Fuel/Air Screw?

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Fuel/Air Screw?

Post  despres on Tue Nov 19, 2013 7:42 pm

Hi All,

I have 2000 BRP, Uncorked, stock carb with a White Brothers Exhaust (header and cannister).

I am riding at sea level to about 600 feet of elevation, in temps ranging from 20-35c most of the time. When I moved here (shortly after purchasing the bike, and from about 7,000 feet elevation) I rejetted with a 68s idle jet, the upgraded needle on third clip, and a 172 main jet.

I don't know too much about BRPs, but am reasonably handy with carburetors, so I assumed I should set the idle by screwing the air/fuel screw all the way in, then reducing the idle speed until it stalled, then back the air/fuel screw out 2 turns, start her up and fine tune.

BUT when I attempted that, it wouldn't start. I increased the idle speed, and the air/fuel screw seems to have no impact on the idle speed (from screwed all the way in to backed out three full turns). The funny thing is, I can get it to start and idle just fine, my only gripe I have with the way it runs is that it seems a bit farty when I close the throttle while rolling & engine brake.

The bike starts easy, idles fine when it is cold and hot and the throttle responds smoothly in all ranges, so I am inclined to do nothing, but it is bugging me that there seems to be something wrong with it even though it runs well.

Any thoughts? I should mention that I am in a fairly remote part of mexico with limited access to tools or chemicals, so no major work is likely to get done for a while...
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Re: Fuel/Air Screw?

Post  Mad Frosty on Tue Nov 19, 2013 9:34 pm

Just play with it , you will get there , also i think you need to go bit bigger on the main jet .
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Re: Fuel/Air Screw?

Post  AURORA on Tue Nov 19, 2013 10:47 pm

Set the idle speed. Then play with the F/A mixture.
You really have to be patient when adjusting the idle mixture.
Make a change then wait a minute to determine the results. Repeat the process until you have your desired idle F/A mixture.
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Re: Fuel/Air Screw?

Post  despres on Wed Nov 20, 2013 4:56 pm

Thanks for the responses. I do think there is something wrong with it though. The F/A screw literally does not affect the idle at all. With the bike warmed up and the idle speed set low, I can screw the F/A screw in until it seats or back it out 3 full turns from seated with no noticeable change in idle speed or throttle response. That can't be normal, right?
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Re: Fuel/Air Screw?

Post  Mad Frosty on Wed Nov 20, 2013 9:11 pm

Check the condition of the iddle adjusting screw , the tip can be bent also make sure that the rubber seal its still there and has not desintegrated or got lost , best way is to take the carb apart in front of the exploded diagram and check all the parts are there and in a good condition .
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Re: Fuel/Air Screw?

Post  Mauser on Wed Nov 20, 2013 11:18 pm

despres wrote:Thanks for the responses.  I do think there is something wrong with it though. The F/A screw literally does not affect the idle at all.  With the bike warmed up and the idle speed set low, I can screw the F/A screw in until it seats or back it out 3 full turns from seated with no noticeable change in idle speed or throttle response.  That can't be normal, right?
This might sound silly, but when I got my bike there wasn't an air filter fitted just the screen...I could take my F/A screw out completly and it didn't make any difference....added the foam filter and it worked Frustrated 

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Re: Fuel/Air Screw?

Post  despres on Wed Nov 20, 2013 11:38 pm

Well, fortunately I can confirm that there is an air cleaner. It is dusty here, so I've been changing it pretty regularly.

I was thinking I'd pull the air screw out and make sure it had a tip that was aimed in the right direction and all that. I need to work on my other bike this weekend, so maybe I'll do both (although I hate risking having both down at the same time)
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Re: Fuel/Air Screw?

Post  despres on Thu Nov 21, 2013 3:31 pm

Well they are both down at the same time, per my other post. I guess I will have the opportunity to spend my saturday on carburetors, so maybe I will have some more info to report back on.
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