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Discussion Starter · #1 ·
I have an 87 Monte SS with a H.O. 350 crate engine with an LT4 Hot cam kit. It has an Edelbrock 750cfm and an MSD ignition. The problem i am having is that it stumbles at cruising speed and when i accelerate. When it gets up to real high rpm's it seams better and thats about 5000 rpms. I just put that carb on there. But it was doing that before i put the new carb on. I changed all of the plugs and wires.

What else could this be? could it be a worn distributor gear? It doesnt seem like a fuel problem. Anyone have any sugestions?
Thanks guys.
 

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Is it a stumble, hesitation, bog? Are there any noises or backfiring/popping?

Where is the timing set? Do you have vacuum advance? If so, where is it connected? How much timing at idle, and at what RPM is it all in?

These are a few things that will help determine what your problem is.

How was the carb adjusted (air mixture screws, the two on the front of the carb).

Royce
 

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Discussion Starter · #3 ·
The thing is that nothing was adjusted between the time it ran fine untill now. The timing set is on the front and the timing is set properly. It does have a vacuum advance.

Come to think of it there is a slight backfire sometimes. I think it feels like a hesitation.
 

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Well if nothing has changed since it was running fine until now. I would suspect bad fuel. I bet something has changed, How about the weather? This can have a big effect on performance. I would guess it is much cooler now than it was before. If that is the case you might just be running a little lean now. This would cause surging and can cause backfiring. Put a fresh set of plugs in it and go for a ride, shut of the car at speed (careful not to lock the steering) pull over and read the plugs, see if they are showing lean.

I just saw your other post about timing. So we won't go there.

Royce
 

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Discussion Starter · #5 ·
I do live up here in Maine and it has got a lot colder. That is what i thought at first but i figured it would stop as soon as the car warmed up all the way. I will try to richen it up a little and see what happens. If i burnt a valve or something would this cause this and if so how would i find out if i burnt one?.

I checked my distributor gear and did my valve lach while i was waiting for a reply and i did find one rocker that was kind of loose. Maybe that will straighten it up a little.
 

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When I mentioned the weather. I was not talking about problems warming up the car, I was refering to when the air is cold it is more dense. This means there is more oxygen in the air and you need more fuel to keep the proper mixture. If you were right on the edge with your carb tune before (in the warm weather) it is possible that in the cooler weather your carb is now lean.

Yes, a loose rocker can cause what feels like a miss. If you burned a valve (warped) you would know it. You would have what feels like a misfire and or have backfiring. The valve would basically not close all the way.

Royce
 

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Discussion Starter · #7 ·
Ya i know that you were refering to the cold atmosphere. I thought my car would actually run a little better with the colder air but only if my car was warmedup all the way.
I tightened up that valve and it seems to be working good now. Thanks for all of the good advice!
 
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