I bought a basketcase '05 YFZ450 with a bad crank. I put a '06 crank in it, with a '07 oil pump w/nozzle. I took the carb apart and cleaned everything up inside. I made sure I had the all the jets cleaned. When I spray choke cleaner through the pilot air jet passage, it flows out through the pilot jet passageway, the pilot screw passage way and into the passageway into outlet into the center of the carb (behind the slide). The previous owner had installed a 168 main and a 45 pilot. I set the idle mixture screw (pilot screw) at 2 turns for starters - I was going to adjust it correctly after I got it running. I'm sure there are no plugged passageways anywhere. I had to replace the stator as the the original was damaged and I replaced the battery. My problem is it will start, but not idle. I can keep it revved up and it sounds ok, but it acts like it is not getting anything from the idle circuit. I'm not a newbie to this, but I can't figure this thing out. Anyone got any ideas?

Thanks in advance.

 

i replaced the stator in my friends kfx 400 hundred and if we pulled started it it would run fine until i tried to let is idle i found that the stator had not been working properly and not charging the battery and on the yfzs you notice that the headlights dim when it idles this is because the bike is majoritly run of the stator. if you can't find the carb issue id check if your stator is working properly what kind of mods are in this yfz ?

 

Thanks for the quick reply...other than the 06 crank, 07 oil pump and rejetted carb, it's bone stock. The voltage at the battery is 13.0 engine off - 13.3 to 13.7 when it's revved up some - same voltage with or without the lights on. The stator is a new factory Yamaha, but I know the latest number supercedes the older number - not sure what the difference is. Factory spec looks to be 14v at 5000 rpm. I'll check the stator resistance. Perhaps it's the rectifier/regulator? My guess this is this isn't the problem as it seems to run ok when it's revved up and there isn't that much difference in the voltages - battery vs. charging?

 

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if i remember right i had a k@n and a slip on big gun and i don't remember my main jet being that big it could be over fueling it on the bottom so i would double check if you have the right pilot jet also

 

I'm at sea level and did a little reading that this jet combo shouldn't be too far off. I may try to turn the mixture screw in 'til it's only out a 1/2 turn or so. I'm pretty sure it's a fuel screw and not an air screw - screwing it in should shut the fuel down. It pops and backfires when I try to let it idle, which to me it acts lean or like a non-existent idle circuit. It's such a pain to get to the screw... I may play with it after dinner. Again, thanks for the help.

 

sounds like the carb might still be slightly out of whack, have u performed the zip tie mod on the carb? i would also try and put your hand over the intake boot and try to cover it like 1/2 or 2/3s, 1/3, just seeing if it will idle with less air being drawn into the carb as a way to tell if the fuel/air ratio is still a little off.