FCR carb lean pilot circuit

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3/5/2018 7:23 AM

Have an 09 kx250f. Currently trying to get the pilot circuit situated. Carb has an R&D powerbowl 2 on it with the adjustable leak jet.

Right now its got a hanging idle. Sprayed carb cleaner around the boots and it made no difference. Im pretty sure its something to do with the pilot circuit. Also pulling the hot start kills the bike.

Pilot jet is a size 40. Fuel screw set at 2.125 tiens out(stock). Turning the fuel screw further out causes a really lean condition where the bike will backfire when revved and the idle hang gets worse. Turning the screw in 1/4-1/2 turn helps the hang but doesnt fix it. Its got a brand new tusk thumb screw. So i wouldnt think air is getting in that way would it?

Looking for suggestions on what to look at on this thing. Should i reduce the leak jet size? Up the pilot jet to a 42? Its weird that turning the fuel screw out makes it leaner. To my knowledge its supposed to do the opposite.

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3/5/2018 7:54 AM
Edited Date/Time: 3/5/2018 7:56 AM

When you turn the fuel screw out, it should richen the mixture. Yours is not right. Check the oring on the needle.
When you pull the hot start lever it will lean out the engine and what yours is doing seems correct.
Have you cleaned the pilot jet or replaced it?
Have you removed the carb and done a complete soak cleaning?
How long did the bike set with out running and fuel in the carb?
A hanging idle can be caused by an air lean, fuel screw set too lean, plugged pilot jet, or other dirty issues.

Paw Paw

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3/5/2018 8:03 AM

I cleaned the carb and let the jets soak. Didnt soak the entire carb. The pilot jet is clear at least from what i can see visually. I dont have another #40 to compare the hole size to to see if its partially clogged. can blow air through all the passages in the carb body itself.

The carb has fresh race gas in it. No gas has sit in it since assembly.

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3/5/2018 8:38 AM

The pilot jets will have a "clear" look to them even when clogged. This includes the smaller side holes as well as the center hole. Run a wire through them.
At some point the carb has set with fuel in it that dried causing this issue. The carb needs a total break down soaking cleaning.

Paw PAw

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3/5/2018 9:17 AM

Yea the jets arent a shiny brass anymore. I got the bike in boxes. From what i understand its really low hours but wasnt maintained. If it helps, i cant get the tusk safety wire through the hole. I dont have anything thinner than that.

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3/5/2018 2:05 PM

Pick up a welder tip cleaner.

Paw Paw

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3/5/2018 3:22 PM

get a brand new pilot jet, and also replace the seal for the slide plate, a broken or stiff slide plate seal does exactly what youre describing.

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3/5/2018 4:50 PM

kb228 wrote:

Yea the jets arent a shiny brass anymore. I got the bike in boxes. From what i understand its really low hours but wasnt ...more

If you want to use the old jets get some electric guitar strings. .008, .009, .010, .011, .012. They are .50 cents each and 30" long so a lifetime supply of each size.

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3/5/2018 5:30 PM
Edited Date/Time: 3/5/2018 5:31 PM

DTHA70 wrote:

get a brand new pilot jet, and also replace the seal for the slide plate, a broken or stiff slide plate seal does exactly what ...more

Or putting the floating plate on upside down, which intuitively “looks”’correct...found that out the hard way after R&Ring my carb 3 times and tearing it down...

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3/6/2018 1:09 AM
Edited Date/Time: 3/6/2018 1:27 AM

kb228 wrote:

Yea the jets arent a shiny brass anymore. I got the bike in boxes. From what i understand its really low hours but wasnt ...more

Frank wrote:

If you want to use the old jets get some electric guitar strings. .008, .009, .010, .011, .012. They are .50 cents each and ...more

Duh i should have thought if that. Ive already got 3 gutars lol.

Alright guys ill work on all the suggestions and report back on the results. Last night i showed everything to someone with more carb experience and they said my pilot was partially clogged. Might be easier to just replace jets instead of trying to clean them

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3/6/2018 11:43 AM

Wal-Mart has those welding tip cleaners. 4 bucks. They work great on jets

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