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

Jumpn · Veteran Member

front sprocket changed, float bowl gasket changed, won't start

Kaos · Senior Member

front sprocket changed

Jumpn · Veteran Member

Yea, tried fresh fuel already. Thank you, I'm just hoping it's not something strange. It started after new fuel, ran for 10-15 seconds, then coughed, and died. I'm not sure if a backfire or not.

diggermanbob · Senior Member

front sprocket changed, float bowl gasket changed, won't start

TTRfan · Super Guru

Check the simple stuff first.

Put an old cloth under the carb, switch on the fuel and undo the float bowl drain screw.

Do you get a consistent flow of fuel out? If so, it's not a clogged filter or sticking float causing the lack of fuel to the engine.

Did you check the accelerator pump was working before you fitted the airbox? If it does, can you keep the engine running by blipping the throttle to squirt fuel in from the accelerator pump?

Brian

Jumpn · Veteran Member

I drained the carb prior to winter. it was empty. I've done new fuel. It drains fuel from the bowl when I undo the float drain screw.

TTRfan · Super Guru

Jumpn wrote:
I drained the carb prior to winter. it was empty. I've done new fuel. It drains fuel from the bowl when I undo the float drain screw.

A steady flow?

ttr steve · Super Guru

Could the float be stuck and not letting fuel in to the right level in the carb? But still lets a small amount of fuel in, so you get a bit out of the bottom drain screw?

Just a thought.

Jumpn · Veteran Member

I will check the float and such soon. didn't have time today, and work 5 of the next 6 nights. Plus it' going to rain a bunch, so I will post a report when I know more. Thank you

Jumpn · Veteran Member

Well, i believe one of the jets was clogged. I sprayed it with carb cleaner, couldn't get a small wire through it. I had a spare one, but smaller, so replaced it. But, it was getting dark and the damn airbox is fighting me. I absolutely hate getting the air box onto the carb. No room, and it never seems to fit well. Brian, I watched your youtube video, and mine never goes on that smoothly. I was to the point of throwing tools, so I quit for tonight. What are the little hints for carb replacement? I hate trying to get this thing back on.

Jumpn · Veteran Member

Well, a week has passed, and no luck. I took carb off again, cleaned it again, put back on and still no start. I changed the spark plug, and visually confirmed blue spark grounded against the head before I put it in. It cranks for a long time, then it backfired from the airbox. For some reason, I'm wondering if the cam timing got off somehow. Originally, when it ran for 10-15 seconds, it was a little rough, then backfired, and alas, no start since. What else am I missing? I have good flow from the carb bowl when I open the drain screw. I have spark. I took the plug back out, didn't smell flooded.

Jumpn · Veteran Member

I apologize the top photo went sideways. Just showing at TDC mark. To me, cam timing seems OK when compared to tutorial. I have to run and get feeler gauges now to check clearances.

Jumpn · Veteran Member

Valve clearances within spec. Back to fuel. I didn't take the choke apart. Will try that next.

TTRfan · Super Guru

Cam timing looks good.

I know its an obvious one but will ask anyways - does the engine have compression - enough to blow your thumb off the spark plug hole when you turn it over?

From your symptoms, my suspicion is that there is an issue with the pilot jet........

Brian

Jumpn · Veteran Member

Well, compre55ion i5n't enough to blow finger off. what'5 next? Bad exhaut valve? Apologie5, my keyboard won't let me type the letter that before t in the alphabet, u5ing 5 in5tead. :)

JOHNYBOY · Super Guru

check valve clearense may be too tight

Jumpn · Veteran Member

I can check valves again to make sure. It briefly ran for a few seconds when I tried starting fluid. Couldn’t reproduce. That was without the carb in place. Figured maybe with carb back on, with gas in the bowl, maybe it would fire. Nope. Double checked again, I have spark and I have fuel in the bowl. Took off exhaust header, can see exhaust valves moving. I’m done for tonight. Really thought I was gonna get it going today. Now I’m just lost with it.

Jumpn · Veteran Member

It just baffles me. It ran when I parked it last fall. Drained fuel, battery placed on trickle charger, etc for winterizing. What am I missing?

PlumasDude · Senior Member

TTRfan wrote:
From your symptoms, my suspicion is that there is an issue with the pilot jet........
Brian

I'll bet you a beer Brian is right. I think you said you replaced the pilot jet with an undersized one -- its probably worth replacing with an OEM #50 (not Mikuni). Super common problem with this carb if it does turn out to be the pilot.

Jumpn · Veteran Member

Well, I don’t know what happened, but today it runs!! I don’t know what happened, other than persistent niggling with things. I added more gas to the tank. I kind of think it wouldn’t start because it was very lean without the filter in the air box. Whatever, it starts and runs now. Whew.

TTRfan · Super Guru

Result!!! biggrin biggrin

Although it leaves an unexplained mystery confuse

7kilps9 · Newbie

Good morning bois. My son bought and rebuilt a 2004 TTR250. It ran rough and wouldn't shift. He split the case. Put in a transmission. Honed the cylinder, new piston, new rings, new valves lapped in and leak tested. He couldn't get it to start. It's got spark. He claims he cleaned the carb out. Timing should be right. But it won't even fire when we put starting fluid in the cylinder. If we pull the plug out and "clear the flooded cylinder " it blows a good flame back out the plug hole. But won't even cough when it's all together. I'm going to double check the valve clearances, and clean the carb again. But it bothers me that I can't get a fart or even a cough when I prime with starting fluid. HELP!

TTRfan · Super Guru

My guess is that there is an issue with the valve timing.

Need to check he used the correct timing mark as per the guide here

Brian