Crm250AR misfiring

[cosmos17]

Hi
I recently bought a CRM250AR which misfires at approximately 4200rpm (according to the fitted trailtech vapor trip comp).
it only does this when on the move and is fine at a stand still.
I have had the carb removed and cleaned and have altered the jetting from standard to a 155 main and removed the airbox snorkel (as per this websites recommendations for an aftermarket DEP pipe).
This has made no difference although adjusting the air screw has made a slight improvement but doesn't eradicate it.
Assuming that the carburation is fine, can anyone suggest why the misfire is occurring and in particular why it only happens when on the move.
ps. The misfire doesn't occur when accelerating, only at cruising revs i.e. riding through town at 25-30 mph, very annoying!
Thanks
Jason

[fallenmikethebike]

What plug are you using, have you tried other types?
Perhaps the fuel level in the carb is off.
Mike

[cosmos17]

Hi Mike
It had a ngk br8es in it which is burning biscuit brown, I tried a br9es in it which made it worse so I'm back with the br8es. Forgive my ignorance but how do I check/adjust the fuel level in the carb?

[davecee92]

This may sound stupid stick your finger in your silencer and see if you can feel any blockages etc or strip it. This exact problem happend on my mk2 causing me to break down with what i thought was a blocked jet and it was just the packing had collapsed being so old. Worth a try that or check the condition of the ht lead.

[cosmos17]

I've repacked the dep silencer and it wasn't/isnt blocked. The whole exhaust is dep and hasn't any dents in either.

I'll get the ht lead tested, could be a little before I do though.

Thanks

[davecee92]

No problemo mate hope you get it sorted theres nothing worse

[fallenmikethebike]

I've repacked the dep silencer and it wasn't/isnt blocked. The whole exhaust is dep and hasn't any dents in either.

I'll get the ht lead tested, could be a little before I do though.

Thanks

And the cap, cut the lead back 10mm.
Are the carb breather pipes clear of muck?
Mike

[gregorious77]

how bad is this misfire? are you sure its a misfire and not just 4 stroking? My AR (DEP system too) hates 25 - 30mph in town it doesnt help that they have no cush drive either so every surge and ding is felt through the bike.
2t like to be working. cruising is not something they enjoy.

[gregorious77]

also DEP I would put the snorkel back in if you plan any off road watery fun. Mine still runs the snorkel no probs

[cosmos17]

Speaking to my brother who is more knowledgeable than I and he says it's not really a misfire but a hesitation/poor running, like you suggest.
I appreciate a 2t likes to work and on the trails you don't notice it so much but I've had old 2t mx & enduro bikes that run cleaner than this!
The reason I got a crm was for its versatility so if it would be a bit disappointing if it's supposed to run like this.
I think we're going to continue tweaking the carburation to find improvement

[davecee92]

While you have the carb out id check the reed valve theres a good chance they could be broken or open too much

[knackeredMk1]

I was thinking that it might be hesitation as your brother suggests. If you find it really irritating try increasing your sprocket gearing. What is it currently?

[cosmos17]

While you have the carb out id check the reed valve theres a good chance they could be broken or open too much

yep, will do.

[cosmos17]

I was thinking that it might be hesitation as your brother suggests. If you find it really irritating try incregasing your sprocket gearing. What is it currently?

Sprockets appear to be 13/42 (might be 45). I was thinking of getting new chain and sprockets and maybe lowering the gearing slightly.

My brother suggested leaning out the pilot jet, so I'm gonna buy a few smaller ones and see how it goes.

[fallenmikethebike]

I was thinking that it might be hesitation as your brother suggests. If you find it really irritating try incregasing your sprocket gearing. What is it currently?

Sprockets appear to be 13/42 (might be 45). I was thinking of getting new chain and sprockets and maybe lowering the gearing slightly.

My brother suggested leaning out the pilot jet, so I'm gonna buy a few smaller ones and see how it goes.

Altering the pilot setting is unlikely to have any affect on the condition in the rev range you flagged up.
Two strokes want to be pulling all the time, lowering the gearing will move the perceived problem down the speed range.
Try managing the condition by changing up a gear so as the engine is under load.
Any one else got an AR near you to confirm it is the old two stroke phenomenon.
Mike