Need more speed!!!!!

[myyz]

Hi there a while back I posted a problem with my 2010 agility scooter I put a 80cc big bore kit through it and at top speed it starts popping and back firing through the carby, I was told that I should have put a smooth boss in it before anything else and it turns out I already have a fully smooth boss(no step up) not sure how seeing as I bought it of the show room floor but my scooter still only gets to 43mph all tho nearly never lags on hills or into wind because of the bigger cc I was looking at how to make it go faster (top speed) any one be able to give me some good ideas? And also any thoughts again on the back firing problem? I'm running a bigger carby but only a 95 jet shoud I be running a bigger one? Thnx for any help.

[blue]

if you are geting to much back fire something not tuned right.and maybe you need to work on the air flow are you running open air filter or the stock box.and yes a bigger jet might help.

[myyz]

I have removed stock air box and relpaced it with a uni filter straight on the back of the carby. Also I have a aftermarket exhaust on it.

[streido]

Main jet size?

[wordslinger]

...95 jet would be way small, i think...i'm running larger than that with oem carb with a K&N, and oem pipe...


 

[myyz]

Yeh after reading what other people are running in there 50s I thought maybe 95 might be to small. Any ideas on the top speed issue?

[streido]

Yeh after reading what other people are running in there 50s I thought maybe 95 might be to small. Any ideas on the top speed issue?

Could be a worn belt or the belt is too short to hit the top of the variator. What rpm torque spring do you use? What weight of rollers? Is variator stock or racing, ie Multivar/pollini/other?

[myyz]

Stock everything as far as drive goes the belt looks to be riding about 3mm of the top of the variator plate and rollers are still nice and round bike and belt has done 2500km can the belt be made to run a little higher then the variator plates?

[streido]

Stock everything as far as drive goes the belt looks to be riding about 3mm of the top of the variator plate and rollers are still nice and round bike and belt has done 2500km can the belt be made to run a little higher then the variator plates?

You may need a longer belt, i use a 736 long one (stock length is 729 long). If you dont hit the top of the variator you wont get it to full speed. Some even shave a fraction off the boss length to allow the belt to ride higher but its a tricky process to get right, too much and its toast.

[myyz]

Would a larger belt or shaving some of the boss down change my down low power at all?

[streido]

Would a larger belt or shaving some of the boss down change my down low power at all?

When i fitted my longer belt i felt it was maybe a little slower from a standing start but it really was minimal and tbh it may have just been my imagination.  I had never been to 50mph on the speedo but after the longer belt i got to maybe 52 mph downhill, speed on the flats was not much higher maybe 1-2mph. I would concentrate on getting the bad running/popping sound fixed 1st before i messed with anything else.

[myyz]

Yeh thanks for the info mate I going to try track down a 105 main jet and see if that fixes the popping problem.

[streido]

I take it you checked your plug to see if your running lean or rich? How did it look? If you havent then do a plug chops asap to get an idea of you need more air or more fuel.

[myyz]

Seems to be rather black not wet tho so definetly not running lean. What would you expect to be a normal condition of a plug tip?

[baddi]

Hi there a while back I posted a problem with my 2010 agility scooter I put a 80cc big bore kit through it and at top speed it starts popping and back firing through the carby, I was told that I should have put a smooth boss in it before anything else and it turns out I already have a fully smooth boss(no step up) not sure how seeing as I bought it of the show room floor but my scooter still only gets to 43mph all tho nearly never lags on hills or into wind because of the bigger cc I was looking at how to make it go faster (top speed) any one be able to give me some good ideas? And also any thoughts again on the back firing problem? I'm running a bigger carby but only a 95 jet shoud I be running a bigger one? Thnx for any help.

Heres how it goes: The popping spound is you hitting the rev limiter, so it doesent ignite every time. You can solve this, by cutting the CDI, as it is told billions of times on this forum, which will give you 9000 limit instead of 7000 RPM limit. If you have already done this, you can buy a fully derestricted CDI, but this is not recommended on a 4-stroke, because of the valves, and because of the narrow effectband. The 9000 should normally be enough to get to 50 mph, when the variator is fully geared out.
BUT it is recommended, that you put stronger valve springs in too, when you do this, to prevent the valves from "floating".

The backfiring: This is because the intake valve is not closed fully, when the engine ignites, and it can have 3 causes: first, it could be, that you have put your crankshaft in the wrong place, when you mounted it, and you should check this. The second cause can be, that your valve springs arent strong enough, and your valves is floating at max RPM. If it is one of these two causes, you're lucky, that it hasnt crashed your engine yet.
The third and last cause of backfiring is, that your valves has been burned around the edges, and no longer does a airtight close.

Anyway, check your valve clearence too, as they wont close, if the clearence are too tight ^^ 

Good luck fixing it, and post pictures, if youre able to :p