Rear Plug fouling up

M600 2001 vintage, 40,000 miles. Does 60 miles a day five days a week. The rear plug has started to foul up after a couple of days riding, it runs OK at higher revs but will cough and splutter at low revs. Change plug and it runs as well as it should. A few days later chug chug splutter. Any pointers as to where I need to start looking for the cure to this affliction?

MikeG

can't help you at all but mines just done exactly the same thing. its a 94 m600 with 35,000 on it but had new pistons, rings and barrels 2000 miles ago.
was ridin last sat and after a few miles it gradually worse until it was running on one cylinder. played about with it a bit then thought of changing the plugs, started running sweet as. its odd because i'd changed the plugs only 2 weeks before this happened.

I would start off with the basics and get your hands on a compression tester and check the reading on each pot.
Regards
Craig.

Mine does this occasionally. Are you running standard champion plugs? I found it gets less fequent if you fit the NGK's listed for the monster, they have a better temperature range or summat. Also use super rather than premium fuel. I think it's associated with the carb icing symdrome and the way you warm up the bike, mine is more prone if I try to leave it idling on part choke before its properly warm. It doesn't do it straight away, but waits a couple of days!

Only real solution I found is to always carry a spare set of plugs.

I use NGKs, it may be the cause is the pretty foul weather that me and the bike have had to put up with the past week, rain, sleet, snow and sub zero early mornings. Its cold on the bike when its below freezing. Maybe I should move south to the sun, Italy I guess. Spare plugs are always carried as are other bits "just in case". A throw back to the BSA and Norton days of my late teens - rosy glasses - ha!
Seriously I hope its not rings or something, at 40K miles it may be starting to wear a little here and there!

Originally Posted by MikeG

Seriously I hope its not rings or something, at 40K miles it may be starting to wear a little here and there!

You should be able to tell if it is petrol or oil fouling your plug(s). Oil fouling will be sooty and oily and probably caused by a mechnical fault (such as worn rings). Petrol fouling will smell of petrol due to the fuel not being burnt properly and can be caused by numerous faults including ignition and possibly the weather!

Oil fouling will be shiny black, a rich mixture will make the plugs looks sooty wont it?

[boppy]

I had the simillar problem. Dealer suggested changing the suppressor caps as old ones could be faulty. Got NGK's, goes great now.

It sounds like a crappy plug, despite what the dealers tell you there are duff ones. I had the exact same thing as someone else who had the exact same thing..new plugs, 5 days later...only one cylinder, change the caps..swap the plugs...ohhhh now the fronts not firing? replace the plug, go for a hotter dpr 8 and throw 1/2 a tea cup of pro fst in next time you fill up -when you fill the tank not when you next drink darjeeling darling.

[gary tompkins]

Have you noticed if the bikes oil consumption has gone up much?

[spacemonkey]

Would suggest a need for a good carb setup. Mine did similar and a good dynojet and setup cured it-but by then the damage had been done, and the bore wash from running rich had worn the rings..

[CK & AK]

when were the shims & belts checked last?

I ask this, as if you keep getting the same problem with constantly changing the plugs, there could be a deeper seated cause.

I have a 2001 bike, done 18thou miles, and because the shims hadnt been checked in such a long time (if ever) there was no valve clearance - so it wore the rocker shafts.

In extreme circumstances, it could be slightly holding a valve open - so not getting correct compression - and therefore fouling the plug, through low compression.

So - as has been mentioned, checking the compression is a good starting point & also the cam belts - as if they are slack or worn though wear - it could put the valve timing slightly out!

Have a good check over - good luck.

Alan

Rather bizzarly on the way home last night the bike died, took the plugs out and they were fine, and a good spark. Engine turned over fine but would not fire. Fuel I thought! Open filler cap and have to pull it open against the vacuum!!! Aha - trapped breather pipe, no thats fine. Start the bike with fuel cap open and it runs fine. Is this by any chance connected to the original plug fouling, I know it seems unlikely but it is a Duke! So now I need to know how to unblock the breather pipe, is it possible that salt and sh1t have blocked the pipe or is it more likely to be at the tank end? Anyway rode to work with the filler cap slightly open (thats why they supply two keys!) and the plugs are fine. Hey ho what now?
Thanks to all so far!!!!

If bike runs fine with filler cap open and poor without surley it has to be a breather problem.
As fuel comes out of the tank it has to be replaced by air otherwise little or now fuel will be getting to carbs.
Double check your breathers Do they run internal inside tank could one off fallen off/perished inside tank?

[crust]

Open the filler cap.

At the hinge end (nearest seat) there's a black rubber chimney.

That should line up with a hole in the underside of the cap, if you look you can sometimes see the black ring it leaves, the hole should be inside the ring.

Line the rubber tube up with the hole and try it.

Crust