Long story short...... I recently had my twin 540's rebuilt, basically valve job, new cam, lifters, bearings ect.....basic rebuild. Everything is exactly the same as it was before (same exact cam, lifters, just new from the same manufacturer's....same emi exhaust) (have ran these 540's for 8 years) . Get them all back together, run them on the stand and the one is getting reversion pretty bad. The other engine is fine. The cams were degreed when installed.

I am running EMI thunder exhaust, if I dump the water from the top of the manifold out (basically skipping the tails) it runs great. If I hook up water on one side and run the other dry all good. If I put water through the other side (left side looking at the engine) and run the other dry it gets reversion so bad it won't idle. I switched the manifold from the other engine and it didn't help still same results.

I really don't know where to go from here. Any Ideas would be appreciated. I didn't get into all the specs because I have run this exact setup for years.

Thanks in advance
C

Is it possible the one tail is leaking? Try switching tails between the motors and see if the problem follows, or even left tail for right on the same block.

Ryan

Make sure spark plug wires are correct and Do compression test take a few mins and learn a lot. Same spark advance?

I swapped manifolds and risers didn't help. I will try a compression test and check the wires.

Did a Compression test, all the cylinders were within a few lbs of each other. Could the ignition timing cause reversion? I could swap the whole distributor from the other engine if it's a possibility?

If it's a hydraulic cam you may have a lifter a little to tight (back the adjuster off for maximum compression with the compression tester. If it's a solid cam tightening lash 4-5 thousandths is like advancing the cam 2 degrees. You if it's solid try giving it a few more .001's lash. You can also try backing the cam up a few degrees. What were the cams put in at? Did the same guy degree them with the same wheel originally?

It's hydraulic roller. Cams were put in straight up. We degreed them just to make sure they were right. They were installed straight up originally too.

yes timing could have something to do with it did you put a light on it. What kind of distributors u have?

Any exhaust leak will promote reversion.

MSD distributors. Timed it with a digital light .

It's not an exhaust leak that is what I thought it was at first but everything is good there.