Hi, Fantic 307 1991, 250 cc air-cooled.

Running on about 50:1 petrol oil mix, and ran fine for a full days 'playing' at the weekend, left with fuel turned off in shed, got it out yesterday, started up, didn't get warm before stopping it, and it just won't run now.

It will start, will run for a minute or so, but then dies and won't start again without a plug clean and re-fit. Tried a brand new NGK B9ES plug, same thing happens.

Checked fuel flow from tank to carb and all seems well, no obstructions in either airbox or in exhaust, though there is a lot of black oily spray over the rear of the front mudguard as though the exhaust is leaking, which it doesn't appear to be whilst running !!

When the motor dies it does so slowly. Hard to describe, but it doesn't just stop dead, it slows, won't rev and then seems to miss a cycle or so every so often, then dies ... I haven't stripped the carb yet, I haven't done more than the most basic checks of fuel and air, but would like some pointers as to where to look next.

This is a new (second-hand) purchase, so there may be more problems than are immediately apparent ..

When we first got it, it ran sweet as a nut. Run maybe two tank fulls of fuel through it. Same fuel, same fuel pump, same 2-stroke oil, same mix. The carb hasn't been played with that I know of, though my son did have the bike out the other day to show his mates, though it wasn't started.

you say it runs aminute or so. Is this at idle, or higher rpm?

Time related might hint to exhaust restriction, or fuel supply running out, or heat buildup. Changing the plug may solve the plug prolblem, or it might be allowing time to bleed the exhaust out, or replenish the fuel. I have been embarassed by both.

Try a higher rpm and check the length of time it runs. Maybe pull the exhaust off and see if it will continue longer than a minute. Try turning off fuel immediately when it stops, check the carb bowl, etc.

k

Thanks for the suggestions, it seems so silly now ...

Changed Spark plug again, and same thing, runs at low revs but lumpy, when revs added it runs, but very roughly then eventually dies ... had to be a fuel or breathing problem.

Took plastics off, carb off, tank off, shed-loads of cleaning etc replaced it all, didn't change a blind thing. Had air filter side off, couldn't see a problem, but started it with it off and it ran badly again, but then I saw a movement. There was a single leaf inside the airbox/tube to carb and at low revs it was flapping about and letting air through. At higher revs the carb was acting like a hoover, sucking the leaf in, and closing the airway, and the leaf occasionally stuck there but also occasionally unsticking and letting air through again .. pulled leaf out, cleaned it all up and hey presto, all is now well ..

I _AM_ a happy bunny again ..

Now I'm gonna strip it completely and do 'everything', seals, gaskets, all those little jobs that rarely get done. Then I'm gonna play ..