Hard starting kx250f

black wheel
Posts
4
Joined
8/11/2019
Location
East China, MI US
8/11/2019 11:15am
Have a 2017 kx250f very very hard to start when and if it starts,wont idle,bought the bike used,getting spark,fuel pressure,injector pulse,valves are in spec,timing is spot on,compression test shows 55 psi after 5 kicks,I wired the decompression lever up and compression went to 110,but still no start,is this compression to low to start???
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kb228
Posts
6161
Joined
1/31/2018
Location
Mansfield, OH US
8/11/2019 2:49pm
Do a leak down test to verify the valves are sealing and clean/replace the injector
1
pCp 252
Posts
669
Joined
1/1/2008
Location
Hampden, MA US
Fantasy
2497th
8/11/2019 3:35pm
Check Tps voltage output. Should be around .59v -. 62v at closed throttle. If that checks out, next I would test both fuel injectors for a good fuel spray. Are you sure fuel pump is good? The filter gets dirty quick and causes problems with delivery. If the valve clearances are within spec and it has low hours (below 50) I’d say chances are the valves & seats are still good.
Paw Paw 271
Posts
3640
Joined
4/3/2013
Location
Benton, LA US
8/11/2019 8:33pm
Cam chain could be worn which will alter the cam timing and make it hard to start. It is a very over looked wear item in the engine that does have service limits.
I also say to check the valves for leaks.

Paw Paw
black wheel
Posts
4
Joined
8/11/2019
Location
East China, MI US
8/12/2019 5:43am
Cam chain could be worn which will alter the cam timing and make it hard to start. It is a very over looked wear item in...
Cam chain could be worn which will alter the cam timing and make it hard to start. It is a very over looked wear item in the engine that does have service limits.
I also say to check the valves for leaks.

Paw Paw
Not the cam chain,timing Mark's are perfect,also it wont even start with starting fluid,I have,spark,fuel,timing,air what's left except low conpression??

The Shop

Radfonz
Posts
145
Joined
1/6/2012
Location
AU
8/12/2019 11:59pm
Have you tried simply turning up the idle? The cold start button is the idle speed control as well and i have seen that when you operate it over time(pulling it out and in awkwardly) the knob can be turned in by accident causing idle issues.
black wheel
Posts
4
Joined
8/11/2019
Location
East China, MI US
8/13/2019 3:47am
It's not an idle screw issue,did you see about the compression?
Radfonz
Posts
145
Joined
1/6/2012
Location
AU
8/13/2019 4:35am
Yep compression is on the low side. But not low enough for it not to start i wouldn't think. Try unplugging the capacitor wiring a 12v battery in instead and see what happens to rule out an alternator issue. If no good, its time for a top end.
NoMuff2Tuff
Posts
192
Joined
2/11/2015
Location
La Place, LA US
8/15/2019 6:24pm
110 PSI kicking does seem a little low. Could a bad tip over sensor possibly be causing your issue?? Part number 21176-0704. a buddy has a 18 that all of a sudden started running bad on the bike stand and was told to check/replace tip over sensor. Bike ran perfect on the track the day before, next day it started easy on the stand and ran fine for a minute or so then all of a sudden started running like shit then became hard to start. Bike was never washed so water shouldn't be a issue. Just throwing out some possibilities

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