HONDA 24hp V-TWIN problem

This engine is fitted to the JoBeau chipper I've been raving about recently.

I'm unsure whether to say the engine has disgraced itself or not but it is playing up nonetheless. Here's a list of the symptoms and my thoughts. Anyone with experience of this engine etc?

1) Was serviced recently and has done 10 hours since (total hrs 50). Genuine filters were used but I suspect cheap engine oil and perhaps minimal overfill.

2) The engine was running fine this thursday but I noticed after lunch that the exhaust sound had changed - a splutter was evident. The engine also backfires when the throttle is dropped suddenly. The machine was parked on a mild slope for the days chipping.

3) Todays chipping: exhaust note increasingly "popping" and strong smell of UHCs (sorry, unburnt fuel) from the exhaust accompanied by an ever decreasing level of power. It's running on one methinks.

4) Remove spark plugs and sure enough - #1 plug nice and dry and light brown and #2 plug black and wet. Interestingly, the spark counter for the hours meter feeds off #2 HT (still counting) lead so I assume the plug to be at fault and change the plug. Additionally, I swapped the "good" plug from cylinder one to cylinder 2 and sure enough it ran just on #2 altho as expected was hard to start and slow to rev. Deffo the plug I thought.

5) New plug in #2; symptoms no different but now when removing #1 ht lead during running the engine dies whereas it will still run on #1 with #2 HT lead removed. So despite a spark evident at #2 it then refused to run on this cylinder.

6) Got home - put spark plug tester on both; each flashed away nicely when cranking and when running. Also rest removed plug on earth to check for spark - both sparking.

7) #2 cylinder deffo aint burning fuel right. I did notice that when it refused to run on just this cylinder, closing the choke made it try to keep going.

8) The plug change and test confuses me since one test is then contradincted by another; does the coil do that for some reason?

9) I guess if not an ignition problem, a deeper problem with #2 may be present. #2s plug was a bit spongy when being tightened as opposed to #1; I'm always wary of overtightening one in an ally head for obvious reasons. However I bit the bullet and tightened it a little more (not thread stripping sensation!) and just wonder if compression was being lost (will do a compression test soon), since it idled a little smoother after all this paraphernalia.

10) Oh and plug 2 much cooler after running...

We'll see - any thoughts from the other boffs on here?

Lot to take in there will think about it.

To go on with get coils checked or swap if possible. its easy to spark in free air much harder under compression.

Check for air leak on manifold. You may have an air leak on the good cyl so the carb has been set rich to compensate.

Check valve clearances and timeing .

Have the spark plugs been replaced with the right ones?

Sorry didnt read the whole post and now see you have changed the plugs!

I was telinng the garden mach shop down the road that i wished i had a honda v twin not the b&s that i have got on the sawmill, and he reckoned that the hondas had become really awkward about the fuel that they burn. Is your fuel system SPOTLESS and filters like new etc etc?

I'm scouring the internet trying to suss the problem and there's all sorts of possibilities - bleedin nightmare - last thing I need. Perhaps I should fit a nice blown diesel to it!

take it back to the dealer if still under warranty.

take it back to the dealer if still under warranty.

I wish!

Would the exhaust valve not seating and fully closing cause these symptoms ? Contamination of oil perhaps ?

Thanks for the input guys, really is appreciated. T9 - point taken re the fuel, I've heard that too and in my case, it could be crap in the tank, altho it has a new fuel filter. I've always used super unleaded - why would a higher RON fuel have a negative impact, if indeed it has?

I've just read that this engine might be equipped with automatic decompression - something else to go wrong

Another point - not using oil and thus no smoke from exhaust...

Been looking at the Kohler, Subaru Robin and Kawasaki equivilents of this engine; they all LOOK better than the Honda; I love Kawasaki engines - the best imo.

Managed to download the manual for the GX670; transpires that the wrong plugs were installed at last service - wrong heat grade perhaps.

Gonna change oil, check valve clearances, muffler etc. GX670 doesn't come with muffler; added by manufacturer of machine to which it is fitted.

So many possibles - does my head in not knowing...