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post #1 of 18 (permalink) Old 09-13-2018, 06:54 PM Thread Starter
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Kfx450 help

I'm new to the site but been using it this site to try to trouble shoot my problem so I have a 08 kfx 450 I did a compression test on it read 45 psi so I rebuilt the head with new valves from kibble white and put a cp 13:8.1 piston in it did the compression test again and it read 50 psi it will run if I put fuel in the cylinder it will idle rev up a little but backfires and boggy I took the injector out and cranked it over and it sprays I'm stumped on this one can anyone give me some points that I can check
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post #2 of 18 (permalink) Old 09-14-2018, 11:10 AM
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Quote:
Originally Posted by Lavalley156 View Post
I'm new to the site but been using it this site to try to trouble shoot my problem so I have a 08 kfx 450 I did a compression test on it read 45 psi so I rebuilt the head with new valves from kibble white and put a cp 13:8.1 piston in it did the compression test again and it read 50 psi it will run if I put fuel in the cylinder it will idle rev up a little but backfires and boggy I took the injector out and cranked it over and it sprays I'm stumped on this one can anyone give me some points that I can check
With a 13.8:1 piston your compression tested psi should be around 100 psi+... not 50 psi as it is now...So you have a low compression issue...

Did you check the cylinder wall for scuffs/damage & did you gap & install the piston rings correctly...!

Can you do a leak down compression test...to determine where the leak is...???

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post #3 of 18 (permalink) Old 09-14-2018, 03:01 PM Thread Starter
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Yeah I examined the cylinder still had some of the cross hatches in it I put the ring in the cylinder squared it all up used my feeler gauge and it was good they were not close to touching I think it was .015 and it was good I re shimmied the valves and re did the compression reading and it was exactly 50 psi cold and I did it when it was hot and got the same result
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post #4 of 18 (permalink) Old 09-14-2018, 05:15 PM Thread Starter
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I just performed a leak down test and it say 80 percent at 15 psi of air I can hear air going in but I cant find where its leaking the valves are good I have the inspection plugs out of the fly wheel cover rad cap off and vent tube off the intake and even the oil fill plug out and cant feel any air
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post #5 of 18 (permalink) Old 09-15-2018, 11:21 AM
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Quote:
Originally Posted by Lavalley156 View Post
I just performed a leak down test and it say 80 percent at 15 psi of air I can hear air going in but I cant find where its leaking the valves are good I have the inspection plugs out of the fly wheel cover rad cap off and vent tube off the intake and even the oil fill plug out and cant feel any air
15psi is too little pressure to test valves, rings, & head gasket for leaks

A leak down should be done with 80~100 psi you should really hear where it's leaking...

Are you using this type of tester...see pic below

Make sure your piston is at Top dead center compression stroke (static test)..remove the decompression spring & hold the weights apart to prevent it from holding the exhaust valve open...!!!

https://dannysengineportal.com/how-t...eak-down-test/
Quote:
A threaded coupling attached to a leakage gauge is screwed into a spark plug hole. Compressed air (80 to 90 psi) is then fed into the cylinder.
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Last edited by Dust Devil; 09-15-2018 at 11:26 AM.
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post #6 of 18 (permalink) Old 09-15-2018, 03:53 PM Thread Starter
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Yeah I have the same tester did it at 60 psi and feel no air coming out the intake or exhaust and crank case breather but I adjusted the exhaust valves where as before they were .017 of clearance and I reshimmed it so it is roughly .025 and I got 75 psi of compression and this might be off topic about the compression but after I did that the bike will sometimes start on it's own when I get it running its sounds good most of the time every now and then it will bog and pop I shut it off and it won't fire back up unless i spray some carb and choke cleaner in the filter and fires right up and will sit there and idle I removed the injector and and cranked it over with the fuel line attached and its spraying but spraying enough to just cover my finger so my question to that is is it spraying enough or not enough it's all stock except a trinity stage 5 full exhaust
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post #7 of 18 (permalink) Old 09-16-2018, 08:02 AM
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Quote:
Originally Posted by Lavalley156 View Post
Yeah I have the same tester did it at 60 psi and feel no air coming out the intake or exhaust and crank case breather but I adjusted the exhaust valves where as before they were .017 of clearance and I reshimmed it so it is roughly .025 and I got 75 psi of compression and this might be off topic about the compression but after I did that the bike will sometimes start on it's own when I get it running its sounds good most of the time every now and then it will bog and pop I shut it off and it won't fire back up unless i spray some carb and choke cleaner in the filter and fires right up and will sit there and idle I removed the injector and and cranked it over with the fuel line attached and its spraying but spraying enough to just cover my finger so my question to that is is it spraying enough or not enough it's all stock except a trinity stage 5 full exhaust
Sounds like your cam timing might be a tooth off causing the compression loss...

Make sure that all 3 timing marks are lined up ...count 29 pins between the timing marks..see pics below...

reminder: 13.8:1 compression will need 110 or higher octane...!!!
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Last edited by Dust Devil; 09-16-2018 at 08:05 AM.
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post #8 of 18 (permalink) Old 09-16-2018, 03:56 PM Thread Starter
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Yeah I'm running vp 110 in it and I'll double check the timing and get back to you with a update I also adjusted the tps sensor last night or was reading .53 adjusted it to .62 now
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post #9 of 18 (permalink) Old 09-17-2018, 03:01 PM Thread Starter
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Cam timing is all in spec
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post #10 of 18 (permalink) Old 09-17-2018, 08:21 PM
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Quote:
Originally Posted by Lavalley156 View Post
Cam timing is all in spec
0.17mm is too close for exhaust valves to close & 0.25mm is too wide for it to open...!!

Set the valve clearance to factory..0.14mm Intake & 0.21mm exhaust...

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.)

Then do a compression test...?

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