no ported vacuum off carb...
 

well its always something...
87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
and have bypassed most of the emissions stuff - including the charcoal
canister, the O2 sensor, and the CTO.
now here's the problem:
following the instructions for the "nutter" i routed the dist. advance
directly to the ported vacuum port on the BBD (the one on the valve
cover side), in the process i discovered that i have no ported vacuum
off this port at any rpm. i'm measuring directly off the carb so it
cant be the hoses etc. i dont have a vacuum gauge but i have to assume
that it would be detectable and that covering/uncovering the port would
produce detectable change in the rpm etc. -
i DO have manifold vacuum - quite a bit. also i can blow thru the
ported vacuum port so its not clogged...
here's the thing - she's running just fine, starts fine, no stumble, no
hesitation, the only thing i notice is that she doesnt idle totally
even. little mini-surges from say 600-700 rpm around 1 per second.
so what gives? am i missing something? i thought the ported vacuum
supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
but like i said she seems to be running ok. just a little unsteady at
idle.
any ideas?
sorry for the long complex post. i know some of you are going to say
"if it aint broke..." and thats fine - i just want to understand this
system... at least until i can replace it with something better...
which given the state of my finances (somewhat limited) and the state
of everything else on this thing (somewhat worn out) - is going to be
quite a while... if ever :(
cheers,
bennett

Re: no ported vacuum off carb...
 

> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett Hook a vacuum gauge to the ported vacuum port, should be zero at idle, and increase as you advance the throttle... Gene AMC75CJ-5, orignal owner...
Howell TBI
GM HEI

Re: no ported vacuum off carb...
 

> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett Hook a vacuum gauge to the ported vacuum port, should be zero at idle, and increase as you advance the throttle... Gene AMC75CJ-5, orignal owner...
Howell TBI
GM HEI

Re: no ported vacuum off carb...
 

> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett Hook a vacuum gauge to the ported vacuum port, should be zero at idle, and increase as you advance the throttle... Gene AMC75CJ-5, orignal owner...
Howell TBI
GM HEI

Re: no ported vacuum off carb...
 

> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett Hook a vacuum gauge to the ported vacuum port, should be zero at idle, and increase as you advance the throttle... Gene AMC75CJ-5, orignal owner...
Howell TBI
GM HEI

Re: no ported vacuum off carb...
 

You are not assuming correctly. Ported vacuum is actuated from above
the throttle plates so it doesn't interfere with anything. It would be
something like just poking a hole in the air filter. The original
canister suction was ported from the air filter snout even.

You can just hook it up to the distributor and watch the vacuum advance
levers move when the throttle is opened or you need a vacuum gauge. You
should be able to feel suction if you hold your finger over the nipple
and goose the throttle too.

The surge you mention is normally associated with a canister issue or
the solenoid for the PCV system just behind the carb.

That canister cannot be taken out of the loop without an amazing amount
of gas fumes gathering or your engine starving for fuel as a vacuum
builds on the gas tank and vacuum builds on the carb float bowl. The
canister is the gas tank and carb vent and is needed. I tried to run
without it for a while, but the gas smell got in our hair and clothes
even.

What did you do with all the lines going to it? If the purge line isn't
blocked as it goes into the PCV system, your engine will run super lean
and the vacuum will be non existent almost.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


bobvonbob wrote:
>
> well its always something...
> 87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
> and have bypassed most of the emissions stuff - including the charcoal
> canister, the O2 sensor, and the CTO.
> now here's the problem:
> following the instructions for the "nutter" i routed the dist. advance
> directly to the ported vacuum port on the BBD (the one on the valve
> cover side), in the process i discovered that i have no ported vacuum
> off this port at any rpm. i'm measuring directly off the carb so it
> cant be the hoses etc. i dont have a vacuum gauge but i have to assume
> that it would be detectable and that covering/uncovering the port would
> produce detectable change in the rpm etc. -
> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett

Re: no ported vacuum off carb...
 

You are not assuming correctly. Ported vacuum is actuated from above
the throttle plates so it doesn't interfere with anything. It would be
something like just poking a hole in the air filter. The original
canister suction was ported from the air filter snout even.

You can just hook it up to the distributor and watch the vacuum advance
levers move when the throttle is opened or you need a vacuum gauge. You
should be able to feel suction if you hold your finger over the nipple
and goose the throttle too.

The surge you mention is normally associated with a canister issue or
the solenoid for the PCV system just behind the carb.

That canister cannot be taken out of the loop without an amazing amount
of gas fumes gathering or your engine starving for fuel as a vacuum
builds on the gas tank and vacuum builds on the carb float bowl. The
canister is the gas tank and carb vent and is needed. I tried to run
without it for a while, but the gas smell got in our hair and clothes
even.

What did you do with all the lines going to it? If the purge line isn't
blocked as it goes into the PCV system, your engine will run super lean
and the vacuum will be non existent almost.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


bobvonbob wrote:
>
> well its always something...
> 87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
> and have bypassed most of the emissions stuff - including the charcoal
> canister, the O2 sensor, and the CTO.
> now here's the problem:
> following the instructions for the "nutter" i routed the dist. advance
> directly to the ported vacuum port on the BBD (the one on the valve
> cover side), in the process i discovered that i have no ported vacuum
> off this port at any rpm. i'm measuring directly off the carb so it
> cant be the hoses etc. i dont have a vacuum gauge but i have to assume
> that it would be detectable and that covering/uncovering the port would
> produce detectable change in the rpm etc. -
> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett

Re: no ported vacuum off carb...
 

You are not assuming correctly. Ported vacuum is actuated from above
the throttle plates so it doesn't interfere with anything. It would be
something like just poking a hole in the air filter. The original
canister suction was ported from the air filter snout even.

You can just hook it up to the distributor and watch the vacuum advance
levers move when the throttle is opened or you need a vacuum gauge. You
should be able to feel suction if you hold your finger over the nipple
and goose the throttle too.

The surge you mention is normally associated with a canister issue or
the solenoid for the PCV system just behind the carb.

That canister cannot be taken out of the loop without an amazing amount
of gas fumes gathering or your engine starving for fuel as a vacuum
builds on the gas tank and vacuum builds on the carb float bowl. The
canister is the gas tank and carb vent and is needed. I tried to run
without it for a while, but the gas smell got in our hair and clothes
even.

What did you do with all the lines going to it? If the purge line isn't
blocked as it goes into the PCV system, your engine will run super lean
and the vacuum will be non existent almost.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


bobvonbob wrote:
>
> well its always something...
> 87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
> and have bypassed most of the emissions stuff - including the charcoal
> canister, the O2 sensor, and the CTO.
> now here's the problem:
> following the instructions for the "nutter" i routed the dist. advance
> directly to the ported vacuum port on the BBD (the one on the valve
> cover side), in the process i discovered that i have no ported vacuum
> off this port at any rpm. i'm measuring directly off the carb so it
> cant be the hoses etc. i dont have a vacuum gauge but i have to assume
> that it would be detectable and that covering/uncovering the port would
> produce detectable change in the rpm etc. -
> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett

Re: no ported vacuum off carb...
 

You are not assuming correctly. Ported vacuum is actuated from above
the throttle plates so it doesn't interfere with anything. It would be
something like just poking a hole in the air filter. The original
canister suction was ported from the air filter snout even.

You can just hook it up to the distributor and watch the vacuum advance
levers move when the throttle is opened or you need a vacuum gauge. You
should be able to feel suction if you hold your finger over the nipple
and goose the throttle too.

The surge you mention is normally associated with a canister issue or
the solenoid for the PCV system just behind the carb.

That canister cannot be taken out of the loop without an amazing amount
of gas fumes gathering or your engine starving for fuel as a vacuum
builds on the gas tank and vacuum builds on the carb float bowl. The
canister is the gas tank and carb vent and is needed. I tried to run
without it for a while, but the gas smell got in our hair and clothes
even.

What did you do with all the lines going to it? If the purge line isn't
blocked as it goes into the PCV system, your engine will run super lean
and the vacuum will be non existent almost.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


bobvonbob wrote:
>
> well its always something...
> 87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
> and have bypassed most of the emissions stuff - including the charcoal
> canister, the O2 sensor, and the CTO.
> now here's the problem:
> following the instructions for the "nutter" i routed the dist. advance
> directly to the ported vacuum port on the BBD (the one on the valve
> cover side), in the process i discovered that i have no ported vacuum
> off this port at any rpm. i'm measuring directly off the carb so it
> cant be the hoses etc. i dont have a vacuum gauge but i have to assume
> that it would be detectable and that covering/uncovering the port would
> produce detectable change in the rpm etc. -
> i DO have manifold vacuum - quite a bit. also i can blow thru the
> ported vacuum port so its not clogged...
> here's the thing - she's running just fine, starts fine, no stumble, no
> hesitation, the only thing i notice is that she doesnt idle totally
> even. little mini-surges from say 600-700 rpm around 1 per second.
> so what gives? am i missing something? i thought the ported vacuum
> supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> but like i said she seems to be running ok. just a little unsteady at
> idle.
> any ideas?
> sorry for the long complex post. i know some of you are going to say
> "if it aint broke..." and thats fine - i just want to understand this
> system... at least until i can replace it with something better...
> which given the state of my finances (somewhat limited) and the state
> of everything else on this thing (somewhat worn out) - is going to be
> quite a while... if ever :(
> cheers,
> bennett

Re: no ported vacuum off carb...
 

mike! good to see you still live on this list! actually i used an old
post of yours where you discussed bypassing the canister - dont have
the reference handy just searched the forum for 'bypass charcoal
cannister' [sic] - i blocked off the puge line and the purge signal
line to the canister, and left the vent lines open with some filter
material in them as you specified - the reason i did this is because
the local jeep dealership tells me that they no longer make or carry
the canister! so far the fumes havent been noticable...
as for the PCV solenoid - PO removed it. i DO have oil spitting back
into the air filter but then there is no filter for the PCV breather so
maybe thats the problem...
and re: the ported vacuum, yes i understand it is PORTED vacuum - as in
only when the PORTS in the carb are open - correct?
i have no detectable vacuum at all at the ported vacuum line port at
ANY rpm... i do have manifold vacuum... and i can blow thru the ported
vac port so it is not clogged...
ideas?
thanks in advance,
bennett

PS i appreciate all the time you've put into this list over the years
and many of your previous posts have been extremely helpful to me. so
thanks.



Mike Romain wrote:
> You are not assuming correctly. Ported vacuum is actuated from above
> the throttle plates so it doesn't interfere with anything. It would be
> something like just poking a hole in the air filter. The original
> canister suction was ported from the air filter snout even.
>
> You can just hook it up to the distributor and watch the vacuum advance
> levers move when the throttle is opened or you need a vacuum gauge. You
> should be able to feel suction if you hold your finger over the nipple
> and goose the throttle too.
>
> The surge you mention is normally associated with a canister issue or
> the solenoid for the PCV system just behind the carb.
>
> That canister cannot be taken out of the loop without an amazing amount
> of gas fumes gathering or your engine starving for fuel as a vacuum
> builds on the gas tank and vacuum builds on the carb float bowl. The
> canister is the gas tank and carb vent and is needed. I tried to run
> without it for a while, but the gas smell got in our hair and clothes
> even.
>
> What did you do with all the lines going to it? If the purge line isn't
> blocked as it goes into the PCV system, your engine will run super lean
> and the vacuum will be non existent almost.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> (More Off Road album links at bottom of the view page)
>
>
> bobvonbob wrote:
> >
> > well its always something...
> > 87 YJ 4.2L 258 - carter BBD recently rebuilt by me, i did the "nutter",
> > and have bypassed most of the emissions stuff - including the charcoal
> > canister, the O2 sensor, and the CTO.
> > now here's the problem:
> > following the instructions for the "nutter" i routed the dist. advance
> > directly to the ported vacuum port on the BBD (the one on the valve
> > cover side), in the process i discovered that i have no ported vacuum
> > off this port at any rpm. i'm measuring directly off the carb so it
> > cant be the hoses etc. i dont have a vacuum gauge but i have to assume
> > that it would be detectable and that covering/uncovering the port would
> > produce detectable change in the rpm etc. -
> > i DO have manifold vacuum - quite a bit. also i can blow thru the
> > ported vacuum port so its not clogged...
> > here's the thing - she's running just fine, starts fine, no stumble, no
> > hesitation, the only thing i notice is that she doesnt idle totally
> > even. little mini-surges from say 600-700 rpm around 1 per second.
> > so what gives? am i missing something? i thought the ported vacuum
> > supplys the distr. with advance at low to mid rpm (from ~1000 - 2400)
> > but like i said she seems to be running ok. just a little unsteady at
> > idle.
> > any ideas?
> > sorry for the long complex post. i know some of you are going to say
> > "if it aint broke..." and thats fine - i just want to understand this
> > system... at least until i can replace it with something better...
> > which given the state of my finances (somewhat limited) and the state
> > of everything else on this thing (somewhat worn out) - is going to be
> > quite a while... if ever :(
> > cheers,
> > bennett