This has me stumped.

[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.