Need Someone Smarter Than Me
 

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.

Are you dumping the exhaust and water right out the end of the riser without any other hose attached? If so, that is your problem. Add some hose to it. In the boat, you have a piece of hose and a tip on the end of the riser to help with scavenging. If you have an engine that is close to reversion and you run it with the risers open, they will revert. You can add about a foot or 2 of exhaust hose and it should stop. I found this out the hard way once.
Eddie

Eddie is on point when he mentions the hose and tips. I had a lot of reversion on mine while running it on the test stand, but when I put the hose and tips on, it helped a lot. I think in my case the salisbury flappers on the ends of the tips helped to interrupt the back pulse of the exhaust. I still had enough issues to force me to modify my header collectors, and I am still scratching my head over that, as it is a fairly mild cam.

Since you are only seeing reversion with one engine, I don't know if this completely answers the question. Did you replace the timing chain in both engines? I wonder if a stretched timing chain could retard the cam timing enough to induce reversion on an engine that is on the edge.

A leakdown test might be in order, especially since it only seems to be an issue on the even bank of the one engine. If for some reason a valve is not sealing properly, it could induce reversion. It's possible for such a situation to not really show up on a simple compression test, but the leakdown will tell the tale.

Try Eddies advice.

I've seen where bravo setups with short tails, revert, where on TRS/SSM tails, it doesnt revert. Basically because the tails/hoses are longer, even if the water is introduced at the same distance from the riser to manifold joint.

Thank you all for the help. I tooks the hoses from the boat and installed some tips and it made a big difference. There was still a little reversion but it idled much better and after a carb adjustment it ran really good. I am going to throw them in the boat and try them this week. Just for fun I took the hoses and tips off again on the stand (after adjusting the carb and timing) and it began to revert again. I am happy with the easy fix just wish I would of found it sooner.

Great ideas thanks again!!!!!!!!!!!!!!!!!!!