450, hard to start and bacfiring..


6 replies to this topic
  • Grae

Posted October 03, 2007 - 06:03 AM

#1

I`m having some trouble with my bike,05 yz450f. It`s a bit hard to start I have to kick it like 5- 20 times to get it to start when it`s cold, and if it stops when it is hot it`s almost impossible to start again. And it is popping and backfiring like crazy when I shut of the throttle. My main jet is 170, and pilot is 45. Don`t know where the clip is at the needle. The exhaust is a powerbomb header with a leo vinci silencer, twin air filter and hot stage cams. Hope someone can help me with this.. I`m a bit lost..

  • maddogyz250f

Posted October 03, 2007 - 09:16 AM

#2

I recommend you check your valve clearances. I know Hondas act this way when the valves get too far out of adjustment.

  • Ga426owner

Posted October 03, 2007 - 10:01 AM

#3

More info needed...
Did this just start?
Has the carb been cleaned ever?
when was valves adj?
Jetting ...what is your altitude and temp?

popping after the bike is turned off may be a sympton of a exhaust valve sticking....Does it pop while running?

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  • konkubine

Posted October 03, 2007 - 10:42 AM

#4

1. Play in the hot start lever/cable (It will idle high and backfire on decel, then stall quite often)
2.Needle jet is gunked up and sticking(usually in this case it won't even start, but you might be getting close.)
3. Valves? I doubt it. My 03 valves were checked at 350 hours. Perfect. No exaggeration.

  • Grae

Posted October 03, 2007 - 11:34 AM

#5

More info needed...
Did this just start?
Has the carb been cleaned ever?
when was valves adj?
Jetting ...what is your altitude and temp?

popping after the bike is turned off may be a sympton of a exhaust valve sticking....Does it pop while running?



I just bought it couple weeks ago. It was fine when I rode it at his place, but this startet when I got it home.
I`ve taken the carb appart and it looks clean.
The engine was rebuilt a year ago from a bottom end crash, but the bike was put together just before I bought it. The rebuild was done at a shop so I think the valves is good, but maybe I`ll check it out.
Altitude is 800ft , and temp is about 50-65 deg.
Thanks.

  • Ga426owner

Posted October 03, 2007 - 02:02 PM

#6

Seems a little rich for 800ft...read the top 450 Jetting guide thread
Have you adjusted the fuel screw?
Is the Hotstart working properly or sticking in the carb?

  • Grae

Posted October 03, 2007 - 10:37 PM

#7

Seems a little rich for 800ft...read the top 450 Jetting guide thread
Have you adjusted the fuel screw?
Is the Hotstart working properly or sticking in the carb?


I have tried from 1 1/2-3 turns out on the fuel screw.
To me it looks like the hot start works.
I`ll try a 42 pilot and see if that works? Or try to change the main aswell?
I`ll read the Jetting tread and see if I can figure something out.





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