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Discussion Starter · #1 ·
Finished building my KFX motor last year and it’s been running pretty good since other than my Ecu dying on me. Had a XC race this past weekend and brought it home cleaned it up and I had noticed during the race everytime i stalled the quad was struggling to start. Figured it was valves because it started really good when it was cold. Checked valves and what do ya know. They’re .25mm on the exhaust valves and .17 on the intake valves. Consistent. No big deal. Quick adjustment. Did the intake valves and got the cam chain side exhaust valve done. But the other valve was a different story. Pulled the bucket off and there’s like a 1/4” difference from the 2 exhaust valve stems. Checked to see if they were leaking. It pushed the motor over when I filled the cylinder with air. So the question I have is. Is this just my valves fully seating and the other 3 will also do this? Or should I be concerned. It ran like this for atleast a few months And it ran like a bat out of hell. Head is brand new oem along with stage 2 hot cams and kibblewhite black diamond valves.
 

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You may want pull off the head and inspect the valve seat in the head of that valve.

The valve "length" is set by the valve grinder. What ever they take off the valve seating area they should grind the same off the end of the valve to keep the length the same. Either you have an issue with the seat in the head or the last valve job was done poorly.
 

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Discussion Starter · #3 ·
You may want pull off the head and inspect the valve seat in the head of that valve.

The valve "length" is set by the valve grinder. What ever they take off the valve seating area they should grind the same off the end of the valve to keep the length the same. Either you have an issue with the seat in the head or the last valve job was done poorly.
Valves are seated for sure. Pressurized the cylinder and nothing leaked. Also as I added more and more it rotated the motor since I had it at TDC while checking clearances. Motors been running awesome over the last 55-60 hours. The head was straight from Kawasaki and has had the same valves in it since I bought it in March 2021. Valves were NOT reused. I replaced the head, valves, and cams all at the same time. I would imagine if there was a seat issue it would leak when i pressurize it. Also I’d prefer not to pull the head unless I have to being I have another race on the 24th and I’d have to spend another $100 in coolant, gaskets, and a set of rings because I never pull the head and just change the head gasket. Always do the cylinder base as well!
 

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.25 (1/4") is HUGE when talking about valve shim difference. If the head is a stock head and never been apart, this would make me inspect it even more. Just because it's holding pressure and running good doesn't mean something isn't wrong. I've had a cracked piston and the quad ran great, until it didn't run great...then it became a money hole!
 

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Finished building my KFX motor last year and it’s been running pretty good since other than my Ecu dying on me. Had a XC race this past weekend and brought it home cleaned it up and I had noticed during the race everytime i stalled the quad was struggling to start. Figured it was valves because it started really good when it was cold. Checked valves and what do ya know. They’re .25mm on the exhaust valves and .17 on the intake valves. Consistent. No big deal. Quick adjustment. Did the intake valves and got the cam chain side exhaust valve done. But the other valve was a different story. Pulled the bucket off and there’s like a 1/4” difference from the 2 exhaust valve stems. Checked to see if they were leaking. It pushed the motor over when I filled the cylinder with air. So the question I have is. Is this just my valves fully seating and the other 3 will also do this? Or should I be concerned. It ran like this for atleast a few months And it ran like a bat out of hell. Head is brand new oem along with stage 2 hot cams and kibblewhite black diamond valves.
Your quote (They’re .25mm on the exhaust valves and .17 on the intake valves)

Your valves are way out of range Too wide...They're barley opening...
re adjust them to...0.14mm intake & 0.20mm 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.)
 

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Discussion Starter · #6 ·
.25 (1/4") is HUGE when talking about valve shim difference. If the head is a stock head and never been apart, this would make me inspect it even more. Just because it's holding pressure and running good doesn't mean something isn't wrong. I've had a cracked piston and the quad ran great, until it didn't run great...then it became a money hole!
Your quote (They’re .25mm on the exhaust valves and .17 on the intake valves)

Your valves are way out of range Too wide...They're barley opening...
re adjust them to...0.14mm intake & 0.20mm 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.)
Ya but the issue is it’s only 1 exhaust valve that almost seems to have shrunk… it sits way lower than the other exhaust valve.
 

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Discussion Starter · #7 ·
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i pulled the head and the seat and valve, springs and retainer appear to be perfectly fine. The quad has been running quite a bit rich but I just got that dialed in last week and it seems a bit better.
 

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Do you have a 4" or 6"dial caliper?

If so, pull the other exhaust valve and measure the overall length of them and compare. I measured my stock valves and they were: 3.240 and 3.238 (within .002 of each other)
 
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