Vacuum leak

[dirtbag7]

When I installed the new carb, and the HEI (much to the delight of everyone on here) my blazer ran. Now the issue I'm having is high idle, even after adjusting the fast idle cam and from a stand still if I put my foot in it, she'll fall on her face until I let off. Once I do that once, she'll pick back up just fine for the most part. Every now and again it will idle down when you come to stop so much that she all but dies. I am about 98% sure its a vacuum leak but haven't started looking yet. A couple questions for you gurus. If I read the vacuum on a gauge, what SHOULD I read if there were no vacuum leaks, and what is the margin of error? (its a sb 350) What I mean is if it is 10" merc, at what point do you say "I for sure have a vac leak?" Also, what is the best vac leak detection liquid? At work we use shaving cream, which works GREAT, but I'm not sure I what that will hurt getting sucked into the engine. Help please?
Thanks

 

[iroc-z]

if you have access to a oxy acetylene welder or torch. just use the pure oxygen around any areas you may think there is a vac leak, if the idle kicks up a bit then thats the source of the leak.(Oxygen burns better then normal air). Works wonders for me.

 

[3 on the tree]

Carb cleaner works pretty well.

 

[GNERGY]

What is your timing set at? Should be around 10* with the vac. advance disconnected. You could always put heavier weights and lighter springs in the distributor to give it a quicker timing advance.
Tarey

 

[Brodie]

Also a SBC should have around 17lbs of vacuum at idle.

 

[badmix]

Ive got a vacuum gauge mounted in my engine bay for tuning my carb. anywhere from 15-20hg is what you want, the higher the better. vacuum leak will give you erratic issues (as you are having). Personally, I wouldnt waste my time trying to hunt it down. Just get 10-15 of new vacuum hose and just start replacing, stuff doesnt cost that much and you get peace of mind of having good lines anyways. These lines are soft rubber and fall apart from all the heat, etc. The vacuum leak I had was from the back of the intake manifold, there was a thingy that had a couple vacuum ports on it and those lines were cracked and split. But I just replaced all the lines in my engine bay.

Jus re-read your post. If you have a 10hg. your truck will be running like crap. It could be vacuum leak more than likely or a number of other things. A vacuum gauge does diff. things for diff. problems. Ive got a link that tells what it does, ill have to post up. But I use mine for tuning carb. You adjust the a/f mix to get the highest poss. hg reading, and as you keep adjusting , if it starts to go down than your at that limit and you just set it where everything is smooth. Mine is set at around 18hg and im content. Im not going to mess with it to try and get any higher. Truck runs good. lol.

 

[dirtbag7]

Thanks for all the tips guys. I haven't had a chance to get back to working on it (my project-funding job requires I be there from time to time) One thing of note though, I did indeed replace every hose I could find in there except the heater core feed and return lines, but those will be done when I replace the heater core (more fun)