c3 engine stutter

Since several private forums like JLA Enterprises have begun copying all we say and do on alt.autos.corvette and getting their piece of advertising dollars for it, while we the originators of the information get nothing, several have begun to migrate away from here so you may not get a lot of helpful answers. So to JLA and the others like them I say...

FUCK OFF!!!

Having said that, there could be multiple reasons for your stutter. It could be fuel, ignition, or valves float due to improper valve lash or a bad lifter or two (not likely, but possible, besides it would make lots of noise and run very badly at idle, if this was the case). Sounds as if you already ruled out ignition, so fuel delivery is the next more likely cause. Fuel filter, vacuum leak, carb adjustment. I'd start with those first, then move to the more expensive, more difficult possibilities. Are you sure it's a Weber Carb? I can't say that I've ever seen a single Weber carb for a small block, or a big block for that matter. Is it one of those nifty multiple two barrel setups, or what?

TomC '90 ZR1

H'm, I had a very similar problem in another car once - ignition got raggedy and "broke up" over a certain RPM but everything checked out fine in the garage. Turned out to be a badly routed ignition primary wire that was creating an induction misfire over a certain RPM.

-- Vandervecken

I had the same problem with my 74 L82, after doing a fuel pressure test we found out that the pump was only putting out 3.5psi and the specs call for

This is a possibility, but I think you would see some manifestation of this problem in the tach needle, bounceing or fluttering, jumping around somehow. I would key in on the fuel delivery like you suggested on your first post. And to chime in with the other fuel suggestion, test for the pumps delivery volume as well as pressure, with two carbs to feed volume might be a problem that is hard to detect. I would also be interested in how the power valve(S) were set up and functioning inside the carbs. Was this car tuned at a high altitude by the first owner and then you bring it to a much lower alt.? If the engine was dialed in for high alt. It might be running lean all the way around. Good Luck

valve float

Is a phenomenon independent of stem-rocker clearance. Valve float occurs when engine rpm is high enough that the force of the valve spring is insufficient to overcome the inertia of the pushrod and lifter and keep the lifter in contact with the cam lobe. Early roller lifters did not have guides to keep the rotating center of the roller aligned with the centerline of the cam lobe. As a result, the lifter could partially turn in the lifter bore. It turns out that a roller lifter turned sideways on a cam that has a really steep opening ramp is a bad combination and usually made really expensive noises when everything started coming back in contact again. Modern engines have indexing guides to prevent that.

Charlie

You're right about the tach. Good point.

-- Vandervecken