ttr 250 backfiring....

Hey all,

I recently had a '00 TT-R250 given to me. It had been sitting for over a year before I dug into it. It was parked due to starter problems but the carb was ran dry prior to parking.

I replaced the brush holder assembly, threw in a fresh battery, put it back together, and after a few cranks she fired up. Initially the bike wouldn't hardly idle. I adjusted the idle and took it out for a spin. As I ran through the gears, I couldn't help but notice that the mid-range rpm's had a huge flat spot but the low-end and the high-end were fine. Also, as I would let off the throttle, it would backfire terribly.

I got it back in the garage, we tore down the carb and checked everything over. Everything appeared to be fine but we soaked it down with some carb cleaner and blew air out everything with the compressor anyways. We also set the air-screw at 1.5 turns out like the book calls for.

We put it back on the street and the flat spot in the mid-range rpm's was completely gone. But, the backfire is still there. My buddy and I tore off the cam cover and checked the timing. Everything lined up perfectly. But the backfire is still there and I can't figure it out for the life of me. The only thing that I can possibly think is that it's either the CDI or that maybe the o-ring on the air-screw has been compressed for too long and it isn't doing it's job.

Could someone give me some advice?



You may want to open the air screw to 2 or 2 1/2 turns and try that. I know the '05 TT-R250 was very lean at idle.

I agree. They were lean right from Yamaha (at least for Wisconsin altitude). I had a similar issue and had to run a small numbered drill bit through the pilot jet. I had cleaned it at the store (I work for a dealership) but there was a grain of dirt firmly stuck inside which I missed. BE CAREFUL not to dir out the jet and ruin it. One size bigger than stock worked for me but don't go crazy.

You think this will eliminate the backfiring problem?

After opening the airbox and installing the Big Gun; I started my '05 (with then stock jetting). It stumbled and backfired a lot.

After re-jetting by Beechmont Motorsports it does not. It occasionally cackles back a bit if you use the engine for braking but its not back-fireing.

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