250r -runaway (reving)

[3wheelrider]

I have a problem with my R- but Im a little confused about why its happening & not sure what to try to solve it.
So... when I run it full throtttle for 1/8 mile or so- when I let off -it revs up high & I have to give it full throttle (done while coasting) to kill it. (Doesnt happen everytime though but it has happened many times now). If I wait a couple seconds and turn it back on (popping the clutch while its still coasting) its fine-no self reving anymore. Under normal hard riding -it doesnt happen either.
-I semi-recently did the top end. Im at 68.50mm now from 68.00mm. I put back the 3 layer of the metal headgasket at the time I did the topend (had 2 layers before). Still running pump 93 & Supertechniplate 32:1. I also reduced the ignition timing from +4 down to +2.
Main is at 172 -I didnt change that. Carb is a 38mm A/S
-I did move the DGH needle from 3rd notch to 2nd. Also had reduced the pilot from 50 to 48. I figured I was still on the rich side?-it does run much crisper than before rebuild. However its still fouling plugs after a long ride or 2.
-Sparkplug gets very BLACK? still-even on the threads. It runs damn good though. not much smoke.
-Running a BR9EG (racing plug)-supposed to be more resistant to fouling too.
-Reeds are new- VF3
- I keep forgetting to do the compression check...but should be less than before rebuild
-I pulled the head today to see if piston was melting-nope-looks good & did leakdown test again & passed again

Any ideas???-It dont have an air leak & I dont think Im lean?? -should I try some race fuel to see if it goes away????.

[86 350x]

Do a compression test to see if race gas is needed or just a waste

[ps2fixer]

I'm not the greatest with 2 strokes, but my cousin's old 250r would rev out when he was running out of gas (lean). I have read that if you add more oil, it will lean out the mixture more due to the oil displacement. If you don't ride the 250r hard, it might be a fair option to go a little lighter on the oil assuming the buildup on the plug could be the oil rather than the gas?

My cousin's machine would foul out the plug like crazy, he was mixing too much oil in the gas, and the carb i think is over sized for stock airbox / pipe and is currently adjusted lean as possible and the fouling problems are gone now. This bike is used for trail riding, not mx/racing, so 40:1 has worked well for him. I know the carb needs re-jetting though, or swapped to the OEM carb.

Another thing to point out, how about your throttle cable hanging up? Try turning your handle bars side to side while it idles and see if it changes at all.

Just my 2 cents, i'm sure someone else with better experience will have a more solid answer for you

[barnett468]

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post a photo of your plug.

heres a plug guide I assembled today.

If it stutters/burbles even the tiniest bit when you accelerate, it is rich somewhere . . If it simply hesitates as if it is out of gas, it is lean.

Post a photo of the plug . . The plug on the right is shiny which means it is wet which means its oily . . It is possibly rich too but its hard to tell because of black deposits from the oil . . This engine should be repaired . . The middle plug is perfect . . The left plug is lean.

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This plug is bone dry so the black means it is rich . . If both the threads and the porcelain is black, i would start by reducing the main jet size first . . In the case of a plug that has extremely heavy deposits like this, I would go down 3 sizes on the main because just one will not be nearly enough and two will likely no be enough . . Four would be too much.






I would start by doing the following:

If the gas is old or yellow at all, change it . . Yellow gas is either oil or contaminated by rust in the tank or both.

Check the float level . . If it is excessively high, it can cause a rich or flooding condition.

..................Here's an example of it a little too high . . It should be just below the solid black line in your case . . If it is at the dotted line, it will still not cause a problem even though it is just a little high . . If if is above the dotted line, I would definitely fix it by bending the small metal tab slightly that depresses the needle, slightly upward toward the top of the carb.

If the float is plastic, it requires heat to bend it, and this should only be done by someone whom is very experienced, otherwise you might end up with a puddle of melted plastic which will no longer fit very well.

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............................................. Here's another in which you can see the is level way too low.


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[barnett468]

- I keep forgetting to do the compression check.

i would do this asap . . you can typically run 170 - 180 on 91 or higher octane.

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[ps2fixer]

@barnett468

That is a nice write up, i'd say make a thread with that info and throw a link in your sig for reference . Never knew about the float level check with the drain, which the service manuals had that info... or maybe I just never saw that section lol.

[3wheelrider]

Plug is BLACK! but no stutter/stumble -even with slightly larger main/pilot jets.
Its definately not the throttle cable hanging up.
I thought it maybe was getting too hot from being lean or from an air leak -but it dont look that way???
Im pretty sure float level is correct but gonna check that out again next time I get a chance along with the cmp. check...
cant do ^^ that^^ trick to see the level on these carbs-shucks lol
Fuel flows well thru petcock also.

[barnett468]

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@barnett468

That is a nice write up, i'd say make a thread with that info and throw a link in your sig for reference . Never knew about the float level check with the drain, which the service manuals had that info... or maybe I just never saw that section lol.

Thanks, unfortunately I don't know how to make a link to it, but I know from our previous pm exchanges of helping you with your KLT110 shifter and clutch, that you definitely do, but for some reason, I am the only person on the site that can not have a signature, or an edit button, or an avatar, or edit my profile . . Over 40 years of experience, and several years running the ATV department for US Kawasaki R and D, plus years of Professional level Motorcycle AND ATV racing, AND over 3,000 posts trying to help people what little I may be able too, and I guess I am still not worthy.


You're right for a change Barn...You definitely ARE not worthy, and it is because you lack experience.

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[barnett468]

Plug is BLACK! but no stutter/stumble -even with slightly larger main/pilot jets.
Its definately not the throttle cable hanging up.
I thought it maybe was getting too hot from being lean or from an air leak -but it dont look that way???
Im pretty sure float level is correct but gonna check that out again next time I get a chance along with the cmp. check...
cant do ^^ that^^ trick to see the level on these carbs-shucks lol
Fuel flows well thru petcock also.

oki, well if your plug is black and DRY, it is still rich . . it does not have to stutter and stumble to be rich . . it would be helpful to see a photo of the plug but i will take a guess that you should go down 2 sizes on the main providing the float is not too high, then try a new plug so you get a good reading, or clean all the stuff off of your current plug.

i'm also guessing that your compression is .lower than it could be.
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[barnett468]

@barnett468

That is a nice write up, i'd say make a thread with that info and throw a link in your sig for reference . Never knew about the float level check with the drain, which the service manuals had that info... or maybe I just never saw that section lol.

oh...I have also been an automotive instructor on occasion, and can more often than not, actually form a coherent, articulate sentence, and even spell properly.
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[3wheelrider]

Compression is definetely not low-will get a reading next time
Im not planning to lean it out especially with it revving up like that -not so worried about the plug fouling. I wanted to figure out the revving-if it was too lean ,air leak, or was getting too hot. Gonna check the float level as stated & do a compr. check. Wont be till next weekend......thanks. I'll report back my findings.

[yaegerb]

Sounds like either an air leak or your slide may be sticking. How many turns out on your airscrew with a 48 pilot? You would benefit from a crank case pressure test and a compression check.

[barnett468]

Compression is definetely not low-will get a reading next time
Im not planning to lean it out especially with it revving up like that -not so worried about the plug fouling. I wanted to figure out the revving-if it was too lean ,air leak, or was getting too hot. Gonna check the float level as stated & do a compr. check. Wont be till next weekend......thanks. I'll report back my findings.

it is not good to run an engine so rich that it turns the plug black even if it revs to 20,000 rpm . . it is illogical to do that because it is obviously not burning the fuel, and you will not get much, if any cooling by going super rich . . when i have an engine that will spend a lot of time at high rpm, i jet them 1 or maybe 2 sizes rich at the most, from a "perfect" setting . . also, you can cause premature ring wear by running it too rich.

if it runs hot at wot, you need to fix the actual cause . . reducing the ignition timing can actually make an engine run HOTTER, if the timing is less than optimal.

once it is properly jetted on the main, then it will likely be easier to jet it down low because increasing the pilot will also make it richer on top, which is the opposite of what you want.

[3wheelrider]

As stated-I did a leak down at the time of the rebuild a few rides ago. I just did one again .It passes-so NO air leak. Slide & cable is NOT hanging up. Only happens after a long straight run- but not every time.
Still dont see how leaning it is gonna help anything right now...?

[barnett468]

Still dont see how leaning it is gonna help anything right now...?

You dont need to "see" or understand how it may help . . I don't "see" or understand how E=MC2 works but it still works as evidenced by several city blocks evaporated and half a million dead people.

I also don't know how brain surgery works but I'm not going to go to medical school for 12 years just to find out before i let them operate if i have an aneurysm.

From your description, your bike seems WAY too rich, not just a little rich . . Way too rich is a problem . . The most intelligent thing to do is to fix obvious problems when you see them, but you refuse to do that, so all you can do is live with your high idle problem.

I don't understand why someone would ask for help with a problem, then not take the advice given . . Anyway, I hope you get it fixed someday but it doesn't sound like it will hurt anything so I wouldn't worry about it damaging anything.

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