Moped Dangerously Slow

[ukkid35]

I have just bought a ’98 Yamaha 50cc Two Stroke that is dangerously slow going up any sort of hill. It reaches 45 on the flat (even with the variator restriction), but will slow to under 20 on even a moderate gradient. Following a very helpful online guide I have now removed the variator ring, and looked for the exhaust restriction on the Leo Vince Touring, but there was no restriction. Anyway the engine still bogs down after the initial acceleration, in fact it has the opposite of the very sharp 2 stroke acceleration I was used to with my previous ’96 Piaggio. I can perhaps get a hardly noticeable increase in power if I use a little (manual) choke. What should I check/change/adjust next?

One suggestion I have read is to lighten the variator rollers, another is to check the main jet. Any thoughts?

[ukkid35]

GreatPretender said:

OP - are you generously proportioned per chance?

All this effort to extract extra 'performance' is futile. Why on earth are you dicking about with a 50cc scooter anyway?

No, I'm 60kg.

I've had a CBT certificate a couple of times, but it always expires before I get round to doing the full test, so I am riding on a Full Car licence only.

[ukkid35]

MajorProblem said:

Check the rear pulley unit. They have a 'kick down' mechanism for when load is high - the main spring might be broken or the slides gunked up.

What are the surfaces of the pulleys like? Totally smooth? Belt in good nick?

Also have a look at the plug see what it's like.

Thanks that is really helpful. I didn't check the rear pulley when I derestricted the variator, but the variator was in excellent condition, and the belt seemed new too.

I ordered some lighter rollers before I read your post, and since they only cost a fiver it won't be a disaster if I remove them again. At the moment it certainly feels like it's 'changed up' to top gear within 30 yards of pulling away from stationary, and it doesn't 'change down' again unless I come to a complete stop.

I will definitely check the rear pulley mechanism for dirt and wear when I fit the new rollers. Thanks again.

Edited by ukkid35 on Monday 18th August 20:48

[ukkid35]

TooMany2cvs said:

<scratches head>
Isn't part of the requirement for Class P - the driving licence class that you're riding under, if you've only got a full car licence - that the bike is <50cc and maximum design speed of 30mph? So derestricting it is going to take it out of Class P and into A1. And you don't have a licence for that.

If you don't like riding something with a maximum speed of 30mph, take your CBT and stick L-plates on a 125.

Absolutely right, but unless I'm involved in a fatal RTA then that is likely to be irrelevant.

More to the point, I'm not actually interested in maximizing the top speed, I just want it to be able to go up hills without me having to get off and push.

Edited by ukkid35 on Tuesday 19th August 09:21

[ukkid35]

Thank you so much for your concern about the legality of this issue. Just to reassure you that of course I have no intention of riding the moped myself, I am merely interested in improving the performance before selling it. At the moment it would be too embarrassing if a prospective purchaser on a test ride failed to get back up the hill where I live (I would inform them of any modifications).