Vacuum Issue

[RDF]

As some may know, I've had issues with my trani lately.  I took it to a trani shop and they told me 2nd gear was gone.  But while under the hood this past weekend, I noticed a vacuum cap on my carb (Edelbrock) was cracked (See pics) and looked like it may be leaking, so I took the cap off and drove the car to the parts store to get a new one.  I noticed while driving that the car seemed to shift better, a lot better to be frank.  So I tested the car with a new vacuum cap on and then off and the car seems to shift 10x better with it off.  My question is, should there be a vacuum hose on this tit going somewhere?  I'll try to get the model # off it and post that soon.

Thanks,

[Mopar73340]

On my Edelbrocks that is a source of manifold vacuum, so unless you need it for something it should be plugged. My first guess is your carb is jetted to rich and the extra air entering the engine is making it run stronger and is probably why it seems to shift better. Sounds as though you may need to do some carb tuning. Actually you should notice the idle change with and without the cap. Just my    I'm sure Chryco will have some more ideas.

[GoodysGotaCuda]

On my Edelbrocks that is a source of manifold vacuum, so unless you need it for something it should be plugged. My first guess is your carb is jetted to rich and the extra air entering the engine is making it run stronger and is probably why it seems to shift better. Sounds as though you may need to do some carb tuning. Actually you should notice the idle change with and without the cap. Just my    I'm sure Chryco will have some more ideas.

I agree. that port has nothing to do with the transmission, as mentioned it was probably rich and with that cap off it leans out a little, probably running harder making it seem like it shifts better.

[MEK-Dangerfield]

I agree with what has been said above. You don't want to be driving with unmetered air being sucked into your carb.


  Mike

[RDF]

I agree with what has been said above. You don't want to be driving with unmetered air being sucked into your carb.


  Mike

Ok, so I shuold definately cap it then, and adjust my carb settings.  I've never tinkered with my carb all that much, is it just the 2 front screws that adjust how rich/lean it runs or is there other things? 

[MEK-Dangerfield]

Ok, so I shuold definately cap it then, and adjust my carb settings.  I've never tinkered with my carb all that much, is it just the 2 front screws that adjust how rich/lean it runs or is there other things? 

Yes, that tit should definitely be capped. I wish I could help you with your carb., but I have only messed with Holleys. I am only taking a wild guess here, but screws are usually to adjust the idle, and air/fuel mixture at idle.


  Mike

[Mopar73340]

Ok, so I shuold definately cap it then, and adjust my carb settings.  I've never tinkered with my carb all that much, is it just the 2 front screws that adjust how rich/lean it runs or is there other things? 

Cap the port. The 2 screws only adjust the idle mixture as MEK said. Find out what model # carb it is and go to edelbrock's web site, www.edelbrock.com there they will have a downloadable owners manual. Inside you can find a chart for the carb showing what size metering rods/jets you need to install to change the fuel mixture. I'd start by going 4% leaner and see how it runs.

[RDF]

Cap the port. The 2 screws only adjust the idle mixture as MEK said. Find out what model # carb it is and go to edelbrock's web site, www.edelbrock.com there they will have a downloadable owners manual. Inside you can find a chart for the carb showing what size metering rods/jets you need to install to change the fuel mixture. I'd start by going 4% leaner and see how it runs.

Ok, did just that, and if you're looking at the carb, from left to right, it states the ports are:
Ported Vacuum
PVC Valve Port
Full Vacuum

Currently, I have the vacuum hose hooked up to the ported vacuum then to the distributor.  Is that correct or should it be on the Full Vacuum?   What's the difference between the two?

[Tubbed440]

Ported vacuum pulls vacuum all the time, and varries with engine speed.  Manifold vacuum goes to somewhere around zero at WOT, then slowly climbs up as the revs get higher / load lessens.  Most say to hook your vacuum advance to manifold vacuum.  It all depends on the manufacturer of the distributor, and how they designed the vacuum advance to work.  If it's a Ma Mopar unit with no electronic solenoids hooked into the vacuum path, it (vacuum advance) needs to be connected to manifold vacuum. 

Theory of operation is as follows......(just in case you're unfamilliar...I'm not sure, so I'll go the extra bit and explain it)  The vacuum advance is there to pull in more timing advance to help the engine burn cleaner / get better fuel economy.  Your advance at Idle could be as high as 50 degrees at times, depending on how it's adjusted.  When the vacuum pot is hooked to manifold vacuum, and you depress the throttle, the vacuum drops to near zero, and the dizzy then depends on the mechanincal advance only.  After the load is removed from the engine, (you get to cruise speeds) the manifold vacuum comes back up, the vacuum pot pulls in more timing and helps burn all the fuel....netting cooler run temps at cruise and higher fuel economy.  Ever smelled a car at idle that would burn your nose?  They're probably running a race only dist. with no vacuum advance.

[moper]

You're close tubbed...Mopar always used ported vaccum tho. not manifold. Ford used manifold vaccum on some cars. At idle, there should no vaccum (or resulting advance) present at the carb's ported vaccum port. There will be full vaccum on the manifold vaccum nipple at idle. I always thought it was the righ side (next to accelerator pump arm) was p[orted..But I could have that backwards...lol. Otherwise, same ideas apply. You want the right timing under power, and all the extra it can tolerate at cruise and light throttle.

[RDF]

You're close tubbed...Mopar always used ported vaccum tho. not manifold. Ford used manifold vaccum on some cars. At idle, there should no vaccum (or resulting advance) present at the carb's ported vaccum port. There will be full vaccum on the manifold vaccum nipple at idle. I always thought it was the righ side (next to accelerator pump arm) was p[orted..But I could have that backwards...lol. Otherwise, same ideas apply. You want the right timing under power, and all the extra it can tolerate at cruise and light throttle.

Ok, so I'm a little lost (excuse the ignorance).....should I keep the Vacuum Advanced (the one hooked up to the distributor) hooked up to the ported vacuum or put it on the full vacuum?

[Chryco Psycho]

Vacuum advance should be connected to Ported vacuum , I often see it hooked to manifold which is wrong , this will kill power & milage & cause overheating

[Tubbed440]

So, the vacuum advance on a mopar distributor is a vacuum retard instead?  Explain.

[Chryco Psycho]

no there is no vacuum above the throttle plates at idle [ported vacuum ] so the advance is at rest , as ported vacuum increases & the throttle is opened the vacuum increases advance
 if it is hooked to manifold vacuum you will have full advance at idle & as the throttle is opened vacuum will decrease retarding timing with more rpm

[Mopar73340]

   Keep the dist hooked up to ported vacuum it will run better that way (unless you are racing it) try leaning out the carb 4% and see if it runs any better.