xr250L carb problem

[fencr]

xr250L carb problem
I've got a '91 xr250L model w\a supertrapp.. used strictly offroad..
problem is that the engine 'hunts' .. that is, it won't idle evenly it will start low (like when the throttle is blipped) then climb back up to a relatively high rpm.. if I back the idle speed and it won't accelerate well.. it'll bog then catchup.. it gets to its high rpm then the rpm will vary .. seems like an air leak .. I did spray some wd40 around the carb/manifold union thinking if it were sucked in it would rev the motor. but, i realize now that i missed the engine side of the manifold

prev.owner put a larger main in it but, that clearly isn't an issue now .. there is a limiter cap on the idle air screw.. heard it was reccd. to burn it off and get full adjustment on the screw.. not done yet.. Any thoughts appreciated..

fencr@hotmail.com
marc

 

[dual-sporter]

on my '94 i heated the cap on the needle with a small torch & the limiter came right off. the screw is a standard slotted head.
i haven't experienced the problem like you have, it does sound like an air leak. i lost a screw on the float bowl during a ride which caused it to dribble gas out slowly.
i'll be replacing the carb when i get a chance, i recently bought a 2001 stock R carb taken off another DRNr's bike just haven't had the bike apart since i got it. for now i have a 128 main and 40 pilot in my stock carb and it does OK. the XRL bowl doesn't have a plug on the bottom which allows easy access to the main jet.
that carb may just need to be cleaned, sometimes they build up a varnish that clogs jets & passages, clean it up & run carb cleaner through the passages. who knows it may be the bowl 's loose & sucking air through it.
good luck.

 

[yardpro]

I had an xr250l with the same problem after I installed a supertrap. I had to install a larger piolt jet ( that's the jet that affects idle-1/4 throtle). Also, get hold of a factory manual, set the idle, and air screw as directed (it's more entailed that merey turning an idle screw, you still need to remove the cap on the air screw though)

I lover my dual sport, i had the white bro's 330 kit installed in mine ( after the idle problem), and may I say heck yea, yee haw :) It's definately worth the money.

 

[fencr]

I pulled the carb friday night.. found that the cap on the idle screw was spinning and the screw was stuck in place ( at first i thought the screw was stripped) ..then i actually sheared off one side of the screw slot trying to turn it.. i spritzed it down with carb cleaner and put some gasket sealant between the mainifold and the carb and that helped the wandering idle speed some.. it ran well over the weekend but, i think i'll put the R model exhaust header i bought on it to get more flow.. my friend thinks it isn't breathing well enough.. it climbs like a goat and pulls well but, off idle isn't too impressive.. i'm not expecting a 2stroke jump but, a cleaner/lower idle speed and a bit more pop would be what i'm after..

i did pick up a larger idle jet but haven't installed it.. i'll need to get another needle to make that happen .. i grabbed a 42 'cause that's what the shop had but, i wanted the 40 just to go up one step..

I wouldn't mind finding a carb for the R model bike to put on this L.. but, it isn't a real priority.. thanks to you both for your thoughts.. it helps to bounce the ideas around..

 

[yardpro]

fencr-
If when you say the idle jet you mean the pilot jet, you won't have to change the needle. The needle seats in the main jet and has absolutely no effect on the idle. it's a different circut. Thw supertrap system, as with most aftermarket systemd actually take power from the bottom, but add power to the mid and up. If bottom end is what you want than the easiest way to do that is to increase compression(make sure you run high octaine gas) or to increase displacement.

 

[fencr]

You're right i am referring to the pilot jet .. and i see now that i was saying idle screw when i meant the mixture screw..
but, i think what is somewhat lost here is that i am starting from an L model bike with a carb that was factory jetted to comply with emissions rules for the street.. it was a dual sport not an XR-R model.. also it will probably benefit from a good thorough cleaning if i could get all the openings open (like getting the mixture screw out) .. i've done a couple partial cleanings but, something has always held me back from stripping it completely.. most recently its that the mix screw won't come out without a fight.. so i'll order a new one and convince the old one its time to go..
as to the trapp opening up the middle and top end more and robbing from the bottom .. ok .. i would have thought it would have increased power across the whole band since it was less restrictive than stock and more flow means more fuel burnt etc .. of course when you change the exhaust you need to match or optimize your mix setting to match.. and i don't know how well that was done until i get the screw to move..
so .. there are a couple things i can do now that may improve the situation before overboring etc..
but i'll ask around about what i should be expecting from that trapp.. thank you