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As some of you may know we are competing in the BMF tail end 50cc moped enduro in september.
We left the preperations for May till mid-april to work on the scooter, and not to be left behind by the pack this time we are starting a little earlier.
The biggest problem all 3 riders came up with was the length of pickup time between opening the throttle and getting the bike upto speed.
I hear that adjusting the weights of the variator rollers are the way to go.
We weighed the rollers today, and bearing in mind they are slightly worn, the scales came up with 5.4grams.
Does anybody know which way we should go, lighter or heavier?? And by changing the weights are there other issues we need to think about? Belt strength, clutch springs, etc.Thanks in advance.
I think lighter as that would have less inertia to overcome initially, but I am not sure. katana is normally on the ball with this sort of thing, he might be worth a PM
Hi Champs. I think it totally depends on the bike. Increasing the roller weight means the engine has to work with a lower number of revs, so it has to have more low-rate power. Decreasing the roller weight means the engine has to work at a higher number of revs so you need an engine with less power couple and more acceleration (high-rate power).
Springs are also in the equation because they give the right amount of load to the transmission belt (if it is a belt-drive of course). The belt could slip if you get the springs wrong.
Hope this helps you squeeze some more out!
OK here goes (sorry if I’m teaching you to suck eggs):
As the variator spins the weights move out forcing the 2 parts together, increasing the pully size thus raising the gearing. If you use heavier weights this will happen at lower engine revs and if you go lighter at higher engine revs.
So what you need to do is dependant on how the bike was behaving. If it was bogging down then go lighter if it was revving out then go heavier. I’d guess that you never reached top speed so the former is likely to be true. If your looking for better acceleration but not worried about losing top end then I’d go lighter.
Go too heavy and the engine will stall, go too light and it will over rev.
Thats what I need mate cheers. The bike took a good 3-4 seconds longer than the other bikes to accelerate, but once we were half way down the straight we kept up with everyone.
Lighter rollers seem the way to go, they are only £7 a set so I might get a couple of different weights.7 quid a set is very good.
The other even cheaper way (or if you find the ideal weight is betweeen the 2 sets) is to drill a hole down the middle – gradually increase the hole size untill you get it just right.
So… we may have solved one issue and made ten more!
Changed the rollers, which made the scooter pickup quicker. But we also made a couple more changes (typical blokes!).
Removed the standard air filter and fitted a short bolt-on race filter, changed the stock exhaust to a ‘hand made’ leo vince, and increased the carb/engine manifold to a larger diameter.
Now there is so much power low in the range, but as the throttle reaches half way the engine stalls until the revs drop, then it picks back up again.
I am probably guessing we have completely screwed up the air/fuel mixture, but what do we do? The bike (sorry scooter) still has the stock carb, so stock jets etc. Do I need to change the carb? sports or maybe 70cc, or can I just change the jets???Answers on a postcard.
Hehe, what about dropping a Hayabusa lump in, do you think the marshalls would spot that?
Was the increase of carb manifold size recommended somewhere because that sounds a strange mod to me? I think you are right about the mixture being screwed up somewhat. To know what size jets you’d need to balance that would need someone who has done it before to advise or some serious trial and error I guess. Have you tried dropping the standard exhaust on to see if it still stalls?
did you take the manifold off a bigger bike or bore it out yourselves?
if its off a bigger engine see if you can find a matching carb to bolt on if you bored it out yourselves its pot luck what jets you’d need the needles might also need re-positioningI’d change the pipe back to standard and see it it improves the situation. Sounds to me that the pipe is over scavaging.
This might help to explain:
https://www.southernskies.net/page_info/runningtwostrokeengine.htmlYou can get software to help design an expansion pipe here:
https://www.southernskies.net/page_info/runningtwostrokeengine.htmlThere is a free version (look about half way down the the page) which you could use to check if your home made one is anywhere close.
We were advised to bore out the manifold, but we got this because we didn’t trust ourselves!
https://www.adrenalin-pedstop.co.uk/p/PIAGGIO-GILERA-INLET-MANIFOLD–1005.aspx
might try putting the old manifold back on and seeing if that sorts the problem out.
Hey champs, how about a few pics and reggular updates on the ped, be interesting to follow your trails and tribulations.
Bit like this thread…
https://www.bikemeet.net/forums/topic/a-slow-moving-project-gsx-r/
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