This has me stumped.

[David Wayne]

My mower has a Kawasaki FH680V +- 1400 hrs. Lost power ran rough- no spark on right side.
I replaced both coils and plugs and thought it was fixed runs smooth as silk, but at anything above about half throttle and it loses the left cyl. I have checked spark to ground and it throws a strong half inch spark, set valve lash on both sides, cleaned carb, swapped coils and plugs side to side, confirmed the choke is not closing, tested compression 80lbs on right its the good running side, and 90lbs on the left. I don't know what to do next short of a complete teardown and I never was confident in rebuilt small engines. Any ideas ?

Thanks,
David

 

[dodge man]

A problem with the valves or cam? Just a wild guess. You might switch coils and plugs side to side to make sure the new coils and plugs are good.

 

[oldnslo]

Does that model have both coils and igniter for each cylinder? If yes have you checked or replaced the igniter?

NOTE: Not 100% positive igniter is correct term but it is what sends signal for spark for each cylinder.

 

[MossRoad]

My mower has a Kawasaki FH680V +- 1400 hrs. Lost power ran rough- no spark on right side.
I replaced both coils and plugs and thought it was fixed runs smooth as silk, but at anything above about half throttle and it loses the left cyl. I have checked spark to ground and it throws a strong half inch spark, set valve lash on both sides, cleaned carb, swapped coils and plugs side to side, confirmed the choke is not closing, tested compression 80lbs on right its the good running side, and 90lbs on the left. I don't know what to do next short of a complete teardown and I never was confident in rebuilt small engines. Any ideas ?

Thanks,
David

If you swapped coils and plugs and that right side is still not working correctly, you can eliminate those as the problem for now.


Here's a link to the electrical on that engine. Maybe it'll help you out.

https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/kawasaki/4-stroke-engine/fh680v/fh680v-as23-4-stroke-engine-fh680v/electric-equipment

You might take a look at the 59031 charging coil.

https://www.jackssmallengines.com/jacks-parts-lookup/part/kawasaki/590317009

It could have a break in it that opens up at high RPM/temps. I had a chainsaw that would do that.

 

[David Wayne]

I did swap side to side, and before I did that I put the old coil back on that side, it didn't help so went back to new coil. Yes it is two coils and the trigger when the magnet on the flywheel passes them.

 

[David Wayne]

Wouldn't the charging coil effect both sides?

 

[MossRoad]

Wouldn't the charging coil affect both sides?

You'd think so. But if you think about it, it's keyed to the crankshaft. So a bad portion could be going past the bad cylinder's coil on every ignition stroke.

Anyhow, since you've changed everything else, what's left?

 

[zzvyb6]

Fouled spark plug from excess oil contamination. Change brand of plugs. Been reported as poor quality.

 

[WinterDeere]

If your Kawi v-twin is like mine, they are somewhat sensitive to flywheel/coil gap, so obviously make sure that's right. You rmanual should have the number, and it's an exercise is moving the magnet under the coil and pushing it down onto a feeler gauge while you torque the mounting bolts. Simple but tedious.

If a dual spring model, obviously make sure your inner valve spring isn't cracked, causing valve float at higher RPM.

All of the Kawi v-twins (I believe) suffer from valve guide slippage, which can cause a bent push rod or rocker arm damage. This reduces overall valve lift, which is a real problem, but I wouldn't expect that to be so dependent on RPM.

Clean / un-fouled plugs are obviously important, but also not so distinctly dependent on engine RPM.

 

[oldnslo]

I did swap side to side, and before I did that I put the old coil back on that side, it didn't help so went back to new coil. Yes it is two coils and the trigger when the magnet on the flywheel passes them.

One trigger or two triggers, one for each cylinder?

Did you check for spark when engine was hot?

 

[WinterDeere]

One trigger or two triggers, one for each cylinder?

These engines have no trigger, just DC to a coil per cylinder, which is mounted to crank case adjacent to flywheel. Magnet on flywheel spinning next to coil, with direct connection from coil to spark plug. Typical magneto setup.

 

[David Wayne]

Plugs are new and I haven't seen bad reviews on NGK and switching side to side the problem doesn't move. Flywheel gap double checked, took video of valves running and played back in slow motion and they are working with no sticking or floating, no bent rods, charging coil maybe? But I doubt it since it runs great up to half throttle but I can check it's resistance. All good troubleshooting guidelines but charging coil is the only one not done and still not running right. Mossroad as to what else? Might be a new motor and be done with it for another 1400 hrs.

David

 

[RandyT]

If twin barrel carb don't overlook the possibility of a partially clogged jet for the left cylinder. Supplies enough fuel up into a certain point and then basically can't supply enough fuel to keep running on the cylinder.

 

[WinterDeere]

The intake manifolds are known to crack on those motors, causing a leak on only one side. I think it's a stretch, but since vacuum generally drops as RPM climbs, I guess that's always a remote possibility.

I agree with your thinking that, at 1400 hours, there's only a limited amount of effort and money you want to put into the thing. I just rebuilt mine at 1200 hours, and given the time and costs involved, I sort of regret not just replacing the damn thing. Depending on exact configuration, replacement cost is around $3k.

 

[David Wayne]

I disassembled the carb removed the jets and soaked it all in cleaner and blew out. Thought about a vacuum leak, kinda is a pain in the butt to take the shroud off because of the oil cooler on top, gets old taking it apart and putting back. I guess one more time won't hurt, spray some cleaner on it and if it doesn't make a change I might just go ahead and remove it and be done.

David

 

[tomplum]

There's a lot here that doesn't really apply to this engine. Compression is questionable which could very well be the gauge itself. One more than one occasion, I've found myself wanting to go down the rabbit hole. Checking valve lift, lash etc. and came up with a failed intake gasket where the intake mates to the head. You'd need new gaskets if you pulled the intake as they are grafoil now. But the carb is off. . .

 

[Fuddyduddy1952]

I prefer a leak-down tester like one of these over a compression test because supplying with air you see if it's leaking past a valve, gasket, rings.
At idle you can spray starting fluid or just some propane see if it revs up, spray carb base & around intake.

 

[M59]

I know nothing about this particular engine, however I'm agreeing with RandyT. You likely have a fuel starvation problem on the L cylinder BUT this only makes sense if each cylinder has a dedicated carburetor. If they do then try manually pouring gas directly into carb just after rpm point the L cylinder begins to act up. Spraying engine starter into carb throat will also work. If L cylinder temporarily begins to run properly then you have higher rpm fuel delivery issue. If this does not solve L cylinder high speed then you have ignition related issue.

Good luck

 

[CalG]

I know nothing about this particular engine, however I'm agreeing with RandyT. You likely have a fuel starvation problem on the L cylinder BUT this only makes sense if each cylinder has a dedicated carburetor. If they do then try manually pouring gas directly into carb just after rpm point the L cylinder begins to act up. Spraying engine starter into carb throat will also work. If L cylinder temporarily begins to run properly then you have higher rpm fuel delivery issue. If this does not solve L cylinder high speed then you have ignition related issue.

Good luck

On a V twin engine with a single carb, one cylinder is always sucking hind tit.

If there is a fuel delivery issue, it will show on that cylinder first!
Check with the Harley -Davidson crowd for confirmation.

 

[RandyT]

On a V twin engine with a single carb, one cylinder is always sucking hind tit.

If there is a fuel delivery issue, it will show on that cylinder first!
Check with the Harley -Davidson crowd for confirmation.

Without knowing the exact spec number the normal configuration for the OP's engine is a single twin barrel carb.