"When" you get ported vacuum is not determined by RPM. Throttle
position determines it.

If you're checking ported vacuum right at the port on the carb, and
you're not getting any, you have a problem in the carb. The most
likely cause would be an improperly installed, or wrong gasket between
the throttle plate & main body.



On 6 Aug 2006 20:50:56 -0700, "bobvonbob"
<bennettvonbennett@gmail.com> 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

 

"bobvonbob" <bennettvonbennett@gmail.com> wrote in message
news:1154922656.280186.76820@b28g2000cwb.googlegro ups.com...
> 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'm not sure about the engine changing its tune, but an open vac line will
produce an audible hiss even if it does not disturb the motor.




> 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
>

 

"bobvonbob" <bennettvonbennett@gmail.com> wrote in message
news:1154922656.280186.76820@b28g2000cwb.googlegro ups.com...
> 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'm not sure about the engine changing its tune, but an open vac line will
produce an audible hiss even if it does not disturb the motor.




> 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
>

 

"bobvonbob" <bennettvonbennett@gmail.com> wrote in message
news:1154922656.280186.76820@b28g2000cwb.googlegro ups.com...
> 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'm not sure about the engine changing its tune, but an open vac line will
produce an audible hiss even if it does not disturb the motor.




> 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
>

 

"bobvonbob" <bennettvonbennett@gmail.com> wrote in message
news:1154922656.280186.76820@b28g2000cwb.googlegro ups.com...
> 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'm not sure about the engine changing its tune, but an open vac line will
produce an audible hiss even if it does not disturb the motor.




> 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
>

 

Bennet,
I recently rebuilt my carb and am having some similar issues with my
exact same Jeep. I'm using much of your info to troubleshoot some of
my identical problems. I was wondering though what state you live in?
I was hoping you could post the information on the emissions label
under the hood. I live in California and my Jeep was wrecked years ago
so I don't have that emissions label and Jeep will not sell me a new
one. Even if you're from another state I am interested about the specs
on that label. Otherwise I am removing the carb again to closely study
the gaskets and try to determine if one of them is blocking a port
somewhere. I've tried most everything else, and I had none of these
issues before rebuilding the carb.
Good luck and please post that label info if possible.
Best,
Kevin

 

Bennet,
I recently rebuilt my carb and am having some similar issues with my
exact same Jeep. I'm using much of your info to troubleshoot some of
my identical problems. I was wondering though what state you live in?
I was hoping you could post the information on the emissions label
under the hood. I live in California and my Jeep was wrecked years ago
so I don't have that emissions label and Jeep will not sell me a new
one. Even if you're from another state I am interested about the specs
on that label. Otherwise I am removing the carb again to closely study
the gaskets and try to determine if one of them is blocking a port
somewhere. I've tried most everything else, and I had none of these
issues before rebuilding the carb.
Good luck and please post that label info if possible.
Best,
Kevin

 

Bennet,
I recently rebuilt my carb and am having some similar issues with my
exact same Jeep. I'm using much of your info to troubleshoot some of
my identical problems. I was wondering though what state you live in?
I was hoping you could post the information on the emissions label
under the hood. I live in California and my Jeep was wrecked years ago
so I don't have that emissions label and Jeep will not sell me a new
one. Even if you're from another state I am interested about the specs
on that label. Otherwise I am removing the carb again to closely study
the gaskets and try to determine if one of them is blocking a port
somewhere. I've tried most everything else, and I had none of these
issues before rebuilding the carb.
Good luck and please post that label info if possible.
Best,
Kevin

 

Bennet,
I recently rebuilt my carb and am having some similar issues with my
exact same Jeep. I'm using much of your info to troubleshoot some of
my identical problems. I was wondering though what state you live in?
I was hoping you could post the information on the emissions label
under the hood. I live in California and my Jeep was wrecked years ago
so I don't have that emissions label and Jeep will not sell me a new
one. Even if you're from another state I am interested about the specs
on that label. Otherwise I am removing the carb again to closely study
the gaskets and try to determine if one of them is blocking a port
somewhere. I've tried most everything else, and I had none of these
issues before rebuilding the carb.
Good luck and please post that label info if possible.
Best,
Kevin

 

Kevin, the bottom base plate has a top and bottom. The notches need to
be at the top and the gasket needs to have these notches cut out so you
get your manifold vacuum at the base nipples.

Did you mess with the mix screws or the timing?

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)

Kevin wrote:
>
> Bennet,
> I recently rebuilt my carb and am having some similar issues with my
> exact same Jeep. I'm using much of your info to troubleshoot some of
> my identical problems. I was wondering though what state you live in?
> I was hoping you could post the information on the emissions label
> under the hood. I live in California and my Jeep was wrecked years ago
> so I don't have that emissions label and Jeep will not sell me a new
> one. Even if you're from another state I am interested about the specs
> on that label. Otherwise I am removing the carb again to closely study
> the gaskets and try to determine if one of them is blocking a port
> somewhere. I've tried most everything else, and I had none of these
> issues before rebuilding the carb.
> Good luck and please post that label info if possible.
> Best,
> Kevin