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slyck(at)frontiernet.net
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 Posted: Fri Aug 08, 2008 1:16 pm Post subject: carbs |
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I went through some of the archives but didn't find anything pertinent.
My neighbor has a VERY low time flightstar that he assembled. It ran
fine initially
but now is experiencing too much rpm reduction at idle, to the point
of quitting.
It is a dual carb 503. He hasn't made any changes since start except
recently rechecking
the recommended screw settings.
Any insight would be appreciated. I have never held a bing in my hands.
BB
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The BaronVonEvil
Joined: 23 Jun 2006
Posts: 76
Location: Walla Walla, WA.
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| Posted: Fri Aug 08, 2008 10:22 pm Post subject: Re: carbs |
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HI SLYCK,
I would start by checking the carbs bowls for dirt and gloop. Make sure everything is clean and fresh fuel is being used. Check the keepers on the jet needles to make sure they are matched and in the same groove position.
If that is okay then check for synchonization of the carbs. Basically make sure they are both opening and closing at the same time and at the same amount. You will have to remove the airfilter to do this.
There are two needle adjustments on the Bings. The large needle sets the idle speed stop or the position of the slide valve. You can use a drill bit as a gauge to do the initial setting of both carb idle stops. You want the stops at the carb to be the ones that control the idle speed and not the throttle cable or throttle stops at the throttle lever.
Once you are sure the carbs are opening and closing equally and at the same time, reinstall the airfilter.
There is another smaller needle screw that set the idle mixture of the carb. I start by lightly seating the needle screw then backing it out one full turn. Do this for both carbs. This will get you "In the ball park" to start the engine.
Once you have the engine running you can make further adjustments to suite the situation.
If the idle speed is too high, stop the engine and back both idle speed screws off about 1/8th turn. Check idle speed again. You want to have the idle speed set at about 1600 rpm. This may seem low but then you have a little wriggle room with the throttle handle to set the desired rpm up a bit so that the gear box doesn't rattle at idle.
To adjust the mixture I start the engine and listen and watch it carefully.
Listen to the rpm and watch the exhaust. If it is too rich, the engine will gradually slow and blubber and the exhaust will be come excessively smokey. The EGT's may not even show on the gauge. If so, stop the engine, then just screw in the idle mixture screw of both carbs a 1/8th of a turn. Start and check again.
If the engine is to lean. the engine will start and speed up slightly for a moment or two then slow down. There will be very little smoke in the exhaust. The EGT's may show a rise and then a decline in temps. If so stop the engine and open the idle mixture screws a 1/8th turn and start again.
What you want is a steady rpm at idle and a clean acceleration of the engine from idle to higher power settings. You'll end up with a slightly rich idle since there is no accelerator pump in the carb. The engine will idle for extended period of time but will eventually load up with fuel. It may sputter a bit from prolong idleling as the engine is accelerated to higher power settings.
If the engine is lean, it will die from idle to a higher power setting because it needs that extra bit of fuel to help it accelerate (Remember, no accelerator pump in carb).
If you can get your hands on a carb vacuum gage, this will help balance the carbs even better because you are setting by airflow rather than just mechanical adjustments. But, if not these adjustments will be pretty darn close if you take your time.
If all else fails, find a friendly motorcycle or a snowmobile mechanic as they should have a good idea as to how to make any needed adjustments to a multiple carburetor 2 cycle engine.
Just my .02$
Carlos G
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frank-margie(at)worldnet.
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| Posted: Sat Aug 09, 2008 1:43 pm Post subject: Carbs |
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REF:
HI SLYCK,
I would start by checking the carbs bowls for dirt and gloop. Make sure everything
is clean and fresh fuel is being used. Check the keepers on the jet needles
to make sure they are matched and in the same groove position.
If that is okay then check for synchonization of the carbs. Basically make sure
they are both opening and closing at the same time and at the same amount.
You will have to remove the airfilter to do this.
There are two needle adjustments on the Bings. The large needle sets the idle speed
stop or the position of the slide valve. You can use a drill bit as a gauge
-------------------------------------------------------------------------------------------
First try cleaning the air filters. (Assuming they're K&N's) Clean the outside with dish soap and water, gently. Flush from the inside, gently, don't use hi pressure from a hose nozzle. Air dry---don't use compressed air. We get better results NOT oiling them on 2 strokes; the backflow from the carbs will oil them for you.
Frank Clyma
Jax FL
[quote][b]
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