[JacobBell006]

Hello. I recently bought a 2011 CRF100F from a good friend of mine. Everything is mint except for a missing spark arrestor. He said the spark arrestor off and was lost when he moved it from his old house to his new one. The bike runs great, except, even when heated up, the choke acts as a kill switch when you turn it off. It will run on no choke if you stay on the throttle. But as soon as you let off it, it dies. I asked my friend about it and he said he never had a problem with the choke. I was wondering if anybody knew if the missing spark arrestor would mess with the choke. Like would that make it run lean or rich if it was removed? Thanks

[JimDirt]

So you are saying the bike always will not idle unless the choke is on ?? , and it has done that since you got it ??? ..... If so , then I would expect the Pilot Jet to be clogged ... that is what runs the idle and lower RPM ranges , if nothing else has been adjusted or altered , that would be the most likely cause .... however , the spark arrestor might have a slight impact , if the last time the prior owner ran it , it had the S/A in it , then that may be why he did not experience any idling issue , the spark arrestor will give some back pressure , which can slightly richen the mixture , with less back pressure from the removal of the S/A it could cause a slight lean condition , though I doubt it would cause the engine not to idle without the choke , that sounds more like the clogged pilot , but with the pilot clogged and the S/A removed , it might cause it to be lean enough not to idle , but , you should also have significant popping thru the muffler when letting off the throttle .......

If that is the case , I would expect the pilot to be the main culprit , what you can do , is instead of cleaning the jet , remove it and look at the number on it , go to the local bike shop or dealer , and get 1 size larger jet , and that should help with your issue ..... I would also while in there , give the carb itself a thorough cleaning , if it has a adjustable fuel screw (underneath at the front of the carb bowl) turn it all the way in till it gently seats , counting the turns , it should be around 1-1/2 to 2-1/2 turns out , if it is less than the minimum that might also cause a lean condition on bottom end RPM ranges .... and if the gas is really old , I would drain it and put in fresh so you know you are not trying to tune a bike on bad gas , as usually gas is only "good" for a couple months after that it deteriorates , especially if it has Ethanol in it , 2 months tops .... and even then it will start clogging things up ...... and make sure there is a air filter in it , if the filter is missing that will cause a lean condition .... if it is really dirty , it will also make it hard to idle as it will cause a rich condition , but as you mentioned , it needs the choke to idle , so I doubt that is a issue ...... Report back with findings .....