08 450 trouble starting... stumped

flyingdutchmen · 06-21-2011, 10:42 PM

i have a 08 sxf450 with a brand new motor and just had a 5 angle valve job done to the head with all new valves and everything. ever since i put it back together it has been getting harder and harder to start and at first it was only when the bike was warmed up but now it wont even start when its cold. their might be 10 hours on it now but i doubt it. after i checked electrical and spark plug carb pilot jet ect i checked the valve clearance and they were within spec but barely (exhaust were tight and intake were loose) so i shimed it back to where it should be tonight and now it wont start at all not even when its cold. right now the only other things i think it could be is timing (appears to be correct) a weak pick up coil or possibly the valve work lowered the compression because maybe the valves seat higher and combined with the decompression valve on it there isnt enough compression to start it. i do have a larger and smaller pilot jets on the way but it is getting fuel and when it is running it does idle half decent but not perfect. im getting frustrated and am running out of ideas and possibilities so any help would be great thanks.

WoodsRiderParts · 06-22-2011, 08:48 AM

That is a tough one...sounds like you have covered most of the bases. I had a friend with an 450 EXC that had a similar issue after rebuild. His air screw was turned out too far which caused HARD starting. I mean 25-30 kicks. It was lean, and with a re-adjustment by turning it in a full turn, it sprang to life in 5-6 kicks, 2-3 when warm. Just a thought. The only other issue could be electrical if you have checked mechanical.

flyingdutchmen · 06-22-2011, 09:52 AM

yea i was playing with the air screw before and even bought an aftermarket one so it was easier to adjust (hard to get a screw driver on stock screw) but it helped the problem slightly and the bike would start eventually but not every easily. like i said im out of ideas and everyone i talked to said it was my exhaust valves but now that they are adjusted there was no difference, it might actually be worse.

bajadog · 06-22-2011, 11:24 AM

Just have to ask, how much compression your bike showing PSI?

flyingdutchmen · 06-24-2011, 12:06 AM

well i think i found my problem... finally got a gauge and did a compression test. turns out it only has 77psi with the decompression valve out so it looks like i will be doing another motor job. im taking it apart tomorrow to try and see what the problem was.