Problem with carburetors at 7-8k

[SHeva4ever]

I have a little problem with my carburetors. I tested it with WOT at 5th gear at 4k rpm. I feel a delay before it start accelerating. I also have just a 3 cylinders working at 7-8k. I believe it?s too rich, so I taked of the "Y" from my filter. It is runs better. All cylinders worked without "Y". So mix was too rich. I lowered my float level from 16mm to 17mm. It is works better, but I still have 3 cylinders working at 7.5-8k. I have stock parts (stock exhaust, jets and filter). How can I solve this problem? Any ideas?

P.S. I also checked my ignition according to service manual. It works good, so it must be carburetors.

P.P.S. A/F screws in stock position.

 

[naughtyG]

I'm curious, how do you know that only 3 cylinders are firing at 7.5-8k rpm?

 

[maleko89]

Carbs might need cleaning. How many miles and when were the carbs last serviced? What altitude? It sounds like your mains are too large.

 

[SHeva4ever]

I fill loosing a lot of power at this revs. And I have it again at 8k+

 

[naughtyG]

yes, probably doing the shotgun and the peashooter will help you.

http://vmax.lvlhead.com/tips/shotgun.htm

http://home.comcast.net/~onlyone12/carbs1.htm

 

[SHeva4ever]

Carbs might need cleaning. How many miles and when were the carbs last serviced? What altitude? It sounds like your mains are too large.

I clean it up 2 weeks ago. Maybe 500 miles after cleaning.
I live at sea level.

 

[naughtyG]

did you inspect your diaphragms? Make sure they're all in good condition and seated properly. Also, did you have a look at your spark plugs? Often they tell a good story on what's happening.

 

[SHeva4ever]

did you inspect your diaphragms? Make sure they're all in good condition and seated properly. Also, did you have a look at your spark plugs? Often they tell a good story on what's happening.

Diaphragms looks fine (no cracks or holes).
Small diaphragms looks good too.
Spark plugs have light brown color.

 

[naughtyG]

All sounds good. Did you also check your coils for cracks, and measure the resistance and check the state of your HT leads?

 

[SHeva4ever]

All sounds good. Did you also check your coils for cracks, and measure the resistance and check the state of your HT leads?

Yes I have cracks on all coils. I isolate it with silicon. I also measured the resistance. It is ok.
I checked minimum spark gap. It is more than 6mm, so it is ok too.
HT leads and spark plugs are new (2-3k miles)

 

[maleko89]

Diaphragms looks fine (no cracks or holes).
Small diaphragms looks good too.
Spark plugs have light brown color.

Brown is rich. Air filter clean?

 

[naughtyG]

hmm it sounds like a similar problem to HDKila's bike - I don't think they've found the cause yet.

It could be your ignition, your pickup coils, or something in the harness. Do you know anyone who could lend you a CDI to swap and make sure that isn't the problem?

 

[SHeva4ever]

Brown is rich. Air filter clean?

It is not new but seems clean. I blowed it with compressed air.
My Max runs better on top revs without "Y", so I believe air filter is clean.

 

[SHeva4ever]

. Do you know anyone who could lend you a CDI to swap and make sure that isn't the problem?

No.

Pick-up coil has normal resistance too.

I think it is carb related problem, because it works fine without "Y" (leaner mix)

 

[naughtyG]

Well, when carbs get older some of the rubber gaskets inside can perish. I had idling problems on mine that no amounts of cleaning would help. Then I opened up my carbs and renewed some of the gaskets that were perished and it fixed it.

Another thing you might want to check is that your float bowl vent tubes are clear and routed properly (not pinched).

 

[SHeva4ever]

Another thing you might want to check is that your float bowl vent tubes are clear and routed properly (not pinched).

I will check it.

Another thing. It is reproduced only on top gears (3,4,5) when I give it WOT. When engine is hard loaded. I believe diaphragm/needle/spring/float level works in this time. Is it correct?

It is 25k miles on my Max. Can it be needle wear or spring weak? How can I check it? I can't find stock spring length in the service manual.

 

[SHeva4ever]

Another thing you might want to check is that your float bowl vent tubes are clear and routed properly (not pinched).

I checked my vent tubes this morning. It is clear and routed correctly.

P.S. I also tried 18mm float level today. It is worse at 7-8.5k.