Plug Fouling - Still Got issues

[m3-paul]

Looking for a little help if possible. Went to take the bike out today. Started it fine but within a minute of riding it had bugger all power. Will slowly rev but pulling away mean't I had to slip the clutch a bit and rev it alot as it just kept bogging down. I heard no funny noises or anything at all, just slowed down.

Checked the plugs and the left cylinder plug is oiling, the right one is a lovely deep brown.

I cleaned the plug, started it up and immediately it did the same.

Even changed the plug and it still did the same. It isn't dripping in oil but there is a fine layer over the plug tip every time I remove it.

I take it this means I am looking at a minimum of a new set of rings but more than likely a rebore to the next size up with the associated new pistons and rings? Bike has around 19800 miles and I don't think that the engine has ever been opened up so to be honest it is not like it doesn't deserve a little attention. Opinions very welcome.

[calgap]

I'd think it was odd that one plug was nasty, the other not, if it was a bore problem.

Have you checked the jets? I'd go there first.

Change the plugs over too and see if the problem swaps. Need new plug then.

Don't despair just yet...

[m3-paul]

Must admit, I would have expected maybe more smoke out of the exhaust etc of I had blown a ring or something but there is no more than usual. Never heard any kind of abnormal noise. It still starts okay but if left to tick over it dies. Can easily keep it going on the throttle though, just no where near the power as it just doesn't rev well.

I really want to avoid pulling the cylinders as, a) I haven't pulled a 2T cylinder in 20 years and b) if it doesn't need them pulled I would be a bit annoyed.

Regarding swapping plugs, I haven't done this but I have put a spare good plug in the left cylinder and the same happened.

As I say, it is not dripping in oil but does have a very thin film on the end when removed. If you wipe it on a tissue there is minimal oil left behind on the tissue.

Bit odd really. Kind of at a loss as to what to do. I can check the jets but I know that the carbs are/were spotless inside a year back. I wonder if it could be a HT lead or something?

[m3-paul]

Bringing up the HT thing i wonder if that plug is not firing or has a weak spark hence the really low power? Still getting exhaust pressure out of the left pipe. Gonna have another dig around, pull the HT lead and see how it sparks.

[m3-paul]

Just checked the Left HT lead and the plug is firing the same as the right.

Started it up again for around 10 seconds and put my hand behind the right exhaust (still got a dark brown plug tip) and there is nice warm/hot gasses coming out.

Moved to the left exhaust and there is only what I assume air being pumped out. It is cold air at that so guess that cylinder is not firing at all. The right cylinder and exhaust downpipe are hot to the touch after 15 seconds but the left cylinder and downpipe are stone cold.

If I turn the engine over with the left plug out you can hear the compression sounds.

Looks like as a minimum i need to get the cylinders off and see what I have exactly. Once that is established then I guess new Mitaka pistons and rings will be required plus a possible rebore?

Does this all sound correct?

[m3-paul]

Just been thinking about this but could it be something as simple as fuel not getting to that cylinder? Is there a relatively easy way to find out? Should the plug tip smell of neat petrol if fuel is getting through but not firing?

I am trying to avoid pulling the cylinders unless I really have to. Been too happy bumbling around on a pretty healthy bike so am a bit pee'd off that this has happened, ah the joys of owning two strokes .

[louis]

Hello Paul,

Have you tryed to pull the choke and see what is happening, the choke allows fuel to flow in to the carbs that don't go's thought the mains.

The bike will nor run great, but you can see/feel if the lift is starting to work.

[m3-paul]

Will try that now and report back. Thankyou.

Nope, didn't work. The left exhaust remains stone cold with nothing coming out of the exhaust but cold air. Whereas the right cylinder/downpipe gets hot very quick.

Think I need to drop the left exhaust and have a look in the port and crank the engine to see what is the deal.

Reckon I am facing a top end rebuild. I would love the bores to be good and just fit in a new set of pistons and rings.

[calgap]

Out of my 2 cylinders, its always the left that plays up. I always thought it was because it gets flooded a little on the side stand.

It always kicks in after a while, even with the bike been standing for a while.

If you've a decent spark, and the plug is wet, then try the left carb. It does sound like a petrol or air restriction. If you've not looked at the carb in a year then that would be more than enough time for cr*p to get in from the 20 odd year old fuel tank.

If it's the top end, don't fret too much. I did mine for the first time last year and I still haven't been able to blow it up yet. At least it's done then and you can rest easy for another 20k+.

[Warwick]

It's a two stroke... Worn bores or ring damage will not noticeably increase the amount of oil in the combustion chamber. It'd be worth checking the oil pump setting and ruling out an ignition problem before anything else though perhaps? If all is well there, it might just be running a bit rich on part throttle or something on that side. I'd have the carbs off for a check over, give all jets and airways a blow thorugh, clean the airfilter, fit a new plug and see how it went then in the first instance.     

[m3-paul]

Okay, I am being a little thick here. I don't know if it is excessively oiled or not .

I am going to clean the plug now, take a pic of it to post up, start the bike and remove the plug and take another pic and again post it up for opinions.

Will also pull the carb(s) tomorrow if I get time and have a look and blow through the jets etc.

Thankyou for all the help so far. Incase I forget to add the info, last year it had a brand new genuine airfilter element and new float needles and pilot jets plus i set the float heights to be within spec as I had a big problem with the carbs puking gas everywhere. Also I had to slightly lengthen the spring in the petcock to help it shut the gas off to the carbs when the bike was not running, have i screwed up by doing this? Has been running for two/three months with no issues since then though.

[Warwick]

Fuel tap issues shouldn't affect carburtion in use so long as there's enough fuel getting to the carbs. Float heights could of course, so re-check them if/when you're in the carbs. If one plug is dark and wet and the other dry and brown, then Id suspect a carburation issue in the first instance - assuming the plug, lead and cap are all good of course.

Are you losing any gearbox oil?   

[Martin77]

I would suggest measuring the coil resistance to see if it indicates a breakdown internally. Put a probe in each HT cap to measure from one side to the other and it should be around 15ohm (roughly....check the manual). If it reads 0 (ie no circuit) then it means the coil is on it's way out.

Plus of course checking all the carb/oil pump settings etc... sometimes it takes time to fix these things, so be patient!

[m3-paul]

I went back out to it earlier and checked for spark again. Both left and right plugs seem to be sparking as strongly as each other but that is only visually of course. I don't have a multimeter as I had to give it back to work so i am picking one up tomorrow morning and will test the HT leads as stated. Have also got the workshop manual so will check via that as well. Will also get the carbs off and check the left one in particular of course.

This is the left plug once I cleaned it with a clean rag. This is exactly how the right one looks.


This is the same plug after 10 seconds of running.


The bike starts very easily with the clean plug but after one second you litterally feel it bog down and it really feels like the left cylinder has shut down.

Thanks for all the help, it really is very much appreciated.

[oldbiker]

you have replaced, cleaned and swapped the plugs for new.  SO I doubt that it`s a plug problem.

the plug gets wet after a few kicks or a little revving, and using the choke doesn`t help.  So I doubt that It`s fuel starvation.

I would try to swap the H.T. leads\suppressor caps (move the coil ?) that would eliminate a problem with the coil\H.T. leads.

As you would then have eliminated all parts of the ignition, check the float height is correct, blow compressed air through the jets and airways (even though it`s unlikely to be the problem) just to eliminate carb problems.

It`s unlikely to be an oil pump problem as one side is working ok.

The only thing left is wear and tear,
I would expect to need rings at 10000 miles or about 5000 on a ported barrel or an engine that gets a lot of hard use, the rings go in with 12-18 thou end gap, I would change them at about 30 thou even though you could run them up to about 40ish. 

I would expect he piston to be ok till about 35000 miles