50cc struggles on take-off

[Fox]

Okay, so I have this 50cc scooter with a new-ish engine (1800 mi.) with a standard clutch/variator and 4.5 gram Dr. Pulley sliding weights. No other mods. I change the oil regularly and take good care of it. It starts easily and idles perfectly.

It runs good and strong once it reaches the higher revs, but it takes a few seconds for it reach the revs from a dead stop. I always thought this was normal until recently when I repaired and rode a 50cc scooter that belonged to some girl and it was dramatically quicker than mine off the line and climbed hills better. It had less than 300 miles on it but was stock. The only difference I could see was the tires were smaller. They were skinnier and not as high profile as mine. It was a Znen Retro purchased here:

(It had "Lance" badges on it)

www.scooterdepot.us/50cc-4-Stroke-Znen-Moped-Euro-Gas-Motor-Scooters-p-618.html


I installed a new carburetor on my scoot today with my old jet thinking it might just be a tired carb. My old carb had a fixed washer on the needle but the new one has a movable one. I went ahead and moved it to the bottom notch. Long story short, it's seems a little better than before once it gets going but the initial take-off is still lacking what that girls scooter had so...

After reading the Znen Zen-King thread I saw that the contra springs will soften up over time. Do you guys think maybe I would benefit from a stiffer contra spring or clutch pad springs and if so what would you recommend?

Has anyone else ever had this slow build-up on take-off?

Could it be a compression issue?

The smaller tires?

Any and all thoughts on this matter are welcomed and appreciated.

Thanks!

BTW, the issue with that girls scooter was the starter wouldn't work. It turned out that the bushing for the starter Bendix that goes inside the belt cover was missing so it was all sloppy in there and eventually ruined the Bendix and she cooked the starter attempting to start it. Znen is one of the better factories but they slipped up on that scoot. It happens...

I will say that after repairing it with perfectly good used parts I had in my shop I called the guy at scooterdepot.us and he immediately sent me replacement parts free under warranty. Good dealer!

[90GTVert]

The fact that a lot of retros have some of the smallest tires, lightest curb weights, and shortest wheelbases doesn't hurt them for takeoff. I'm not sure that any of those things are the whole issue though. The fact of the matter seems to be that 139QMBs vary in performance for no apparent reason in some cases. If you check out my Sunl thread in the builds section, you will see that I struggled with a little retro scoot trying to make it a reliable 40MPH cruiser and never did do it. Some of the things I tried included CVT tuning, a big bore kit, porting and polishing a 50cc head for better compression than the 70cc head offered, a big valve head, a higher duration cam, advancing the ignition timing, 150cc carb/intake, 50cc carb mods, and more. All of that work and it never would run like some stock 139QMBs would. It did accelerate to 20MPH pretty well though.

I had the best luck with roller weights in the 6.5-8g range and either stock or 1000RPM contra springs. My 139 never liked clutch springs above the stock stiffness.

[2strokd]

I would recommend a new contra, get the set if you can.
I had a 1,500 soften up on me after a summer of fun. I wouldn't have realized how much if i hadnt of gotten a new one.

[Fox]

Well, I guess it couldn't hurt to try new springs. I'll post back the results.

Thanks!

[Enviromoto]

First do not put a larger contra spring on a stock motor. It takes a very serious motor to pull anything larger than your stock one.

In fact im running a stock contra in my drag race scooter (for now).

I think you need to check your valve lash.

[2strokd]

Dec 10, 2009 20:31:32 GMT -5 Enviromoto said:

First do not put a larger contra spring on a stock motor. It takes a very serious motor to pull anything larger than your stock one.

In fact im running a stock contra in my drag race scooter (for now).

I think you need to check your valve lash.

Thanks for the correction Doc .
I had know idea how much different cvt tuning would be with the fours. On a 2T that would be the first thing i would change if everything else was good.

[Fox]

Thanks for the replies. The scooter seems a little better once it warms up. The new carburetor made a difference. The hesitation lasts for a shorter duration than before and it pulls better than before. I am going to leave like it is for now. I finally have all the parts I need to get my 2 stroke running so I'm gonna concentrate on that.