98 cr250 screams uncontrollably today @ track..please help.

[BlackCR25098]

Sup fellas, well today me and a mob of riding buddies took all the hondas out to a local track. (My 2nd time on a real track) I've just re-discovered the sport after selling my 98 cr250 3 years ago and then buying it back about a month ago.

The bike runs amazing but a couple weeks ago I fired it up and it just started screaming. I mean top level rpm as high as the motor could go and held it....After freaking out trying to choke it and everything else I finally kept searching gears till I dumped the clutch in like 4th gear and it killed the motor.

I brought it over to my buddies and we pulled the needle out thinking the needle had stuck. It ran great for a few weeks until today..... I was just starting to get my speed up and get comfortable on the track while coming up a hill I stood up wheelie'd to the top of the hill and well, it decided to hook up and SCRREEEEAAAAAMMMMMM uncontrollably again...The bike literally did a back flip or 2 before falling to it's side.

My buddy picked it up and noticed it was screaming but the throttle WAS NOT held wide open. In other words, the bike was just screaming regardless of where the throttle was at. This was where we figured that instead of the needle sticking, the "Composite racing valve" aka power valve, RC valve, was sticking since the throttle was closed and it was still screaming.

Basically fellas I'm looking for an answer on what I can do? Is there a way I can clean it or something?

BIKE STATS:

-98 cr250

-it has the power jet system with the keihin PJ carb with the power jet solenoid system

-32:1 Klotz

-93 Octane

The night before we put in a fresh carb rebuild kit basically with new O-rings and such along with all new jets....We didn't really touch the needle or the RC valve...Just trying to see if this was common what so ever. I can't really enjoy riding or legitimately try and jump or hit rhythm sections without being scared shitless.

The bike ran great after the incident the rest of the day. A friend just suggested the reeds weren't strong enough or something, but looking to nip this in the bud fellas...Give me your opinions ask any questions or stats I left out. Thanks for any of your time

Griffin

[Third-Reef]

The power valve sticking will not make the bike rev. It would make it lose low end or top end depending on if it was stunk open or closed. You ether have a problem with your throttle cable, cable routing, slide/return spring Or you have a massive air leak. The first things actually hold the throttle open just like our wrist does and the bike has full power and you know the rest. The air leak will usually show up as super fast idle even screaming with the clutch pulled in but should no cause it to take off and weelie. I think you have a problem with the throttle cable or slide

[BlackCR25098]

Yeah well the thing is like I said when my buddy went to pick the bike up and it was screaming the throttle was not stuck wide open at all....It was actually probably closed, and also my bike actually has idled down lately but I think that was cuz my buddy Bill twisted my choke knob (idle knob) last night when we had the carb off....

So just remember the throttle wasn't stuck open so wouldn't the cable or needle caught up make the throttle stay wide open like that? We rebuilt the carb last night but did not mess with the needle...I may need a new return spring or something since the kit did not come with one...And since the bike is idling LOW I wouldn't think air leak especially not since it ran amazing all day and randomly took off and did a double back flip....Lemme know what you think...Remember this isn't the first time this has happened it happened once like a few weeks back....Other than these 2 little random times the bike is great and idles however I want based on turning the idle knob....

[choppertown]

somthing is going on with your card/throttle cable/throttle.

the problem lies in one of thoughs three.

[426 hemi]

mine did the same thing it was the cable getting messed at the carb side hold it wot

[erik_94COBRA]

Sounds like your throttle slide is sticking.

[heart_of_darkness]

A pinched or frayed cable, or a sticking carb slide, will effectively hold the throttle open. Obviously it can be pretty dangerous.

Get a new throttle cable, lube it well, then when installing it check the routing to be exactly the same as the manual.

Also check that there isn't flaking or burrs on the carb slide or the slide's bore within the carb body. Check that the carb needle slides smoothly into the needle jet holder (the brass thing that the main jet screws into). You can also lube the slide itself with some two stroke oil.

[BlackCR25098]

Thanks a ton fellas! I'm actually kind of glad it is something with the throttle instead of the "mystery air leak" !!!

I plan to buy a whole new throttle cable, slide, and probably return spring...F it, just get it all and install as perfectly as I can.

I'm still wondering though if the cable or slide got stuck wouldn't the throttle physically open as well? My buddy said the throttle wasn't stuck wide open even though the motor was SCREAMING.

[BlackCR25098]

Also fellas do you physically replace the "carb slide" or is there a way to lube it to get her from sticking?

[Pontificus Maximus]

I had a '95 that did that (throttle sticking) a number of times before I figured out that the reed petals were fraying and blowing back into the slide. The slide was a close fit in the carb body and it didn't take much to stick it. Haven't been a fan of fiber reeds since then...

[MrBlahh]

on most bikes, if you pull on the throttle cable, it will be the same as twisting the throttle

can be scary in the woods if something yanks on the cable

[BlackCR25098]

The reeds are another definite possibility we took them out and inspected them when we did the carb and the gasket was 90% complete and 10% gone. I think the remainder of it was stuck on the intake part of the engine...

It's just weird that my bike runs great 99% of the time and then there's that 1% that it will go wide open!!! Lemme know what yall think on that and my reeds situation.

[Keith72]

Are you positive its not an air leak? Have you done a leak down test?

[BlackCR25098]

I am not and no I have not. The only clues I have that it isn't an air leak is the bike has not idled up at all, and this bike has been mainly sitting for 3 years so I'm thinking all the sudden it's getting all this use and I haven't lubed my throttle cable so I'm thinking it has to be the cable/slide/or return spring or something around there.

We took the reeds out and they looked okay although the gasket was busted a little. The broken parts of the gasket were stuck on the motor side so when put back on atleast it sealed up somewhat...If not cable/slide I am thinking reeds.

Were about to go through and replace all of everything I just mentioned and I would love to do a leak down test on it but the bike runs excellent 99% of the time and has only stuck wide open twice. Once a few weeks ago and then again yesterday. Lot of ride time in between both occasions of it sticking....Idles perfect.

If it was an air leak wouldn't the bike constantly stick wide open?? I rode it the rest of the day after it stuck and it ran great...

[Keith72]

You should be able to do a leak down test without removing the engine from the bike. Just remove the exhaust and carb. Seem to remember a thread here somewhere that showed the set-up to do it.

[Keith72]

From the sticky at the top of the page: https://www.thumpertalk.com/forum/showthread.php?t=506699&highlight=leak+down+tester

Every 2-stroke rider should have one of these testers.

[BlackCR25098]

Awesome that seems very do able. I'm not too good with the motors but I have friends who are. Were going to start by replacing the cable/slide/everything along with new reeds and gasket..Next step will be a leak down test along with a kill switch.

My bike don't got a kill switch so when it hits wide open like that it gets real real REAL stressful/scary REAL quick.

I just found a leak down tester me and my buddy can use so we'll do it ASAP. I sure hope it is something in the cable or slide rather than a leak...So with the leak down test will I be able to determine exactly what's leaking or will it just let me know that it is leaking somewhere?

[BlackCR25098]

Okay guys let's pretend like this is not an air leak but instead somewhere physically in the entire throttle assembly. I want to replace anything and everything that is possibly causing it to hang up so help me make a list. I'll be ordering everything friday.

Throttle cable (obviously)

Throttle tube

Slide?

What else?

I'm still very new to mechanics of my bike so any help would be greatly appreciated! For the safety factor I just want to replace all of it for a little re assurance so please help me with my list!

[slowthump]

I have a 98 cr250 and have had the exact same thing happen. It a was a big air leak caused from the top of the carb not being screwed down tight. It took out my crank and scored the piston and cylinder. Absolutely do the pressure test. You can make the parts needed for about 5% of the cost of the parts you will wreck, not to mention the hassle. 2 strokes should be pressure tested frequently. Small air leaks will lean out the air/fuel mix and mess with your jetting. Once you have the parts and procedure down it takes about 15 minutes.

[BlackCR25098]

Yea yours did the same thing but did it run great 99% of the time and only do it once every couple weeks with a lot of riding in between? I would think if it was an air leak it would do it more constant. My throttle cable is 4 years old.....lemme know!