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Hey everyone, I’ve got a 99 TRX300fw that I inherited from my dad. It had been sitting for several years so I got her running with a new spark plug, CDI, oil change/filter, air filter, new gas, and deep carb clean with a rebuild kit. It fires up right away on full choke and sounds like it’s pretty healthy but it won’t idle without it. I’ve read what seems like hundreds of the forums on here saying to clean the carb again and make sure the pilot jet and air/fuel mixture screw are clear and I can assure you they are. Ive cleaned it several times now and blown compressed air through all the jets and passage ways in the carb as well. I’ve also adjusted the valve clearance and that didn’t help either.

I think it’s also important to note that it smokes on startup as well as when you rev it up. I’m planning on putting in new valve seals and rings but I didn’t think that would affect the idle.

Any help is much appreciated thanks in advance.
 

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Usually when an engine wont run without the choke, it's because the air/fuel mixture screw isn't adjusted properly or the jet is plugged. Try turning the screw out and maybe adjust the idle screw, See what happens. Is your plug getting black or running clean? Good luck...
 

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I agree with what Kevcules says. I cleaned my carb yesterday and found lots of small particulates and also noticed for my elevation, the air idle screw was opened too much. I set it at 1.25 turns open from full closed and it had been 1.75 or 2.25 turns. It made a huge difference in idling. I bet I still need to adjust it after its warmed up from running for a while. Also, there is a section in the service manual that explains how to adjust the synchronization of the butterfly valve and the piston valve. They should both be full closed and as you actuate the throttle linkage, they should both start to open at the same time. Mine had to be adjusted as the butterfly valve opened a few degrees before the piston valve. I still had to turn the idle screw in a few turns to get the engine to idle but I could actually set it after those adjustments. Now she fires up in 12 degree F weather on the first crank.
 

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One more thing to look for. a crack in the boot that connects the carburetor to the cylinder. I found a 1 inch crack on one of our other 4 wheelers that starts hard and has a weak idle without the idle screw turned way up.
151325


151326
 

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Hey everyone, I’ve got a 99 TRX300fw that I inherited from my dad. It had been sitting for several years so I got her running with a new spark plug, CDI, oil change/filter, air filter, new gas, and deep carb clean with a rebuild kit. It fires up right away on full choke and sounds like it’s pretty healthy but it won’t idle without it. I’ve read what seems like hundreds of the forums on here saying to clean the carb again and make sure the pilot jet and air/fuel mixture screw are clear and I can assure you they are. Ive cleaned it several times now and blown compressed air through all the jets and passage ways in the carb as well. I’ve also adjusted the valve clearance and that didn’t help either.

I think it’s also important to note that it smokes on startup as well as when you rev it up. I’m planning on putting in new valve seals and rings but I didn’t think that would affect the idle.

Any help is much appreciated thanks in advance.
have rebuilt carb 1yr warranty 95.00 including shipping -910-885-1861
 

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Discussion Starter #6
Usually when an engine wont run without the choke, it's because the air/fuel mixture screw isn't adjusted properly or the jet is plugged. Try turning the screw out and maybe adjust the idle screw, See what happens. Is your plug getting black or running clean? Good luck...
Finally got some time to mess with it again. It looks like the plug is getting black. I've been messing with the idle adjustment (the screw with the black plastic knob) and I can get it to idle without choke, but then when I hit the throttle it dies? Any ideas? Thanks in advance everyone.
 

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Did you replace the choke (SE) valve?
If this valve is worn it’s like running with choke on
 
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