[44/45]

Please save my marriage! I had my cylinder bored .20 over with new piston and rings and also had new valves installed by local Honda dealer. I was running the ATV 1/2 throttle in the field after ring break in and it just lost power, but yet idles. When I let it cool off it started right up again until it got hot and shut back down. Checked carb several times which is to me not the issue. Fuel flows easy when draining tank back into can. I did adjust the valves to .006 when the motor was still on the bench, so I am confident it is correct. I will be checking the coil next but do not believe it would go out at the same time as my rebuild. This thing ran flawless until my rebuild. I went through 1388 posts on this forum and found others with similar problems, but nobody comes back and posts what their solution was.

 

[fishfiles]

Oil filter backwards ?

 

[44/45]

fishfiles, the oil filter is on correctly.

 

[mrbb]

what does a compression test show?

 

[fishfiles]

next question I would ask is who did the machine work , maybe the tolerances are too tight on the piston and it is heating up and seizing , or maybe the wrist pin is seizing

 

[SamUK]

next question I would ask is who did the machine work , maybe the tolerances are too tight on the piston and it is heating up and seizing , or maybe the wrist pin is seizing

I'm betting the same odds @fishfiles

Only other thing I can think of would be aftermarket ignition components failing giving a false fault diagnosis against the recent top end rebuild.

 

[44/45]

I'm going to pull the head this weekend and see if something is binding in the top end. The machining of the bore looked superior, and it was done to match the piston.

 

[SamUK]

I'm going to pull the head this weekend and see if something is binding in the top end. The machining of the bore looked superior, and it was done to match the piston.

What brand is the piston, any idea?

Measure the bore, I'll bet you a dime to a dollar that it's 'egg shaped'!!
What are your views @retro??!

 

[retro]

Its hard to guess at this point, not enough info. How long does it run from cold startup to when it begins to lose power?

One thing I would do within the 1st 10 hours of runtime on a topend rebuild is readjust the valves. It might be unrelated to your issue, but it should be done after a few heat/cool cycles, ya got new parts breaking in and new gaskets taking a set... the valve lash always changes during the 1st few hours of runtime. Change the oil & filter too at the same time.

As for whats causing your issue, thats gonna require some more diagnosis. Need to eliminate ignition & carburetion faults as the cause and determine if the motor is overheating or not. Theres no point in tearing it down yet unless you know that you screwed up somewhere....

 

[44/45]

The piston was purchased from Honda along with the valves. I will look at the box tomorrow as I believe that I saved all. I do want to check the valve clearance even though I am confident that it was set right when I did it on the bench, yet I am as human as the rest. It almost seems like the exhaust valve may be sticking open. Maybe a seized rocker? This bike is up at the cottage so I am only able to work on it on weekends!

 

[retro]

Its possible the new exhaust valve is sticking if the guide has old carbon and burnt oil caked inside it from a leaky valve seal. I use a .22 caliber rifle cleaning brush & solvent to scrub out the guides before installing new valves in them. If a valve sticks open it can get hit by the rising piston... which can make a mess of the new piston, valve and head, so ya wanna be sure those guides are clean and lightly oiled during assembly.

The valves should be checked & readjusted during the breakin period. Don't put that task off too long...

How long does it run before it begins to lose power?