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

Thomas ttr250 Williams · Veteran Member

Spluttering when going full throttle

Cubber · Super Guru

If I were you, Thomas, I'd clean or replace the air filter. Check that it has got one too. smile

If the bike has been sitting without being ridden for some time or if it has been a while since the last carburettor service, then I would check over and if needed possibly clean/rebuild the carburettor.

Check for leaks around the intake boot, located between the engine and carburettor. Spray some carburettor cleaner in the area and if the revs change, you have an intake leak. If the boot is cracked or torn - replace it.

Check your ignition lead and spark plug cap for splits or cracks. Replace if damaged.

Basically, if it starts and runs below full throttle then there ain't much that can be wrong.

Martyn

Thomas ttr250 Williams · Veteran Member

Got a new k&n filter when I first got the bike . I also taken the carb of and blew them through with compressed air . And still the same . Do you think it could be the air box mod and the exhaust mod that's causing the problem . I will check to see if it's any leaks around the intake boot today and check the wiring . Thanks for your replie Martyn

barra8 · Guru

What method of cleaning did u use?

The holes in the side of both the main jet and pilot jet need to be spotless aswell as the main hole. (see pic below)

Also spray carby cleaner or similar around the rubber intake boot (bolts carby to motor) and around the top of the carby (making sure its reletively clean first) while idling bike. If you notice a change in revs then you have an intake/vacuum leak.

The float needle should be removed being carefull not to snap pin support (like it did ''see repaired pic below'' lol )and cleaned and seat (where float needle sits inside) needs to be either blown out or squirted through with carby cleaner aswell as any holes ie. two air holes at back of carby,air fuel mixture screw hole,fuel line ect.

Give the slide and slot a light oiling (synthetic two stoke preferably)for a snappy responce

Before refitting (with bottom carby screws out and holding bowl in place) connect fuel line to carby check that the fuel level is about 10mm from top of bowl (roughly just over 3/4 full)

If it's not the right level either the float needle is not shutting off at the right point (ie.wrong float level) or it has dirt in it

You can also check the float level by taking note of what angle the float shuts at. It should be closed (ie no fuel coming through float needle) when the line on the float is level with the carby (horizontal)

To adjust the air-fuel mixture idle bike and turn fuel-air mixture screw in until it nearly stalls. It is then 1 and a half turns out (roughly). NOTE: one turn is a full revolution of the screwdriver line.

See this thread for more details on cleaning carby ...... http://ttr250.activeboard.com/t47674647/simple-pictorial-guide-to-stripping-and-checking-a-carb/

Questions..

Is your Diaphragm assembly okay? Take it apart and check (Two screws holding it in under carby). You can also check its pumping by filling the carby bowl up and pushing down gently on the top of the diaphragm pin. (see pic below)

Carb strip 006.jpg

Did you try dropping the circlip on the pin (needle) down one slot?? NOTE: to do this obviously the circlip would go one higher on the pin settings.

What does your plug look like when removed??black??white??normal??

Tried a new spark plug?

What size main jet do you have?

What size pilot do you have?

You can check your jet sizes by looking at the numbers on them.

The pilot jet will have it on the flathead head

The main jet it will be on the side of the jet.

The red arrows in the pic below points to the Main jet and pilot jet numbers

-- Edited by barra8 on Saturday 1st of September 2012 12:25:12 PM

barra8 · Guru

Here is a link to it CLICKHERE

-- Edited by barra8 on Sunday 2nd of September 2012 03:53:58 PM

Thomas ttr250 Williams · Veteran Member

Checked all the things you advissed me to do Martyn

Still no luck tho . Can't really do much on the bike green lane wise . If I come to something when i need full power it just dies its starting to become a pain for me . I can't follow the other riders up any sort of climb . If I get a fmf and re-jet do you think it could solve the problem . And also how do I check my jet size ? Any info would be great . Thanks

TTRfan · Super Guru

Have you a close up pic of your pin support repair please Jarrah? I bet quite a few TTR carbs have been scrapped because the support broke when the owner tried to remove the pin cry