The Stovebolt Site Forums The Shop Area Engine Shop Intermittent miss at idle

I have been maintaining a 1964 Nova 230 with Powerglide for a customer for about 10 years now. This car has had a intermittent miss at idle sense they have owned it. I recently rebuilt the engine and thought finally it would idle smooth. Well three rebuilt carbs later, it still has a intermittent miss at idle. It is not like one cylinder is missing but more like all cylinders cut out. Being an automatic trans this can be quite annoying. This car has a Pertronix ignition which I temporally removed and installed a HEI distributor. I hooked power for the HEI directly to the battery, to eliminate any wiring problems. Still no better. I still believe it is carburation that is the problem but I am at a loss to know what I should do next.
Any ideas? Thanks, Dave

Dave,

My thought would be if you don't have the answer, I sure as heck don't, but that has never stopped me from sounding off before.

Were the valve spring pressures checked when the head/engine was rebuilt. I had the same issue on a SBC and it turned out to be weak valve springs.

This would be a perfect troubleshoot for a scope. Good luck


Stuart

Dave,

Did the engine rebuild include new hydraulic lifters?

Stuart

you must be kidding me..........i picked up a 67 nova with a 250 in it a few years ago........the nova would always run rough....i took off the old carb rebuilt it.....it didnt help...ran rough....went through the whole car...coil..plugs..wires...on and on and on.....i had a few single barrel carbs lying around and starting messing around with them....5 total .....no change in rough idle running.....the intake manifold where the gasket goes between manifold and carb is flat as is the manifold top..(
no notches on carb intake)...so this went on for years...yes years...i found a 250 6 cyl. out of a 67 camaro with all the goodies....power steering...carb....etc...so this carb was the same specd. for the 250.....well guess what....the car now idles nice......if i would have rejeted the first carb i had i would have found the problem earlier.....i must admit i did have one small crack in vacuum line from intake manifold to valve cover and that was 1/2 the problem....i hope that helps....that thing tormented me for a few years............

It does sound like a lean idle miss, my 250 will kind of do the same thing if I lean out the mixture screw to much. Joe

Had the same problem with a completly rebuilt 235. At wits end I pitched the rodchester intstalled a new Tillotson carb problem solved,.

Lean carb will definitely do it and so will plugs that are too cold. This is why I buy every AC C44 that hits Ebay for my GMC inliners. Vacuum leak will do it too. I used to squirt upper lube all over the manifold while it was running. White exhaust smoke meant sucking upper lube in through a vacuum leak.

A Tillotson carb on a 235 Chevy?
Denny G

Dave - sounds like vacuum leak. may also be partial plugged vent to float chamber, will cause fuel level to starve/surge causing lean mix. Simple test and check for vacuum leaks. Start engine and fast idle (no breeze) use small propane torch to check. just turn on the gas, no sparks. go over all manifold junctions and hoses and carb base. you will know when you find the vacuum leak as the engine will increase RPM. Think Chevy!

It's a tillotson universal. I bought two of them on ebay as nos with manufacture dates in the late 50's. Bolted one on works perfectly, beter than any rottenchester I've ever ran. Good idle mid and high range and improved my mileage.