What happened?

[Eddiesanders250]

I just got my motor completely rebuilt. btm end done by neil and i put the rest together. Stock cylinder bored .100 over running thin head gasket 180 psi. I was breaking it in for half of a day then it started to idle real high... i pulled in the clutch then ibogged out and died, it made that buuurrrrrr sound. I figured it was running hot. I started it up the next day and just let it idle for a couple minutes and it cut out again. I read the plug it is a brown paper bag color, i figure its fine. What do you guys think happened? I am running this peak antifreeze and coolant for a car and mixing 50/50 with water, that might have something to do with it?


I am lost all you experts i need help
Thanks

[fireburns99]

I am by no means an expert but heres my thought:

I can't see how the coolant would be causing this. And idling for a couple of minutes shouldn't cause it to overheat. Was the plug a consistent brown, or was there a spot on side where it was a different color. Maybe the head gasket is leaking? I know the thin gaskets are hard to seal.

Also if it had overheated you would have seen that coolant coming out of the overflow. One idea is to route the overflow line so that it is right over the pipe. If it gets hot it will overflow onto the pipe and you will smell it.

Did you check for any vacuum leaks?

electrical? :confused:

[Eddiesanders250]

there is no white spot on the plug. It ran fine before with the same jetting and almost identical cylinder, i am ruling out that it could be a jetting problem. I put new reeds on maybe i put them on wrong?

Is there anyway i can find out if there is a leak in the boot somewhere with out just looking for it? leakdown test?

I am also thinking it probably isnt an electrical problem because it ran fine for almost a day then suddenly quit... I could be wrong though.

[C-LEIGH RACING]

Reasons a 250R engine will start revving up with the throttle closed.

Air leaks,,,check for,
Around the areas of the cylinder base gasket.
A bad seal,,,yours are new though, but that dont mean it cant leak,
Carb lean, fuel level low in the bowl, pilot jet W A Y to lean, petcock off, or tank out of gas,
Gaskets leaking around reeds or intake manifold rubber cracked,
Center case gasket not sealed,

If the head gasket is leaking, coolant can be drawn into the cylinder bore & cause the engine to smoke real heavy & most of the time end up seizing up the piston.

One thing I was thinking about sence you said it started reving up while it was idling,, did you put all the crankcase bolts in place that hold the cases together.
There was only three case bolts in the box for me to use when bolting the cases back together,, just a thought.

If you have the tools to do a leak down test I recomend doing that.
One way to check for leaks with the engine all together & running, take a spray can of carb cleaner & while the engine is running, spray small amounts around the areas of the cylinder base gaskets, reed gaskets, & on the rubber intake manifold, if you have an air leak the engine will draw the cleaner into the engine & stall out the engine.
DONT for any reason spray the carb cleaner around the exhaust pipe where it connects to the cylinder while the engine is running.
Neil

[Eddiesanders250]

well while i was pulling off the reeds, carb and boot i found that the plastic overflow wasnt calmped tightly onto the boot.... im thinking that couldve been it? I havent found any holes or cracks in the boot. before i put it back together i am going to do a leak down test... neil i did put the rest of the bolts in the case.....

[C-LEIGH RACING]

Plastic overflow,,,??, I dont understand what that is.
If you mean the plastic tube under the reed chamber hooked to the cases, thats a vent tube for the transmission & shouldnt affect the running of the engine.

If you still have the engine all together, do the carb cleaner trick first, that will tell you which gasket is leaking, BUT be carefull, that carb cleaner can flash up if to close to a flame or spark.
Neil

[86 Quad R]

Originally posted by C-LEIGH RACING
be carefull, that carb cleaner can flash up if to close to a flame or spark.
Neil


hehehehe :eek: thats the very reason i use wd-40 or some sort of liquid wrinch. that carb cleaner can get RUDE lmao

[fireburns99]

Originally posted by 86 Quad R
hehehehe :eek: thats the very reason i use wd-40 or some sort of liquid wrinch. that carb cleaner can get RUDE lmao

Hey but thats half the fun! :D Haven't you ever seen that show "mythbusters," its not very exciting without some kind of pyrotechnics. hehe.

But in all seriousness be careful, using carb cleaner.

[C-LEIGH RACING]

Yeah,
I can tell you first hand what it will do spraying it around a head gasket on a blaster engine, WHOOOHAWWWW

But, did you know WD 40 will produce a hotter & more lasting fire than the carb cleaner. Lower flash point than the cleaner but harder to BLOW out in an emergency.
:D :D :D :D :D Neil

[fireburns99]

Originally posted by C-LEIGH RACING
Yeah,
I can tell you first hand what it will do spraying it around a head gasket on a blaster engine, WHOOOHAWWWW

But, did you know WD 40 will produce a hotter & more lasting fire than the carb cleaner. Lower flash point than the cleaner but harder to BLOW out in an emergency.
:D :D :D :D :D Neil
Thanks a lot neil, now i'm going to go home and try it. :D I know that wd-40 burns in a pretty controlled manner though. When i was younger i used to make flame throwers with wd-40 and a lighter. Never played with carb cleaner though.

Thanks for the info.

[C-LEIGH RACING]

I wouldnt play with either one, I can tell you what its like to get burning gas on your legs with a pair of shorts on, rolling, tumbling & kicking laying in a gravel driveway is a bad day.
After that, somebody just turning on a light in a room will make you jumpie.
Neil

[Rich250RRacer]

Originally posted by C-LEIGH RACING
Reasons a 250R engine will start revving up with the throttle closed.

Air leaks,,,check for,
Around the areas of the cylinder base gasket.
A bad seal,,,yours are new though, but that dont mean it cant leak,
Carb lean, fuel level low in the bowl, pilot jet W A Y to lean, petcock off, or tank out of gas,
Gaskets leaking around reeds or intake manifold rubber cracked,
Center case gasket not sealed,

If the head gasket is leaking, coolant can be drawn into the cylinder bore & cause the engine to smoke real heavy & most of the time end up seizing up the piston.

One thing I was thinking about sence you said it started reving up while it was idling,, did you put all the crankcase bolts in place that hold the cases together.
There was only three case bolts in the box for me to use when bolting the cases back together,, just a thought.

If you have the tools to do a leak down test I recomend doing that.
One way to check for leaks with the engine all together & running, take a spray can of carb cleaner & while the engine is running, spray small amounts around the areas of the cylinder base gaskets, reed gaskets, & on the rubber intake manifold, if you have an air leak the engine will draw the cleaner into the engine & stall out the engine.
DONT for any reason spray the carb cleaner around the exhaust pipe where it connects to the cylinder while the engine is running.
Neil

I don't know how everybody else here rebuilds motors, but another source of an air leak on 250R motors are on the crank collar on the clutch side. If it's worn a new seal won't do a bit of good. I replace it EVERY time I do a rebuild. The seal will wear a slight groove in the collar, which means potential air leak. It's cheap insurance, and any professional rebuilder who doesn't replace it shouldn't be called a professional.

[Eddiesanders250]

neil i wasnt talking about the vent tube off the cases.... idk what its called i guess its not an overflow, to be honest idk what it is, but it is connected to the side of the big boot beofrew the carb..... anyway i tightened it up put it back together and it seems fine but i will try a leak down test, and cthe cleaner trick if there is a leak... thanks fellas

[C-LEIGH RACING]

You mean the white box looking thing on the side of the filter boot that is connecting the carb & the air filter box.
If thats it, that is a noise resonator for the air intake boot.
That being loose wouldnt cause it to rev up.
Neil

[Eddiesanders250]

hmmm the clamp wasnt tight around the resonator causing it to suck more air almost like a leak in the boot...... that couldnt of been it? I will have to ride it for a longer period of time...
Neil what do you use to block off the exhaust port when doing a leak down test?

[86 Quad R]

i use a section of bicycle tube as a gasket that i stencil out using the exhaust flange. when ya pressure up the system it will swell and form into a lil bulb.

[C-LEIGH RACING]

That rubber gaskets a good idea.
I use one of the rubber hub caps off of a LT80 Suzuki & just clamp it over the exhaust flange nipple. Sometimes the flange will leak where it bolts to the cylinder, so a gasket would be better. I do use a gasket on a blaster engine.
Neil

[rhino250r]

For leakdown testing i often use plumbers plugs or expandable freeze plugs. Both are made of rubber and can be tightened to obtain a good seal in the exhaust flange.