Intermittent carb completely lean

[Pablo]

Anyone ever had an issue with a carb intermittently running super lean? Dual BJ 46 carbs with a single fuel feed (single filter that's clean) split with a Y. R&D dominator with VF2's. Confirmed good fuel pressure from tank. Return lines are Y'd together too. Good spark confirmed but ultra lean on front cylinder and normal on rear. Both butterfly's are synced and carb throats are clear. I'm assuming internal filter or jets clogged or reed malfunction (noted some exhaust backing up from lean carb). Haven't pulled carbs yet but will do tomorrow to confirm.


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[CRJ]

I diagnosed a blown reed from air blowing back up the carb. stretch a paper towel over the carb and crank it (dont start) and watch it to see if the paper towel get pushed above the top surface of the carb. The blue shop towels work well for this.

 

[Big Kahuna]

could have a small crack in the carb. That depending on situation if crack opens, you loose pressure........ Had a set of 38's that had a crack and did not know it. Could not get them tuned for anything.

 

[CRJ]

could have a small crack in the carb. That depending on situation if crack opens, you loose pressure........ Had a set of 38's that had a crack and did not know it. Could not get them tuned for anything.

thats one thing i would never have thought of, ive never seen one crack!

 

[Freakrider]

XS doesn't advocate running the internal filters, I guess Art does. Before disassembly, I would check for an air leak on that front cylinder intake area. Does that intake have a speed plate with a gasket ?

 

[Pablo]

XS doesn't advocate running the internal filters, I guess Art does. Before disassembly, I would check for an air leak on that front cylinder intake area. Does that intake have a speed plate with a gasket ?

Thx for input boys. Will verify reeds when I pull it.

Yep. Speed plate and gasket. Good idea on gasket leak. Will inspect carbs for cracks too.


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[Quinc]

How do you air leak the carbs/test for a crack?

 

[Freakrider]

How do you air leak the carbs/test for a crack?

While the engine is running you spray can flammable liquid like carb cleaner ( with straw) around gasket areas to detect increase in engine idle speed. A significant leak will be noticeable. With the check for a crack you remove carbs, get a nice magnifying glass and inspect carefully.

 

[CRJ]

How do you air leak the carbs/test for a crack?

ive always wondered why poeple dont leakdown test them with the carbs on the ski, and just plug the fuel fittings.

 

[Quinc]

ive always wondered why poeple dont leakdown test them with the carbs on the ski, and just plug the fuel fittings.

It wont leak air through the fuel discharge ports?

 

[Big Kahuna]

How do you air leak the carbs/test for a crack?

on my 38's. They had gas on the outside.........

 

[Pablo]

Stumped. I'm working from the outside in...
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.

Plan tomorrow is pull mani and inspect gasket between mani and cases but doubt any good findings there since this is a single cylinder problem. Plan to inspect cylinder for loose cylinder to case bolts on the lean cylinder side for air leak potential. Last year, had the whole jug come loose after initial few tanks. Strange, I know, but it happened. Re torqued and hasn't missed a beat in 15 months...till now.

Symptoms are front cylinder ultra lean. Rear cylinder fine. Runs like a plug is fouled or bad plug wire. Spark is present/equal. Plug inspection shows almost dry/white on front and normal wet/brown on rear. Plenty of fuel feeding carb and found fuel within carb on inspection.

Will bad reeds provide a lean situation? Need to inspect them carefully tomorrow since I noticed exhaust in bilge when symptoms started.


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[Vumad]

Could an issue with the throttle shaft bushing cause this?

 

[Pablo]

Although this article is from skidoo and for sleds, 2-strokes are 2-strokes. Bad reeds can cause a lean condition and or seizure. It is rare, but a definite possibility.

http://www.dootalk.com/content/showarticle.php?ID=122


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[Big Kahuna]

Stumped. I'm working from the outside in...
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.

Plan tomorrow is pull mani and inspect gasket between mani and cases but doubt any good findings there since this is a single cylinder problem. Plan to inspect cylinder for loose cylinder to case bolts on the lean cylinder side for air leak potential. Last year, had the whole jug come loose after initial few tanks. Strange, I know, but it happened. Re torqued and hasn't missed a beat in 15 months...till now.

Symptoms are front cylinder ultra lean. Rear cylinder fine. Runs like a plug is fouled or bad plug wire. Spark is present/equal. Plug inspection shows almost dry/white on front and normal wet/brown on rear. Plenty of fuel feeding carb and found fuel within carb on inspection.

Will bad reeds provide a lean situation? Need to inspect them carefully tomorrow since I noticed exhaust in bilge when symptoms started.


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Did you check the actual wires? As in pull the boot and tug on the ends to make sure there are no brakes?

 

[Pablo]

Did you check the actual wires? As in pull the boot and tug on the ends to make sure there are no brakes?

I didn't check the plug wires other than verifying I had spark on both. Coil was a refreshed one from JSS with new wires 2-3 seasons ago.


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[loictahiti]

I don't see anywhere, did you check the POp off presure ? If not you have to check it before doing something, it's the most important check for carb, on side visual check, joint leak, etc....

Hope you could understand my bad english ....

 

[Pablo]

Pop offs are good. They're right around 22-24. This engine/carb setup has performed flawlessly for 16-18months...I mean crisp and jetted to perfection per Art/Jetworks and this symptom turned up last week out of the blue.

Pulled mani/reeds today. VF2's in R&D dominator. Just gross visual inspection didn't show anything. When I started to play with the petals I noted one Reed not sealing all the way. I'm going to replace the whole set. Additionally, gonna redo all fuel line and filters as a precaution. Gaskets were fine between mani and cases. All cylinder and head bolts were snug. Kinda stumped. Maybe there was enough blow back with this one Reed petal??


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[Quinc]

Needles are probably worn. Replace them.

 

[jo5hi3]

Pop offs are good. They're right around 22-24. This engine/carb setup has performed flawlessly for 16-18months...I mean crisp and jetted to perfection per Art/Jetworks and this symptom turned up last week out of the blue.

Pulled mani/reeds today. VF2's in R&D dominator. Just gross visual inspection didn't show anything. When I started to play with the petals I noted one Reed not sealing all the way. I'm going to replace the whole set. Additionally, gonna redo all fuel line and filters as a precaution. Gaskets were fine between mani and cases. All cylinder and head bolts were snug. Kinda stumped. Maybe there was enough blow back with this one Reed petal??


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A lot of times they wont sit flat and seal until there is pressure pushing them closed.