New to this forum thanks for the add. I have a 08 and 09 kfx450 both bikes are doing the same thing run great up to half throttle and then cut out and loose power when you let off the gas they pick right back up to half throttle again . Doesn't seem to matter if they are under load or just sitting. I have replaced the fuel pumps on both and have new injector in one i have swapped all the electrical parts from on to the other except for the stators. The only thing they have in common is they both have had the top end rebuilt. The 09 was running fine till then the 08 had the case replaced and top end done and hasn't been right since. Also they both where rebuilt by two different shops and have been to different shops since this problem has started no one can seem to find the problem has anyone on here had this problem and could help me out. I love the bike but it's getting expensive just putting parts on them and not fixing the problem. Thanks for any help you may have.
With a new top-end on both I recommend you do a compression test to make sure the piston rings are seated...65~75psi warmed engine, throttle wide open...!!!
I have done all the things you have suggested. Had a friend bring his over and swapped part from it and still no luck. Getting to be a real pain but need to find the problem thanks for the help
Sorry I haven't had time to look at them the last couple weeks. They are both charging between 13.2-14.8 volts. I have noticed the one of them doesn't do it until it get hot and if it sets for a few min it will be fine till it heats up again. The other one will rev as soon as its started cold but once it runs for about 30 sec it starts it and wont rev past 1/4-1/2 throttle. I have no idea what to do and I have heard of other people with the same problem but no solutions. Any help would be appreciated.
Have you check your valve clearance...?? blue99stroker also recommend for you to check...!
Valve Clearance: between cam and valve lifter
Standard:
Exhaust 0.17 ∼ 0.22 mm (0.0067 ∼ 0.0087 in.)
Inlet 0.10 ∼ 0.15 mm (0.0039 ∼ 0.0059 in.)
If the valve clearance is not within the specified range,
adjust it.
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