Greetings all,

My turn to post engine problems. The bike as a MC21SP, supposedly done around 2000km on the top and bottom end. It was rebuilt by the previous owner (a former forum member) witha fresh top end, and a crank from TYGA. It's running a drilled airbox, jetted up two sizes from stock on mains and pilots, and JHA GP style pipes. The RH pipe has been dented inwards, and been pulled out to resemble a state that it originally was.

When I start the bike, the bike runs fine. When the bike gets warm, the bike will run for a little while, then start misfiring on the right cylinder. If the throttle is not holding up the revs, it will just drop and stall.

Carbies swapped over to another bike and they ran fine. The exhausts were swapped over to that bike and it ran no problems on that as well.

I've done the gasket check by spraying engine started on the base, barrel and head gasket and nothing happened (revs stayed the same).

Plugs appear to be fine, and are gapped properly. I couldn't see any damage to the piston crown, and I'm in the process of borrowing a compression gauge to do a compression check.

My mate suspects it is fuel fouling, but i'm at a loss as to the reason why it is fuel fouling. I would also like to know what other things I should suspect and check.

Any ideas on what I should do next? Many thanks for the suggestions too

A few things to check are. Plug caps. HT leads Coils. Filter on feul tap. I would start by swapping coils over and see if the problems swap over to the other cylinder.
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If only i knew then what i know now.

Thanks, I forgot to add that. I have swapped coils and plug caps over from a different bike and it still displays the same sympton.

I will check the tank fuel filter, but wouldn't it affect both cylinders rather than just one?

It only does it once it gets hot?

Look for things that will effect it when it gets hot then! Most likely the plug, coil, HT lead, or cap.

When you swapped the parts to the other bike, did you just run it up and say "yeah, that works... can't be that" and remove them again, or did you actually go out and ride around for 30 mins to check when it was hot?

Heat won't effect the carbs, as it's not like you have an auto-choke, and there's no cold/hot idle system like injection systems that could be playing up. The PGM is well away from anywhere that gets hot, so unless something mechanical (i.e. servo strain) is causing excessive resistance then it's probably not a problem, so you are back to parts that traditionally fail when it all heats up. Coil windings and anything connected to the spark side of things. I've also seen plenty of plugs that look fine when out of the motor and sparking on the engine cases, but fail when under compression/load... even new ones.

If the filter in the tank was at fault, then it's a single line to the carbs. One float bowl will possibly fill faster than the other, but both would starve at a similar rate if the float levels are the same.

in all cases it has been swap parts out and warm it up.....great she's working. Grab gear, start up bike again, get out of drive way and down the street......!@##@!@ push bike back up the hill back home.

What it is currently running right now is the other carbs, other lead, coil and plug cap (which is new). All the other stuff ran real well on the other bike no problems at all.

I will try and trace things upstream of the coil, maybe even try a PGM swap (highly unlikely).

As a side note. The kill switch wiring on this bike had issues, so that was replaced. I'm not surprised at all if it is a loom problem.

ok, today i had more of a tinker. Both plugs got cleaned up, sprayed with carby cleaner and regapped.

This time, it's the left cylinder that won't fire when cold, when revving it, it will occaisionally fire. I cleaned both pickups and noticed that the upper pickup (at the 1o'clock position) has a larger gap than the lower pickup. I swapped over with another pickup I have, and it still made no difference, the left cylinder didn't like to fire much.

I've swapped coil packs on that, and still no difference. I swapped PGM and no luck there, I'm now just trying to get my hands on a compression tester.

As a side note, the bike has been rejetted, and the pilot jets will be returned back to stock sizing jus as a check.

Once I sort out the left cylinder, then I will able to get the bike running properly.

If they are NGK plugs I wouldn't bother trying to clean them.

Once they have been fouled they never perform right again no matter how much they are cleaned etc. Been here a number of times.

Fork out for some new plugs and try again.
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If I have to take the carbs off once more...

What's the betting the plug that was in the right cylinder is now in the left one Steve?!

Like I've said before, I've seen plenty of plugs (even new ones) that won't work once fitted and under load. Load isn't just WOT at low RPM, load is also operating load.
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Andy.
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Well I was going to ask that question but though that must of been covered.

Plug gap is 0.7mm (thats 0.027559055118110236 of an inch for Fontyyy).

NB Noting the postion of the decimal place
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If I have to take the carbs off once more...

How many microns is that?

Note: That's micron, not Micron!
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Andy.
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Andy wrote:
Like I've said before, I've seen plenty of plugs (even new ones) that won't work once fitted and under load. Load isn't just WOT at low RPM, load is also operating load.

Plugs weren't swapped from L to R. I can try it if you want to see what happens

Andy, do you believe that these plugs are prone to fuel fouling? I have a mate that believes this same theory too, and for me I just can't fathom it, although I'm willing to believe it.

I will try new plugs today (and gap them!), I was told that they are new plugs by the previous owner.

How much do the plugs cost in the UK? They are AU$13.95 here, they had a price hike from $11.95 in the last couple of months no thanks to this economic crisis.

Plugs are strange things in my experience. I've had new ones that won't work, and grubby ones that perform perfectly. I only ever use NGK's.

I've personally never needed to gap a new NGK. Unless it's been dropped or something, in my experience they've always come spot-on.

I've no reason not to believe Steve. I've not come across that specific problem myself though, as far as I'm aware, but he deals with a lot more cases than I ever will.
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Andy.
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Of course the other thing with heat is the hotter the engine gets the less fuel it tends to require.

You said the other own had increased the pilot jets. It's rather uncommon to do that unless your'e running premix.

I would try dropping the pilots back to stock and see how it runs then. Even though you say you swaped the carbs onto another bike. Each and every engine is different.

We often drop pilot jet sizes on stockers/lightly mod'ed ones.
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If I have to take the carbs off once more...

That was my plan to swap back to stock jetting (after ensuring the jets were not blocked)....

Being a long weekend I had to spend all yesterday in the garden and hunting for garden supplies. I'll try and get the carbies back to stock and see how that goes.

Garden supplies in Australia? Surely that's a cool box and BBQ? I thought that was all installed by default as the property is built?
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Andy.
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