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

uncletooty · Member

TTR carb guru required

TTRfan · Super Guru

Sorry to hear of your problems Dave.

Couple of suggestions:

1. Did you ream the pilot jet when you had the carb apart? They are notoriously difficult to clean thoroughly with carb cleaner etc as the hole is so small and it is common for the jet to remain partially blocked if not reamed.

2. Could the main jet be loose?

3. If you open the drain screw on the float bowl is there a steady stream of petrol?

Brian

uncletooty · Member

Thanks for your reply Brian much appreciated.
I have spent alot of time reading posts on this very helpful site and because of this can confirm I have already reamed the pilot jet as you have suggested on previous posts with a small piece of copper wire,main jet is tight and the drain screw when opened provides a steady stream of petrol.
To me (although far from an expert) it does seem carb related,and points to the engine getting far to much fuel (at least between 1/8 to 3/4 throttle) but I have ran out of ideas.??

Dave.

ttboof · Super Guru

also check the accelerator pump is working OK , and the inlet boot for air leaks . if you have recently cleaned the air filter its easy to apply too much of the filter oil (sticky stuff ) and that can cause the bike to run over rich as well rare but possible (some brands have a color added so you can see when its evenly dispersed and not too thick) .

Ive done the pre ride oil change and air filter clean and made it run worse a couple of times over the years .

good thing is that the bike ran OK before so no need to change any settings just find the problem

edit , i recall someone having strange problems recently , Brian helped track it down to a loose screw above the slide somewhere ( disclaimer my head has had a few knocks over the years memory isn't that great ).

-- Edited by ttboof on Monday 31st of July 2017 05:32:41 AM

TTRfan · Super Guru

I'm stumped!

One last check. Does the TTR run better if you leave the airbox cover off?

Brian

petenz · Super Guru

float level to high ..

..

ttboof · Super Guru

petenz wrote:
float level to high ..

..

Second that good call

ttr steve · Super Guru

Have you tried adjusting the pilot screw?

uncletooty · Member

Many thanks for the suggestions.
Just to recap the TTR is fine on tickover or full throttle but inbetween coughing and sluttering.
Runs good a few seconds after shutting the fuel off?
Plug sooty carbon black....running rich.

Taking the airbox cover off...no difference
Pilot screw adjustment... no difference
Acelerator pump squirting ok.
Everything clean.

I took the whole airbox off to have a better look and looked down the carb when it was running fuel was bubbling out of where the slide needle goes in that much little waves where heading the airbox way.
I think you guys are correct the float is set to high....
When I first tackled the problem and had the carb in bits I did adjust this but I have obviously done it wrong (I blew down the fuel inlet and manually lifted the float until the float needle jet would not let air through and then measured from bottam of float to where the carb bowel gasket goes and adjusted NOT the way to do it as when I checked it today using the clear pipe attached to the carb drain the height was way up (above the bowel gasket) I have now adjusted it hopefully correct (9mm below the carb bowel gasket and will test tomorrow.

One question when looking down the carb the slide needle is straight but kinda sits to the side of the hole it goes in? is this ok,will this effect performance? can you adjust/centralize it?

Thanks again Dave.

-- Edited by uncletooty on Monday 31st of July 2017 10:32:22 PM

-- Edited by uncletooty on Tuesday 1st of August 2017 12:42:32 AM

ttboof · Super Guru

sounds like progress

quiet normal for the needle to wobble around

uncletooty · Member

Update.
TTR running 100%....
Ticks over like a sewing machine and revs smooth and strong right through the rev range.
It has never ran this good before and is a pleasure to ride.

I would like to report exactly what the problem was and a little frustrated I can not.

It was running crazy rich,coughing/spluttering and spitting,virtually drowning in over consumption of fuel,it reminded me of the mother-in-law on a Saturday night.(Wish I was joking)

The diagnosis: float to high was correct but I suspected there was more to it than that as the float height was inconsistent each time I measured it,I suspected the float was leaking/not floating correctly.
I decided I must tackle the dreaded float pin and remove the float.I very gently tap,taped,taped and after a long while it did work lose and I managed to remove it with float posts intact.
However after a simple test the float was ok floated fine, no leaks.
I then removed the float valve and small filter under there to find a few specs of dirt (maybe this was the problem,consistently cutting of the fuel?)

I then decided to check slide needle and position,it did seem to be to one side and not central but not bent and was very ridged...no movement (although maybe not a problem)
I adjusted the needle to factory spec. middle and reassembled.
When reassembled the needle was central in the hole and had a little bit of "give" in it I am wondering if orginally the little locking washer that the needle sits on was orginally seated correctly?

I can not pin point what was wrong maybe a number of things? but so happy it is now running spot on.

This is the first time I have tackled a problem like this so many thanks for peoples suggestions and to the excellent posts/instuctions on this site which really helped.
Thanks again Dave. (Happy Days)

TTRfan · Super Guru

biggrin biggrin biggrin

Thanks for reporting back wink

ttr steve · Super Guru

+1 smile