JCL MP250 won't keep valve adjustment By rneely3 (Read 1,095 times)

[rneely3]

I have adjusted the valves several times on this scooter but for some reason they keep closing.  After the adjustment it will run about 300 miles and then you notice a loss of power and within another 300 miles it gets to where it don't want to start.  Any idea WHY this keeps happening?  Not sure what to do to really fix the problem, but I'm kind of tired of constant adjustments.

[olivertwisted]

Check this thread I found, you have some form of "VALVE-ITIS", lol! No but, its an excellent thread on the subject.
link

[jct842]

There are two completely different engine styles and before any one can help you we need to know what you have.

[4950cycle]

I have this same problem with my Linhia 257cc JCL. I actually cut a trap door in the bottom of the scoot, lay it down on a furniture blanket and loosen the exhaust valve lock nut. Then turn it counterclockwise a half turn. Never even checking the clearance with a feeler gauge anymore. Tighten the lock nut and button her up. She then runs just fine. I never even touch the intake valve anymore. Its the exhaust valve that's causing all the problems not being able to take the super high heat generated at the exhaust HEAT. They used a substandard exhaust valve in our engines around that time. They found out you can not chinse on the exhaust valve when building an engine. They must be of the highest quality steel for the job at hand.

[4950cycle]

As jct842 has said, It also depends on which engine you have. I have the Yamaha Clone (Linhia). Sorry I didn't catch that before I wrote the post above about the furniture blanket valve adjustment. My advice only works on a Linhia AFAIK. "AND" How this guy said in the above link, This is how I deal with my exhaust valve clearance issue. Works for me. I went the Loctite route first to no avail. So I guess my exhaust valve is not stretching with heat so to speak. The valve seat is receding instead. Which I hate to say, Means its time for a replacement head to stop it. The seat is in the head. If the metal is not up to the job of retaining a valve seat as time goes on then it is part of the main body of the head. Means the head has to go ! I don't like the sound of that myself.

[4950cycle]

BTW, The Linhia manual says 0.08mm-0.10mm intake valve clearance, 0.16mm-0.20mm for exhaust valve clearance. Translation for us Yanks is .003 inch -.004 intake , .006 -.008 inch for Exhaust . No wonder us Linhai engine driven scooter guys and gals have to adjust our exhaust valves so often. The typical valve clearance specified by your friendly neighborhood scooter mechanic is .005 - .006 of an inch. for the exhaust. Couple that with the inferior valve seats that recede as miles go by and you have to adjust the exhaust valve sometimes every 500-1500 miles. That is " WAY TO MUCH WORK " To have the privilege of riding a scooter around. Especially with all the body work that needs to be removed to do it. So turns out it is perfectly OK to adjust your exhaust valve out to .008+ inch clearance. This should maybe double your ride time before it starts stalling at stops needing the valves adjusted again.     PS I have a JCL MP 250 A, just like a Roketa-54 (Linhai engine) scooter and I have made removable access panels so I don't have to take my whole scooter apart to adjust my valves. Just turned a 2 day job into an hour and a half. Working on and off of course on the 2 day thing. Best thing I ever did !

[4950cycle]

$5 will get you $10 This guys got the Linhai engine.

Jul 30, 2016 10:03:17 GMT -6 jct842 said:

There are two completely different engine styles and before any one can help you we need to know what you have.