40hp Dead Top Cylinder

[saltchuckmatt]

timsoutboard.com

This is a recommended site that this forum promoted. They have always done me well.

 

[cyclops222]

WE know the carb is the problem............I have done several carbs over the decades.............BUUTTTT
I have rebuilt carbs and they ran.....WORSE !!..... I left out a tiny round gasket under the main jet. I redid the carb 2 times before I found the tiny left out gasket. I always work on a WHITE towel . I take parts out and leave them there to be sure the kit has all the replacements. And the exact same as my old parts. Went to lunch 1/2 way thru the rebuild. BIG MISTAKE !!!!
If you start a rebuild ? DO NOT get any interruptions !!!
I also have a medical excuse. Cyclops only have 1 eye.

 

[ct1762@gmail.com]

an often simple but overlooked part of the carb is the tiny IDLE PICKUP TUBE! if its clogged, it cannot pick up enough or any fuel to keep the cylinder firing at idle. why its not hitting even if you squirt premix directly into the carb makes no sense, but does if its not a carb issue. your diagnosis of it not being spark might be incorrect, or some other procedure. taking the head off with only 110psi (if those #'s are correct) will show you scoring on both cylinders (no or low oil) or one cylinder (usually #1 on these, as the poppet valves and t stat get neglected. water cant reach top cyl. at idle and gets hot). is the restrictor present on the indicator hose in the lower pan? if not, this can combine with a worn water pump or neglected poppet valve setup. as can a worn exhaust seal...remove head to inspect damage.

 

[jimmbo]

I'm not going to reread everything, but can the Ignition System produce a Spark that can Jump a 3/8" gap. I know you said you used a Spark Tester, but those range from Good to less than Useless

An Engine requires 3 basic things to Run.
1) Fuel and Air delivered to the Combustion Chamber
2) Compression
3) Spark at the proper time

loss of any of the above and it won't run
Some basic Troubleshooting should reveal the Problem Area
Those engines will run/fire with 85 psi Compression, I said run, not run well

 

[ct1762@gmail.com]

I'm not going to reread everything, but can the Ignition System produce a Spark that can Jump a 3/8" gap. I know you said you used a Spark Tester, but those range from Good to less than Useless

An Engine requires 3 basic things to Run.
1) Fuel and Air delivered to the Combustion Chamber
2) Compression
3) Spark at the proper time

loss of any of the above and it won't run
Some basic Troubleshooting should reveal the Problem Area
Those engines will run/fire with 85 psi Compression, I said run, not run well

i'd say at 85psi the leakdown would be so high it wouldn't even fire but i guess its possible.

 

[jimmbo]

In the mid 50s the biggest OMC 2 strokes had a 5:1 Compression Ratio, upped to 5.5:1 in 56 or 57/ 14.7lbs/sq in with 5:1 would yield less than 75psi, and they ran

 

[Crosbyman]

my 9.5hp run very well at 65psi... it is almost as old as it's PSIs rating

 

[racerone]

See post #8------I can't believe all this doubting / confusion with compression on various motors !!

 

[mebehoof]

I'm not going to reread everything, but can the Ignition System produce a Spark that can Jump a 3/8" gap. I know you said you used a Spark Tester, but those range from Good to less than Useless

An Engine requires 3 basic things to Run.
1) Fuel and Air delivered to the Combustion Chamber
2) Compression
3) Spark at the proper time

loss of any of the above and it won't run
Some basic Troubleshooting should reveal the Problem Area
Those engines will run/fire with 85 psi Compression, I said run, not run well

jimmbo,

At this time I'm waiting for a couple carb kits w/everything. We'll see how to shakes out. This 40hp was not run this Spring for any length of time hopefully no damage done.

Will post as soon as have results.

To All, I really appreciate all the input from all of you folks, Thank You!!!

 

[ct1762@gmail.com]

jimmbo,

At this time I'm waiting for a couple carb kits w/everything. We'll see how to shakes out. This 40hp was not run this Spring for any length of time hopefully no damage done.

Will post as soon as have results.

To All, I really appreciate all the input from all of you folks, Thank You!!!

why not take Racer's advice and remove the head to inspect cylinder walls?

 

[mebehoof]

jimmbo,

At this time I'm waiting for a couple carb kits w/everything. We'll see how to shakes out. This 40hp was not run this Spring for any length of time hopefully no damage done.

Will post as soon as have results.

To All, I really appreciate all the input from all of you folks, Thank You!!!

Well, here's results of my efforts:

Overhauled just the top carb, reinstalled it and it's acting the exact same as before doing the carb. Runs on lower cylinder only, when I pull the top wire there is no change, when pulling bottom wire it dies.

Spark is normal on both plug wires, I had two more new spark plugs so just to be sure I installed the new ones, no change.

While it's running I put my hand over top carb mouth, it has vacuum and will wet my hand with fuel. Top cylinder is not popping, spitting or showing any signs of backfire or positive pressure from below throttle plate.

When I spritz fuel/oil mix in top carb there is no change in rpm at all. The spark plug is firing.

Since racerone had told me that these cylinders and crankcases are independent of each other and since I'm dealing with the top cylinder is it possible for this cylinder / crankcase to be drawing ambient air instead of through the carb? Wouldn't there be signs of fuel/oil leaking somewhere due to crankcase positive pressure when piston is on downstroke? Wouldn't it likely be leaking up top somewhere? I don't have any visual oil running down anywhere that I can see.

I realize that I've been advised to just pull the head and I have no problem doing that but want to exhaust external possible problems first. I know that there is always a possibility of a scored, galled or otherwise damaged cylinder or piston and I'd have jumped to pull the head first if it didn't have somewhat reasonable compression.

Anyone have any thoughts on this? Look forward to any comments and thank you all for reading this and the help you've all offered. Much appreciated!!!

mebehoof

 

[jimmbo]

While it's running I put my hand over top carb mouth, it has vacuum and will wet my hand with fuel.


mebehoof

That right there is significant. Your Hand should be remain Dry, as any Fuel should be entering the Engine, not being pushed out the front of the Carb. Check the Reed Valves

 

[mebehoof]

That right there is significant. Your Hand should be remain Dry, as any Fuel should be entering the Engine, not being pushed out the front of the Carb. Check the Reed Valves

jimmbo,

OK, I understand what you mean but one of the things I did in working with this is to swap the carbs and when I did I moved the problem to the bottom cylinder. So what I'm saying is that the problem followed the carb.

So I'm really perplexed on this. I keep hearing "pull the head" and I do understand why but when you're dealing with a 2 cylinder engine and can move the carb from the good cyl to the bad cyl and effect change doesn't that point to a carb problem? I went through this carb meticulously, it's a simple system certainly not a quadra-jet LOL.

The short version of this is that I'm at a loss on this. So I guess just to say I've done it, I'll pull the reeds, who knows maybe I'll find something?

Thoughts on all this would be most appreciated

mebehoof

 

[mebehoof]

jimmbo,

OK, I understand what you mean but one of the things I did in working with this is to swap the carbs and when I did I moved the problem to the bottom cylinder. So what I'm saying is that the problem followed the carb.

So I'm really perplexed on this. I keep hearing "pull the head" and I do understand why but when you're dealing with a 2 cylinder engine and can move the carb from the good cyl to the bad cyl and effect change doesn't that point to a carb problem? I went through this carb meticulously, it's a simple system certainly not a quadra-jet LOL.

The short version of this is that I'm at a loss on this. So I guess just to say I've done it, I'll pull the reeds, who knows maybe I'll find something?

Thoughts on all this would be most appreciated

mebehoof

I just came back in from swapping the carbs once again and the problem followed the carb yet again.

top to bottom, bottom to top then pulled plug wires to see which cylinder was carrying the load and as mentioned above the problem follows the top carb.

Thoughts???

 

[jimmbo]

Is Fuel getting into the Carb Bowl?
Is the Fuel getting through the Circuits within the Carb?
Correct Gaskets used inside the Carb, which have all Fuel and Air Circuit Passages open?

Keep in Mind, we can not see, hear, or touch your motor. We can only go by what info you are telling us. Sometimes Videos help, but don't often provide good Audio, so they are of limited Value

 

[racerone]

It has been clearly stated that ---" spritzing fuel / oil mix into the top carburetor there is no change at all "----- This issue should be so easy to resolve !!

 

[mebehoof]

It has been clearly stated that ---" spritzing fuel / oil mix into the top carburetor there is no change at all "----- This issue should be so easy to resolve !!

racerone,

Easy to resolve? How so? What am I missing here? It was running perfect when put up last Fall but this Spring, well, you know the story. Please share what you obviously see that I don't. Really want to use this boat.

 

[racerone]

Gasket around the nozzle ?

 

[mebehoof]

Gasket around the nozzle ?

racerone,
I don't know what that is? What do you mean by nozzle?

I know what the nozzle gasket is, there was a new one in the carb kit. It is a Johnson Brand kit.

The little brass tube sitting inside the larger one with the holes in the side is way off center I think that's the idle fuel pickup??? I measured it to be sure it didn't bottom out in its chamber and according to my measurements it has bottom clearance.

So, when I installed it (the nozzle gskt) it was in place.

Thanks, mebehoof

 

[mebehoof]

racerone,
I don't know what that is? What do you mean by nozzle?

I know what the nozzle gasket is, there was a new one in the carb kit. It is a Johnson Brand kit.

The little brass tube sitting inside the larger one with the holes in the side is way off center I think that's the idle fuel pickup??? I measured it to be sure it didn't bottom out in its chamber and according to my measurements it has bottom clearance.

So, when I installed it (the nozzle gskt) it was in place.

Thanks, mebehoof

Attached is a blowup of this carb showing the nozzle gskt.