Another issue for the brain trust..
 

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..

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.

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

Do a compression / leak down test.

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?

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

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.

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.

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.

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.

Has this motor Ever pulled the same RPM's the other motor pulls? Or did it start after the backfire problems.

Chris

Did this issue start after you replaced the left side head gasket ? You had to pull the intake to replace the head gasket....MIGHT be an intake gasket on that side. I know it's a long shot...but spray some WD around the intake/head joint the next time you run it...you never know.

Do you have fuel psi gauges installed ? Wondering if the troubled side has a little too much psi and overpowering the needle and seat ?

Alternator charging well at idle on that motor ?

Distributor clamp and bolt clean on that motor ? Threads in intake ? Only way for distributors without ground wires to ground is thru the clamp grounding distributor body to intake manifold. if questionable try separate ground wire from dist body to ground lug.

Do these carbs have electric chokes ? If not grounding properly on this motor maybe choke staying closed or partially closed ?

Yes, they pulled the same rpm's when we had the air gap intakes on them before the blowers.

The problem was going on before the head gasket deal. Good point sprink, I've thought of that and looked closely at the gasket when we swapped the blowers and didn't see any signs of backfire, good idea on the wd40 though.

SB, we do have gauges installed and both sides are showing 7.5 psi at 4 grand. Haven't checked the alternator but its new (doesn't mean anything) I'll chec the distributor ground. Motors are manual choke held open all the time.

Something I thought of yesterday, back when we were having the msd ignition problems, we were trying anything. A friend of mine suggested gapping the plugs at like 045. Thats a good bit more than what it was or what the right motor is. I wonder if it's too wide and the ignition is putting out a weak spark across that gap. When I replaced the ignition parts saturday I noticed the rotor was fried. Maybe because the plug gaps are way too wide?

.045" should be okay but the norm is .035" with a close second amt of people setting at .040"

Yes, the larger the gap the more energy the coils/modules/boxes will put thru the entire system.

With the large cap HEI's If you have stronger coils and/or use ign boxes, the caps must use the low resistance MSD center button or they will literally melt and erode in very short use.

https://www.summitracing.com/parts/MSD-8412/

https://static.summitracing.com/glob...sd-8412_ml.jpg

Thanks SB. Good information.

Here's the old one..
http://i159.photobucket.com/albums/t...svfjtnhhq.jpeg

New one..
http://i159.photobucket.com/albums/t...pst0eu528r.png

Since all of the hard parts are in order and you're getting unburnt fuel passing through it seems like only the ignition is left.

Apparently a collapsed lifter can cause the valve to hang open and backfire through the carb. Just one more thing to look at.

We pulleded the distributor out and examined it. We went ahead and swapped the distributors. I checked continuity between the distributor and the block. Good continuity. We pulled the plugs out and gapped them to .035 like the other side. Nothing has helped. I've got some msd plug wires coming. That's the only part of the ignition we haven't swapped out. If that has no effect I'm not sure.

Also I sprayed wd40 around the intake at idle, no difference. And I feel pretty good that the intake gasket isn't leaking.

Double check the ground strap in the cap under the coil which goes to the center spade connector.
I have seen them left out before and cause all kinds of crazy problems.

I'll check it all out again this afternoon or in the morning.

Guys I'm at a loss. I took the distributor back apart and checked everything to do with the ground. It all checks out good. Perfect continuity. I'm as convinced it's not ignitition as I was convinced it was the ignition a week ago.
How would I get a backfire out of the carb from ignition?

I plan to pull both valve covers, intake manifold, and really check out the valves rocker arms and especially the lifters. Heck I might pull the heads just to look at the valve seats.

I took my wife out and ran the boat some today at low rpm's and noticed the power is dropping even more. I hope I haven't hurt it by running it.

Symptoms:
Backfire and die at idle
Hard to start, (usually backfires thru carbs once or twice before starting)
Lack of power, only turns about 4K now
Found raw gas sitting in two front exhaust passages of right exhaust manifold

Things done/checked/replaced:
Swapped whole blower/carb assemblies
Replaced coil, cap, rotor, button with new parts
Swapped the whole distributor from other motor
Checked the ground on the distributor numerous times.

What gets me is the backfire thru the carbs. Do you guys know of a situation other than valvetrain issues that could cause this? (Other than ignition timing which is good)

I guess I'm going to check the compression and leak down on all cylinders next. (I did this on the right side already and the two front cylinders checked good but have raw gas in the passages??)

This is definitely a strange one. Like you said last post comp test amd leak down on all cylinders. Is it possible to swap out one harness plug at the engine to the other? Not saying to do this at all at the moment without thinking it through but... Kinda process of elimination if is somewhere in harness. Hold that thought for now.

Very lean will cause this too.

Double, triple check the firing order and the plug wire locations. I know it sounds silly but worth a look!

That never sounds silly cause we all work long hours and can get agrivated with issues that keep us from doing what we love to do. Sometimes it is those things that are so basic that can be the ninja bug that drives us nuts. Even going back to confirm tdc. Did we address possible timing chain etc? Can't remember.

Correct but sounds like OP has raw gas in his exhaust. Yet with that said perhaps not firing on those cylinders. This isn't even my boat and it's driving me nuts.

Problem solved. I always preach to the guys here to check the simple stuff first. Always check fuses etc. first, then after the easy likely stuff checks out, then the complicated conpiracy theories.

Well, I bamboozled myself.. The #2 and #4 plug wires were crossed. I'm too happy to be embarrassed. Both sides are peppy and healthy now.

Thank you all for your time! Sorry it was something stupid. Thank you Jim for pointing out the obvious.

You just proved your man hood ! Kudos.

Thanks for the follow up.

For others, when we suggest to check simple things like this, don't give us an attitude back, because schit happens !

How long do you think it took me to find a soda bottle cap under the carpet (not floor mat, actual carpet !) that was causing ignition issues in a car ?
Battery was in trunk, and ignition box behind glove box. Wires ran under carpet. Cap needed a little pressure to short a wire. No pressure, no short !

No issues when back to the shop because there would be no passenger !

Fuk !!!!!!!!!!!!!!!!!

I spent two hours at the boat ramp trying to figure out why I had a miss a few weeks ago because of the same thing. Happens to the best of us! Glad it was an easy fix!

Always remember: "18436572" LOL. My Dr is a Car guy and has restored a few Camaro's and Corvettes. He did my last surgery and when I was just coming around after general anesthesia after surgery he asked me " OK John...firing order Chevy V-8?"...My answer...18436572...He said..".ok...He's ok...turn him loose in about 30 minutes !!!" LOL

I'v replaced probably more ignition wires than 95% of the people here, and I still use these at the distributor when I have them, not to just make it easier for me, but the next guy (owner included) also.

http://static.summitracing.com/globa...RG-4472_xl.jpg

My new BBC has a double swap firing order... "1-8-7-2-6-5-4-3"
REALLY messing me up.. LOL

Guess who's going to the river this afternoon?
I just love the sound of these things. Music to my ears...
https://youtu.be/6blqc3QndwU

So glad you found the issue and glad I could be of some help! Now go out and enjoy that beast!

Thanks
Jim

These are great. Doesn't matter if your a novice or a pro. Can't screw up. Especially when your azz deep up upside down looking like a wine cork puller in your bilge doing multiple things at once. Then a little burn here and there (ouch) to top things off. Gotta love it though.

when engine is dressed and marinized it would appear all the plug wire lengths etc could never get switched around but with a little trouble shooting here and there wires can get pulled and the next thing you know you have two or even three the same length dangling in the bilge. I always make a habit of following from and to but these are time savers.

She was running good. I was real happy with it. I am still running 22 pitch props. I have some 25 pitch I just bought but the hub adapter is different so I can't run them yet. I spun the Rt motor up to 5700 rpm which was apparently more than it wanted. I checked my guages and noticed the oil pressure was low on the Rt side. Killed motor. Opened hatches. Rear seal apparently let go. Oil everywhere on the back of the motor. Limped back on lt side. Got back to shop. Put oil in Rt side. It was 2 quarts low. Fired it up. No oil pressure. Killed it. That's where I am right now. Supposed to carry family to gulf shores in a few weeks. I'll be pulling the motor, cutting the oil filter open and going from there. :lolhit:
This school of hard knocks is expensive.

Did you weld the pickup tubes in the oil pumps? If not, do your self a favor and pull both engines and weld those pick ups to the pumps...