250r wont shut off. this is crazy.

[200x Basket]

the 85 in my sig had a worn out engine but i rode it even after i restored the rest of the trike. well i just put the new bottom end together with a 100 over piston on a ported and polished cylinder, cr head gasket, boysen ram valve with carbon fiber reeds, 38mm mikuni flat slide, and a fmf fatty exhaust. i have been breaking it in nice and slow over the last few nights. i will crank it and let it run for about 5 minutes to get up to normal temp then i shut it off. after the first couple heat cycles i would blip the throttle on occasion but nothing big. well after about 10 of these i decided to give it a little more rpms. well i am blipping the trottle and all of a sudden the rpm dont go down. it is reving at about half throttle. i hit the kill switch and it will not die??? WTF it was in the back of my truck so i could not put it into gear and clutch it out. i cut off the fuel and it died. i messed ewith the trottle cable and it was fine. i fired it back up tried the kill switch a few times and it was working perfect. ????? so i start blipping the throttle again and the same thing occurs. it will not cut off. i can give it more gas and it will rev. i can rev it up and kill it with the switch but not when i goes to its half throttle idle. everything is perfect. the only thing i can think of is that it is running like a diesel because it is not getting any fire to the plug. the switch works fine. so what can you think of? sorry so long.
chris

[DixiePlowboy]

Try removing the plug wire with an insulated pair of pliers just as soon as it goes into "demon posessed mode" to be 100% sure that the switch is working at that point and to eliminate the possibility of dieseling.. As for the high idle, check the full length of the cable(again just in case), the carb slide for ease of opening/closing, and possibly for an intake air leak. I know those are basics you've probably already thought of, but those have been the causes of problems for me in the past.

it is either an air leak, or the slide could be sticking on the body. as far as the kill switch, try doing it when the engine is cold, if it doesn't "deseil" then it isn't in your kill switch

[Mike Fort Laud]

My 85 did the same thing a couple times. When the problem happened to me it was under a different circumstance. I turned my fuel valve to off so to run the fuel from the carb after a ride. As the fuel ran out, the motor started racing like I had the throttle wide open. Instead of just running out of gas and dying. When I turned the switch off nothing happened so I put it in gear to stall it. All I could guess was the extreme lean condition caused by running the fuel out. After it raced out of control another time under the same circumstance I just run it a minute now to drain off a little fuel at shut down time. As to your exact cause is beyond me. But I have seen my own rev out of control and the switch will not shut it off.

[Lots_Of_Nothing]

this has happened to many people that i know, and me....what it is when the engine wont die, and just keeps going, even when theres no spark....is...on the top of the piston carbon builds up from all the oil, or to rich gas...once enough gets on there, the engine will run really high untill it burns all of it off....even if you hit the kill switch, take the plug wire off...it will keep going...no matter what, untill it burns all the carbon off

[atc's]

I know exactly what your talkin about 84250r same thing happened to me on my 85 R after using that crapy walmart brand 2stroke mix. Now that i have the topend off i can see the carbon on the top of the piston. that i will get off with some degreasser.

[200x Basket]

this has happened to many people that i know, and me....what it is when the engine wont die, and just keeps going, even when theres no spark....is...on the top of the piston carbon builds up from all the oil, or to rich gas...once enough gets on there, the engine will run really high untill it burns all of it off....even if you hit the kill switch, take the plug wire off...it will keep going...no matter what, untill it burns all the carbon off

mine is all new and polished so i doubt that is it. maybe but not likely. something is getting hot enough to light the fuel off. i am going to do a leakdown on it and see what i come up with. i am thinking air leak. that is about all it can be.

[Lots_Of_Nothing]

well do that, and let me know what the outcome is

[200x Basket]

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well i done a leak down (air pressure test) on it today. i pressed it up to 10psig and looked for a leak. i checked the intake, the exhaust, the head, the base, the tranny vent hole, and the case to case gaskets. there were no leaks. i did not check the crank seals but after 1 hour there was still 10 psig on the gauge.

the idle is a little high so maybe it is just lean at an idle?? i done two full speed 4th gear throttle chops and it was just right. (light tan). how do i richen the idle with a mikuni 38mm carb?

here are some directions on my $6 leak tester.

1. buy a 1 1/2" PVC cap at a hardware store
2. buy the cheapest valve stem at autozone and the 1 3/4" rubber freeze plug.
3. drill a home in the cap to match the diameter of the valve stem. you may have to sand a flat spot on the cap to seat the stem. insert the stem in to the cap with a little sliicon (just to be sure it does not leak).
4. remove the carb and insert the cap.
5. remove the pipe and insert the plug
6. press it up to 8psig (or so)
7. soap it down and look for bubbles.
8. be sure to check the tranny vent and the bottom of the case.
9. did i get it all???

[TimSr]

MikeFL is right about the engine racing when its lean. If you have any doubts, shut of the gas while its idling and wait a few minutes. It will race like crazy right before it dies. Most common cause of engine racing like this is an intake air leak, but sounds like youve covered that.

Dieseling, also caused by running lean, is when the plug gets so hot, the tip glows, and it ignites the fuel without spark. I would pull the plug wire as Dixieplowboy said, to make sure its actually Dieseling.

If it is actually dieseling, its unlikley this is caused by idling too lean. Even with a lean idle, its hard to get it hot enough to diesel. It usually requires upping the RPMs by riding it, in which case, youre probably lean all the way through.

To richen it up at idle speed, you need a larger pilot jet, but in my opinion, if its light tan, your treading on very thin ice. Its better to err' on the rich side, where the greatest consequence is a fouled plug. Id go with a larger main jet until you darken the plug a little bit. I like mine a dark tan or brown under normal riding. then I dont have to worry about meltdown when Im on the race track.

[REEB RACING]

some times mud gets into the switch and will not allow it to make contact, take contact cleaner and spray it into the kill switch, it works for me, as for the rpms sticking check the carb slide