How to get 5 MPH more top end from a 257 cc Linhia ? By 4950cycle (Read 1,647 times)

[4950cycle]

Sept 6, 2016 19:30:18 GMT -6 zack said:

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.

Zack, My exact thoughts about the same day/night you posted . Thanks for reminding me about this could be problem.

[4950cycle]

Got the scooter running good with all new fuel delivery parts. Hoses, Right size pump and such. Carb has no issues and away we go. Did the marker variator test and came up just under a 1/4 inch from full belt Diameter at top speed (67-68 mph right now)on said variator. Hovering around 6700-6800 RPM. Max hp is supposed to be at around 6500 RPM on 257cc Linhia. That being said I think I could go up a gram to 15 gram sliders. BTW My stock rollers are the typical for 250 Linhia 14 gram rollers. If 15 gram sliders make it a bit sluggish (a little heavy) I could always drill a half gram or so out on each slider. Any input Guys ?

Read more: scooterdoc.proboards.com/thread/13015/gram-sliders-linhia-257cc-260?page=1#ixzz4K9kfgdTy

[4950cycle]

My idea worked on the variator. I worked on it late yesterday afternoon and today. Finally by nightfall tonight I got the modded variator back on the JCL 250 up and running. Well... up and running on the center stand anyway. I wanted to do a static test first to see what the variator was doing and at what RPM. I got my belt all the way out now at about 6600 RPMs I believe. It was getting dark so I didn't see so good even with a drop light. I will redo it tomorrow. I drilled out 1/2 of the 14 gram rollers down to 12 grams. so I have an average of about 13 gram rollers. Truthfully I don't even need sliders now since I'm getting full range with these old beat up drilled out rollers. But I will still buy a set just to complete my refurbishing the variator dealy. The real test is will the belt go all the way out on the variator with my 264 lbs. butt on it. That will be tomorrow to see if I can get any more top end out of it.

Read more: scooterrebels.proboards.com/thread/2683/gram-sliders-linhia-257cc-scooter?page=1#ixzz4KaF4iN6n

[zack]

If you still suspect a fuel delivery problem try using high quality vacuum line to the fuel pump.
At idle, or just manually suckling and blowing the pump will perform perfect. At higher rpm the cheap-$h!t hose may soak up the vacuum pulses that operate the pump.

[4950cycle]

Makes Sense to me Zack. I will do this if I'm still having problems once I get spark again. Put a coil on it only to get spark only for about 4 minutes of running. Then no spark again. CDI maybe ?

[4950cycle]

Sept 6, 2016 19:30:18 GMT -6 zack said:

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.

Tryed your gas cap idea. Even drilled an extra vent hole though the gas cap. "No" It didn't change a thing Zack. But thanks anyway.

[4950cycle]

Its running fine now. The 12 gram DP style sliders are 2 grams per slider less than my stock rollers were. But instead of increasing RPM per speed / mph my RPM decreased ? I was going 67-68 mph with my old 14 gram "rollers" with 6600-6800 rpm . Now with 12 gram "sliders" at 67 mph I'm only revving 6000 RPM ? Thats 500 rpm below my peak HP @ 6500 rpm. I am going to experiment with putting 4 rollers in at 13 grams (I drilled them to 13 grams) each mixed with 4 of my 12 gram sliders tomorrow just to see if I can get the best of both worlds ? If I don't gain any RPM I'm prepared to drill one more gram out of my 4 rollers that are 13 grams now.

[4950cycle]

Nov 1, 2016 22:02:07 GMT -6 4950cycle said:

Its running fine now. The 12 gram DP style sliders are 2 grams per slider less than my stock rollers were. But instead of increasing RPM per speed / mph my RPM decreased ? I was going 67-68 mph with my old 14 gram "rollers" with 6600-6800 rpm . Now with 12 gram "sliders" at 67 mph I'm only revving 6000 RPM ? Thats 500 rpm below my peak HP @ 6500 rpm. I am going to experiment with putting 4 rollers in at 13 grams (I drilled them to 13 grams) each mixed with 4 of my 12 gram sliders tomorrow just to see if I can get the best of both worlds ? If I don't gain any RPM I'm prepared to drill one more gram out of my 4 rollers that are 13 grams now.

JCL MP250A Lihai 257cc powered / This is how it all ended up here. This info is not for a 50cc-150cc scooter. They are a different animal in some ways to the Yamaha 250 / Linhia powered scoots. I have come to the conclusion that my 257cc Linhia will not go any faster on the top end without a meaningful power upgrade. Like a "real" 295 cc (300) cylinder / piston change plus maybe a little upjetting ? It just dosn't have the torque in its present form to go any faster than 68 mph with my 270 lbs , head right up in the wind resistance situation. I don't care what I do to my variator it just can not change this fact. But I have learned a lot about what works and what is a waste of time. #1 Forget about a bigger or a performance carburator if you don't improve your flow in some meaningful way ie: porting your head and exchange some torque for HP , And get an open / noisy exhaust and and lets not forget a performance pod style airfilter, also more noise. Yes , your intake makes noticable noise with no airbox. " It will sound faster " with just a pod airfilter and a more free flowing exhaust, But in reallity the numberes will change no more than slieghtly if at all. But if you are young and like to be noticed this may have some value. #2 Variator changes gave" ME " (big and heavy) no more top speed. But if a rider is much lighter than 270 lbs. this is what you want to do. #1 On the variator improvment, Shorten your variator boss by 1 1/2 mm do not exeed 2 1/2 mm shorter than stock or your belt will almost climb off your variator at top speed. This will allow your variator to reach its full out high gear. In stock form they stop short of this. #2 on the variator improvement, Exchange your 14 gram rollers for 11 gram "sliders" This will give you everything this motor can offer (with the boss mod too) IMO. I have four 12 gram sliders and four 11 gram sliders. This is what I personally want because I am going to get more power in this engine in the near future. But number 2 will keep you in the higher RPM for maximum excelleration and number 1 will give you full top end capibillities. You CAN have the best of both worlds this way.

Read more: itistheride.boards.net/thread/9619/mph-more-great-257cc-linhai?page=5#ixzz4PQde3hJC

[gorj]

If you were carrying about 30 pound less weight you might get that extra 5 MPH!