Help tuning 52.4mm

[scootboy87]

Hey all I have a Kymco Agility 50cc euroII 16 with the 90cc Naraku kit upgrade, Before I put the upgrade on I tried upgrading the rest of the bike, and could not get it pasT 30mph, I've upgraded every part you could imagine except gears. And the bike still struggles to make 30mph, I brought a digital tach and set it to 1 spark per revolution, and if this is correct I'm making around 30mph and 9200RPM.

If the 9200rpm is correct, could a weak spark still make the bike slower, I have a new spark plug and a new stator to install, I really don't know where to start now I've tried everything.

I think it's stator/electrical problem, or a CVT problem, should I start with roller weights? I have from 3g to 7g I think.

[scootboy87]

Okay so changed the rollers to 7.5 grams, now the bike pulls away okay and maintains 8k rpm upto 20mph and then the revs climb to 10k and max speed is 30mph, do I have belt slip, or is the clutch not engaging fully?

[scootboy87]

The bikes pulling away at around 5krpm

[90GTVert]

Try going a little heavier on the rollers again and see how it reacts.
www.youtube.com/watch?v=YkNhqEFeWVQ


Also check belt width. A worn belt would make it rev higher and lose top speed.

[dexameth]

I'm going with belt issue. The way you explain the RPMs acting it sounds like the belt is thin, that the variator is pushing it only so far, the belt travel stops and the motor over-spins.

[GrumpyUnk]

What they said. As others have posted, the idea is to get the engine to its peak, and keep the rpms somewhat constant as you accelerate to cruise speed. If the rpms jump too high, something is slipping, or possibly the variator cannot move the bits to 'shift' the ratios.
tom

[scootboy87]

Thanks for the replies, can I ask one question, is 10k RPM, 10k RPM in the sense of there is no such thing as a low quality 10k RPM and a high quality 10k RPM, I am asking in the sense of, this isn't a compression issue or the bbk issues, if I am making 10k RPM and holding it then they aren't WEAK "Rpm's" i.e. this CANNOT BE  An electrical issues right this is transmission correct, CVT or Gearing, I know what I'm saying is a little confusing it's hard for me to word. Also here is a photo of my malossi multivar to show you how much travel I am receiving using a "18 * 9 * 743" malossi X special belt. imgur.com/a/MzZBowj

[dexameth]

10k seems REALLY high, as these motors make the best power around 7500rpms. But you are correct as the issue is related to your transmission and NOT an electrical issue.

That variator marking does show us the limited belt travel and with the super high rpms only means one thing: too light of roller weights. I would put all 7 gram rollers in there and go for a ride, see what the belt travel is and RPM reading.

[scootboy87]

I put 7.5g rollers in there, and it's hardly made a difference except slightly slower acc, top speed as remained the same, and with the same symptoms, the bikes accelerating decently at around 8.k RPM to perhaps 20mph, then the RPMS start climbing to 20k with a top speed of 30mph still at 10krpm. Should I try 10g rollers as an experiment? Should I try shortening the boss?

[dexameth]

I would try heavier weights if you have them, yes. What's your clutch setup like?

[scootboy87]

Malossi Fly clutch and bell with factory, white springs. I think I currently have a white contra spring, but I have a feeling the clutch is causing the problems. If I out in some 10 gram weights and try 3 different belt sizes, and still have the same top end then this will prove its a clutch problem?

[islandscrub]

It's not 1 spark per revolution on a 4t right? Set it for 4t, spark every 2nd rev. I guess cut your values in half.

[scootboy87]

I thought there's still a spark per revolution of the crankshaft, it's just that the second spark is a "wasted spark" and isn't part of the power stroke?

I thought there's still a spark per revolution of the camshaft, it's just that the second spark is a "wasted spark" and isn't part of the power stroke?


4 strokes per cycle
2 crankshaft revolutions per cycle
2 sparks per cycle
1 camshaft revolution per cycle

[ratdog]

You are correct, there is one spark per revolution.

There is no scooter that is geared to give you 10,000 RPMs at 30 MPH, so something is slipping or you CVT is not working right

Do you have the stock clutch assembly? If so, for now, put it back to stock. Let’s eliminate as many variables as possible.

While you have it apart to change weights, check that the pullies slide back and forth freely.

My suggestion for selecting the correct weights is to look at your RPMs while accurate from about 10 mph to 20 mph. We would like that number to be around 7500. If it’s higher then 7500, heavier weights are indicated, if it’s lower, lighter weights are indicated. For now, don’t worry about your RPM at top speed. Also use a felt tip to make the inside of the front pullies. While not a recomended procedure, you should be able to put the bike up on the stand and run it with the cover off. This will allow you to see if the front pullies are closing and the belt is getting to the outside of the pullies. After running up to speed this way, turn the bike off, and look at the marks you made inside the pullies. Most of that mark will be erased except about 1/2 to 3/4 of an inch on the out side.

This should tell us if the front is working OK

I would put on a new belt of the exact correct size. Belts aren’t cheap, but spending hours trouble shooting when the whole problem was a bad/wrong belt is not a fun thing to do. I had a kid come over last fall with issues and I spent a ton of time before I realized he had decided to “upgrade” the belt ( different size) based on suggestions he read on the Internet. Of course he didn’t mention that until after I fixed it.

if I recall correctly it should be a 669-18-30.  At least that is the size indicated on the bikes I have been working on

[islandscrub]

So it's 1 per rev with only 1 being 'under power' got it. I suppose it doesn't matter if it's on the power stroke or not, it's still spinning either way.