hey guys, this is my first post to this group but ive seen a lot of good
things and knowledgable responses so i wanted to post. I have a 79 L48 w/
edelbrock intake and 3/4 cam , weber carb. I dont know specs on cam as it
was installed by previous owner. Anyways the car runs/ looks great with the
exception of whenever i give hard acceleration or a steady acceleration
between 2nd to 3rd or 3rd to 4th , if i let the rpm go over 4000 rpms the
engine stutters and acts like it drops a cylinder. When you let off the
accelerator and shift, it accelerates fine until i hit that 4000 mark again.
Mind you I dont make it a habit of pushing the engine that hard but its just
one of those things that drives me nuts. Ive replaced the plugs and wires
( plugs looked fine btw) the weights in the advance are fine, the only thing
i havent looked at is the fuel system , tho after reading a post here about
a stuttering 69 i may. any thoughts?
Larry in Va Beach
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...
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
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?
yeah, im sure its a weber lol..obviously an aftermarket setup from previous
owner and yeah its multiple 2 barrell with adjustments for left and right. I
had one guy mention valve float before and i guess my only thing is , is if
the lash was loose enuff to float a valve, wouldnt ya hear a rocker arm
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.
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.
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
7-8psi. Replaced the fuel pump and the problem was solved. good luck
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.
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