Intermittent carb completely lean
- Thread starter Pablo
- Start date
Still lean on front cylinder. Not intermittent, but constant now. Initially starts off and feels normal for about 30 seconds and then reverts back to lean like it's running on on cylinder with a faulty coil/pickup, but spark is equal and strong. Unable to flip carbs front to rear due to throttle bracket location without disassembling the throttle shaft assembly. When I run it on trailer I see both carbs delivering what appears to be equal amounts of fuel down carb throats. Screws and turns rechecked and equal. No dribbling.
1. All fuel and pulse lines check out fine.
2. Pulled carbs. Gaskets from carbs to speed plate are fine and speed plate to mani fine. Haven't pulled mani off yet.
3. Disassembled carbs. Internal filters had some debris but definitely no clogs. Jets are clear. Internal gaskets, seals and disks fine. Reassembled carbs. Inspected for cracks and nothing found.
4. New VF2 reeds
5. New OCD coil
6. All new fuel lines and filters
7. New gaskets for speed plate and carbs to plate
8. Performed leak down test today. Negative x 20". Zero drop in pressure reading.
Since condition persists in same cylinder carb, plan to pull front carb and blow it out like Freakrider suggested. Found a fair amount of debris in fuel filter???
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1. All fuel and pulse lines check out fine.
2. Pulled carbs. Gaskets from carbs to speed plate are fine and speed plate to mani fine. Haven't pulled mani off yet.
3. Disassembled carbs. Internal filters had some debris but definitely no clogs. Jets are clear. Internal gaskets, seals and disks fine. Reassembled carbs. Inspected for cracks and nothing found.
4. New VF2 reeds
5. New OCD coil
6. All new fuel lines and filters
7. New gaskets for speed plate and carbs to plate
8. Performed leak down test today. Negative x 20". Zero drop in pressure reading.
Since condition persists in same cylinder carb, plan to pull front carb and blow it out like Freakrider suggested. Found a fair amount of debris in fuel filter???
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Last edited:
Pulled trouble carb and completely cleaned and blew it out. New jets, new filters and new gaskets. Same results. About 45-60 secs of feeling crisp then it falls on its face and leans out the front cylinder.
Swapped both carbs with mcdogs full specs and same results again. I'm completely stumped. Gonna pull the complete intake off tomorrow and inspect the new reeds/cages and maybe pull head and look down the jug too. Doubt it's the reeds since I swapped in a new set but it's becoming a diagnosis of exclusion.
If all mechanicals make a visual check then it's gotta be the brain...I guess.
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Swapped both carbs with mcdogs full specs and same results again. I'm completely stumped. Gonna pull the complete intake off tomorrow and inspect the new reeds/cages and maybe pull head and look down the jug too. Doubt it's the reeds since I swapped in a new set but it's becoming a diagnosis of exclusion.
If all mechanicals make a visual check then it's gotta be the brain...I guess.
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Last edited:
D-Roc
I forgot!
- Location
- Dirty River Rider
Are you burning water?
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Doubt it but I'm gonna pull the head and inspect it. I'm leaning hard on the ignition now.
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D-Roc
I forgot!
- Location
- Dirty River Rider
Seems like the same amount of time it takes to prime the cooling system and then your running one one cylinder. Worth a check.
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by move them i meant turn them around, so the throttle cable drum is opposite of where it is now. keep them connected to eachother, unbolt both, rotate both as one unit, rebolt down. unless your intake has some interesting bolt pattern to mount the carbs down on an angle.
- Location
- South Florida
Can't be done due to throttle tab is only one one side of the manifold. He switched the carbs to my full specs and it still had the same problem. That eliminates the carbs as the cause.
- Location
- Tri-Cities, WA
Out of curiosity, is each carb on it's own pickup line in the fuel tank? If so, have you inspected the plumbing in the tank/pickup? I've always ran dual pickups (independent for each carb) and once had a tiny crack in one tube right above the clunk fitting. On the trailer when the ski was flat and fuel level in the tank, it would draw fuel through the crack and run fine. Once in the water riding nose high, the fuel would run to the back of the tank and that line would suck air and lose prime.
- Location
- Charlotte NC
i like d-roc's water idea. Is the culprit cylinders plug white?
I appreciate the input. Single fuel pickup feeding both carbs. I pulled the pickups out yesterday and inspected them.
Plugs are normal brown slightly wet on good (rear) cylinder and lean/dry, light light brown on front cylinder. Haven't pulled head, but will inspect this week before I go further.
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Plugs are normal brown slightly wet on good (rear) cylinder and lean/dry, light light brown on front cylinder. Haven't pulled head, but will inspect this week before I go further.
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your rear cyl is wet and brown but your front is brown and dry? are you sure its the front going super lean?
Sounds more like the rear cylinder is intermittent not burning the fuel. Just something id consider an option.
If it was me id pull the motor apart and rebuild it fresh to eliminate any possibilities. Does it pass a leakdown test?
Leak down was perfect. Didn't drop a psi in over 20".
As far as a tear down goes...Mechanically I think it's sound. Fresh, professional rebuild last season and had cylinder nikasil plated. Less than 50 hours on it since then.
My boy Mcdog has a oem ignition I can swap in but will require a flywheel/stator swap too. Anyone have a Gen 1 ATP Flame brain I can borrow/buy. Stefan has a complete system I may grab but would like to trial a brain before I go buying one.
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As far as a tear down goes...Mechanically I think it's sound. Fresh, professional rebuild last season and had cylinder nikasil plated. Less than 50 hours on it since then.
My boy Mcdog has a oem ignition I can swap in but will require a flywheel/stator swap too. Anyone have a Gen 1 ATP Flame brain I can borrow/buy. Stefan has a complete system I may grab but would like to trial a brain before I go buying one.
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Quinc
Buy a Superjet
- Location
- California
Maybe it needs staggered jetting?
D-Roc
I forgot!
- Location
- Dirty River Rider
You running an atp ignition now?
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- Location
- South Florida
His jetting has been fine for two years.
Yes. He runs a first generation atp flame ignition.
Yes. He runs a first generation atp flame ignition.
Round 3000000 and 1 ...
Swapped out the ignition thinking it was a dying TL Flame brain. Wrong. Same symptoms. I used mcdogs oem 62t ignition/stator/flywheel. Water test was exactly the same results. Feels crisp initially and then goes lean on front cylinder like it's only firing one cylinder. Spark is equal. Starts and idles fine. On the trailer it sounds great and is super crisp. Once in the water for 30-60 seconds it falls off.
One caveat is that when I pulled my TL system I noticed a small round piece of metal pinballing around inside the flywheel housing. It was a perfectly round piece and exactly the same diameter as one of the magnets on the ATP flywheel? I inspected the flywheel and all the magnets looked to be in place. If it wasn't inside the flywheel housing I would have said it was the tail end of a bolt that just sheared off. I inspected the flywheel area and looked for obvious damage and couldn't find any. The leak down test would have picked up a leak inside here...I think. Crank seal was good too.
After that, I pulled the head off to inspect. I couldn't find any signs of water intrusion. The rings looked to be in good shape as well. I'm assuming the negative leak down test confirmed all my top end orings and gaskets are tight.
I'm seriously stumped. Most likely, I'll pull the entire engine out and inspect the flywheel housing ultra close. I sprayed soapy water everywhere on the leak down to help spot obvious leaks. Negative though.
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Swapped out the ignition thinking it was a dying TL Flame brain. Wrong. Same symptoms. I used mcdogs oem 62t ignition/stator/flywheel. Water test was exactly the same results. Feels crisp initially and then goes lean on front cylinder like it's only firing one cylinder. Spark is equal. Starts and idles fine. On the trailer it sounds great and is super crisp. Once in the water for 30-60 seconds it falls off.
One caveat is that when I pulled my TL system I noticed a small round piece of metal pinballing around inside the flywheel housing. It was a perfectly round piece and exactly the same diameter as one of the magnets on the ATP flywheel? I inspected the flywheel and all the magnets looked to be in place. If it wasn't inside the flywheel housing I would have said it was the tail end of a bolt that just sheared off. I inspected the flywheel area and looked for obvious damage and couldn't find any. The leak down test would have picked up a leak inside here...I think. Crank seal was good too.
After that, I pulled the head off to inspect. I couldn't find any signs of water intrusion. The rings looked to be in good shape as well. I'm assuming the negative leak down test confirmed all my top end orings and gaskets are tight.
I'm seriously stumped. Most likely, I'll pull the entire engine out and inspect the flywheel housing ultra close. I sprayed soapy water everywhere on the leak down to help spot obvious leaks. Negative though.
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- Location
- South Florida
It wasn't perfectly round. It was a disc. Same diameter as flywheel magnets though.
I'm thinking nothing is left but gas tank pickup sucking air somehow or something is off with the shortblock.
I'm thinking nothing is left but gas tank pickup sucking air somehow or something is off with the shortblock.
Think I've found my culprit.
Went out for another water test today. I regreased my orings on the head and made sure everything was buttoned up tight. Same results. Lean front cylinder after 30-60 secs.
Decided I need to pull engine and do a real deal inspection. I Put ski on stand and pulled engine completely out for a leak test on the bench. The last leak test was negative over 25-30". After all the symptoms and all my components checking out fine I was certain there's a leak somewhere. The leak I found is super subtle and hard to detect without soapy water or submerging the cases in a water bath. My buddy @Waternut did a leak test that way years ago and saw bubbles emitted from his cases. Turns out to be a leaking front crank seal. Last leak test I did with the FW cover on and I seal the FW cover with yamabond to make it watertight...and possibly air tight. On the bench I pulled the cover, Fw, stator and the bendix to investigate the FW housing during the test. I pressured it up and sprayed it down from top to bottom. Found the leak around seal and a small pin hole in the epoxy. I figure the piece of metal that was pin-balling around in there contributed to the pin hole. Gonna send it off for some new epoxy and rebuild with new gaskets and seals.
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Went out for another water test today. I regreased my orings on the head and made sure everything was buttoned up tight. Same results. Lean front cylinder after 30-60 secs.
Decided I need to pull engine and do a real deal inspection. I Put ski on stand and pulled engine completely out for a leak test on the bench. The last leak test was negative over 25-30". After all the symptoms and all my components checking out fine I was certain there's a leak somewhere. The leak I found is super subtle and hard to detect without soapy water or submerging the cases in a water bath. My buddy @Waternut did a leak test that way years ago and saw bubbles emitted from his cases. Turns out to be a leaking front crank seal. Last leak test I did with the FW cover on and I seal the FW cover with yamabond to make it watertight...and possibly air tight. On the bench I pulled the cover, Fw, stator and the bendix to investigate the FW housing during the test. I pressured it up and sprayed it down from top to bottom. Found the leak around seal and a small pin hole in the epoxy. I figure the piece of metal that was pin-balling around in there contributed to the pin hole. Gonna send it off for some new epoxy and rebuild with new gaskets and seals.
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