[neil_home]

I was wondering if anyone had some pointers on what to look for on a 302 that surges in a "no load " condition. Other than that its great. I have the timing at 10 degrees before TDC initail timing. Bumping the timing up helped. I put a new cap and wires on, that also helped. It does it just a little now. Seems to be when hot and just cruising under no load.
Here are some spec's on the engine:
79 302, GT40 -p heads, stock flat top pistons, 4100 carb from 352, 79 Duraspark ignition, Comp cam nostalgic hydralic cam, roller rockers.

The tach stays constant. But the car feels to pull and let off slightly with out you changing the position of the gas pedal. Change the position toward the floor and it pulls like crazy.

Thanks, Neil

By the way, someone suggested that the Dura spark distributer might have way to much advance with the cam thats in it( cam was degreed to 0). I still have to try running it with out the Vac advance connected.

 

[Sportsroof1970]

Have you already ruled out the brakes as a possibility? When drums are out of round or discs warped, the brakes drag, it can make the car surge until you get some speed going, then you no longer notice it.

Good luck..

 

[L20068]

I agree with the brakes idea. I was thinking "carburetor" but you said the tachometer stayed at a constant RPM, suggesting two things:

1.) The problem is not related at all to fuel delivery or actual engine velocity

or

2.) The problem IS related to fuel and engine velocity, such as a carburetor pump or a bad power valve, and your tachometer is working incorrectly.

I'd definitely have those drums/discs taken a look at. Might try running some Marvel Mystery in a tank of gas too.

 

[neil_home]

Everything in the engine is brand new except the distributer. The carb was rebuilt by me. Ill have to watch the tach again, I just put it in yesterday. I also have a lifter that comes and goes, or maybe an exhaust leak, haven't figured that out either. A mechanic I trust seems to think it is just " that tin sound from the headers". The brakes are a good candidate. Ill have to check into that.

Others have suggested just to run it for a while. I have about 200 miles on the complete rebuild.

 

[motorhead]

If you can't see it on the tachometer, there is a distinct possibility that what your hearing is perfectly normal for a carbureted engine. This is especially true at idle with a performance cam. Put a vacuum gauge on the engine and see if you can see the surging on it. Try disconnecting the electrical to the alternator (BE SURE TO NOT SPARK THE WIRE TO THE BATTERY). Maybe all your hearing is when the alternator is pulling power. A volt meter caould show if the surging was caused by the alternator. You can see the voltage spike when the engine drops. Disconnect and plug the vacuum advance to make sure your just not hearing a minor change in timing caused by vacuum.

Assuming it is a real problem. One thing tha came to mind is the float in the carburetor. If the level is too high maybe a very little can splash over and into the engine causeing a temporary situation. The power valve in the carb could also cause a situation but its not high on my list.

 

[camachinist]

Seperate your plug wires and see if anything changes...

Nice engine, BTW *G*

 

[cobrapatrol]

I know you said everything was new but did you install new spark plugs? And set the gap? I cleared up low speed surging problems before by installing a new set of plugs.

 

[neil_home]

Thank you, The old wires were stock. They were separated. And it was a little worse. The plan is to separate them again. I have not found a path to run the wires that would make them neat and not cross each other. Also they touch something metal the whole path. So I thought I would try to bundle them to keep them off the headers and valve covers. They are numbered and 9MM so they are run pretty much the best way I could. I did not think that cross fire was much of an issue with the newer wires today.I have to find some wire management that can handle the 9MM wires.

 

[neil_home]

Yes I did put new spark plugs and checked the gaps. I had to. I used the GT40-P heads and they take a unique plug.
Thanks, Neil