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Originally Posted by budfreak1
me and my dad are putting together a 1977 nova RS with a olds 455 motor. when we start the engine and run it for any length of time, as soon as you kill the motor antifreeze begins shooting out of the overflow and the radiator is full of suds bubbles! we don't think there's a thermostat in it. theres no oil/antifreeze mixing and we checked the intake with spray and found no leaks. we are completely stumped!!!! also, we can't get the idle below 1500 rpm and the idle screw is all the way out. the engine won't even die when we tighten the mixture screws all the way in, it actually speeds up! we found every vacuum leak we can and plugged them all off. we found 4 ports that were open and we plugged them but it only brought it down 300 rpm from the previous idle of 1800rpm. HELPPPPPPPP!!!!
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As for the coolant problem:
You sure you have the coolant mixed right? Could just be that there's not enough antifreeze. I know the water neck on SBC and BBC motors is always a problem source...make sure it's tight and not damaged. Maybe you got some kind of chemical in the mix. You could drain and replace the coolant if you haven't done that in awhile.
As for the idle problem:
It could be that either the screw is stripped or maybe it's the wrong screw entirely and not making contact. What size carb are you using...it could be too big. Also check to make sure the throttle cable and/or cam are not sticking.
This could be a ton of things so i'm just throwing out ideas.
How about the intake...hold old is the gasket? Even the slightest pinhole could cause a high idle like that.
I think most likely the problem is with the carb. If it's an old carb maybe you simply need a rebuild. Make sure the butterfly(s) is/are sealing in their seats when the throttle is at idle.
If they are seating correctly, then that means the problem is somewhere between the carb and heads. So then concentrate on the intake. A gasket change is pretty simple on that motor, so it might be worth it if the gasket is not too new. It would at least eliminate a major possible problem source.
If none of this works, check your plugs for residue and see if maybe you are running too rich. It's unlikely that a fuel problem would cause this sort of behavior, but not impossible.
Since I don't know how old this motor is or what kind of new parts are in it, it's hard to say. But if the gaskets haven't been done in awhile, that would be a great place to start. Especially at the intake.