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Discussion Starter #1
When I purchased my 08 450 recently it ran begrudgingly. I had charged the battery, changed the oil, spark plug (original was black), and fixed a broken wire to the tps sensor, it would run with a lot of backfiring. Fast forward, changed the tps sensor (set to .62), fuel injector, water temp sensor, air filter, tip over sensor with eliminator, Dynatek coil/wire, and battery. Compression is a hair over 50lbs cold. I did check the timing and valve clearance, the exhaust was in spec (decomp spring is present) but the intake was at .4mm. It is now back to spec between .1 and .12mm, which it will no longer run at all. How does the large intake valve clearance relate? I have a programable ecu on the way and am leaning towards rebuilding the top end to see what's in there. The exhaust is aftermarket slip on and welded together so there is no checking the packing. I did try a Dynatek FS controller but the error light came on so I removed it. It makes me nervous after reading about a problem with the same unit. Any suggestions would greatly be appreciated.
 

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Welcome to the Forum....!!!

The compression is too low/even with a cold test...49.0 psi is the bottom of the range...But before you tear it down...thinking it's the piston rings are worn....

(Service manual)
•Hold the throttle wide open and crank the engine with the
electric starter several times. When the gauge stops ring,
stop cranking and read the gauge.

Cylinder Compression
Service Range: 49.0
∼ 81.8 psi) @900 r/min (rpm)

Re-do the valve clearance.... (Range) intake 0.10~0.15mm Exhaust 0.17~0.22mm range...

The intake clearance is around 0.13~0.14mm...New from the factory...!!
The exhaust is around is around 0.19~0.20mm...

(Service manual)
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.)
 

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Discussion Starter #3
Thanks for the welcome. How much difference will it make to increase the intake clearance up .01 to .02mm?
 

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Thanks for the welcome. How much difference will it make to increase the intake clearance up .01 to .02mm?
Metal expands when heated...if the valve clearance is at the minimum of 0.10mm..the difference is a valve seating completely or not as the motor get to operating temp..causing a compression loss...bad performance...!!!

You should re-shim your valves to the wider range of the specs...

Hotrod shim kit...$64.00 free ship in the US...https://www.ebay.com/itm/Hot-Cams-9-48mm-Engine-Value-Shim-Kit-HCSHIM02-KX-450F-KFX-450R/332866178384?hash=item4d805ecd50:g:KwgAAOSwKSRa86oR:sc:USPSPriorityMailPaddedFlatRateEnvelope!86404!US!-1:rk:8:pf:0
 

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Discussion Starter #5 (Edited)
Thanks. Already have a shim kit, used it to shim it down from .4mm. I'm not sure about the exact measurement but a .1 feeler will fit, a .13 will not. I did try out the procom ecu, it no longer backfires but still won't run. I set it at 4 because of the aftermarket exhaust and K&N air filter.
 

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Thanks. Already have a shim kit, used it to shim it down from .4mm. I'm not sure about the exact measurement but a .1 feeler will fit, a .13 will not. I did try out the procom ecu, it no longer backfires but still won't run. I set it at 4 because of the aftermarket exhaust and K&N air filter.

(Service manual)

Valve Clearance: between cam and valve lifter
Standard:
Exhaust 0.17 ∼ 0.22 mm

Inlet 0.10 ∼ 0.15 mm

Make sure to retract the cam chain tensioner properly when installing... see picture below...!!
 

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Discussion Starter #7
Update, I loosened up the valves and rechecked the compression. I am getting around 60 psi cold. I can get it running but it won't idle (switch in or out). I have to hold the throttle, basically running like I first got the quad. I also tried adjusting the idle setting in both directions and it doesn't seem to change the idle. The header glows after a few minutes. Sensors I haven't changed yet, air and pressure sensors. Thanks for any suggestions.
 

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Update, I loosened up the valves and rechecked the compression. I am getting around 60 psi cold. I can get it running but it won't idle (switch in or out). I have to hold the throttle, basically running like I first got the quad. I also tried adjusting the idle setting in both directions and it doesn't seem to change the idle. The header glows after a few minutes. Sensors I haven't changed yet, air and pressure sensors. Thanks for any suggestions.
Is your KFX stock or has upgrades like an after market intake & exhaust system...???

What procom map are you running...!!
 

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Discussion Starter #9
It's a factory airbox with K&N filter and filter cover, it runs and starts easier with the airbox cover on. The exhaust doesn't look factory based on YouTube videos and is rusty. I can't take it apart because the joints are welded. The muffler has an 1 1/4" exit. Most likely, I will replace it with an HMF. The Procom ecu is set at two. When I first installed it, the fuel injector was not working. After running a continuity test on the wiring, it started working. After repairing one of the TPS wires, the FI light went out and has remained out. There are no codes when I ground the test wire. Thank you for your help.
 

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It's a factory airbox with K&N filter and filter cover, it runs and starts easier with the airbox cover on. The exhaust doesn't look factory based on YouTube videos and is rusty. I can't take it apart because the joints are welded. The muffler has an 1 1/4" exit. Most likely, I will replace it with an HMF. The Procom ecu is set at two. When I first installed it, the fuel injector was not working. After running a continuity test on the wiring, it started working. After repairing one of the TPS wires, the FI light went out and has remained out. There are no codes when I ground the test wire. Thank you for your help.
Note: the procom doesn't have the code error scanning ability...you'll need to install the stock ECU to check for codes (only)...!!

Try other procom maps until the motor idles...If not...you might have a faulty water temp sensor or another wiring fault...

If you can Test the water temp sensor...How to see below picture...
 

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