How to get 5 MPH more top end from a 257 cc Linhia ? By 4950cycle (Read 1,706 times)

[4950cycle]

Hi, I was told on another scooter forum that this is the place all the JCL MP 250A / Roketa 54-250B scooters owners hang out. I have 07 JCL MP 250A Linhia 257cc powered scoot. I have a usual top speed of 64-68 MPH now. I weigh 260 lbs. , I am 6'3 and have my head above the windshield. My scoot tach says I'm doing about 6900 RPM at just about 69-70 MPH top speed. I know I said my top speed was 68 but she was just running good today for some reason. I would like to have about 5 mph more top end. I have ordered a 32mm 150 main jet carburetor. I think the stock carb should be 30mm 110 main jet. And I'm gonna change from rollers to Dr. Pulley sliders. I've been told I should have 14 gram rollers stock. What weight sliders should I convert to to get my 5 mph top end I'm looking for ? Anybody have any experience doing anything with these 250s ? Thank you for your efforts in advance

Read more: thescooterprofessor.proboards.com/thread/4566/mph-more-top-257cc-lihia#ixzz4H35O0p1F

[4950cycle]

OK, No one seems know much about that. How bout another question. I managed to go 68-69 MPH yesterday on the scoot. I guess she was glad to finally get out of the stable. Anyway, I was revving 6900 indicated on my JCL scooter tach . Could I maybe be hitting a rev limiter built in to my stock CDI . Some say they only will let it rev 7,000 RPM ?

[4950cycle]

Yea, no one likes to mess with me much, since I proved you don't have to fine tune your valves on these Linhias. They didn't like it when I proved mine ran fine even though I just layed my scooter down on a furniture blanket in the grass and just backed the exhaust valve adjustment bolt out a half turn and locked it down never even touching the intake valve adjustment or a feeler gauge I might add. Got tired of adjusting the valves 4 times the right way. Had to come up with a quicker solution for these old defective head 06-07s. I would and still do this every time she starts that stalling every time you come to a stop sign when she gets hot crap.

[4950cycle]

So far it looks like it fixed the problem (Fuel pump). Then put my scooter up on the center stand and took it up to the rev limiter a couple times to find out where it topped out. The RPM went up to about 8400 without breaking up at all. Any higher and the RPM was unstable. But it would go up to about 8700 as indicated on the not so precise scooter tach. What that means is I might get my 5 mph on top if my variator isn't maxing out already. And 16.7 HP will haul my 260 lbs any faster than it already will go. While I've got the belly and side exposed I am gonna do a much needed valve adjustment. " Again " About the 4 th one I've done. "THEN" next on the agenda will be that Marking the inside of the variator test we talked about

[4950cycle]

New fuel pump would starve out the motor at about sustained 60 mph running. I can't understand why because when I pulled the hose off the carb so I could turn the motor over and see how much fuel it pumps with each engine vacuum pulse it pumped plenty to run a 250. Hell, It looked like enough to run a car ! So anyway I put another new fuel pump I have on the scooter, Adjusted the exhaust valve while I was right in the area of the belly. Started her up with no issues. In a tuck it will get my 260 lbs butt up to about 71. But still couldn't go any faster than 64-68 one up top speed. I may put that 32mm carb I got in the mail today on tomorrow. I hope it's won't become a nightmare to make run right.




Read more: scooterrebels.proboards.com/thread/2676/miles-hour-257-linhai-jcl#ixzz4Hw8ffDzv

[4950cycle]

Well, I put in the 32 mm carb today. Lost some acceleration and gained ZIP / nodda on the top end. It has a main jet the size between a #56 and 57 drill bit. I know because I checked. The seller said it is a 150 main jet (no markings) I think. I will at least have to back off to a 138 Main jet. I would bet money I'm running rich. Havn't checked the plug yet. Got dark on me. BTW I bet this 32mm carb is no more than a mm bigger than the Japanese made stock carb. Definitely do not buy one of these. Just mod your own. Save $100

[ellpee]

How 'bout only running one thread on one subject? Annoying when three show "NEW" and they all say the same thing.

[4950cycle]

Hey I'm havin fun out here all by myself !

[ellpee]

[4950cycle]

I went to put on my old carb on today to get ready to do the variator test. What a bitch working through that hole underneath the seat. Especially when I'm not using pod air filter (K&N style). When I finally get it in there and all hooked up I try to start it. Gas started coming out of the overflow tube as fast as the fuel pump would pump it. I guess all that wresting with the carb somehow got the float stuck inside the float bowl is all I could figure. Tomorrow's another day

Read more: scooterdoc.proboards.com/thread/13008/mph-more-top-speed-mp250a#ixzz4IJVfHYMq

[4950cycle]

Finally got my old carb back together and got it back in my JCL 257cc. "THEN" I leave the driveway on a test run and something gets sucked up in the main jet I figure . Blasted up the small hill from my driveway entrance. Ran great for 200 + yards got to the top of the hill and started starving and sputtering. All I can figure is the WOT up the hill sucked a piece of debris right up against the bottom of the main jet I guess. I'm starting to get a complex here. Someone doesn't want me to ride I'm starting to think ? I can't get a block down the road without something lousing up on this otherwise good running scoot.

Read more: scooterrebels.proboards.com/thread/2676/miles-hour-257-linhai-jcl#ixzz4IPGhinjD

[4950cycle]

My problem was my main jet fell out in the bottom of the float bowl, Holy crap I feel like a total YO Yo. I guess in all the junk I was screwing with that day I forgot to torque the 115 main jet I moved from the new 32 mm carb (trying to get it working) back to the old 30mm carb. Anyway, I got it running good again except for my float bowl running empty often. Seems this fuel pump I bought off Ebay just isn't enough. I will return it. I don't want to go electric fuel pump like a lot of 250 and up guys do. I got another Vacuum Jin Bo Chinese fuel pump just like my last one on the way. Hey, The last one lasted almost 8 years before it quit. That's good enough for me. It is somewhat equivalent to a Mikuni DF 52-21-D fuel pump. But under half the price. I'd like to adjust my valves and pull my cover and mark my variator while I'm waiting for my Fuel pump

Read more: scooterrebels.proboards.com/thread/2676/miles-hour-257-linhai-jcl#ixzz4IgvWXpdw

[4950cycle]

While I'm waiting for my fuel pump I'm making a trap door to get to my intake valve easy. I made one years ago to get to the exhaust valve. These Linhia's with receding valve seats (exhaust valve mainly) need valve adjustments often. And since the engine lays down the exhaust valve is accessible from the belly and the intake has to be accessible from under the seat. If you don't make these access doors or holes you would have to take off all the body work just to get to the top and bottom of the cylinder head to adjust the valves. The trick is to make these mods as invisible as possible. We wouldn't want to louse up the beautiful lines of a Reflex clone would we .

[4950cycle]

Took me a while to get the scoot running good . No sense in worrying about sliders and rollers if the engine isn't even running good. Had to adjust valves and drill a vacuum fitting out that was restricted I believe. I did something right because it runs right again. Anyway, I have the variator cover off and the the variator marked real good. It doe's seem to have a weak spring on the clutch to. I can move it in and out fairly easy. Should it be like that ? A stronger spring would give me real good take off and low speed power. But I don't want it to keep my variator from letting my belt go all the way out either at top speed. But one thing at a time. First the variator check. Tropical storm blowing in right now so probably a couple days of sprinkling rain at least before I can take her out for the variator research.

Read more: scooterdoc.proboards.com/thread/13015/gram-sliders-linhia-257cc-260#ixzz4IyRILlsc

[zack]

Just a thought.....
You suspect you're not getting enough fuel at top speed. Try loosening your gas cap and test. Perhaps when you're going balls out its creating vacuum in your fuel tank.
Your pump can only deliver as much fuel as your gas cap vent will allow.