Bike screams at start-up - '99 RM250

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#1
My bike has started to scream for a few seconds at start-up. I know it's a sign of a lean condition, but I can't seem to find it.

I have a '99 RM250 jetted with a 152 main, 52 slow and clip on the second notch.

I bought the bike used a few months ago and have not done any top end work since I've had it. I changed the jets to the current setting because when I got it, it seemed rich and I couldn't get it to idle very good. It idles ok now(after warm), but it sounds like it's going to blow up on intial start( a few seconds) from high revs.
 

atc3434`

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#2
There's a thread going around on this already about a KX250... and we beat this topic to death a month ago on the Maintenece and Repair forum, so do a search over there and you'll find a ton of info regarding this subject. A general consensue is its going to rev a little, especially when cold, so just working the choke seems to work best. If it wasn't a little lean on a cold start, it would be pig rich at normal operating temperatures. The colder out it gets, the more obvious the cold lean condition will be.
 
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#3
A friend of mine had a 99rm250 that did that to him.
As soon as the motor got slightly warm it would quit.
The orings(from an aftermarket top end gskt kit) that seal off the powervalves were leaking.
As soon as he replaced them with stock orings (the aftermarket ones were really soft) the problem went away.
If you try this you may want to replace the gaskets to just in case.
He reused his gaskets so it was definitely the orings in his case.

Hope this helps
 
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#4
Originally posted by berno11
A friend of mine had a 99rm250 that did that to him.
As soon as the motor got slightly warm it would quit.
The orings(from an aftermarket top end gskt kit) that seal off the powervalves were leaking.
As soon as he replaced them with stock orings (the aftermarket ones were really soft) the problem went away.
If you try this you may want to replace the gaskets to just in case.
He reused his gaskets so it was definitely the orings in his case.

Thanks, I'll check that out too. It's about time for a topend anyway....I think.

Hope this helps
 

CaptainObvious

Formally known as RV6Junkie
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#5
If the bike returns to a normal idle after a few seconds of a high (screaming) idle I would not suspect jetting, however, it could be a lean condition brought on by something other than the jetting.

If you had used too small of a jet, or had a clogged jet, the problem would continue beyond a few seconds.
 
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#6
RV6 - that's whats got me stumped a little. It seems if it were jets or seals or whatever, it would do it longer than 5 seconds or so. It acts like a real lean condition(like right before you run out of gas, it will scream), but I can't figure out why it only lasts a few seconds at intial start-up, but not the rest of the day.??
 

rickyd

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#8
my bike used too do it, i lean it over til fuel comes out the vent hoses too get fuel into the carb.. When i was working at a watercraft shop, when i would fire new watercraft for the 1st time (or watercraft that had been sitting for awhile) they would do it.. Would run real lean til the carbs got some fuel..
Rick
 

darringer

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#9
Sounds like a lean pilot jet. Try going up 1 or 2 sizes on the pilot, then adjust the idle mixture screw to compensate when it's warmed up. If you notice, the weather has gotten a little colder, making it run leaner. I usually go up 2 sizes on the pilot in the colder months. Then in the spring return to the smaller ones. It was even more prevalent on my 99 rm125.