blow by By gaurdian101 (Read 1,214 times)

[gaurdian101]

I have a mp 250a pcl and it's not running just right I've tried the carb the floot everything found a cracked hose on the carb and thought that was an easy fix still the same but the problem is that it get going and it seems to stall and starve for fuel and cut's out allot and don't get up to full rpms and I noticed when it was running if the oil cap was a little lose it had allot of blowby a lot of air was going out to the crankcase is this normal or does it sound like it needs rings or valve ajustment? any help would be most help full thanks vince

[speedracer]

You didn't say how many miles on it, but a valve job just may do the trick. Have you checked or changed the fuel filter? Another problem could be the spark plug being fouled. I don't want to hit you with a list of things but there is also a bad coil would cause the problems you are having. A dirty carb or pilot jet certainly can cause hard starting and stalling.

As far as having the oil cap off or loose it will blow oil out with a lot of air. Keep it tight.

[gaurdian101]

it only has 340 miles on it and I just fineshed the valve job was a little tight but not bad still not running right haven't tried the spark plug just asumed it was still good I didn't think of that. Got a new filter to and cleaned the carb out....thanks for the info trying the new spark plug it's a work in progess but don't mind and agian thanks...

[speedracer]

Only 340 miles, it's new. One thing that happens a lot is the spark plug wire is not pushed tight enough on the plug. Make sure you press it on hard.

[bhinch]

Hi....the blowby is normal...every engine has it...you can not seal up the cylinder 100 percent...so you will see crankcase pressure or blowby... the valves have nothing to do with the blowby you speak of....blowby will be less as the rings seat...the valves have to close completely to have compression....which gives you vaccum to operate the fuel pump and draw fuel into the engine...intake-compression-power-exhaust....a 4 stroke engine...the engine does not have hydraulic lifters so we have to adjust the valves.... .004 intake and .005/.006 exhaust...this allows the valve to close when the engine comes up to operating temp...enjoy the ride...

[gaurdian101]

I found the problem well I hope I did....I took the carb out to clean it thinking maybe something wrong there will cleaning and taking out and put back in the chineese vacuum hoses have cracks in three of the line to the carb so replace with american hose oh my drove the thing 120 miles last night not a problem.....it stalls if you come to a stop from coming down from high speed but I can live with that a little more fine tuning and I'm doing some fun runs.... thanks guys for all the help....


vince

[jcl250a]

Try adjustingthe idle,
I found mine had backed off the stop

[imnts2]

If it continues to stall after release of the the trottle from cruising speed, you might chech the decelleration diaphram for a leak.

Cheers
lefty2

[beachbum]

Your a/ f mixture may be lean. At higher rpm motors run more lean than at lower rpm, so when you come down from high rpms if the mixture is already lean that can cause it to die.

[Alleyoop]

It could also be just idleing to low the 250s like to idle around 1800-2000 rpms any lower and they tend to stumble.
Alleyoop

[beachbum]

Wow, Alleyoop....I didn't know the 250cc needed to be set so high.

[Alleyoop]

Yes most like it around higher rpms, the 150s you can bring down to around 1500-1800 mine I have it idleing right at around 1600 rpms.

Forgot to mention if a scoot is poping coming down on the rpms a little higher idle will help that as well.
The reason they pop is the ACV is now feeding it more fuel so it does not run lean due to the quick closeing of the Butterfly. So a little higher Idle leaves the butterfly a little more open letting in more air.
The Popping is caused by to much fuel and getting into the muffler and being ignited there.
Alley