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

jimmyg · Newbie

Help Please! Possible carb and fuel issue

TTRfan · Super Guru

Hi Jimmy and welcome to the forum!

Is this a new phenomenon or has your TTR always suffered these problems?

If its a new problem then is the air filter clean and the airways unrestricted?

If so, and assuming the engine is OK with good compression, decent plug, etc., the likely remedy is to whip the carb out and give it a good clean concentrating on the jets.

To check that there isn't a problem with fuel getting through, undo the drain plug and make sure that you have a good flow. If not, that could be the cause.

If you have always had the problem, have you had the bike from new? If not, could a previous owner have messed around with the jetting? If you don't know, then the carb would need to come off for checking anyways.

There are a couple of carb items in here plus make sure you get copies of the owners and workshop manuals here if you haven't already got them.

Brian

jimmyg · Newbie

Hi Brian,

Ive only had the bike since March and only in my possesion since October, previously it had been down in Devon with a relative who stripped and rebuilt the carb after a thorough clean and new jet, the bike had been stored by the previous owner for 5 years, needless to say there had been water in the carb. My biggest worry is the problem at high speed, i think fuel economy could be down to my right hand, ive made the move from in line four cruise missiles to a thumper, im aware it requires a different style of riding. The bike was bought with a view too be used as a run around and short trips to work with the hope of getting some freen laning in time permitting. I have the workshop manual, having read a few other threads i think its possibly not the air fuel mix as tick over and low revs its fine.

barra8 · Guru

+1 to Kents post.

Also......If it is running too rich you can always move the clip postiton up until you find that it's right. Also having your fuel metering screw out 2-1/2 to 3 should help.

We will all be waiting to find out what jets you have installed so please update this as you go.

................................

Jarrah.

-- Edited by barra8 on Friday 25th of January 2013 09:56:22 AM

KentJ · Veteran Member

Jimmy,

It sounds like it may be running rich, although it might not be caused by the mixture screw. The mixture/fuel screw only affects the primary circuit, so it would have more effect on low rpm and part throttle, less effect on high speed fuel delivery.

I've run out of gas several times and have always had at least 180km (on 10 litres). Thats off road riding so i wouldn't expect good mileage, so yours does sound low comparatively.

One thing you can try before pulling the carb open is removing the side cover on the air box and take it for a rip. If it is running rich, it *should* run a little better. Ive done this when riding in a different part of the province where it was hotter and higher elevation than here on the coast. It was farting and coughing so bad that i was having a hard time making it up some hills. I think it helped bring the air fuel ratio closer to where it should be and smoothed out significantly. Of course the solution is to remove the larger jet i put in and put the stock one back in.

Also, pull the spark plug and note the colour. If its sooty then its probably rich. Plugs are good indicators of how the engine is running.

Like Brian says, open up the carb next and clean it up. Note the jetting, someone may have put larger jets in hoping for better power (like me). Dont overlook the float level as it does impact how fuel is metered through the carb.

Oh, and make sure you have good gas.

Thats where I would start.

-Kent

jimmyg · Newbie

Many thanks for the reply, unfortunately the bike was stolen a week ago in Northumberland!

barra8 · Guru

jimmyg wrote:
Many thanks for the reply, unfortunately the bike was stolen a week ago in Northumberland!

Sorry to hear that

..................

Jarrah.