Honda GX630 Engine Problem

Used this new (bought NIB 16 months earlier) engine as a repower on a Terramite backhoe last year. Only ran it for ~4-5 hours but it ran very smoothly and had a lot more power than the Briggs it replaced. Parked tractor for about 6-7 months (well tarped) and upon restart it is only running on 1 cylinder.

Checked ignition (2 coils, interchangeable on this engine). Pale whitsh blue spark on "bad" one, but jumps a good 1/2" to ground; plug is somewhat carboned and appears wet. Odd in that this system uses "ground to run/open to kill" logic on coils. Measured resistances on both coils and they are within about 5% of each other, wiring is good to coil connectors, low oil level kill switch not yet hooked up.

Swapping components is a bear as engine must be removed from tractor each time due to engine being mounted "backwards" to get correct pump rotation (power from adapter on fan side).

Contacted 19 Honda parts/dealer places within 100 miles and none stock coil as "they don't fail". 5-6 days to get 1 ($80.00), IF available from factory. Internet research shows a few like problems , but in several instances a new coil reportedly DID NOT cure the issue. Note: only used non-ethanol in it from day 1.

Not 100% convinced on coil, any other suggestions? TIA. (Really disappointed in 4 hour old engine, especially Honda).

'Well Tarping' is probably the problem. It keeps moisture in there so it can cause damage, especially to electrical connections. Just like a Terrarium.

If you can't get to the coils on the tractor you probably just need to remove it and get it running on the bench, then re-install it.

Since you say its the 'ground to run' system, Have you tried running ground jumpers directly to the coils? You probably will have to pull the spark plug wires to stop it.

Actually the most common issue on this entire engine series is coil failure.

You did not state you replaced the plug on the bad cylinder. I would do that before buying a coil. I have a 20 HP water cooled v-twin in a lawn tractor - several years ago it developed a miss/limp at idle. The plugs were not old and looked good however, replacing them cleared the problem. I never seen that before....?

One other comment concerning non-ethanol fuel. If you are using aviation gas it has lead and can foul plugs. Lead is conductive to the high voltage at the plug gap. Airplanes have a back-up ignition system.

Thank you guys for the suggestions.

Ken-"assumed" plug good (red faced for overlooking it), will try your idea FIRST. Not av gas.

t.r.k.-afraid you're right, worst case is to pull engine, hate working on low equipment as knees/back don't like it anymore.

juicy-thanks for comment, I don't see enough engines to know what common failure modes are.

Thanks again!

How old is your terramite? Mine is a 2004 T5C with a 20 hp kohler. I wasn't aware they powered them with a Briggs. Must be an old one. On another site, I've been reading where some have changed over to a honda power. The boys at my local DIY rental say they stay with Kohlers, too much an effort changing over to honda.

I recently removed one head on my kohler and lapped the valves in. Now engine runs fine, 1600 hrs, doesn't burn oil. Some say engine is on last leg, some say it good for 3000 hrs. Head gaskets and valves seem to be an issue with kohlers. I fixed mine with a $10 head gasket and two days work.

I ran across a site for terramites. If you still have issues go there.
tractorbynet forums for terramites.