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Bogging at WOT, choke in runs better.

R

riopga

Regular Contributor
1990 Johnson 90 hp with VRO pump only using fuel side. Premixing 50 -1. Compression with plugs out 120, 122, 122, 128. Spark on all four jumps 1/2 inch gap. Checked timing using JoeReeves method. Timing light shows 24 which is just what it should be as WOT for this engine is 28. Now for the problem: The engine starts easily and quickly and idles well. Right around 650 -700 in the water. When you give it throttle it speeds up, and sometimes runs on up to WOT and off we go no trouble. Next time it will start to speed up, but then will bog down. At that point if I push in choke, it speeds up and runs at close to WOT as long as I hold it in. Does this sound like air leak or weak pump? Thanks for your help.
 
Forgot to mention. Tried pumping the bulb when running. No change. And I recently ran a piece of wire through the high speed jets.
 
The fact that the rpms increase when you engage the choke (fuel primer solenoid), you are actually changing the fuel flow to flow directly to the intake manifold... bypassing the carburetor.

It sounds like something is intermittently fouling the carburetor(s). If it was a fuel pump problem, pumping the fuel primer bulb (acting as a manual fuel pump) would have corrected the problem.
 
joereeves said:
The fact that the rpms increase when you engage the choke (fuel primer solenoid), you are actually changing the fuel flow to flow directly to the intake manifold... bypassing the carburetor.

It sounds like something is intermittently fouling the carburetor(s). If it was a fuel pump problem, pumping the fuel primer bulb (acting as a manual fuel pump) would have corrected the problem.
Click to expand...

Thanks for the quick response. Sounds like a carb rebuild is next in
my future!
 
riopga said:
Thanks for the quick response. Sounds like a carb rebuild is next in
my future!
Click to expand...

Yeah, based on your explanation, that's where I'd look... BUT... which one? See if the condition of the spark plugs might give you a clue.

Your problem relates to one intermittent engine problem I encountered in my 30+ some years in the trade... a Bass Boat with a V6 Evinrude that would do 78 mph. After running at a high speed for a undetermined amount of time (It Varied), the engine would suddenly lose one cylinder but not always the same cylinder. Having the rig in the shop was a waste of time. I rode with the guy on Hillsborough River in Tampa. Flying along at that high speed, no safety belt, with about8" of free-board... that's not my idea of a fun time... actually scared the hell out of me.

Anyhow, finally, one cylinder cut out completely, and being able to trouble shoot it immediately pinpointed the center carburetor.... a bug of some kind had actually crawled into the float chamber via the air vent passageway, buoyant enough to float on top of the gasoline when at a standstill or low rpm... but at a high rpm would get drawn into one of the two accessible high speed jets. Really hated problems like that!
 
joereeves said:
Yeah, based on your explanation, that's where I'd look... BUT... which one? See if the condition of the spark plugs might give you a clue.

Your problem relates to one intermittent engine problem I encountered in my 30+ some years in the trade... a Bass Boat with a V6 Evinrude that would do 78 mph. After running at a high speed for a undetermined amount of time (It Varied), the engine would suddenly lose one cylinder but not always the same cylinder. Having the rig in the shop was a waste of time. I rode with the guy on Hillsborough River in Tampa. Flying along at that high speed, no safety belt, with about8" of free-board... that's not my idea of a fun time... actually scared the hell out of me.

Anyhow, finally, one cylinder cut out completely, and being able to trouble shoot it immediately pinpointed the center carburetor.... a bug of some kind had actually crawled into the float chamber via the air vent passageway, buoyant enough to float on top of the gasoline when at a standstill or low rpm... but at a high rpm would get drawn into one of the two accessible high speed jets. Really hated problems like that!
Click to expand...

I looked at the plugs, but they all look the same, a nice brownish color. Since I am taking the carbs off I am just going to do both of them.

In researching, I saw that these carbs have a tendency to warp. Would that cause these same symptoms?
 
I have to think Joe developed some grey hair with his above mentioned ride. Probably is some debris in one of the carbs, but you said you had run a wire through main jet, but apparently carbs were not dismantled. I had a tiny piece of gasket act the same way as that bug which Joe mentions. This was in a late 70's 55 horse Johnson. The float bowl gasket was breaking down from ethanol.
The only way I will go 78mph on the water is in a float plane.
 
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So did you find the crap in the carbs? Please Joe, do you have a jet cleaning procedure spelled out? Too many people think that an "open" jet, is a clean jet. Many a motor have been "torched" with that policy. I just rebuilt a 55 Evinrude last year because of that. When a cylinder scores, we all know there is a reason for it that must be corrected.
 
timguy said:
So did you find the crap in the carbs? Please Joe, do you have a jet cleaning procedure spelled out? Too many people think that an "open" jet, is a clean jet. Many a motor have been "torched" with that policy. I just rebuilt a 55 Evinrude last year because of that. When a cylinder scores, we all know there is a reason for it that must be corrected.
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Yes I do Tim, but I entered it so many times, I just assume that others have come across it in their searches. I normally state " Carefully clean the jet with a piece of single strand steel wire as solvent just doesn't do that job properly". The "Mechanics Wire" wire I use is .047 in diameter as the majority of HS jets are larger than that. The smaller jets.... I always used accurate (same size) drill bits graduated in thousands.

I must admit that I never knew the diameter of that wire... just checked it with a micrometer.
 
timguy said:
So did you find the crap in the carbs? Please Joe, do you have a jet cleaning procedure spelled out? Too many people think that an "open" jet, is a clean jet. Many a motor have been "torched" with that policy. I just rebuilt a 55 Evinrude last year because of that. When a cylinder scores, we all know there is a reason for it that must be corrected.
Click to expand...

I haven't got to take them apart yet. Waiting on the kits to come in.
 
riopga said:
I haven't got to take them apart yet. Waiting on the kits to come in.
Click to expand...

My kits have arrived, and I will be taking the carbs apart Monday for a thorough cleaning, including running wire through the jets. My intermediate jets are 26c, so does anyone know what drill bit size that would be?

I will also check the float bowls for warping at that time. After a lot of reading about the plastic float bowls I am worried about them being out of whack.
 
The float bowl on the 1954 Johnson 5.5 that I rebuilt last night isn't warped, its made of a material known as aluminum. The float needle is made of a material known as stainless steel, with a float made of a material known as "cork". If cork is good enough to seal a 100 dollar bottle of fine Italian red vino........its good enough for my 5 horse. What has happened to our brilliant engineers? Seems their goal is to engineer impending failure? Plastic and composites have a specific and often short effective lifespan.......not a good idea for equipment expected to last more than 30 years, is it? These new small engine carbs are totally ridiculous. Add ethanol.......ha!
Okay, I'm going out to work on this big bad Optimax. Prop shaft bent. The guy lost his battle with the rock. I asked him what happened to the prop.....he said that he wasn't wearing his swimming trunks.....huh?
 
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joereeves said:
The number 26C tells it all.... 26 = .026 .
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Thank you. So I took the carbs off and "cleaned" them, but they were spotless. I went ahead and replaced float and needle valve and seat. I ran wire through all jets, but they were not blocked at all. I did sand down the float bowls on glass, and they were a bit warped. I hope to get the carbs back on tomorrow and test Monday.
 
You could also try installing a clear fuel line section between VRO fuel pump and carbs......bet you will see bubbles. Sounds like carbs are golden. Could be air getting in at old VRO......maybe? Or somewhere along the line. I assume the VRO has been disconnected because of ethanol effects.
 
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timguy said:
You could also try installing a clear fuel line section between VRO fuel pump and carbs......bet you will see bubbles. Sounds like carbs are golden. Could be air getting in at old VRO......maybe? Or somewhere along the line. I assume the VRO has been disconnected because of ethanol effects.
Click to expand...

I have a regular fuel pump that I am going to put on tomorrow and completely remove the VRO pump. Do you happen to know the size pipe plug i need to close the pulse hose connection at the engine?
 
Fixed!

Fixed! So It is running great now! I replaced the vro pump with a regular fuel pump. So either the old pump was leaking air OR maybe a float needle was stuck? Or the bowls were warped bad enough that they were letting air in? Not sure, but it's purring at idle and running as long as you want at WOT. Thank you Mr. Reeves and Timguy for your help and input.
 
Re: Fixed!

Great job, brother.......Mr. Reeves is awesome. Maybe more experience than you would ever believe. He has taught me plenty too.
 
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