hblair

A few months ago you guys may remember I had a backfiring no run issue on both engines. After removing the blower setup, going back to N/A, then going back to the HEI ignition, I found out the MSD pro billet ignition was apparently the problem on both engines.
Shortly after that (probably caused by the backfires when were troubleshooting the ignition problems?) we noticed the right side of the left motor had a blown head gasket. Water leaking out between the head and block. When we replaced the head gasket everything looked normal. The oil never got frothy at all. Fast forward two months...

After running the boat since then, trip to the gulf, 6-8 trips to different lakes, etc. Everything is great, except..

The left motor occasionally backfires out of carb and sometimes exhaust and dies at idle. (Does not backfire and die under load) The left motor is noticeably not as strong as the right motor either. The weiand 256 blowers are different, one has teflon strips, one doesn't. To eliminate the carb/blower, I swapped the whole carb/blower assemblies left to right. Same problem. I'm wondering, Possibly need to go back and adjust valves on the head we changed the gasket on? There is no valve noise at all..

hblair

We're thinking maybe we adjusted valves too tight? Noticed the right exhaust flapper on the left motor is torn off and gone from the backfires.

Griff

It is possible that one or more valve is adjusted slightly too tight and causing your issue.

Tinkerer

Do a compression / leak down test.

getrdunn

iTrader: (7)

Like tinkerer mentioned to do comp test and leak down. But before that do what griff said. You mentioned significantly down on power.... How much rpm difference when fully trimmed at wfo? What kind of exhaust valves you running? I would imagine after resetting valve lash and doing a comp test and leak down you'll find your problem. I assume you swapped out distributors this time around also. Check wiring over real well also. I know it sounds elementary but running the engines at night in the dark can detect some difficult to diagnose issues from time to time if something is shorting. Cracked spark plug can jump across and ground out etc? Bad ground?

Tinkerer

That and one stupid setting on a computer in my case. The instructions kind of stink.

hblair

Thanks guys, good info, i haven't swapped distributors. The HEI's can only be turned like 20% of a turn before it hits the intake. I bought another cap and coil to try on the left motor. I'd rather do that than mess the timing up. I'm gonna do that before I pull the exhaust manifold and valve cover.
I hope to get time to check it out tomorrow evening or Saturday morning.

hblair

The right motor turns 5300 and keeps climbing as the left motor will only go 4400-4500 tops.
I'll do a compression/leak down before I turn any bolts on the motor.

Edit...I forgot the brand of valves, will have to look thru my paperwork tomorrow. Getrdunn you're getting my hopes back up for electrical problem.

hblair

I convinced myself last night to go ahead and pull the manifold and valve cover off and check the valve adjustments. I noticed gas in the exhaust manifold on the front two passages as I pulled it off. Hmmm..
Checked the valve adjustments, all good. Checked the compression, right at 150 on all the cylinders on that bank. I charged all the cylinders with 125 psi, I quit after 5 minutes of watching the gauge not move at all.

Soo basically wasted my time on the valve train. I replaced and gapped all the plugs on that bank and replaced the 2 wires on the 2 cylinders that had gas in the exhaust passages. I replaced the coil, cap and hardware on the HEI. I ran that motor in the shop, sounded ok. I plan to put it in the water tomorrow afternoon.

hblair

I ran it today, still the same. That's a head scratcher. The right side cylinders all checked good compression. And didn't bleed pressure off. I'm thinking the valve train is good. There was fuel in the two front exhaust passages on that side. I'm thinking check all cylinders (left bank too) and replace all the plug wires.
I never have simple easy problems.