Plugs fouling quickly, similar to Risccas post

[gwhunran]

I recently aquired a 79 GS1000L. Whenever I first bought it, it would miss or run rough at about midrange between shifts. At low rpms and high rpms ran okay. Took it to the shop (Brickhouse Cycles in Norfolk). They said I needed bigger jets as I had pods, and high flow exhaust (MAC 4 to 2). They put in bigger main jets 120's, I think it had 112.5's in it before. I got it out of the shop, it ran better but backfired some. After a couple of days, I took out the plugs and they were fouled, mostly dry, black. Put in new plugs and for a few days ran PERFECT, lots of power, no backfires. Then it started running a little rough, again around mid-range rpms, low and high rpms okay. Removed the plugs, again same fouling. I took it back to the shop and they put in 117.5 jets, (no additonal charge). I took the bike home and cleaned the plugs. Haven't had a chance to ride it since to find out if it helped. I don't smell gas with petcock turned to on. If I leave it on prime, the whole garage will smell strong of gas in a very short time. Do you think the 117.5 jets are about right. I have no idea what size pilot jets are installed.

[KEITH KRAUSE]

Don't leave the petcock on prime. It's only for when the carb bowls are dry and you need to fill them before starting. Very good chance you now have fuel in the crankcase. Change the oil/filter.
As for your problem/test results, it's all about throttle position.
If your dark plugs are the result of typical riding conditions, some freeway/steady cruising/city riding, then you need to pay attention to the jet needle adjustment.
For an accurate test, if you can do so safely, mark the throttle housing and grip and ride the bike at 1/3 throttle for a mile and chop the bike off and read the plugs. Do what the performance/plugs say. The jet needle controls fuel mixture from about 1/5 throttle to 3/4 , with overlap effect before 1/5. The jet needles have an adjustable e-clip to determine needle height. Your VM carbs should also be vacuum synched whenever the jet needles are disturbed. Also, remove the two floatbowl vent lines and leave the ports open to breath.
Changing mains will only effect 3/4 to wide open throttle, which I doubt is where you've been testing so far, at least on a regular basis.

[gwhunran]

reply to Keith Krause

I have only left the petcock on once and got the gas smell in the garage and some gas did leak onto the top of the starter area. I don't believe any gas got into the crankcase, if it did I have no indication of it.

I have talked to the mechanic that worked on the bike since posting the original message. He says that he thinks the carbs that are on the bike are not the originals. I will attempt to find some numbers on them and try to figure out what bike they may have come off of. I won't get a chance to look today. So, finding out what carbs I have is probably the first step to getting answers about my current problem with the fouled plugs.

Thanks for the help. I am really impressed with this site and the amount of good information available.

Richard[/quote]

[KEITH KRAUSE]

If stock, your carbs will be identical to my '79 GS1000E.
If you like, go to my website and view the close ups of my carbs. Note the bowls also, just in case someone's installed 29 smoothbores or whatever on your bike.
Just click the WWW symbol at the bottom of my post.

[duaneage]

YOu might have needle valves in the carbs hanging open. This would cause the float level to rise up very high so even when driving it it would run rich. you would have plenty of wide open throttle power since that drains the carbs better.

Does it smoke at idle? has it been sitting long? Remember, you cannot tune out a problem caused by dirt in the carb.

[gwhunran]

More info

Does not smoke at idle and person I bought the bike from says that he had been driving it regularly. The only work he mentioned being done recently was: new starter, and new battery, and new tires.

I read on another GS Resource post about the idle. The MC starts and idles without using the choke now. Before it went into the shop it required at least a four or five minute choked warm-up before it would idle unchoked. The bike had the same rough running mid-range before going to the shop, but its better now, just not perfect. And I really don't know if it had fouled plugs before it went to the shop, as I had not looked at them.

I sent pictures of the carbs to Kevin through his website, as I have no way of posting them. I hope that he is able to tell if they are stock or not.

Thanks again for the assistance.

Richard

[duaneage]

When it is chilly out like now a few minutes of choke sitting still is normal. not so normal is running without any choke when cold, sounds like it is too rich or you have a leak somewhere. Check the airbox boots and all the seals there. Check al the carb boots for tight clamps and no cracks. Were the carbs synced? Check the sync port screws and make sure they are tight enough.

[gwhunran]

Don't have an airbox. Mech said I had no leaks and the carbs were synced. Not sure about the sync port screws.

[duaneage]

Don't have an airbox. Mech said I had no leaks and the carbs were synced. Not sure about the sync port screws.

Does not matter what he told you, check em. With the bike running spray a little wd-40 or carb cleaner on the boots and see if the idle changes.

[KEITH KRAUSE]

Ok. I saw your pic's and you have the stock VM26 carbs.
First of all, remove the two float bowl vent lines and leave the ports open if you haven't already.
The 120 mains you have are "ballpark" for those Emgo type pods and that pipe. The rich plugs are most likely not because of the mains. As I said before, the mains only control 3/4 to full throttle, so you would have to be riding around at those throttle positions on a constant basis to blame the mains.
You say slower speeds seem Ok too. The mid-range is the problem. This is most likely the jet needle circuit that's giving you the rich reads. The pilot circuit may also be helping with the problem and we'll focus on that.
For your pilot circuit, your pilot jets should be #15. The pilot fuel screws (underneath and engine side of bowls) are sensitive and may need adjusting. For your mods, try 1 1/4 to 1 1/2 turns out to start. Then adjust the side air screws using the highest rpm method AFTER adjusting the pilot fuel screws. Your bike should idle well, cold and hot, at about 1,000/1,100 rpm. Keep a record of all adjustments. Test and get reads at minimal throttle position.
As for the jet needles, you must test at a solid 1/3 throttle and see what the performance/plug reads say to do. If the reads are rich at this throttle position, we'll tell you what to try. Your needles may be set too rich or even missing some spacers, a common mistake by PO's.
You can test for the mains at full throttle. 120's are probably close or even right, but you should test.
A poor/weak spark can act like a rich condition.
I suggest before making these adjustments/tests that you check the ignition timing and spark quality. Make sure the mechanical advancer is operating correctly with a gun and give it some spray lube. If you have the stock points, their dwell (gap) must be correct and the point surfaces free of dirt, corrosion or pitting. They must also contact each other squarely. You should get a decent blue spark in a dark area. I also suggest cleaning the plug cap connections and the terminals at the coils and the battery posts. Be sure your plugs are B8ES if NGK and gapped correctly.
I'd really like plug reads of all three jetting circuits. Minimal throttle, 1/3 and wide open. Even though you say only the mid-range seems a problem, you may see rich reads at all positions which could also mean your floats have been set wrong or you have some varnished/dirty carbs.
A good carb synch is also necessary for best performance.

[Cajun Cycler]

Keith if he has a 79L model with the original petcock he has no prime on it. FYI

[Cajun Cycler]

Re: reply to Keith Krause

I have only left the petcock on once and got the gas smell in the garage and some gas did leak onto the top of the starter area. I don't believe any gas got into the crankcase, if it did I have no indication of it.

I have talked to the mechanic that worked on the bike since posting the original message. He says that he thinks the carbs that are on the bike are not the originals. I will attempt to find some numbers on them and try to figure out what bike they may have come off of. I won't get a chance to look today. So, finding out what carbs I have is probably the first step to getting answers about my current problem with the fouled plugs.

Thanks for the help. I am really impressed with this site and the amount of good information available.

Richard

[/quote] If you do have a GS1000L model with the original petcock you have no prime on it. It will have only the on and reserve function. If it is leaking gas that means the diaphragm is shot. I have tried finding replacement diaphragms for this model and it is pretty close to hopeless. I ended up buying a replacement petcock instead. It was about $65 a few years ago.

[gwhunran]

edit previous post

Should have said " I have only left the petcock on "prime" once by mistake. The petcock has three positions 1. On- all the way clockwise, pointing forward towards the direction of travel. 2. Reserve- straight down towards the ground. 3. Prime- towards the rear, at my six o'clock.
I don't know if this part is stock or not but it seems to work okay. I don't have the ability to post pictures but I would be happy to email pics.

I am still having problems. Trying to verify that I have no problems with my points/condensers. If no problems there then its back to the carbs.

I haven't figured out yet how to do the spark chop safely. I live in Virginia Beach and traffic is pretty thick everywhere. I am assuming that I will have to use multiple clean spark plugs pulling one of the four out by going slow, holding the clutch coming to a stop, pulling the plug and looking at its condition. Then going med speed, clutching to a stop, then pulling plug, looking at its condition. Then going fast, clutching, coming to stop, checking plug. Obviously replacing the pulled plug with clean one between runs.

Thanks for the help.

Richard

[KEITH KRAUSE]

So are you saying you can't go on a ride somewhere where it's safe to test at high speeds?
Unless you can Dyno the bike, there's no other way to test the performance or the plugs.
Because the carbs are probably not vacuum synched well, reading just one plug isn't good enough. All four plugs should be checked. Unless the bike is running rich on all circuits, you can get reads using the same plugs and get a good idea what each circuit is doing. I've never had a problem re-jetting using one set of plugs. Even if I nearly foul a plug, the corrected jetting will burn it clean/improve the spark at the next test. This of course assumes all other things I mentioned before have been checked and are good.
I like to do the 1/3 throttle test first. Then the full throttle and then the minimal throttle (about 35 mph in 4th gear works.)
I go a good mile on both high speed tests and chop off. Chop off means quickly pull in the clutch lever/close throttle, turn off key and coast to a stop with the lever in. Take a rag and a piece of hose that fits snugly over the plug end to help you remove the hot plugs. Be careful of cross threading when re-installing the plugs. Keep a record of the reads/performance and let us know.
If there's no way to test like this, I suppose you can just ride around normally and chop off as a "substitute test". But this will give you reads where the pilot circuit may be overlapping with the needle circuit, so with no separation you don't really know what to do about re-jetting. With more trial and error you could probably come up with some jetting that would burn well enough during this "normal" riding but your main jet would still be un-tested and I really don't think you should try such a short cut to re-jet. I only mention this because you're worried about testing safely and you need to try something to get the bike running better. You may get away with it and have a bike that runs around town well enough, but I would find a way to test the jetting completely.
Just be sure the motor is completely warmed up (hot) during these tests.

[gwhunran]

Other info

I am still having the mid-range problem but one thing that helped some was to put new points and condensers in. The ones installed were a little pitted and out of adjustment. I will at some point go to an electronic ignition, probably when this set of points starts to misbehave. I will update the post as further experimentation with jetting takes place.
I have been keeping track of mpg and I am only getting about 24 mpg. This seems way low to me.