OK question about my newest addition. Picked up a non-runner 04 KFX80 about a week ago. It ran with Pre-mix sprayed into carb intake. I cleaned up the carb and fuel tank. Then I started it and the bike ran pretty good other than a bunch of smoke likely from the years of sitting and possible motor oil in the injection tank which I then cleaned out. After a few short rides, the smoke is down to near 'normal levels'. Running Lucas 2 stroke oil fed from the injection tank. I also verified the oil injector is working normal and similar to my other KFX80.

It became progressively harder to start over the next few days. The last time I got it to start by pinching the air intake hose nearly completely closed at the carb intake. I have torn into the carb three times. Once found the pilot clogged. Otherwise all looks good.

Now crank, but no start, plug is dry and I don't feel vacuum when I put my hand across the carb intake while cranking. Carb looks clean and good.

Need advice. Is it likely still a fuel delivery issue, or should I be thinking something more serious like crank seals?

My next plan is to compression check(was 110psi when I bought it) and spark check again just to be sure nothing happened to the top end after getting things moving after sitting for many years. If all looks good, on to the carb again.

I can write a long and detailed list, but this is the cliff note version.
Any thoughts or advice is welcome.

 

I would check your compression again. The injection pump may have been working but not fully. so it may not have been supplying enough oil. Personal experience iv really never seen a older injection pump work properly

 

Thanks for the reply.

I only had a short time before heading to work this morning to look at this again. I did a compression check and was still at 110 psi. I didn't have time or didn't want to have gas fumes on me this morning so I haven't tried misting pre-mix into the carb intake port.

I'm not ready to give the carb and fuel system the 'all clear' yet. I'm thinking of swapping the carb from my other KFX80, leaving the oil injection line off and bottle feeding the carb with premix that I know is clean and good while diagnosing this.

 

Does your KFX80 use the vacuum pump style fuel petcock?
They can be troublesome with age and quit working properly

You can try putting the petcock into the "prime" position this will allow the fuel to flow without the vacuum of the engine running. I have heard many of these bikes run this way for years. Your carb float should cut off the flow of fuel before it fills the engine case, so that would be another thing to check (Make sure your floats are working)

I just rebuilt a Suzuki LT80 (same bike IM pretty sure) and the case (bottom end) was full of fuel/oil mix. Likely from a failed petcock and the carb floats sticking?
Regardless I found others pointed me to the solution, plug the vacuum port on carb and use a regular style petcock from a Yamaha banshee

 

I am not running the vacuum petcock. The OEM vacuum petcock was there when I bought it, but I immediately swapped it out for the 'on-off-reserve' type.

As an update to the thread, I dove into it last night. No vacuum being pulled through the carb so I took that off, disassembled and put it in a soak tank then decided to tear it down to see if I was up for the crank seals. I pulled the stator side down and that seal looked good. I realize you can't tell if it is good just by looks. I sanded the stator a bit as it was pretty rusty got it nice and shiny then put it back together mainly so I wouldn't lose the parts while ordering crank seals.

Since I didn't have the crank seals I didn't tear into the clutch side last night. Rather, I decided to put the carb back together. Used compressed carb clean followed by compressed air in all the passages, jets looked good. I figured I'd try to start it again just to see. I put the carb on and it was pulling vacuum so I bottle fed it pre-mix and left the oiler line off the carb. It still wouldn't start. I checked the spark, it was 'good enough', about the same as my other bike, but for grins I put a car jumper cable from the battery negative to the engine. I couldn't believe how fast that starter was spinning and the spark was amazing. Still, no start. Dropped some pre-mix in the spark plug hole, still nothing. Scrubbed the hell out of the spark plug with a wire brush, cranked the bike a bit with no plug to clear the chamber. replaced the plug and it fired up and ran great! The oil injector is definitely working as specified in the service manual, so I feel good about using that with straight gas in the fuel tank.

I don't know if it was a massive intake leak, poor spark, fouled plug, blocked carb or a combination of everything. Perhaps it is still a faulty crank seal that just happened to be sealed at the moment. I'm planning to add a large chassis ground on both my bikes since using a jumper cable made the starter spin better.

Either way I'm happy and was already planning to take a trip with my other bikes this weekend. This new beast will be on the trailer as well. Hopefully it will start when I get to the woods!

 

Did you ever check the compression?

 

I did check the compression. It was still 110psi.

I got to the trail and it wouldn't start. I pulled the carb apart and found the pilot jet plugged. I cleaned that out, reinstalled the carb, but still little if any vacuum. After a bit of cranking it did start up and was running pretty good.

I decided to take it for a good hard ride to help burn out any residual crap in the system. I wish I would have remembered to reinstall the the oil line on the carb! About 1.5 mile into the ride the bike stalled and I could tell there was little compression. Sure enough I burned up the top end from my oversight. Oil from the line was all over the carb. A repeat compression check now showed 40psi.

I tore it down to the connecting rod and have a 'Niche' top end kit on order. I tried to find a 'non-china' parts kit, but I'm not so sure I did. Where do you guys get your parts?

 

I'd also check for rod play (up & down)...the oil lubricates the crank bearings & both rod bearings...hate for you to put in a fresh top-end only to have your bottom grenade shortly there-after...

 

Thanks for the advice. I did check the rod for play and it seems solid with no play. The bearings at the top of the rod(in the piston) were still in great shape. The thought of damage to the bottom end did occur, but all seems good. I suppose I'll be the first to find out if it is otherwise...It's hard to fight stupidity.

I also ordered a set of Boyensen reeds. Maybe I'll put those in while rebuilding. I've never done reeds before. I don't really know what they do, but I read about people swapping them out so I guess I'll give it a go.

The cylinder that was on the bike, I assume it was OEM, but can't be sure as I don't have a history with this bike, looks to be in good condition...at least to the untrained eye. I was thinking about sending it out for repair. I don't really know any shops local, but I see a few machine shops advertising this type of work on Ebay. They offer boring of cylinder and a new top end kit with Pro-X piston for a reasonable price. What are your thoughts on this? My thought is, now that I have two near identical KFX's, sooner or later I will need another top end and it would be nice to have one ready to roll.

 

I use Suzuki parts especially pistons.
powersportswarehouse.com is where I get mine. (look up a 2003 KFX80)
I bore and new piston/rings/pin/pin brg/c-clips head and base gaskets= $125 plus shipping.
I have used the cheapo cylinders with a Suzuki piston. The ports can be very rough with them.