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

Hey everyone,

Some background:

Last summer I bought a junky TTR because I wanted to learn some mechanics and get to know my motorcycle better through indirect practice. This TTR wasn't running when I bought it, but I did some work and cleaned and rebuilt the carb and got it running. I did a complete top end rebuild too because it was smoking. I put in a larger piston and got the cylinder bored at a shop. I also had the valves adjusted at a shop because I didn't want to mess around with buying a shim kit and potentially messing something up. 

So last night the moment of truth came when I had everything cleaned, oiled, and back together. I was honestly shocked that it actually started up on the first try! I was incredibly excited and proud of myself and rode it lightly around the yard once. Everything seemed great so I went in and grabbed a helmet and rode it about 300 yards down the road. I was in 3rd gear on my way back when all of a sudden the bike kind of bogged down a little and died. I rolled into my driveway and figured that it was probably either out of gas (I had only put in a little and it was leaking out of the pet****) or the gas I had used was old. It wouldn't start up again when I tried to turn it over. It was getting dark and I was hungry so I decided to call it a night and I went inside.

First thing this morning I turned the bike on. Fired up great and idled pretty well. I started giving it a little throttle and noticed that when I rev it up and release the throttle, the RPMs would drop really low and the bike would want to shut off. I opened the throttle a little more and then shut it and once again as I shut it the RPMs dipped very low and the bike shut off on its own. I brainstormed what could cause this with my limited mechanical knowledge and thought maybe it had something to do with the bike running lean.

I decided to fire it up one more time with the choke on to see how it ran different with a richer mixture. It turned over very easily (is this a cause for concern?) and then idled at very high RPMs before there was a loud, single CRACK (I think it came from the exhaust but I'm not 100% sure) and the bike died. At this point I was terrified and came running in here to post this in search for answers and hopefully not soul crushing news. I'm hoping it was just unburned fuel in the exhaust, but that wouldn't explain why it immediately shut off after!

Thanks everybody!!

UPDATE: So I pulled the plug which was brand new since starting it up the first time and this is what it looks like. Also I did a compression test on the cold engine and it was only about 110 PSI with the throttle open :/ 

-- Edited by JazzLover on Thursday 19th of March 2020 02:41:26 PM