2001 ZX 50 Corsa ministroker NO low end power?

[mantrans]

Hello everyone, first "scooter"fast build and I Had some questions regarding the bikes power band and possible jetting issue. It is a Corsa 72cc kit with malossi crank, polini 24mm carb (126 main), Phonger long pipe, variator with 8g sliders ( I weight 145lbs) Polini evolution clutch with the blue springs ( stiffest) with the fine tune screw on the 2nd from stiffest setting. and the malossi red contra spring. 7:1 gears, Stage 6 intake and polini filter.

130 main was extremely rich so I dropped to 128 and eventually 126, plug gets saturated from time to time and will make it not start so I have to clean plug, according to how the exhaust looks and how it feels I dont need to go leaner I dont think.

I ran 18.2 @65 mph gps in the quarter, now the time could be off as it was timed with a stop watch so we do multiiple runs and all were under 18.5, the fastest I have gotten to was 70.86 on flat ground.

My Issue is the launch/low end. It takes off like crap and sometimes it will pop really quick like its running bad then at 10mph it just starts coming in good and by 25 its hauling. Is there any wrong turns tuning wise that would cause this or is it just the characteristics of the build? I am positive the Pipe is very peaky so maybe another pipe would bring the Band down a bit but I dont think its going to fix it popping and what not. Thanks for all the Help Guys and Gals, have a good one.

To give a neat comparison my friend has the 139qmb 50 (gy6) and has a true 92cc stroker, big head, cam, intake, exhaust. Obviously due to above he gets me out of the hole and holds out 3 bikes on me till about 20mph then by 65mph I am about 10 bike lenghts ahead. I would like to be able to keep up with him from the start and for my own personal satisfactions most of all.

[Wheelman-111]

Greetings:

Sounds like you're getting all the top-end performance expected from the Corsa. To explain your sluggish low-end; 8 grams sounds very heavy. What is your RPM at full throttle from say, 10MPH on up? With the Corsa's high-revving nature, 7:1 gears are also needlessly tall. This will kill your 0-10. Also, one should tune to temperature and an occasional look at the spark plug. The appearance of the exhaust has no significant bearing on jet selection. The Polini carb seems to like its jets considerably smaller than the OKO requires. Methinks your jetting will end up at 120 or 122.

[1man8scoots]

It's not a mini stroker as the malossi crank is stock stroke.
Your gear ratio is 6.89:1 on a sc10as kymco zx50, lower with a bigger 130/70-12.
Your jetting is too high for a 24mm carb, just right for a 26 mm and too lean for a 28mm.
You will never ever ever have a good low end with those gears and a 72cc. Ever but the alternative stock gearing sucks also but it's fun.

[Wheelman-111]

Greetings:

Easy, big fellow! 1 Man has the right idea though. You didn't name the brand of variator you run. I loaded 30-33 grams TOTAL roller load in my Polini-for-Ruckus variator when I ran the Corsa. You stated you have 48 grams, again that sound like way too much, regardless of the variator brand. The Corsa cylinder really likes to rev, and 9000 should come up almost as soon as you crack the throttle. I have never bought the sliders from Dr. Pulley or anyone else; the concept just doesn't make sense to me. Consider dropping to 42 or 36 grams' worth of cylinder rollers and test if that helps. 8.44 gears or 7.97s should get you the same top speed - maybe even better if the belt-slip improves - while improving your take-off and low-range.

[1man8scoots]

No speculation on 6.89 being too low as I have them in a case and a spare sitting on the shelf. They're good for strokers and that's it. I've hit 86 with them after 2 miles of wot and a mhr. But low end is ridiculous and unsafe. You'll end up snapping belts and burning clutches. I speak from experience, lots of it. But like he said it'll get going good after 30-40. I tried a lot of combos of cvt tunes and broke a lot.of belts and burned up a clutch or 3. The longer belt of the zx50 is a lot of real estate to transfer power with the 12 inch rear wheel also.

[mantrans]

Greetings:

Sounds like you're getting all the top-end performance expected from the Corsa. To explain your sluggish low-end; 8 grams sounds very heavy. What is your RPM at full throttle from say, 10MPH on up? With the Corsa's high-revving nature, 7:1 gears are also needlessly tall. This will kill your 0-10. Also, one should tune to temperature and an occasional look at the spark plug. The appearance of the exhaust has no significant bearing on jet selection. The Polini carb seems to like its jets considerably smaller than the OKO requires. Methinks your jetting will end up at 120 or 122.

Thank you for the two responses, I will sure try going down with the jetting.

[mantrans]

No speculation on 6.89 being too low as I have them in a case and a spare sitting on the shelf. They're good for strokers and that's it. I've hit 86 with them after 2 miles of wot and a mhr. But low end is ridiculous and unsafe. You'll end up snapping belts and burning clutches. I speak from experience, lots of it. But like he said it'll get going good after 30-40. I tried a lot of combos of cvt tunes and broke a lot.of belts and burned up a clutch or 3. The longer belt of the zx50 is a lot of real estate to transfer power with the 12 inch rear wheel also.

Thanks alot, Good advice, I will try the jetting some more and not get my hopes up too high with the low end power. What do they consider the crank? Full circle?

[mantrans]

Thanks Graphite9, ok so I went out today with all my jets and 5 plugs (NGK br7's) warmed the bike up then put the first plug in, I labled each plug and brought pen and paper. I would start it up and hit Wot till about 60mph then shut it off and coast. with 126main and air fuel screw 2 turns out the plug was so beige it was almost white and it covered the whole ground strap... I kept playing with it and ended up witha 132 main! I could have swore I should be going down.. believe me I melted my turbo car engine down like 2 pistons looked like melted candle wax.. the zx plugs looked hot. With the 132 it has a very light oil film on it and a golden brown look it. I agree with you, I think something is just going on.

[Peteyparado]

How much base gasket u using ?

[mantrans]

Just the one supplied with the corsa kit, I have a spare I can take a micrometer to.

[mantrans]

Yep WAY too big on jetting. They are nothing like oko carbs. Install a 114, then work your way down. 90% of the 24mm carb setups I sell, for 72's, guys are 104-110. I run same setup as you, sea level, and Im a 108MJ. Don't listen to jetting advice, from anyone with a oko carb. its completely different.

Graphite, I dont want to say you were wrong so maybe something else is the issue. I went down to a 122main today and i thought the piston seized up after 10 min of riding.. I pulled the plug on the side of the road and it was super hot. It had the grey metal like splatter all aver the electrode and the inner part. The Ground strap was off white and the white porcelane on the outside looked like a barely browned marshmallow like it too was even getting hot. I would be scared to death to go down a jet.

[Peteyparado]

How high is your compression? Take a flashlight an looking down the spark plug hole check out the piston ?or just pull your head an see if it did damage sounds close to a holed piston...

[mantrans]

How high is your compression? Take a flashlight an looking down the spark plug hole check out the piston ?or just pull your head an see if it did damage sounds close to a holed piston...

Compression is Just over 150psi. That was a while back when it still wasnt running right, I will do a more recent test. If it turns out bad I have a .20over corsa piston and I will run the cylinder up to my local shop for a hone. They are a car shop but my friend lives close also and takes his dirkbike atv stuff there all the time for machine work so i dont see why they cant manage a scooter. Thanks.

[Peteyparado]

150over is a little on the high side I would run it rich.. U remember u squish ?

[1man8scoots]

Sounds like an airleak. That jetting is very far off from similar set ups. I run a 130 on my 28mm stage 6 carb on a heavily ported block, high speed track ported corsa, Yasuni c16, ported and flowed stage 6 intake, v force reeds, and a huge polini filter. Also the 130 is pretty rich for sure. Those metal polini base gaskets are a usual suspect of leaks. I recommend to use permatex copper spray gasket on the base. 3 coats at least and let it dry. Not heavy coats either.