A forum for owners of Yamaha TTR250 trail and enduro bikes!

Martinm · Veteran Member

Carb repair

mossproof · Super Guru

Have a quick look through this thread - shows you where the accelerator pump nozzle is.

www.ttr250.activeboard.com/t55374798/rebuilding-a-ttr250-teikei-y30p-carburettor/

With the carb bowl full of fuel, when you twist the throttle a jet of fuel should squirt out towards the intake duct. If it doesn't you either have a blockage, (tricky to fix 'cause there is not a "straight path" you can poke a wire down), or your diaphragm is torn (yours is not), or the o-rings in the diaphragm plate are leaking badly/not seated properly.

The o-rings have a habit of going hard and not sealing and are easily replaced, and the face of the backplate can corrode - easily fixed by cleaning it up by rubbing it on a piece of abrasive paper on a flat surface.

Good luck,

Simon.

TTRfan · Super Guru

Simon has almost certainly nailed the answer(s) but, just in case, if you go here and scroll about a third of the way down the page you will see a photo showing a check valve that is supposed to be sitting under the float bowl gasket. There is a remote possibility that yours is missing which would also explain your carb symptoms.

Martinm · Veteran Member

Thanks Simon for your reply, I have since given it a poke with a strand of wire, like you say not a easy task😉and I have put back together put petrol through it and twisted the throttle, and nothing but as you say could be because I have a rubbish seal around diafram because it did leak around there, maybe worth buying a new diafram because mine is a it stiff and a rebuild kit

Martinm · Veteran Member

TTRfan wrote:
Simon has almost certainly nailed the answer(s) but, just in case, if you go here and scroll about a third of the way down the page you will see a photo showing a check valve that is supposed to be sitting under the float bowl gasket. There is a remote possibility that yours is missing which would also explain your carb symptoms.

Thanks Brian Ill also check under the seal for check valve, do you get a new check valve in a carb rebuild kit or is it just jets

Martinm · Veteran Member

I've just checked the check valve and it's still in there, so hopefully just a blockage 😉

TTRfan · Super Guru

Was the check valve working? It's a one-way valve.

Martinm · Veteran Member

I've just been and checked it an it is now fully working, think it may have been blocked a couldn't blow through it to start with but I can now and as you say only works 1 way.
Would that have caused my carb not to work if it was blocked

TTRfan · Super Guru

Possibly...... I think it prevents the petrol returning to the float bowl when the diaphragm is depressed. So, if it does what I think it does, that may explain why no petrol squirting out the nozzle in the throat of the carb. Possibly.....

Martinm · Veteran Member

All sorted carb is fully functioning, in the end I brought a new diafram as mine was abit stiff (thanks Steve for the parts😉)
Put all back together now it's working as it should.
Thanks for your help guys 👍👍👍

-- Edited by Martinm on Saturday 24th of November 2018 09:45:16 AM