem, my plugs have turned
>black. This along with the popping in the exhaust obviously mean my
>mixture is either too rich, or something is going haywire with the
>timing & causing the fuel to not burn at higher RPM. One thing worth
>noting, is that I have not changed the plugs since they have been
>fouled since I replaced the faulty vacuum advance. I didn't know if
>this would make a difference or not & didn't want to risk fouling a
>new set while troubleshooting. I can literally get flames to shoot
>out of my exhaust if I abuse it enough. This happens on both sides &
>I have dual exhaust, leading me to think it's not a valve issue,
>unless I'm really unlucky & have a problem on both sides of the
>engine.
>
>The jeep is a recreational vehicle of sorts, used primarily to climb
>up & down sand dunes. The symptoms all occured when my fuel pump died
>about 2 years ago. After I replaced the pump, the engine started
>doing this. I've since replaced it again to rule that out with no
>change. I've also rebuilt the carburetor, but it was the first time I
>ever did such a thing, so it's quite possible I missed something. The
>accelerator pump works fine, the idle mixture screws are set very lean
>(since I think the mixture is too rich for some reason), the power
>valve has been replaced & I even checked it again last week & I can
>see spray coming out of the booster venturi when I rev the engine (it
>does this whether I'm moving or not). Another thing I noticed is that
>when the engine is cold, if I hold my hand in front of the exhaust, it
>sprays black fluid on me at idle. It's not a lot, but I noticed it
>when it was sprayed on my leg one day. It has no smell to it other
>than stinky exhaust, so I don't really know what this is. My coolant
>level has not changed noticeably, so I wouldn't think it to be a water
>leak, but I can't say with certainty.


A few things here. First 16 inch of vacum at a idle is LOW for a 304
with 6 BTDC timing. I have a old 79 J20 with a 360 that I have owned
for 22 years now and it pulls about 20 inches at a idle or a bit more.
Have you done a health check as far as a compression check and is
vacum steady at a idle too? Another thing, as another poster said, a
600 is really too much carb for a 304 and it may be loading up over
rich when you get going. You really want someting around a 450 is so
tops and it would give you better responce and toruq throught usuable
RPM range too. There is some mis conceptions on carbs here, bigger is
not always better. The shorty headers are not a good match at all for
that engine and its stock cam and might not be helping things either.
You might try using a smaller power valve and one that come in later
too with current carb say around 4 or 5 inches or maybe size main jets
a few sizes smaller. My gut feeling is that it is going over rich and
loading up when casrb starts to draw some. The reason it appeared
after old pump failed is because it was likely weak on pressure side
before failure which would have lowered fuel level in bowl some and in
effect leaned it out. You could also install a external pressure
regualtor and set it to 4.5 to 5 PSI as 7 PSI is a lot for a carb. You
could also try lower fuel level in bowl about 1/4 iches and see if
that help before you rejet because that will lean mixtures out. You
need to focus on fuel issues here as the plugs are the sign post here,
not the cause. One more question, what heat range plug are you
running? with headers you usually need to go a bit hotter than stock.
-----------------
TheSnoMan.com

Re: CJ5 misfires at high RPM/hard acceleration
 

Thanks for everyone's replies. Here's what I've done from your
suggestions:

- Having the gas cap off made no difference. I actually don't have
any of the emissions stuff on it, so there's no canister, just the gas
tank to the pump.
- Having the coil's + lead hooked directly to the battery made no
difference, I tried switching the leads on the ballast resistor too
first to see if I had it hooked up wrong. I may be wrong, but I think
the ballast resistor leads can go either way?
- I tried what Roy suggested with interesting results. When I
advanced the engine to 10 or 15 degrees, it would run noticeably
better, but not perfect. I could actually get the secondaries to open
up on the carb before it crapped out, which I haven't been able to do
since the fuel pump change. I was grabbing at straws when I replaced
the vacuum advance. I could suck air right through it with my mouth
so I knew it was bad, that & having it plugged in at idle made no
difference in timing advance. When I have the new one plugged in, it
automatically advances it to about 10 BTDC at idle. I didn't see any
adjustments on it, but maybe that's what is wrong? I couldn't get the
engine started with it advanced so far when testing, I could only test
it out by having it started first & then advancing it. The idle was
terrible with a lot of misfiring at that point, if that means
anything.
- I've had a few people also tell me it's over carbureted, but that's
what has always been on it (my dad owned it for like about 15 years
before me) & it seemed to have ran fine for the longest time. That is
an interesting theory though that the old pump could have just been so
tired that it didn't put enough pressure through to put it at it's
full potential. I was considering a 500cfm 2-bbl holley if I had to
purchase one, but it sounds like that might be too much as well? To
clarify, the pump just started leaking when it went out, it didn't
seize up or anything, in fact I didn't know it was going bad until I
started getting sprayed with gas (there's no fenders, windshield,
etc). I don't know if I cleaned the jets out good enough when I
rebuilt the carb, so it's a possibility that part of the diaphragm got
stuck in it. it does seem to flow OK though when I look at the spray
coming out of the jets.
- The vacuum is very steady at idle, maybe 1hg of movement at most
from side to side. I have not performed a compression check, what
would that tell me if it were low? I don't have a compression tester
available so I'm not going to be able to do that one right away.
- The plugs are bosch platinums with a heat rating of 9. I'm not sure
what that equates to heat-wise though, is that a standard across all
plugs?\

Any suggestions on the distributor? I checked the springs & weights
of the centrifugal advance & they seem to be nice & responsive, but
then again, I'm not sure what they're supposed to look like. Should I
try replacing the entire distributor before I go crazy & take the
entire front of my engine apart for the timing chain or start messing
with the carb? Is there any way to test whether or not the timing
chain has slipped a tooth without actually looking at it?

Thanks again guys,

-Matt

Re: CJ5 misfires at high RPM/hard acceleration
 

Thanks for everyone's replies. Here's what I've done from your
suggestions:

- Having the gas cap off made no difference. I actually don't have
any of the emissions stuff on it, so there's no canister, just the gas
tank to the pump.
- Having the coil's + lead hooked directly to the battery made no
difference, I tried switching the leads on the ballast resistor too
first to see if I had it hooked up wrong. I may be wrong, but I think
the ballast resistor leads can go either way?
- I tried what Roy suggested with interesting results. When I
advanced the engine to 10 or 15 degrees, it would run noticeably
better, but not perfect. I could actually get the secondaries to open
up on the carb before it crapped out, which I haven't been able to do
since the fuel pump change. I was grabbing at straws when I replaced
the vacuum advance. I could suck air right through it with my mouth
so I knew it was bad, that & having it plugged in at idle made no
difference in timing advance. When I have the new one plugged in, it
automatically advances it to about 10 BTDC at idle. I didn't see any
adjustments on it, but maybe that's what is wrong? I couldn't get the
engine started with it advanced so far when testing, I could only test
it out by having it started first & then advancing it. The idle was
terrible with a lot of misfiring at that point, if that means
anything.
- I've had a few people also tell me it's over carbureted, but that's
what has always been on it (my dad owned it for like about 15 years
before me) & it seemed to have ran fine for the longest time. That is
an interesting theory though that the old pump could have just been so
tired that it didn't put enough pressure through to put it at it's
full potential. I was considering a 500cfm 2-bbl holley if I had to
purchase one, but it sounds like that might be too much as well? To
clarify, the pump just started leaking when it went out, it didn't
seize up or anything, in fact I didn't know it was going bad until I
started getting sprayed with gas (there's no fenders, windshield,
etc). I don't know if I cleaned the jets out good enough when I
rebuilt the carb, so it's a possibility that part of the diaphragm got
stuck in it. it does seem to flow OK though when I look at the spray
coming out of the jets.
- The vacuum is very steady at idle, maybe 1hg of movement at most
from side to side. I have not performed a compression check, what
would that tell me if it were low? I don't have a compression tester
available so I'm not going to be able to do that one right away.
- The plugs are bosch platinums with a heat rating of 9. I'm not sure
what that equates to heat-wise though, is that a standard across all
plugs?\

Any suggestions on the distributor? I checked the springs & weights
of the centrifugal advance & they seem to be nice & responsive, but
then again, I'm not sure what they're supposed to look like. Should I
try replacing the entire distributor before I go crazy & take the
entire front of my engine apart for the timing chain or start messing
with the carb? Is there any way to test whether or not the timing
chain has slipped a tooth without actually looking at it?

Thanks again guys,

-Matt

Re: CJ5 misfires at high RPM/hard acceleration
 

Thanks for everyone's replies. Here's what I've done from your
suggestions:

- Having the gas cap off made no difference. I actually don't have
any of the emissions stuff on it, so there's no canister, just the gas
tank to the pump.
- Having the coil's + lead hooked directly to the battery made no
difference, I tried switching the leads on the ballast resistor too
first to see if I had it hooked up wrong. I may be wrong, but I think
the ballast resistor leads can go either way?
- I tried what Roy suggested with interesting results. When I
advanced the engine to 10 or 15 degrees, it would run noticeably
better, but not perfect. I could actually get the secondaries to open
up on the carb before it crapped out, which I haven't been able to do
since the fuel pump change. I was grabbing at straws when I replaced
the vacuum advance. I could suck air right through it with my mouth
so I knew it was bad, that & having it plugged in at idle made no
difference in timing advance. When I have the new one plugged in, it
automatically advances it to about 10 BTDC at idle. I didn't see any
adjustments on it, but maybe that's what is wrong? I couldn't get the
engine started with it advanced so far when testing, I could only test
it out by having it started first & then advancing it. The idle was
terrible with a lot of misfiring at that point, if that means
anything.
- I've had a few people also tell me it's over carbureted, but that's
what has always been on it (my dad owned it for like about 15 years
before me) & it seemed to have ran fine for the longest time. That is
an interesting theory though that the old pump could have just been so
tired that it didn't put enough pressure through to put it at it's
full potential. I was considering a 500cfm 2-bbl holley if I had to
purchase one, but it sounds like that might be too much as well? To
clarify, the pump just started leaking when it went out, it didn't
seize up or anything, in fact I didn't know it was going bad until I
started getting sprayed with gas (there's no fenders, windshield,
etc). I don't know if I cleaned the jets out good enough when I
rebuilt the carb, so it's a possibility that part of the diaphragm got
stuck in it. it does seem to flow OK though when I look at the spray
coming out of the jets.
- The vacuum is very steady at idle, maybe 1hg of movement at most
from side to side. I have not performed a compression check, what
would that tell me if it were low? I don't have a compression tester
available so I'm not going to be able to do that one right away.
- The plugs are bosch platinums with a heat rating of 9. I'm not sure
what that equates to heat-wise though, is that a standard across all
plugs?\

Any suggestions on the distributor? I checked the springs & weights
of the centrifugal advance & they seem to be nice & responsive, but
then again, I'm not sure what they're supposed to look like. Should I
try replacing the entire distributor before I go crazy & take the
entire front of my engine apart for the timing chain or start messing
with the carb? Is there any way to test whether or not the timing
chain has slipped a tooth without actually looking at it?

Thanks again guys,

-Matt

Re: CJ5 misfires at high RPM/hard acceleration
 

Thanks for everyone's replies. Here's what I've done from your
suggestions:

- Having the gas cap off made no difference. I actually don't have
any of the emissions stuff on it, so there's no canister, just the gas
tank to the pump.
- Having the coil's + lead hooked directly to the battery made no
difference, I tried switching the leads on the ballast resistor too
first to see if I had it hooked up wrong. I may be wrong, but I think
the ballast resistor leads can go either way?
- I tried what Roy suggested with interesting results. When I
advanced the engine to 10 or 15 degrees, it would run noticeably
better, but not perfect. I could actually get the secondaries to open
up on the carb before it crapped out, which I haven't been able to do
since the fuel pump change. I was grabbing at straws when I replaced
the vacuum advance. I could suck air right through it with my mouth
so I knew it was bad, that & having it plugged in at idle made no
difference in timing advance. When I have the new one plugged in, it
automatically advances it to about 10 BTDC at idle. I didn't see any
adjustments on it, but maybe that's what is wrong? I couldn't get the
engine started with it advanced so far when testing, I could only test
it out by having it started first & then advancing it. The idle was
terrible with a lot of misfiring at that point, if that means
anything.
- I've had a few people also tell me it's over carbureted, but that's
what has always been on it (my dad owned it for like about 15 years
before me) & it seemed to have ran fine for the longest time. That is
an interesting theory though that the old pump could have just been so
tired that it didn't put enough pressure through to put it at it's
full potential. I was considering a 500cfm 2-bbl holley if I had to
purchase one, but it sounds like that might be too much as well? To
clarify, the pump just started leaking when it went out, it didn't
seize up or anything, in fact I didn't know it was going bad until I
started getting sprayed with gas (there's no fenders, windshield,
etc). I don't know if I cleaned the jets out good enough when I
rebuilt the carb, so it's a possibility that part of the diaphragm got
stuck in it. it does seem to flow OK though when I look at the spray
coming out of the jets.
- The vacuum is very steady at idle, maybe 1hg of movement at most
from side to side. I have not performed a compression check, what
would that tell me if it were low? I don't have a compression tester
available so I'm not going to be able to do that one right away.
- The plugs are bosch platinums with a heat rating of 9. I'm not sure
what that equates to heat-wise though, is that a standard across all
plugs?\

Any suggestions on the distributor? I checked the springs & weights
of the centrifugal advance & they seem to be nice & responsive, but
then again, I'm not sure what they're supposed to look like. Should I
try replacing the entire distributor before I go crazy & take the
entire front of my engine apart for the timing chain or start messing
with the carb? Is there any way to test whether or not the timing
chain has slipped a tooth without actually looking at it?

Thanks again guys,

-Matt

Re: CJ5 misfires at high RPM/hard acceleration
 

I'm a small block chevy fan with no hands on with the 304, but...........

I'm betting on a screwed up distributor. Several thoughts:

The vacumn advance works a bit counterintuitive: at full (high) manifold
vacumn (idle or down hill cruising) the distributor advances your base
setting around 15 degrees. I I read your post correctly you are seeing
it advance from 6 degrees to 10 degrees when you plug in the advance vac
line. Not anywhere near enough. Test: let it idle, get out the timing
light, plug/unplug the vac line to the distributor. You should see about
15 degree jump. If not, pull the distributor cap and rotor, check to
see that the the advance plate moves nicely when you really suck on it

The centrifical advance (weights and springs) puts in another 20 degrees
or so, no advance at idle, full advance at 2500 to 3000 rpm (small block
numbers here) Test by plugging the vac advance line, reving the engine
as high as it will go (it usually stuggles to get to 3000 rpm), make
sure you see the 20 degree advance come in with speed increase. It
doesn't jump like the vac advance test. If not, make sure the springs
and cam move easily.

The combination of these gives you advance numbers like this:
Set basic advance to 6 BTDC with vac advance disconnneted
Connect vac advance, should hop to 20 to 25 BTDC
Rev slowly to 3000, no load, should go to 35-40 BTDC.
Rev quickly or heavy load, to 3000, 6 + 20 or 26 BTDC.

I'd consider the 31 degrees of dwell to be pretty skimpy for a V-8, I'd
be setting it at 38 to 40. This changes your timing so you have to redo
that.

matthew.nye@gmail.com wrote:
> Thanks for everyone's replies. Here's what I've done from your
> suggestions:
>
> - Having the gas cap off made no difference. I actually don't have
> any of the emissions stuff on it, so there's no canister, just the gas
> tank to the pump.
> - Having the coil's + lead hooked directly to the battery made no
> difference, I tried switching the leads on the ballast resistor too
> first to see if I had it hooked up wrong. I may be wrong, but I think
> the ballast resistor leads can go either way?
> - I tried what Roy suggested with interesting results. When I
> advanced the engine to 10 or 15 degrees, it would run noticeably
> better, but not perfect. I could actually get the secondaries to open
> up on the carb before it crapped out, which I haven't been able to do
> since the fuel pump change. I was grabbing at straws when I replaced
> the vacuum advance. I could suck air right through it with my mouth
> so I knew it was bad, that & having it plugged in at idle made no
> difference in timing advance. When I have the new one plugged in, it
> automatically advances it to about 10 BTDC at idle. I didn't see any
> adjustments on it, but maybe that's what is wrong? I couldn't get the
> engine started with it advanced so far when testing, I could only test
> it out by having it started first & then advancing it. The idle was
> terrible with a lot of misfiring at that point, if that means
> anything.
> - I've had a few people also tell me it's over carbureted, but that's
> what has always been on it (my dad owned it for like about 15 years
> before me) & it seemed to have ran fine for the longest time. That is
> an interesting theory though that the old pump could have just been so
> tired that it didn't put enough pressure through to put it at it's
> full potential. I was considering a 500cfm 2-bbl holley if I had to
> purchase one, but it sounds like that might be too much as well? To
> clarify, the pump just started leaking when it went out, it didn't
> seize up or anything, in fact I didn't know it was going bad until I
> started getting sprayed with gas (there's no fenders, windshield,
> etc). I don't know if I cleaned the jets out good enough when I
> rebuilt the carb, so it's a possibility that part of the diaphragm got
> stuck in it. it does seem to flow OK though when I look at the spray
> coming out of the jets.
> - The vacuum is very steady at idle, maybe 1hg of movement at most
> from side to side. I have not performed a compression check, what
> would that tell me if it were low? I don't have a compression tester
> available so I'm not going to be able to do that one right away.
> - The plugs are bosch platinums with a heat rating of 9. I'm not sure
> what that equates to heat-wise though, is that a standard across all
> plugs?\
>
> Any suggestions on the distributor? I checked the springs & weights
> of the centrifugal advance & they seem to be nice & responsive, but
> then again, I'm not sure what they're supposed to look like. Should I
> try replacing the entire distributor before I go crazy & take the
> entire front of my engine apart for the timing chain or start messing
> with the carb? Is there any way to test whether or not the timing
> chain has slipped a tooth without actually looking at it?
>
> Thanks again guys,
>
> -Matt
>

Re: CJ5 misfires at high RPM/hard acceleration
 

I'm a small block chevy fan with no hands on with the 304, but...........

I'm betting on a screwed up distributor. Several thoughts:

The vacumn advance works a bit counterintuitive: at full (high) manifold
vacumn (idle or down hill cruising) the distributor advances your base
setting around 15 degrees. I I read your post correctly you are seeing
it advance from 6 degrees to 10 degrees when you plug in the advance vac
line. Not anywhere near enough. Test: let it idle, get out the timing
light, plug/unplug the vac line to the distributor. You should see about
15 degree jump. If not, pull the distributor cap and rotor, check to
see that the the advance plate moves nicely when you really suck on it

The centrifical advance (weights and springs) puts in another 20 degrees
or so, no advance at idle, full advance at 2500 to 3000 rpm (small block
numbers here) Test by plugging the vac advance line, reving the engine
as high as it will go (it usually stuggles to get to 3000 rpm), make
sure you see the 20 degree advance come in with speed increase. It
doesn't jump like the vac advance test. If not, make sure the springs
and cam move easily.

The combination of these gives you advance numbers like this:
Set basic advance to 6 BTDC with vac advance disconnneted
Connect vac advance, should hop to 20 to 25 BTDC
Rev slowly to 3000, no load, should go to 35-40 BTDC.
Rev quickly or heavy load, to 3000, 6 + 20 or 26 BTDC.

I'd consider the 31 degrees of dwell to be pretty skimpy for a V-8, I'd
be setting it at 38 to 40. This changes your timing so you have to redo
that.

matthew.nye@gmail.com wrote:
> Thanks for everyone's replies. Here's what I've done from your
> suggestions:
>
> - Having the gas cap off made no difference. I actually don't have
> any of the emissions stuff on it, so there's no canister, just the gas
> tank to the pump.
> - Having the coil's + lead hooked directly to the battery made no
> difference, I tried switching the leads on the ballast resistor too
> first to see if I had it hooked up wrong. I may be wrong, but I think
> the ballast resistor leads can go either way?
> - I tried what Roy suggested with interesting results. When I
> advanced the engine to 10 or 15 degrees, it would run noticeably
> better, but not perfect. I could actually get the secondaries to open
> up on the carb before it crapped out, which I haven't been able to do
> since the fuel pump change. I was grabbing at straws when I replaced
> the vacuum advance. I could suck air right through it with my mouth
> so I knew it was bad, that & having it plugged in at idle made no
> difference in timing advance. When I have the new one plugged in, it
> automatically advances it to about 10 BTDC at idle. I didn't see any
> adjustments on it, but maybe that's what is wrong? I couldn't get the
> engine started with it advanced so far when testing, I could only test
> it out by having it started first & then advancing it. The idle was
> terrible with a lot of misfiring at that point, if that means
> anything.
> - I've had a few people also tell me it's over carbureted, but that's
> what has always been on it (my dad owned it for like about 15 years
> before me) & it seemed to have ran fine for the longest time. That is
> an interesting theory though that the old pump could have just been so
> tired that it didn't put enough pressure through to put it at it's
> full potential. I was considering a 500cfm 2-bbl holley if I had to
> purchase one, but it sounds like that might be too much as well? To
> clarify, the pump just started leaking when it went out, it didn't
> seize up or anything, in fact I didn't know it was going bad until I
> started getting sprayed with gas (there's no fenders, windshield,
> etc). I don't know if I cleaned the jets out good enough when I
> rebuilt the carb, so it's a possibility that part of the diaphragm got
> stuck in it. it does seem to flow OK though when I look at the spray
> coming out of the jets.
> - The vacuum is very steady at idle, maybe 1hg of movement at most
> from side to side. I have not performed a compression check, what
> would that tell me if it were low? I don't have a compression tester
> available so I'm not going to be able to do that one right away.
> - The plugs are bosch platinums with a heat rating of 9. I'm not sure
> what that equates to heat-wise though, is that a standard across all
> plugs?\
>
> Any suggestions on the distributor? I checked the springs & weights
> of the centrifugal advance & they seem to be nice & responsive, but
> then again, I'm not sure what they're supposed to look like. Should I
> try replacing the entire distributor before I go crazy & take the
> entire front of my engine apart for the timing chain or start messing
> with the carb? Is there any way to test whether or not the timing
> chain has slipped a tooth without actually looking at it?
>
> Thanks again guys,
>
> -Matt
>

Re: CJ5 misfires at high RPM/hard acceleration
 

I'm a small block chevy fan with no hands on with the 304, but...........

I'm betting on a screwed up distributor. Several thoughts:

The vacumn advance works a bit counterintuitive: at full (high) manifold
vacumn (idle or down hill cruising) the distributor advances your base
setting around 15 degrees. I I read your post correctly you are seeing
it advance from 6 degrees to 10 degrees when you plug in the advance vac
line. Not anywhere near enough. Test: let it idle, get out the timing
light, plug/unplug the vac line to the distributor. You should see about
15 degree jump. If not, pull the distributor cap and rotor, check to
see that the the advance plate moves nicely when you really suck on it

The centrifical advance (weights and springs) puts in another 20 degrees
or so, no advance at idle, full advance at 2500 to 3000 rpm (small block
numbers here) Test by plugging the vac advance line, reving the engine
as high as it will go (it usually stuggles to get to 3000 rpm), make
sure you see the 20 degree advance come in with speed increase. It
doesn't jump like the vac advance test. If not, make sure the springs
and cam move easily.

The combination of these gives you advance numbers like this:
Set basic advance to 6 BTDC with vac advance disconnneted
Connect vac advance, should hop to 20 to 25 BTDC
Rev slowly to 3000, no load, should go to 35-40 BTDC.
Rev quickly or heavy load, to 3000, 6 + 20 or 26 BTDC.

I'd consider the 31 degrees of dwell to be pretty skimpy for a V-8, I'd
be setting it at 38 to 40. This changes your timing so you have to redo
that.

matthew.nye@gmail.com wrote:
> Thanks for everyone's replies. Here's what I've done from your
> suggestions:
>
> - Having the gas cap off made no difference. I actually don't have
> any of the emissions stuff on it, so there's no canister, just the gas
> tank to the pump.
> - Having the coil's + lead hooked directly to the battery made no
> difference, I tried switching the leads on the ballast resistor too
> first to see if I had it hooked up wrong. I may be wrong, but I think
> the ballast resistor leads can go either way?
> - I tried what Roy suggested with interesting results. When I
> advanced the engine to 10 or 15 degrees, it would run noticeably
> better, but not perfect. I could actually get the secondaries to open
> up on the carb before it crapped out, which I haven't been able to do
> since the fuel pump change. I was grabbing at straws when I replaced
> the vacuum advance. I could suck air right through it with my mouth
> so I knew it was bad, that & having it plugged in at idle made no
> difference in timing advance. When I have the new one plugged in, it
> automatically advances it to about 10 BTDC at idle. I didn't see any
> adjustments on it, but maybe that's what is wrong? I couldn't get the
> engine started with it advanced so far when testing, I could only test
> it out by having it started first & then advancing it. The idle was
> terrible with a lot of misfiring at that point, if that means
> anything.
> - I've had a few people also tell me it's over carbureted, but that's
> what has always been on it (my dad owned it for like about 15 years
> before me) & it seemed to have ran fine for the longest time. That is
> an interesting theory though that the old pump could have just been so
> tired that it didn't put enough pressure through to put it at it's
> full potential. I was considering a 500cfm 2-bbl holley if I had to
> purchase one, but it sounds like that might be too much as well? To
> clarify, the pump just started leaking when it went out, it didn't
> seize up or anything, in fact I didn't know it was going bad until I
> started getting sprayed with gas (there's no fenders, windshield,
> etc). I don't know if I cleaned the jets out good enough when I
> rebuilt the carb, so it's a possibility that part of the diaphragm got
> stuck in it. it does seem to flow OK though when I look at the spray
> coming out of the jets.
> - The vacuum is very steady at idle, maybe 1hg of movement at most
> from side to side. I have not performed a compression check, what
> would that tell me if it were low? I don't have a compression tester
> available so I'm not going to be able to do that one right away.
> - The plugs are bosch platinums with a heat rating of 9. I'm not sure
> what that equates to heat-wise though, is that a standard across all
> plugs?\
>
> Any suggestions on the distributor? I checked the springs & weights
> of the centrifugal advance & they seem to be nice & responsive, but
> then again, I'm not sure what they're supposed to look like. Should I
> try replacing the entire distributor before I go crazy & take the
> entire front of my engine apart for the timing chain or start messing
> with the carb? Is there any way to test whether or not the timing
> chain has slipped a tooth without actually looking at it?
>
> Thanks again guys,
>
> -Matt
>

Re: CJ5 misfires at high RPM/hard acceleration
 

I'm a small block chevy fan with no hands on with the 304, but...........

I'm betting on a screwed up distributor. Several thoughts:

The vacumn advance works a bit counterintuitive: at full (high) manifold
vacumn (idle or down hill cruising) the distributor advances your base
setting around 15 degrees. I I read your post correctly you are seeing
it advance from 6 degrees to 10 degrees when you plug in the advance vac
line. Not anywhere near enough. Test: let it idle, get out the timing
light, plug/unplug the vac line to the distributor. You should see about
15 degree jump. If not, pull the distributor cap and rotor, check to
see that the the advance plate moves nicely when you really suck on it

The centrifical advance (weights and springs) puts in another 20 degrees
or so, no advance at idle, full advance at 2500 to 3000 rpm (small block
numbers here) Test by plugging the vac advance line, reving the engine
as high as it will go (it usually stuggles to get to 3000 rpm), make
sure you see the 20 degree advance come in with speed increase. It
doesn't jump like the vac advance test. If not, make sure the springs
and cam move easily.

The combination of these gives you advance numbers like this:
Set basic advance to 6 BTDC with vac advance disconnneted
Connect vac advance, should hop to 20 to 25 BTDC
Rev slowly to 3000, no load, should go to 35-40 BTDC.
Rev quickly or heavy load, to 3000, 6 + 20 or 26 BTDC.

I'd consider the 31 degrees of dwell to be pretty skimpy for a V-8, I'd
be setting it at 38 to 40. This changes your timing so you have to redo
that.

matthew.nye@gmail.com wrote:
> Thanks for everyone's replies. Here's what I've done from your
> suggestions:
>
> - Having the gas cap off made no difference. I actually don't have
> any of the emissions stuff on it, so there's no canister, just the gas
> tank to the pump.
> - Having the coil's + lead hooked directly to the battery made no
> difference, I tried switching the leads on the ballast resistor too
> first to see if I had it hooked up wrong. I may be wrong, but I think
> the ballast resistor leads can go either way?
> - I tried what Roy suggested with interesting results. When I
> advanced the engine to 10 or 15 degrees, it would run noticeably
> better, but not perfect. I could actually get the secondaries to open
> up on the carb before it crapped out, which I haven't been able to do
> since the fuel pump change. I was grabbing at straws when I replaced
> the vacuum advance. I could suck air right through it with my mouth
> so I knew it was bad, that & having it plugged in at idle made no
> difference in timing advance. When I have the new one plugged in, it
> automatically advances it to about 10 BTDC at idle. I didn't see any
> adjustments on it, but maybe that's what is wrong? I couldn't get the
> engine started with it advanced so far when testing, I could only test
> it out by having it started first & then advancing it. The idle was
> terrible with a lot of misfiring at that point, if that means
> anything.
> - I've had a few people also tell me it's over carbureted, but that's
> what has always been on it (my dad owned it for like about 15 years
> before me) & it seemed to have ran fine for the longest time. That is
> an interesting theory though that the old pump could have just been so
> tired that it didn't put enough pressure through to put it at it's
> full potential. I was considering a 500cfm 2-bbl holley if I had to
> purchase one, but it sounds like that might be too much as well? To
> clarify, the pump just started leaking when it went out, it didn't
> seize up or anything, in fact I didn't know it was going bad until I
> started getting sprayed with gas (there's no fenders, windshield,
> etc). I don't know if I cleaned the jets out good enough when I
> rebuilt the carb, so it's a possibility that part of the diaphragm got
> stuck in it. it does seem to flow OK though when I look at the spray
> coming out of the jets.
> - The vacuum is very steady at idle, maybe 1hg of movement at most
> from side to side. I have not performed a compression check, what
> would that tell me if it were low? I don't have a compression tester
> available so I'm not going to be able to do that one right away.
> - The plugs are bosch platinums with a heat rating of 9. I'm not sure
> what that equates to heat-wise though, is that a standard across all
> plugs?\
>
> Any suggestions on the distributor? I checked the springs & weights
> of the centrifugal advance & they seem to be nice & responsive, but
> then again, I'm not sure what they're supposed to look like. Should I
> try replacing the entire distributor before I go crazy & take the
> entire front of my engine apart for the timing chain or start messing
> with the carb? Is there any way to test whether or not the timing
> chain has slipped a tooth without actually looking at it?
>
> Thanks again guys,
>
> -Matt
>

Re: CJ5 misfires at high RPM/hard acceleration
 

In article <1184542280.091378.265490@o61g2000hsh.googlegroups .com>,
<matthew.nye@gmail.com> wrote:

> Thanks for everyone's replies. Here's what I've done from your
> suggestions:

Yes the ballast resistor can go either way. The gas you see
squirting out when you move the linkage has nothing to do with the
secondaries working or not. Although the 600 is "in theory" a little
large for a stock 304, if it's tuned right there is no problem. I have
a Holley 600 on a 289 that runs perfectly.

I agree that your total timing is on the conservative side, but I
don't think it would cause your particular symptoms. I had a 390 in a
station wagon that would eventually get up to 70mph, but only at light
enough throttle where the vacuum stayed high. When I started to put my
foot down, it would actually *decelerate*. Nothing I did with the
distributor changed that. (I bought it in this condition, so I had no
frame of reference). The previous owner had the timing apparently set
right. But, just because the distributor is firing with the crank
doesn't mean the cam is in the right place. Of course, it turned out to
be the chain.