Author Topic: Yamaha SR250 carb & petrol tap issues  (Read 828 times)


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Yamaha SR250 carb & petrol tap issues
« on: April 11, 2011, 08:14:11 AM »
Hi folks -

1983 SR250 - the petrol tap still does not shut off when the engine is off, even after fitting a new diaphragm kit. The sealing O-ring seems to be fractionally too small - or does the sealing face (in the zinc tap casing) wear over a long time?

Also the float valve on the Mikuni is worn, so fuel is dripping everywhere. No part number on the carb as far as I can see. Seems to be about 34mm bore. Anyone know of a reliable supplier for a Mikuni service kit?

Thanks, Martin


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Re: Yamaha SR250 carb & petrol tap issues
« Reply #1 on: April 11, 2011, 11:01:49 AM »
Sorry to keep rattling on about Gn250's here, but I recognise a lot of the problems you are having and the bikes seem very similar. I had a constant carb drip on the Gn even when the fuel tap was off. Tried a newfloat valve without success in the end the problem was the float valve jet which lets the petrol into the bowl. When I removed the jet it had an 'O' ring sitting in a little recess to seal the jet. On mine the O ring was worn and let petrol seep around the sides - it should be a push fit and mine fell out!  I got an O ring from the garage but when fitted it stood too proud to put into the carb body so I took out the jet & O ring, put it in the chuck of my 12v drill and carefully ran the O ring against a worn piece of wet & dry until it was a nice push fit. It may not work for the SR, but it cured the Gn's problems...worth a look before you shell out on a referb kit ...about £20 as I recall.
Growing old is inevitable, growing up is optional!


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Re: Yamaha SR250 carb & petrol tap issues
« Reply #2 on: April 11, 2011, 09:13:07 PM »
Aye Martin,

May I suggest a quiet wee look through this site: 'Allens_Performance' and if you can't see what you want, I'm sure a phone call will produce results.  ;)

Dribbling carb drains on the Honda Bros were cleared up by judicious cleaning, flushing and gum removal from all of the surfaces. I mean 'ALL' surfaces. This inflammable brew being sold as 'petrol', just isn't as stable as the stuff we are more familiar with, consequently I am now using a fuel stabiliser more often. I'll see if it makes any difference.

I hope this helps.

My regards, Bill.


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Re: Yamaha SR250 carb & petrol tap issues
« Reply #3 on: April 21, 2011, 10:20:42 PM »
Here I am, proud new owner of a nice little bike, sunny weather, Easter weekend coming up, Annie off to see her sister, I'll nip down to Dorset with my tent.

Got a new diaphragm kit from NRP Carbs, fitted it, fuel tap still leaked. Checked it all very, very carefully. Decided that the O-ring seal might be fractionally too small for its seating.

Rang up NRP and they said send the whole tap to them, so I did. Waited a week, phoned them up  - Oh, it's just about to be done this minute, we'll phone you back! Hooray! ...

Waited all day, then a couple more days, phoned them again, no reply. Phoned again, no reply, no answerphone. Phoned again today, twice. No reply, no answerphone. Emailed them. No response.

Either there is no God or there is a God and he is a mean-hearted bastard who works for NRP. I should have taken Bill's advice. Annie says that's handy, I can finish painting the french windows while she's away.

Happy Easter, folks!