One Rich bank, one lean bank.

[maryhannaj]

I figured I would start a new thread for this issue. I have a 1982 115 hp Johnson. When i run the motor on muffs and then pull the plugs, The starboard bank cylinders are running leaner than the port side bank.
I understand the jetting process and the way the carbs work, so why would the cylinders on one side running off of two seperate carbs and two seperate barrels be consistantly leaner than the other side all together.
The side that is leaner is still what I would consider a good safe tan color so maybe the other side is running too rich. To me this is pretty confusing because I dont know which side is right. Either way, one bank is different than the other and while examining the inside of the combustion chamber with a flashlight, even one of the piston surfaces on the leaner side appears dryer than the other. As usual, I could definatly use some input from anyone willing to help or has experienced this issue as well. Thank you all!

 

[Bosunsmate]

Re: One Rich bank, one lean bank.

Post a picture of your plugs if you can.
It can be caused by spark differences not just fuel too and also temp of the cylinders.
Check they are the same heat and spark is consistent on both sides with a sparkplug tester

 

[maryhannaj]

Re: One Rich bank, one lean bank.

I will post some pics as soon as possible. Allthough the plugs did jump a 7/16 gap and they are all bran new, gapped at the same gap of .030. Thanks for the reply!

 

[maryhannaj]

Re: One Rich bank, one lean bank.

Hey, check it out. I just got promoted. Nice!

 

[Bosunsmate]

Re: One Rich bank, one lean bank.

jolly good show, have some rum

 

[emdsapmgr]

Re: One Rich bank, one lean bank.

I think you are checking plug color at idle. (The other method is a high rpm throttle chop. You'll likely get different results.) Check to be sure both heads are running up to normal temps. If one of the two stats sticks open, that head can run cold and might make enough difference in plug color to make you think it's lean (or fat.)

 

[metriccrescentwrench]

Re: One Rich bank, one lean bank.

Check to be sure both heads are running up to normal temps. If one of the two stats sticks open, that head can run cold and might make enough difference in plug color to make you think it's lean (or fat.)

THAT, plus the fact that running on muffs isn't very indicative of what the engine's going to do with the boat in the water with a lot more exhaust backpressure.

 

[maryhannaj]

Re: One Rich bank, one lean bank.

I am only checking it on muffs for sure. So no intermediate or high oriffice checks even possible this year. I also know that both heads become warm to the touch but not uncomfortable in any way. The thought of a sticky stat never even occured to me. My line of thinking was an air leak somewhere on the leaner bank in an area that combines the two chambers at some point. As far as I can tell, that area does'nt exist.
Question; How would the back pressure of the water on exhaust flow effect it in this way? I dont understand? Also, how would a stuck thermostat change the efficiency of the fuel burn during detonation?
Thanks so much!

 

[boobie]

Re: One Rich bank, one lean bank.

If the cyl is running to cold it will not burn the fuel properly.

 

[joeseif]

Re: One Rich bank, one lean bank.

Could it be related to the reeds?

 

[maryhannaj]

Re: One Rich bank, one lean bank.

I thought about the reeds too but they are seperated as far as i can tell. I think it would be too much of a coincidence that that would occur.

 

[Tim Frank]

Re: One Rich bank, one lean bank.

When i run the motor on muffs and then pull the plugs, The starboard bank cylinders are running leaner than the port side bank.
I understand the jetting process and the way the carbs work, so why would the cylinders on one side running off of two seperate carbs and two seperate barrels be consistantly leaner than the other side all together.
The side that is leaner is still what I would consider a good safe tan color so maybe the other side is running too rich. To me this is pretty confusing because I dont know which side is right. Either way, one bank is different than the other and while examining the inside of the combustion chamber with a flashlight, even one of the piston surfaces on the leaner side appears dryer than the other.

Doesn't sound like a problem to me. You have a 30+ year old motor and expecting a precise symmetry in operating parameters is a bit of a stretch.
Are you chasing a performance issue or just "investigating"?
If it is operating as you would like, just go fishing.

 

[maryhannaj]

Re: One Rich bank, one lean bank.

Tm Frank, I am most definatly just investigating, but only because I don't know just exactly what my parameters should be on an outboard motor that is over 30 years old. After all, I am new to outboard motors and that is why I am relying on good folks like yourself on this forum to offer advice on such matters.
And I wish I could just go fishing right now but im afraid the next time I do go, it will be through a hole in the ice. Ha-ha,

 

[James R]

Re: One Rich bank, one lean bank.

Did you check the compressions. It is quite common for one bank to be different to the other. Higher compression can burn more cleanly.

 

[maryhannaj]

Re: One Rich bank, one lean bank.

I did run compressions. Although, the higher compression readings come from the opposite bank. Any other thoughts? Thanks for joining in James R!

 

[Tim Frank]

Re: One Rich bank, one lean bank.

As stated in an earlier post, if you are simply running this on muffs, I don't think that is a valid test and I would not put much credence in the appearance of the plugs. I'd want to take it for a decent run....in the water, and then check.
In my world, the fact that it runs well for you trumps the spark plug issue.

You could see if you can get a schematic of the cooling flow....if it passes around the port bank first, it may cool that side more as it has picked up more latent heat by the time gets to the stbd side. So stbd side runs a bit hotter etc. etc. ....doesn't take that much.

But I think you may be trying to pick the fly poop out of the pepper.

 

[Tim Frank]

Re: One Rich bank, one lean bank.

Tm Frank, I am most definatly just investigating, but only because I don't know just exactly what my parameters should be on an outboard motor that is over 30 years old. .....

Not knocking 30+ year old motors; I own 2, and they run fine....but their plugs are seldom identical in appearance.

 

[metriccrescentwrench]

Re: One Rich bank, one lean bank.

My line of thinking was an air leak somewhere on the leaner bank in an area that combines the two chambers at some point. As far as I can tell, that area does'nt exist.

No, it doesn't. One carb (well, one carb throat anyway), one cylinder.

On some engines there's a slightly different path through the intake for the fuel/air mixture on one side than the other, I'd suspect that could make a small difference at idle. I can't remember if that's the case with the V4 crossflow or not. Due to the difficulties of stuffing everything into the required space oftentimes there are slight differences between cylinders that are already built into the engine.

I also know that both heads become warm to the touch but not uncomfortable in any way.

That sounds like possibly it's idling on the cool side. I'd think about investing in an IR thermometer (Harbor Freight sells one for pretty cheap) so you can see what kind of temperature you're actually running at idle.

 

[jerryjerry05]

Re: One Rich bank, one lean bank.

Lots of reply's, so just throwing out some other ideas?
You did a comp test what are the numbers?
You check the pumps diaphragm?
I believe the carbs aren't adjustable.
The fuel recirc system could be clogged?

 

[emdsapmgr]

Re: One Rich bank, one lean bank.

You might start with testing the head for temps. You can rent an inexpensive laser temp gun from most any automotive parts store. I'd be looking for 143-150 degrees on both heads when warmed up at idle. With that test, at least you'd know if one side is running cool. It's possible you might have a difference in fuel flow in the carbs. Have you had them apart lately? I'd be checking the jets to be sure they are visually clear. Since you are concerned about their color at idle, I'd be looking at the idle jets specifically. While you are in the carbs, might as well have a look at the mains also.