Fouled plugs - #1 and #2

[Anonymous]

Hey,

I'm having some trouble with fouled spark plugs on my 1980 GS550L. I've noticed recently that the bike isn't responding quite like it did. The gas milage has gone down by about 5-10 mpg.

I pulled the plugs today, and #1 and #2 are all dull black, suggesting carbon fouling, as I understand it. #3 and #4 are a nice greyish/brownish color, like they should be. All four plugs give a nice blue spark when tested.

I also have some trouble when starting the bike at times, especially if it's been sittting for a week or two. It tends to be sluggish at first, with the rpms actually decreasing when I hit the throttle instead of increasing. I have to let the choke keep it idling for about 30 seconds before this problem goes away. After that, it runs fine, except for the occasional soft pop from the mufflers (more frequent before the bike is fully warmed up).

I know this could be due to multiple problems, but I'm not sure which it would be. I cleaned out the carbs a year ago, replacing all the parts and what not. They were last synched in about October or November. The air filter isn't bad, but is probably due for a cleaning soon. If that was the problem though, I would assume all the plugs would be having problems.

Any suggestions on what to check or do?

Thanks a ton!

--Tyler

[KEITH KRAUSE]

Like you said, could be several things.
Try checking the cap and lead connections first because it's easy. If the connections are clean and tight, compare the spark quality to the two cylinders that have good looking plug reads. Use one of the good looking plugs for all four spark checks. They should be uniform. Be sure to clean off the darker plugs and check gaps before re-testing.
If the spark looks good, then I would have to say check/re-synch the carbs before tearing into them again. A good carb synch will last longer than a matter of months, but so should the carb cleaning you did. Is the gas tank rusting or do you ride on dirt roads? Did you remember to re-install the small springs with the mixture screws? The mixture screws can vibrate and lose adjustment without the spring.
Check the carb synch. If you see the vacuum is significantly higher (an inch or more) in #1 and 2, that's probably your problem.

[Anonymous]

I took a brand new spark plug tonight and tested all the connections. They all gave the same nice blue spark, so it's not the plugs or the caps or leads that are bad.

I also cleaned off all the plugs a week ago and re-gapped them. It made no difference, and #1 and #2 are still fouled.

From listening to the bike recently, it also sounds like cylinders #1 and #2 aren't firing at all, or just coughing every now and then as if they're trying to fire. It's gotten worse since someone knocked my bike over a couple weeks ago, and it backfires some while it's warming up. Without those cylinders firing, it seems that it would be hard to synch the bike at all.

The gas tank has some rust on the inside. I've taken the petcock off before and it wasn't clogged (about a year ago). I don't ride on dirt roads.

All the springs were reinstalled with the mixture screws. I believe those screws had some locktite on them before I redid the carbs, but I never put locktite back on. With the springs in there, would they be able to vibrate enough to lose adjustment?

Any further thoughts? Do I need to go ahead and synch them?

Thanks.
--Tyler

[marcovandevelde]

Check the floatbowl ventline & T for plugging. This plugging leads to vaccuum in the floatbowls and will stop the mixture from reaching the throttle bodies. I had this once on a GS750 and it affect the carbs 1-2 and 3-4 independently.
If you doubt the cylinders to fire at all, gently feel the exhaust pipes for heat. If they're off they will remain cool.

Good luck, Marco.

[marcovandevelde]

Got worse after knocking over the bike? Could be that the floatneedles are stuck but that ''accidently'' would have happened to two carbs at the same time.

Marco.

[Anonymous]

I should have thought to mention this before. I have checked the pipes after rides. The #1 will get a little bit warm, but not nearly to the heat of #3 and #4. #2 is usually a little cooler than #1. My guess is that #2 isn't doing anything, while #1 is the one that's trying to fire and is providing the coughing and backfiring. The backfiring only started after my bike was knocked over. I wish I'd studied the plugs and exhaust closer before then to tell if there were any differences.

What's the best method of testing for plugging (I assume you mean by a bubble or something)? Draining the float bowls? The bike was knocked over on its right side, so I'd assume it'd be easier for bubbles to rise and get stuck in the #1/#2 region. But the plugs seem to get a little moist from the gas (it's not moist from oil). Maybe a partial fuel starvation on that side due to plugging?

Thanks!
--Tyler

[marcovandevelde]

Hi Tyler,
I mean really plugged with dirt. So you take the end of it and blow (sorry) throught it to see if it's free of dirt.

Can be both fuel starvation or getting too much because (one of) the carbs flood. Take the carbs off and take off the floatbowls, remove the float and check the needles. Any grooves on them are no good. Should move freely too.

Marco.

[shortlid]

Don't want to hijack but not worth a re-post!

My '80 GS850 is doing the same thing only with JUST the #1 cyl. I found it dark black with a corrosion crusty type deposit on the elctrode ground? All other plugs looked like NEW!! All are NGK's instaled at the same time. The bike runs great has recently had a carb rebuild and fully synced!! The compresion readings are 145 #1, 160 #2, 150 #3, and 140 #4 the bike has 32k on it. What you guys think this crusty corrosion looking deposit could be. If it was grounding out the plug could it casue the fouling?

[SqDancerLynn1]

I would sugest a carb cleaning. The BS vacuum carbs are very susitable to junk in the fuel system & getting pluged

[shortlid]

What?

As I stated in my '80 GS850G I recently had the carbs COMPLETELY cleaned, rebuilt, and synced. I also have a high quality inline fuel filter after the petcock.

[Anonymous]

My carbs were fully cleaned a little under a year ago and I've been riding constantly since then. I guess it's possible that they're gunked up, but I'd hope not.

I just checked the exhaust pipes again, and weirdly enough, the #2 pipe was hot on the last two rides. The plug remains fouled though. #1 was cold. So somehow, #1 isn't firing and #2 is running rich or something? Is that right? I'm about to try cleaning the air filter and draining the float bowls to see if I can find anything there. Any other suggestions?

Thanks,
--Tyler

[Anonymous]

Ok, I drained the float bowls for #1 and #4, since the others were much more difficult to get to. Both had the same level of fuel and filled again at the same rate when the engine was turned on briefly, meaning that gas is getting to the bowls. There were some very fine particles of rust (I assume) that came out as well. Does that mean definite carb cleaning time? or can I use some sort of additive to clean them out or something? I really don't want to have to pull those things off again for a long while.

Just for fun, I looked at the #1 and #2 plugs again. Both are still black, but #2 is a much deeper black. The black coating seems much more consistant on that one, and perhaps thicker.

--Tyler

[SqDancerLynn1]

Take the carbs off & clean the bad carbs You shouldn't need major disassembly. JUst remove the jets & spray some carb cleaned thru them. Double check the float level If it is too high It would run rich also