I would verify cam timing before I pulled the engine. Put a degree wheel on it and check it.

It's more than a vibration, it's the run on that's the bigger issue.

I’m aware, I think it might be a timing issue, but could be caused by the jetting in the carb. What I was wondering was if he has a weak cylinder that could be causing the vibration.


OP, I know this is going to sound off the wall, but do you have another carb you could swap and see how it runs?

I've done a compression test-
1- 215
3- 215
5- 210
7- 215
2- 215
4- 215
6- 205
8- 210

I've actually never heard of a running compression test.

I just replaced my original Muncie M21 with a brand new Autogear M20. I have not had the clutch off, but I feel that's the root of my problem. The rotating assembly was originally balanced with a flex plate. I also got to see, in person, the engine running/revving on a stand before I bought it and it ran normal with the flexplate at that time. I removed that and installed a new flywheel and McCleod clutch, which in theory, should be plug and play since everything is externally balanced. But, I think that is not my case.

I originally had a Holley 830cfm carb and replaced it with a new Holley 750cfm over the winter.

Frankly, I've reached my limit with the unknowns of this engine. I don't know the exact piston spec or the exact compression ratio, etc. I'm ready for a known engine so I can enjoy the car.

This whole deal has been beneficial though because I've learn so much from everyone's help and the troubleshooting research I've done. :thankyou:

Daniel

Well if it ran good before and all you changed was the flywheel and pressure plate I’d pull that off and have it balanced. Good time to run it without the flywheel too. Was it a McLeod flywheel?

It would suck to build a new engine and find out you still have a problem.

It's a PRW flywheel. I spoke with PRW and McCleod and they both said the flywheel and clutch I have should be compatible with each other in terms of balance.

I considered having only the pressure plate and flywheel balanced, but from what I understand, you have to balance the whole assembly for an accurate result- balancer, crank, rods, pistons, flywheel, and pressure plate.

I'm not sure how I'd start the engine without the flywheel.

Daniel

Static compression numbers look good. I ask about a running compression test because I've seen lifters collapse when running a few times and you'll have 7 good cylinders and then one real weak one.

Did this start before the carb swap or after?

Do you have the flex plate that you saw the engine run with? Or just any flex plate for that matter? I'm wondering if the flywheel being a lot heavier then the flex plate is making the vibration worse and its actually been there the whole time, you just couldn't notice when on the stand.

The vibration was there before the carb swap.

Unfortunately, I sold that flexplate last year and don't have another one. You could very well be right with the heavier flywheel exaggerating a vibration that's always been there.

Daniel

You mentioned using a PRW flywheel, which one did you end up using?
https://store.prw-usa.com/products/f...eatured&page=1

I used their part number 1640081. I've spoken at length with Shaun, one of the tech's at PRW, and he confirmed early on that the actual flywheel I received is correct for my application.

Daniel