First time poster and novice small engine repairer here looking for some expert advice.
Last year I bought a non-working 2005 KFX80 for my son's birthday. Previously it sat up for years in a garage and so when I got it the gas tank and carb were full of trash. I cleaned them real good (several times) and changed the oil and air filter.
Got the quad running, but had to hand choke it at the front of the carb to start it. Took it out a few times and it ran well, although it seemed to have a fair amount of power most times and then had turbo power for short bursts. Cleaned the carb several more times thinking that trash was stuck in there, but that didn't help solve the power issue and I couldn't seem to find any rhyme or reason for the turbo bursts.
Then, one day the quad wouldn't start no matter what I tried. After reviewing the threads here I checked the compression and it won't go higher than 85 psi. I took it apart to see if there is any visible damage, but don't see anything with the exception of the deformity by the ports in the cylinder (see attached pic). So as this is the first time taking an engine apart to this extent I don't know what to think of this.

1- Is this 'deformity' inside the cylinder normal or a problem?
2- Is there a way to tell if the rings are bad? They weren't broken and moved freely in the groove around the piston.

Sorry for the long post, but wanted to try to provide as much info as possible up front. I look forward to the experts like LT80 to provide some help!









Thanks in advance.
Travis

 

The ports are normal stock ports.
Unless you had a blown head gasket, I think you need a new bore/piston.

 

What exactly in the pics or my description leads you towards a bore/piston vs. just the rings?

Thanks for the quick response LT80.

 

I've never been a rings only guy. Alot of trouble to do rings only to save 25 bucks.
I recommend you remove the piston and measure the bottom of the piston and the bore. See what the difference is.
To be honest, The pic shows me nothing on needing it, there seems to be minimal blow by. There may be blow by on the front side of the piston.
The bore indeed "looks" fine but, again, better measure.
.007 or so and it needs it all.

 

So you are saying that the parts alone will only be ~ $25 more to go with a new piston/ring set vs rings only? But I will have to get the cylinder bored. Doesn't that run about ~$150? Would you recommend Wiseco?

 

I get $140 for a new bore and piston kit (kit is piston/rings/cir clips/piston pin).
Head and base gaskets are included so is a new piston pin bearing.

I do not use wiseco pistons unless the bore goes to 52mm. Wiseco is the only one to make a 52mm.
I use Pro-X or Suzuki pistons.

 

Ok. So here's what I've done.

I ordered a Wiseco 50mm piston, rings, head, cylinder, & exhaust gaskets, piston pin, & bearing. Bought these b/c the price was right.
Bought a cylinder honing tool to clean up the cylinder. Installed all the new parts. Tested the compression and it only went up to 110psi. I was hoping for more, but that was much better than the 85 that I was getting prior to replacing the hardware.
1st attempt to start I had to hand choke the front of the carb, but it fired up right away. Drove it around the neighborhood slowly since it was after midnight.
Next day, I also had to hand choke it, but it started fine. It ran ok except that it was still having the power band issues that I mention in my first post.
Next day, again, had to hand choke it, but it started fine. Ran it down the block and it died on me. Hand choked it, and it started up fine. Again went down the block and it died. Only this time I couldn't get it started. Pushed it back to the house and much to my disgust the dang thing will not start. It is doing the same thing as before when the compression was low. It turns over, but never fires up. Put the compression tester on it and the psi won't go over 60psi. I am now thoroughly disgusted.
I'm out of town right now so I can't check anything. But the first thing I intend to check is the torque on the head nuts.
Other than those nuts not being tight, what in the heck could be wrong?

Thanks,
Travis

 

"I recommend you remove the piston and measure the bottom of the piston and the bore. See what the difference is."
So what was that measurement??
What was the measurement on the new piston to bore size?

"I think you need a new -->bore<--/piston"
My opinion remains the same.

You got yourself a great deal on the wrong sized piston. You needed to go to .5 over and have the cylinder bored and honed to the piston size.

"First time poster and novice small engine repairer here looking for some expert advice"
You got expert advice, the "novice" didn't listen..LMAO