Thread: Dominik/ idle adjustment

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Ok dominik.(and whoever) I tried sending you another message in the private section, but this message was too long, it wouldn't work.

The situation; a 350 chevy with a 305 duration cam/ automatic/ stalls when in gear at idle.

The thing that is causing you the problem is the cam! The duration you have chosen is HUGE for a 350 ci. If the same cam was in a 400 small block with 11:1 compression, it would be fine.

I am guessing you have flat top pistons and probably 72 cc chamber heads which means you have 9:1 compression. This is extremely low when you take into consideration the cam duration. With a cam which has large duration, you actually lose compression because the valves stay open longer and thereby compression squeezes on the compression stroke, leaving you with even less compression/power at low rpms. In addition to this the exhaust valve stays open thereby sucking some of the spent gases back into the cylinder. This all changes when you get above 5000 rpm, for then the scavenging effect promotes more horsepower.

I know all this doesn’t remedy your current problem, I am just trying to get you to understand the dilemma you are facing. What you need in your current configuration is a large stall torque converter, and a health shot of go-go juice off the line. However, that means more money, soooooo, the immediate fix so that your engine will remain running is, giving the engine more air and not more gas at idle.

With your set-up, what you had to do is set the idle screw in further so that it would idle. The problem with that is that when you do that you are also signaling to the carb that it needs more gasoline. Solution: drill two holes, one in each of the front two butterflies of your carb, about 1/16 - 3/32 large. Or, if you have 2 p.c.v. fittings in your intake manifold, install one in the usual way and in the other hose install a valve that has a large flowing capacity. The second one is not connected to the valve cover, you need to leave it breath fresh air, and when you have the right combo, install a filter of sorts over the end of it so that you do not get dirt into it.

When this is all done, your two mixture screws will actually have an effect on the idle once again. You will have to adjust these.

I will post this message on the forums because some others might need this info at some future date.

so basically i need to let the engine breath i have a question would drilling a hole in the butterfly's work on its own or do i need to do all of the above i think i only have one pvc fitting on the intake....i know that its to much cam and im over loading but i figured there was a way to compensate...have you ever had this prob and exactky how big is the hole gonna have to be..?

i was wonder about how high of a stall and will the holes compensate enough to no longer need a stall or should i go ahead and spend the few hundred dollars...?

Depending on the weight of your ride, you might need a stall as high as 4000 rpm but at some point it will no longer be streetable. I would not go to 5000 rpm.

As for the holes in the butterflies, that is all you need to do. I would start off with one hole in each of the two front butterflies the size of 3/32 of an inch, for a total of 2 holes. This will allow for better air fuel mixture at idle. Let me know how it goes.

Ok man will do so no stall and a couple holes works for me i happen to have a extra set of butterfly's so its not a big deal i will keep you posted..thanx alot

does the position of the holes on the flys matter..?

Yes, I would place the holes in the front half of the flies and then more towards the front of those halves.

Hey, if you find that you get too lean because you drilled a 5/32 hole, just JB weld them shut and re-drill a smaller hole. Good luck, man!

Hey, let me know!

ok one more stupid question..lol the guy that had it before me installed an adjustable vacuum advance that i unhooked and vacuum plugged would that cuase it ...i really apreciate your help man and by front you mean closer to the headlights right...

It's not like your setup makes vacuum.

im gonna take that as a no it doesnt matter..lmao

Originally posted by dominick21m
ok one more stupid question..lol the guy that had it before me installed an adjustable vacuum advance that i unhooked and vacuum plugged would that cuase it ...i really apreciate your help man and by front you mean closer to the headlights right...

The problem with vacuum advance is that with a cam such as yours, when you get to idle, the vacuum falls off as does the advance, which then slows the idle and causes it to stall. In your case it is better to work without vacuum advance, because where you need it, it don't work!

As for "up front towards the left headlight statement", think of it in this way. If the distributor was the face of a clock, and when looking down upon it as if you were standing on the roof facing forward with the wind blowing in your face, place the number one wire in the 11:00 postion. And I am talkin A.M. hehhehehehehe hahhahaha!

Streets nrr.

yea man i dont use my vacuum advance thats why i asked now i just got to find a drill bit..lmfao neways ill get back to you ima find a bit tommorow and see what happens.. once i drill the holes i will need to retune the carb right. damn im saving on gas here hehehe

i was thinkin about getting a really long bit lmfao jk whats nrr mean if you dont mind me asking..?

Originally posted by Streets
Sure hope he takes it off the manifold 1st TY... nrr..

Whatever! Gesch, if I have to tell dom that, we got more problems that the idle of his motor! hahahaha ...rr...

no doubt like a retard on the lose..lmao ok im drilling now..lol wish me luck...