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

colin13846 · Senior Member

Petrol tap /pet**** problem?

TTRfan · Super Guru

I also always leave my petrol tap on. My thinking is that if I don't ride the bike for a while then there is still going to be petrol in the carb. If I switch the tap off then the petrol in the carb will evaporate over time and we all know the problems that can cause

Sounds like your float needle valve is stuck open. The float bowl will fill and then overflow but usually just through the oveflow pipe.

However, if the petrol is coming in faster than the overflow pipe can take it away then it is likely to run into the inlet manifold, through an open inlet valve and into the combustion chamber and thence the sump.

Sometimes tapping the float bowl with the blunt end of a screwdriver can free the float valve so it closes.

Brian

ttrpaul · Member

Hi fellow TTR-ers,

Possibly a stupid question, but what are the signs of petrol tap failure? After I've parked her up, I never turn off the petrol on my 4GY and it's usually fine... til last week when she peed petrol all over the floor and seems to have filled the sump with petrol too :-/

Do I need to rebuild the petrol tap?

Any pointers welcome - thank you :)

Paul

TT-R250M · Super Guru

The good ole petrol tap leak, not sure I could count how many times that has happened to me on various bike's.

Generally speaking, the main cause is that the 0-ring perishes, breaks or gets flattened over time. On the other hand, I would not like to count how many times the tank seal has played up on me. As I write this I am waiting for one lol; the O-ring in mine is stuffed, so I just have a big O-ring sealing it. I cannot use the tap though & it just stays on. If it is leaking from the tank seal, you can use an inner tube, and cut a tank seal out from that using a paper template. These are only temporary fix's though.

If you want it fixed permanantly you can buy a re-build kit or just buy the parts nessesary. The list of parts are below.

(N19.)

(N22.)

(N21.)

Diagram of Yamaha Motorcycle Parts 2000 TTR250 - TTR250MC FUEL TANK Diagram

O-RING

TT-R250M · Super Guru

Good point Brian, I forgot to mention that the fuel over-flowing into the chamber; oil is not normal. I would suggest that you give the carb a good cleaning. If cleaning does not fix this & you are sure it is clean, revise the float level.

Also, before changing the fuel level, connect a pipe to the carb, blow through it while pressing lightly on the float needle; does it shut off when the little spring-loaded pin on the top of the float needle is gently pushed on? If you have to push so hard that the spring-loaded pin bottoms out on the float needle you're float valve or valve seat may need replacing (which is not that common).

My guess is that the float needle has parts of the O-ring stuck in there.

TT-R250M · Super Guru

Just in case you are not sure how to check the float level, this is how I check, and it seems to work well with all carburetor's.

I connect the fuel line to see if it blocks the fuel off at the point shown below in the picture. It is the best way of knowing if this is correct. No fuel should be running or dripping out with the float level with the carb body, as shown below. You can also blow through the inlet with a long piece of pipe attached, but this tends to leave condensation in the inlet, so it's best flushed out with fuel afterwards if this method is used.
Posted Image

ttrpaul · Member

Great replies - thank you very much, although I'll need to re-read those a few times before it sinks in

If it helps, the Off position works when she's parked up and the bike runs fine - she can be a bit of a sod to start sometimes, but I'm not using her frequently at the moment.

Thanks everyone !

Paul