Carbie fouling a spark plug...

[tfb]

G'day all,

Well, as it's been a few years since I cleaned out the Katana 1100's carburettors, I thought I'd spoil the old girl with a total carbie dismantling and cleanout.

I went into it with the philosophy of "prevention is better than cure" -- but now I'm wishing I'd listened to the other proverb, "if it ain't broke don't fix it". Because it was running fine before, but now it's got a real issue...

Problem is that the bike starts fine, but then as you ride it for a few kilometres, it starts missing more and more, gradually at first, and then more and more until acceleration at any speed or throttle position is rewarded with running on 3 cylinders.

It's cylinder #2 -- the plug is getting fouled. It's not oil because it doesn't have a wet oily look; just matt black and sooty.

So I tried various things -- like thinking it's probably a dodgy plug so I swapped it for another but the same thing happened.

So then I suspected that it could be something to do with the vacuum tube to the fuel tap, like a leaking hose -- even though I think that would cause things to run lean. But I replaced the hose anyway.

In the end, I pulled the carbs out again tonight, and removed all the jets from carbie #2 and gave them all another soak in carb-cleaning fluid, and blasted out the carbie passages with carb-cleaning fluid and compressed air (again). I also checked the float height (in case I'd accidentally changed it in the course of things), but it was perfect, same as the others.

After 3 hours work, I put it all back together, and went for another ride. But the problem is still there.

So, any idea of what it might be? Other things I should check? I'm stumped. :?

I think it has to be something carbie-related, because the problem surfaced immediately after my carbie-cleaning work. It wasn't there before; but it is there now.

All suggestions gratefully received.

Cheers,
Mike.

 

[Steve]

How long has it been since the valves have been checked/adjusted? :shock:

To me, it sounds like the intake on #2 is a bit too tight, and the valves are blowing back into the carb on the compression stroke. As the air comes back through, it picks up a bit more fuel, then when the valves open again on the intake stroke, it picks up even more fuel.

That's my three cents (inflation), but you asked for it. 8-[


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[Nessism]

Not sure but maybe float #2 is not floating? Also, check the petcock. Pull off the fuel line and make sure fuel does not flow when the engine is off (make sure petcock is not on the Prime position) - vacuum is required to open the fuel line port and allow fuel to flow. If fuel flows all the time, and the petcock is not on Prime, you need a new petcock - extra fuel may be entering the engine through the vacuum port.

 

[Steve]

I just re-read the original post and saw where you changed the vacuum hose, but did you check the petcock to make sure it is not leaking through the diaphragm?

In normal operation, there is a spring that closes the petcock until vacuum from a running engine opens it. If there is a pinhole in the diaphragm, fuel will flow through it, then down the vacuum line, richening up the mixture for #2 carb only. Check this by leaving the engine off and applying a vacuum to the petcock to see if you get gas in the vacuum line. If you have to use your mouth for suction, be ready for gas. Much better (and safer) to use a vacuum pump, if you can.

It's still a good idea to check your valves, though. 8-[


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[bwringer]

Replace your petcock. This is the classic sign of a leaky vacuum diaphragm in the petcock.

The leak involved is so small that you may have trouble catching it, even if you apply vacuum. Petcocks last about 20 years. Replace yours ASAP and forget about it for another 20 years.

Don't bother with the junk rebuild kits or dodgy "workarounds". Keep in mind that the petcock controls the flow of a highly flammable substance about six inches from your crotch. Install a new one -- it's well worth it.

 

[tfb]

Thanks for all your ideas/ suggestions there, gents.

Steve, I will check the valve clearances, although this was done only 7,000kms ago.

Nessism, yes that had occurred to me too, so I'll check the fuel heights in the bowls with a clear piece of tubing, etc.

Steve & bwringer, that's a good pointer re. a pinhole in the diaphragm; but I hope it's not that, because I installed a brand spanking new fuel tap about 3 years ago. If it's knackered by now, I won't be impressed! :evil:

 

[Steve]

If you do find a hole in the diaphragm, don't bother trying to repair the leak. As someone noted in another post, you are dealing with highly volatile liquids just inches from your crotch. :shock:

If you must ride the bike before fixing it properly, remove the vacuum hose from the petcock and plug it. You can ride the bike by moving the petcock to prime, but I think you lose your reserve function by doing this. The prime position draws from the bottom of the tank through the reserve port. (You could also do this to double-check the hole-in-the-diaphragm diagnosis, then check the condition of your plugs.)


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[tfb]

The saga continues...

The saga continues...

OK blokes, here's where I'm up to.

This afternoon I made up an adapter for the carbie bowl, and had a clear tube up alongside the side of the carbie, to check the actual fuel level. It's not flooding.

As suggested earlier by bwringer & co., it may have been fuel leaking through a pinhole in the vacuum diaphragm of the fuel tap, and running into #2 carbie that way. So I bypassed the vacuum system (pulled the vacuum hose off the fuel tap, plugged the end with a small bolt, and went for a ride with the tap on 'PRI') but it's still fouling the plug, so it's not that.

After pulling the carbies out again and having a good look at them, I paid particular attention to the float needles, and they are a bit worn and probably not seating perfectly. There was also a little bit of muck in the float needle assembly of carb #2, so maybe that has been causing the carbie to flood slightly. Anyway, all clean as a whistle now.

I also checked the operation of the choke; that all looks hunky-dory and I couldn't see anything suspicious there. All the linkages are tightly mounted and all the pistons move out freely and return fully.

** But I found another thing that could be the problem: a corroded jet needle. At first I thought it was just some tarnishing on the side-surface of the needle. I tried some carbie cleaning fluid on it, but the black staining just wouldn't budge. So I used some AutoSol on a piece of cotton, and rubbed away at it for 15 minutes. Got some of it off, but it was then that I began to feel the roughness of the needle surface.

So I looked at it through a high-magnification eye-piece, and wow, it's got very fine pitting in a large patch over the side surface of the needle, where (I presume) it would rest against the side of the needle jet.

Well what do you think, folks? Would that be enough to cause that carbie to run rich? I can imagine it could upset the venturi/ atomising/ distribution of the fuel particles. But I can't imagine why this problem has suddenly made itself felt as soon as I dismantled the carbies. Perhaps disturbing things has been enough to make the corroded needle do it's darstardly thing. I dunno...

Anyway, figuring I've got nothing to lose, I took some 1200 emery paper and have gently polished the side of the needle, and then finished it off with AutoSol metal polish. But I really need to source another needle whatever else happens.

I guess it also raises the question as to why the needle on carbie #2 has corroded, but all the other carbie needles are fine. One of life's little mysteries, I suppose.

I have yet to check my intake valve clearances, but for the time being I've had enough of spannering on a bike that won't run properly!

If you have any other ideas or comments, let me know!

 

[tfb]

I went to the local Suzuki dealership today, and surprisingly the jet needles are still available as a stock part, and they don't cost the earth! Should be here in a couple of days, then I'll slot it in and we'll find out if the corroded needle was the culprit.

In the meantime, if anyone has any ideas, fire away.

Cheers,
Mike.

 

[Nightmare]

This sounds EXACTLY like the problem on my bike (80' GS850) _PART_ of the problem was a leaky fuel petcock (BTW, an easy check it to use a clear tube for the vacume line, if the leak is bad you can actually see fuel flowing through).
My bike has a carbon fouled #2, cleaned the carbs 3 times now, checked the floats 8 or more times (used a fuel meter to check how much fuel is in the bowls so i can rule out the float/valve). Runs rich on idle/off-idle (colour tune plug) haven't checked any higher throttle settings.

I checked the valves, compression, plugs, new coils, new battery, new intake boots & o-rings, rebuilt carbs, swapped all of the jets from a known good carb, new air filter, new airbox boots, new petcock, synced carbs, tried to adjust the air-screws (the #2 doesn't respond) and probably a lot of other things i can't think of...

Your needle shouldn't have any impact on the idle/off-idle, but i'm not sure if yours is running rich on thoes circuits too, I was considering lowering the fuel level below spec or changing the main jet to compensate because i'm out of ideas (so are 2 other mechanics)

 

[49er]

This sounds EXACTLY like the problem on my bike (80' GS850) _PART_ of the problem was a leaky fuel petcock (BTW, an easy check it to use a clear tube for the vacume line, if the leak is bad you can actually see fuel flowing through).
My bike has a carbon fouled #2, cleaned the carbs 3 times now, checked the floats 8 or more times (used a fuel meter to check how much fuel is in the bowls so i can rule out the float/valve). Runs rich on idle/off-idle (colour tune plug) haven't checked any higher throttle settings.

I checked the valves, compression, plugs, new coils, new battery, new intake boots & o-rings, rebuilt carbs, swapped all of the jets from a known good carb, new air filter, new airbox boots, new petcock, synced carbs, tried to adjust the air-screws (the #2 doesn't respond) and probably a lot of other things i can't think of...

Your needle shouldn't have any impact on the idle/off-idle, but i'm not sure if yours is running rich on thoes circuits too, I was considering lowering the fuel level below spec or changing the main jet to compensate because i'm out of ideas (so are 2 other mechanics)

You guys have both got a seriously rich condition which seems to defy logic. You've both checked and double checked all areas that could cause this problem.
Initially I was wondering if the diaphram on #2 carb was holed or not seating corrrectly. But then, I think this would cause a lean condition. Is it possible that the throttle slide on #2 is staying half open when the butterflies are in the idle position? If this happened, the mixture would be rich at idle and in the early off idle stages. Just a thought. I guess for this to happen, you would have a damaged/broken diaphragm spring or a sticking slide. Might be worth a look!

 

[tfb]

Thanks for sharing your own little saga there, Nightmare. Mate these problems can have you stumped, eh. Like 49er says, it almost defies logic. But we can be sure that, being a mechanical system, there will be a logical reason. (Unless some supernatural little gremlin has actually got in there -- in which case we'll be looking for a priest who specialises in motorcycle exorcisms.:shock

I'm absolutely certain that it's not the fuel tap -- in fact as you suggest, I have a clear vacuum hose and there is not a drop, not even a whiff, of fuel coming down it. And that's with a pretty good vacuum that I imposed on it by pulling on a syringe contantly for about 3 minutes. That, and the fact that I still get the plug fouling with the tap's vacuum system bypassed, only confirms for me that it's not the tap.

In response to 49er's suggestion, I'm going to duck out the garage and check the slide's freedom of movement. Stay tuned (pun and irony all at once).

The thing I keep coming back to is that I definitely didn't have this problem at all before I removed and cleaned the carbs. But I definitely had it in all its darstardliness immediately afterwards.

WHAT IN THE BLAZERS IS IT?​

 

[Guest]

On that carb make sure the spring and diaphragm is in its proper place. I had a similar problem and the slide spring wasn't seated in the cap but was bound of to the side.

 

[tfb]

Thanks chef -- yep the carbie's spring is properly located; also I always take care to locate the diaphragm correctly with it's 'tab' on the edge.

I checked the slides, and they all move up and down quite freely. I have spent hours now pondering and checking every nook and cranny in these carbs...

 

[49er]

Thanks chef -- yep the carbie's spring is properly located; also I always take care to locate the diaphragm correctly with it's 'tab' on the edge.

I checked the slides, and they all move up and down quite freely. I have spent hours now pondering and checking every nook and cranny in these carbs...

Well one last shot at it. You said you tried changing the plugs around. How about checking #2 HT lead. Perhaps you disturbed it when working around that area. It may not be sparking as often as it should!!! Check the connections at the coil and plug end.

 

[SqDancerLynn1]

Just a thought ? Have you tried to sync the carbs ????

 

[Nightmare]

I've synced my carbs, oh yeah, forgot to mention i also tried cleaning the gas cap (vent holes)... The ONLY thing that is left to make sense for my bike at least is: I had a problem with the petcock (leaking fuel through the vacume line), replaced the petcock with a new unit...

As a result it MIGHT be possible that: I have carbon build up in the #2 cylinder causing a higher then normal compression reading (last reading was 120 or 130psi, which is normal) BUT, maybe there is also carbon build up (or a burned valve) on the intake valve that is causing lower compression readings (which balances out the higher compression by the carbon build up in the chamber). And its possible that the stuck intake valve is somehow pulling more fuel in..? I know this is a long shot but I can't think of anything else that will cause this problem.

I'm off to pull the carbs off the bike again (maybe through some combustion chamber cleaner in the #2 for "the fun of it") going to quadruple check the #2 carb for plugged passageways and going to try swapping the float/pin and needle/valves with another carb.

 

[Nightmare]

Swapped the remaining carb parts and recleaned the air/fuel passages, guess we'll see, one other side note, i checked my notes and noticed that my #2 intake valve is out of spec (.102mm instead of .08mm) is it possible that .02mm is going to make THAT big of a difference?

 

[49er]

Swapped the remaining carb parts and recleaned the air/fuel passages, guess we'll see, one other side note, i checked my notes and noticed that my #2 intake valve is out of spec (.102mm instead of .08mm) is it possible that .02mm is going to make THAT big of a difference?

No. The extra clearance will retard the valve timing slightly and make the engine a little noisyer.

 

[tfb]

Well, the new jet needle has arrived and I'm about to waltz back out into the shed and spend the next few hours reassembling it all.

Wish me luck! 8-[