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

Bluebandit2g · Member

Running rich no matter what. Stock jetting help please. Stumped

TTRfan · Super Guru

Hi there and welcome to the forum!

The TTR carb is simple so the fault must be simple as well.

It sounds as though you know what you are doing but, just checking, are you sure the float level is correct?

This guide is quite useful wink

Brian

Bluebandit2g · Member

Thanks Brian. Float level is 26.5mm which I believe is at the low end. It was at 29mm so I re set it back to the low side but made no difference. Float doesnt appear to be sticking as no fuel coming out of the overflow lines or into airbox. Thing has me stumped for sure. I don't want to blow a bunch of money on jets. Just seems odd that it's so rich with stock jetting. I got this thing on a trade so I don't have much history on it. Doesn't look beat too bad. Hoping someone here has run into something similar. I've google searched it as well. TTR xr drz any of those bikes with a similar issue could maybe shed some light for me. Ugh 😩

mossproof · Super Guru

Exhaust hasn't collapsed inside has it? Or full of mud?
Cam timing correct?
It's an odd one for sure! Good luck!

Jeff B · Senior Member

Is the smoke from unburnt fuel or is it oil?

Bluebandit2g · Member

its definitely fuel. The smoke is black, exhaust pipe has black soot.. Not blue oil smoke. I have not checked the cam timing or valve clearance but it dont think thats it. It cranks up immediately with no choke and will idle until too much fuel loads up the plug. Runs bad rich even with the airbox removed. Again stock jetting, no airbox mods. Exhaust doesn't have the baffle in the end cap. But that would not cause a overly rich condition in itself.. if anything would lean it out. I noticed fuel coming from the overflow this last time i ran it. Pulled the carb again. Verified float height is 26mm (low side) The oring on the seat and float needle are new (all balls carb kit) so i dont think fuel would be running past the oring. Only thing i haven't replaced is the pet****. Also checked the float, no holes. I let it sit overnight in a bucket of water to check. The fuel coming from the overflow port on the float bowl leads me to believe the float circuit is the culprit but i dont see how when the height is correct. the float is good. The seat and needled are new. Frustrating to say the least. I know my way around a carb pretty well. But this one is whipping me.

Jeff B · Senior Member

It sounds like you have checked everything you could and narrowed the potential cause to excessive fuel feed. Can you verify that the float moves freely on the pin and does not bind against the posts? You can also do bench testing on the carb with water to check.

mossproof · Super Guru

I prefer to measure float height from the float bowl/carb body joint as I think it's less ambiguous. As described in this thread

ttr250.activeboard.com/t57547519/adjusting-the-fuel-level-in-the-carb-bowl-float-height/

And further down that thread, Brian mentions the choke not shutting off properly...

What jets were in the kit? All Balls stuff needs to be checked as they are not always correct - Steve does this for the kits he sells so they have the correct o rings etc.

Is the fuel screw ok? (ie the tiny needle end not broken) I would be suprised if that would cause such richness, but who knows?

-- Edited by mossproof on Monday 2nd of August 2021 09:47:08 PM

-- Edited by mossproof on Monday 2nd of August 2021 09:50:53 PM

mossproof · Super Guru

Valves operating properly?

Healthy spark?

Just trying to run through everything the engine does...

-- Edited by mossproof on Monday 2nd of August 2021 09:44:51 PM

TTRfan · Super Guru

Well remembered Simon! Yes, a damaged choke seat would show these symptoms cry

mossproof · Super Guru

Have we frightened him off, Brian? While we wait, how's your 350 afr tuning going?

Shortleg · Veteran Member

I had a slightly bent choke that did not shut off properly but it took some finding, well worth a look at this possibility.

TTRfan · Super Guru

mossproof wrote:
Have we frightened him off, Brian? While we wait, how's your 350 afr tuning going?

It's a shame if we have Simon coz I am really interested to know what is causing (or caused) the issue!

PS A combination of busy roads with the higher than normal holiday traffic and iffy weather has conspired against my good intentions cry

TTRtramp · Veteran Member

I have been working on TTR and DR650 carbies recently and am intrigued as to what the solution is. Is it possible that the fuel mix screw has been tightened on to its seat by a previous owner such that the seat has been stretched and damaged? It is not clear in posts whether the problem was there BEFORE he serviced the carby! Presumably the bike is not overheating! Or does he need to think about changing to a a hotter plug - ?

Bluebandit2g · Member

Hi folks. Im still here, just working on multiple other projects. I tried to create an artificial lean condition by setting the float lower than spec and it still runs beyond rich. You can't get a carb any cleaner than this one. I dont think its the fuel screw as you can adjust it all the way in or out and it makes no difference. CAn even run it with the airbox off completly and its still way rich. I pulled the choke over the weekend and it looks good.. Looks like the one in the sticky posting on the carb "how to". I ran the OEM jets in my ultrasonic cleaner and put them back in just to verify. No difference. and they are the stock size. I haven't taken the valve cover off yet and the timing mark plug to verify timing. figured i would do that and the valve check at the same time. ive honestly never had a carb i couldnt sort out so this is leaning more towards something internal. If i had a spare carb i would throw it on and check of course. Not so easy to find and i dont want to throw a few hundred on a TM33 just to check you know what i mean? The bike is in very nice shape and doesn't look badly mistreated as far as mud or anything but i have no idea on history of it. It was obvious someone has been in the carb before and didn't use a JIS screwdriver so it was fun getting all the mucked up heads undone.

BIke didn't run at all when i got it due to old fuel. Cleaned the carb/carb kit and tried to fire it up. fires right up but runs beyond bad rich so that black ( i know the difference between oil and fuel smoke) smoke comes from the exhaust and the end cap is black with soot. will barely take any revs and as it revs the black smoke continues. It looked like that before i tried to crank it so im thinking this is not a new issue and the PO gave up on it. I was told of course it didn't run because of old fuel.

So i can't really provide anymore input other than i tried creating a lean condition in the carb by setting the float very low and it still runs rich, bogs, black smoke, sooty pipe, even with the airbox completely off. put in a new OE plug also with same result. next will be to check timing marks to verify no skipped teeth. or anything else you guys can think of.

mossproof · Super Guru

Had high hopes a bad choke seat might have been it. Damn. cry
Normally a ttr will stumble and die if you turn the fuel screw all the way in on tickover, or do you mean the black smoke is still there whatever position the screw is in?
I would be quite surprised if it was the timing, but you gotta check and discount everything. Does the cam chain tensioner work? Also, is there a good healthy spark? If the coil is dying would that cause incomplete combustion?

Flywheel key broken? Now I'm really clutching at straws

Hang-in there - there must be an answer.

Shout out: Any other TTR owners on the forum in Alabama with a carb to test? (Or a bike to test the carb on?)

Jeff B · Senior Member

Does the float move freely or does it bind? This is not that complicated. The carb delivers the fuel mixture to the engine. Is it running rich all of the time? (yes) What causes a constant rich running condition? Jets are replaced. The airbox was removed and ruled out as a problem. That leaves the carb as the problem. Since fuel is coming out of the overflow, that sounds like the float valve is not working correctly. Check the emulsion tube for user modifications and make sure the needle valve clip is in the middle position. Also, verify that the choke seat is ok. That's about it for the carb.

Bluebandit2g · Member

Mossproof, runs rich no matter what position screw is in. Can turn all the way in or out and it make no difference in how the bike runs. its not rideable as is. Its not just a glitch or hiccup too rich. its bad rich. not spitting raw fuel from the exhaust but probably not far from it. Just barely idles and falls flat when giving it throttle until it picks up the main jet then it revs poorly with black smoke. Have good spark. Good spark plug gap.

Jeff, fuel no longer coming from the overflow, Float moves freely as can be. can hear it moving when tilt the carb even when completely assembled not just when checking float height with bowl removed. I will take some photos of the carb opened up and choke removed etc this weekend and post to see if you guys see something that im not seeing or that doesn't fall inline with the parts breakdown. Will also try to make a video of it running.

Thanks for all the help guys.

Jeff B · Senior Member

Can you take a picture of the emulsion tube (main nozzle - Yamaha part #4GY-14341-20-00)? It my be internally worn or the holes may have been enlarged.

Jeff B · Senior Member

Bluebandit2g wrote:
Mossproof, runs rich no matter what position screw is in. Can turn all the way in or out and it make no difference in how the bike runs. its not rideable as is. Its not just a glitch or hiccup too rich. its bad rich. not spitting raw fuel from the exhaust but probably not far from it. Just barely idles and falls flat when giving it throttle until it picks up the main jet then it revs poorly with black smoke. Have good spark. Good spark plug gap.

Jeff, fuel no longer coming from the overflow, Float moves freely as can be. can hear it moving when tilt the carb even when completely assembled not just when checking float height with bowl removed. I will take some photos of the carb opened up and choke removed etc this weekend and post to see if you guys see something that im not seeing or that doesn't fall inline with the parts breakdown. Will also try to make a video of it running.

Thanks for all the help guys.

You should be able to stall the bike by fully closing or opening the mixture screw.

Did you replace this part during the rebuild? If you did, try re-using the old one. The O-rings used in the rebuild kits are slightly thinner.