Vacuum Leak

[palerider94]

I've learned enough from this site to know I have a vacuum leak. Put vacuum gauge and needle is jumping around and lost a good 5 lbs.

I'm pretty sure it is happening at the base of the carb. Previous owner had a 7/8 riser between carb and manifold. The riser was open type where the intake has split - according to Edelbrock hot line that is a no - no. (currently chasing a hesitation problem).

In any case pulled it off, put heat insulator gasket between carb and manifold, fired it up brake line came on and vacuum gauge starting jumping around. Vacuum leak!

I took some starter fluid and sprayed around base - no impact. Just for kicks I pulled one of the vacuum hoses off and sprayed fluid directly into it and no impact. I then took propane torch (un lit of course) and tried the same thing - no impact/change.

My question is what is the best way for checking for vacuum leaks? I read both way starting fluid and propane will find them but I thought I would have sense some change in car when spraying directly into vacuum. Appreciate anyhelp. thanks

 

[thehueypilot]

If you spray it directly into the top of the carb the engine will react (large volume), but would not effect the rpm if you sprayed it through the ported vacuum port (if that is the one you used). I don't think a spacer could cause a hesitation problem. I would check the accelerator pump for sufficient squirt (good volume and no lag). Some insulated spacers do not have enough support to prevent the carb base from warping. Make sure it is torqued evenly (criss-cross) and not too tight.

 

[pabear89]

If your not getting any rpm change from the vacum check with starting fluid or propane, your fluxuating vac needle could be from improper timing in spark or valve train.(loose or worn timing chain/gears)

PB

 

[palerider94]

Thanks - I probably did not need to put all the background information into question. I did not think the spacer was causing hesitation - I was just removing it because I talked to Edelbrock and they mentioned you should not use completely open spacer (no split) on the intake I have 289 performer - which does have split. They said it could cause some erratic performance issues. I just figured I'd clean that up while I was at it.

I'm pretty sure leak it was a problem between intake and carb - pulled heat riser gasket off and it did not look like it was getting a good seal.

The new heat riser I was using had metal inserts in carb flange holes that I think was keeping it from seating completely. I'm going to just put a regular gasket and lose the heat insulator type and see what happens. Hopefully sinse I plud heat cross overs on manifold engine will be cooler and will not need a heat insulator.

I was just surprised when I sprayed starting fluid in open port it did not change RPM. I read on other posts to check for vacuum leaks you should spay around suspect areas and listen for RPM change. I figured if did not change rpm when spraying into open port why would it change RPM if sprayed near leak area.