yamaha wrf 250 problem

gerry b

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My son has a yamaha WRF 250 enduro 4 stroke, single carb, single cylinder, year 2004, when it reaches normal running temp, it wont return to idle when you throttle down, when you do get it to idle it revs up itself to about the same rpm as if choke was out, he swapped the carburetor, the position sensor and the carb joint with another bike, it starts and goes like a rocket, anyone got any advice thanks.
 
idle jet in the carb prob gunked up

so strip carb, clean the parts and if required rejet the it
 
gp to motocross.ie or enduro.ie great lot help there

but for best help on enduro bikes, go to THUMPERTALK

great site

if new card sorted it. then problem is dirty carb. take carb and carb boots out and clean and rebuild them
 
Corporal Punishment said:
That would be my guess too but between the carb and head. Spray WD40 around the joint twixt carb and head, listen for a change in engine note or smoke at exhaust. The oil will be sucked in and burnt hence the change.
Click to expand...

That a very handy one to know, thanks CP.:beerjug:
 
sorry i didn't explain properly, when he swapped all the items from the other bike he still has the same problem, so that rules out the carb, the sensor and the rubber joint between the carb and manifold, he tried the wd 40, good trick but to no avail.
 
You've checked the throttle is fully returning to the stop?

Pilot jet could still be at fault if the other carb had been stood.

Check the idle mixture, eg. 1 1/2 turns out with warm engine, turn in untill revs drop, turn out until revs drop again counting the number of turns exactly then set to the mid point.
 
is the throttle cable snagging, when he swapped the carb did he unscrew the slide or replace the whole carb?
 
replaced whole carb, and no the cables are ok, the problem is only when the bike heats up, so there must be a crack in the head i think ? in fact he put all his parts on the other bike and she runs ok.
 
gerry b said:
replaced whole carb, and no the cables are ok, the problem is only when the bike heats up, so there must be a crack in the head i think ? in fact he put all his parts on the other bike and she runs ok.
Click to expand...

Yep you might be right, has he used his mates tank on there as well?
 
no not the tank, if your thinking petrol problem, it goes like a rocket when you open it up its slowing it down is the problem, it starts very easy, no miss or backfiring.
 
Have you got a blocked fuel tank breather? The running temp of the bike may be a red herring....
Also, have you checked valve clearances, and before you do, do a cylinder pressure test.
The above is only because you sound like the carb that was swapped is good..... so the issue is a little deeper.

Timpo.
 
1 sumple check, check bolts on the header. mate had similar prob on rvf and turned out that header was loose

but i still think its a card issue, check idle screw and jets, these are the main points and cables.
 
There's air getting in there somewhere. As the engine heats up, something is expanding and letting a leak in. Classic symptoms of fuel air mixture being upset.
 
I come on the same symptons 6 months ago on another enduro bike.
done all the same as you swaping parts ect ect, a real head scratcher
and i kept blaming the carbs wrongly:augie

it turned out to be a broken ring on the piston with none of the ring missing.
and there was a wee pipe going from the engine to the carb that looked more like an exeust pipe than a vacum pipe with the engine running. sometimes.

all i could think of was when the bore got hot and expanded the broken piece of ring turned to line the space up with the space on the oil scraper ring allowing back pressure when you are off the throttle creating a blow back on that wee pipe going into the carb and when you are on the throttle the broken piece goes the other way making the spaces on the rings not line up giving a better seal hence leaving the bike no problem starting or accelerting.

This is only my theory but new piston and rings sorted this bike.

Good luck :thumb. these head scratchers are there to keep our brain alive:).
 
hi all, yamaha problem sorted, tried the wd 40 test but to no avail, he fitted a new rubber seal between carb and intake even though the old one looked ok, stripped and cleaned the carb again, adjusted the throttle positioner, started her up, fine tuned it and it now runs like a dream. thanks again for all the help
gerry b :comfort
 
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