If you own a 1998/1999 Yamaha YZ400, you're probably going to know that these bikes are extremely finicky. If the planets aren't in alignment (exactly) and the wind isn't blowing in the right direction, and it isn't the right time of the month, all that kick start is going to give you is...nothing.
I'm exaggerating, but really they are finicky. If you read the previous blog, you'll know I got the bike to start but it was idling rough and was backfiring. Having read a few articles, I figured it must be the pilot jet, which I had screwed completely shut. So...the recommendation is ½ turn out minimum for a lean mixture, 2 turns out maximum for a rich mixture. I had it at 0 turns out so obviously the bike was leaning out, which the rough running and backfiring seemed to confirm.
I want to ride this bike in 2 weeks on my parents in law's farm, so I had to get the idling and running sorted, which I figured would be pretty easy. I had read that a rich mixture resulted in degraded performance and according to me this was fine, I wanted the bike to idle and run smoothly. If performance suffered a bit, I didn't care; the bike has more power than I can handle anyway. I was going to turn the pilot screw out 2 turns; the bike would start and run fine, little less power, no problem.
Ok, that was the theory. First issue is that the pilot screw is hidden in an inaccessible hole right under the carb. You can either buy a special Yamaha tool, which I was not planning to do, or make another plan. After a bit of experimentation, it turns out you can unclip the pipe between the carb and engine, and then pull the carb towards you enough to get a short screwdriver into the pilot screw hole. I did that, turned the screw all the way in and then turned it 2 turns out again. I put everything back again and tried to kick start the bike. Nothing, absolutely friggin nothing. Usually you can hear if the engine wants to start, in this case it was stone cold dead. Right, so I tried all the options for trying to start a YZ400 (previous blog). Nothing, absolutely nothing...
Ok, my logic says that if the engine started with the screw turned fully in, and if the normal range for that screw is ½ turn out to 2 turns out, then logically it should at least start at ½ turn out. So I repeat the whole procedure and set the screw to ½ turn out. Try the kick start thing again...absolutely dead...nothing...
Now this is a problem, I can't really turn the screw back in much more, we're heading back to no turns in again and that's where the bike was idling rough, so what now? Remembering that setting the idling speed helped last time around, I turned the idling screw out 10 turns or so. I did my usual "compression lever in, 10 kicks to clear everything, compression lever out, kick and see if it will start" routine a few times and the bike was still dead. So I started turning the idling out 1 turn, kick start routine, 1 more turn out etc. until I could hear the engine showing signs of life. Another 3 turns out doing the kick start routine every time and the bike started, idling smoothly. I let it idle on choke for a while and then switched the choke off. The bike was still idling smoothly, success!
Right, now for a quick drive around the block. Before I say anything further, I must mention that I have owned and ridden the following: a 1981 Honda XR500, a 1989 Kawasaki KX125 and a 2005 Suzuki LTR250 quad. The first thing I noticed was that the brakes on this was 10 times better than anything I'd ever ridden before. Then I noticed the performance...the previous owner had told me that the bike wheelies in third if you open up the throttle so I decided not to go there yet. I snicked the bike into fourth, lowish revs and opened the throttle ¾ or so. Holy crap, I shit you not, this bike will out accelerate anything I've ever ridden before easily. EASILY...! None of my previous bikes would match this performance in second, at full throttle, at full revs. If this is what a 10 year old bike feels like, I can imagine riding a modern motocross bike must be absolute madness!
Anyways, I'm set for the farm and will have nearly 3 weeks to get to know this bike better. When I'm back, I'll post my "findings". J
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