Hi,

My Speedfight was put away for the winter and when I got it back out it would only go 10mph at the most. I've since had it in the garage with new belt & rollers fitted even though the belt had only previously been on for a couple of months before. Since getting it back it will get to 50mph eventually on flat and downhill but the acceleration is not good at all and going up hills is terrible, the revs will die and the bike almost comes to a stop.

So I sent the bike to a different mechanic who has said the belt has frayed again already, a new one was only fitted a week ago! What could be causing this? He has had the carb stripped & cleaned, the exhaust has been de-coked and although better it's still accelerating poorly. Air filter has been checked and is clean.

Everything is standard apart from it has a Giannelli exhaust & Polini variator. Rollers are light (around 5g) & carb was jetted up from a 50 to 55. These were all fitted a year ago and it absolutely flew back then but not any more.

It's clearly a transmission problem but I've ran out of ideas and would appreciate any help / advice. Many Thanks.

Mikey, July 2010

i still think its low on back pressure by the way you describe it.have you got a mate with a speedfight that will let you borrow it to try?if the rollers are light enough it should rev and create enough back pressure but you may lose top end.the reed block is just a blockmof cast aluminium that holds the reed petals and if they were not sealing up it wouldnt rev at all so its not that.i bet it pulls away slowly and takes ages to get to a certain speed then all of a sudden it starts to create some power and is fine whiles its going at that speed and when you have to brake its back to square one again.if this is true its the lack of back pressure like i said,i am a qualified motorcycle mechanic and i have seen this problem loads of times.also if the belt is fraying its either that your using cheap belts or the belts is rubbing something or its too short,buy a malossi kevlar belt for it they are the best.

adam bike doctor, July 2010

I'm gonna mention trying a bigger jet to the mechanic. Is there aything else that should be looked at in and around the transmission parts for wear and tear? I'm told by somebody else to check the reed block whatever that is? Also to try stronger clutch springs for a better take off?

I no longer have the exhaust because it was a lump of rust but I'm certain it's a transmission problem, the clutch just isn't engaging quickly enough and the top end, when it gets there, is very good.

Also, any ideas about why the belt is fraying almost as soon as it's ridden?

Thanks for your time.

Mikey, July 2010

have you tried it with the old exhaust back on it?if you have it try it.even though you say it was ok when it was first done it may have lost some back pressure due to a broken bafle that you cannot see inside the pipe.thios problem sounds like a lack of back pressure to me not a transmission problem ,although an engine revving high should produce enough back pressure to run even a broken pipe.try this too.take 3 of the rollers out make sure the three left are in a triangular arrangement.see what happens then it may be ok but lose top end .

adam bike doctor, July 2010

changed carb but with the restrictors in they put 50 main jet. deristricted it should have a 72 main jet as standard. try a 72 main jet.

rayb, July 2010

They changed the carb model over at some point because I researched this when I had the exhaust fitted after finding that the standard one in my bike was only a 50. It ran spot on when the 55 was fitted with the exhaust so it's something else.

Mikey, July 2010

standard main jet is 72. yes 72. if yours had a 50 in it then that is also a restrictor. put the 72 main jet in and you will be suiprised at the difference.(haynes workshop manual states 72 main jet as standard.new main jet costs abought £5.

rayb, July 2010