Bowl levels are the same, sooooo.....

[flyingace]

Sounds like you are inferring that there is no gas mixture getting to cylinder #1. I can't think of another way that a plug would look like new. That would mean you are running on three cylinders, and it would run like SHI*. I have to ask the same question as Keith - can you tell if it's running on all 4? If not, disconnect plug wire #1 and see if it runs any different.

[Scud]

Like I mentioned in two previous posts....exhaust port #1 DOES get warm after one to two minutes of starting, to me this would mean that there is some sort of heat being generated via the spark plug igniting an air fuel mix and then pushing it out the exhaust pipe....right????

The thing is is that she does not run like SH.., she purrs

Scud

[flyingace]

Sorry I can't help. I can't wrap my mind around a plug that looks like it never fired with an engine that purrs. But there are far more knowledgeable GSers than me in this forum, so don't give up.

Ace.

[KEITH KRAUSE]

Well, I'll just wait for the results after swapping #1 lead with #4. That will narrow it down.

[Scud]

Thanks Keith, that will be tomorrow more then likely.

Scud

[Scud]

ok....just took a fifty miler and looked at the plugs, #1 still looks as though I just took it out of the box.

I swapped lcoil leads on #4 with #1 and vice versa...hmmmm.......#4 looks good.

Must be an air leak huh....

Looking on the outside of the #1 carb I did notice a little oily substance, kinda dark......

Sorry....just had dinner, went out afterwards and clamped down the boot between the carb and intake manifold then ran her for ten minutes in neutral, figured that would make some carbon and lo and behold......it did not....the plug still looks as though it came out of the box.


Well..what do you guys think??

Scud

[KEITH KRAUSE]

Well, your description of what happened with the 1/4 plug lead swap would suggest the spark is good.
That would leave carburetion and compression in that cylinder as possible problems.
I don't know. I don't know how a plug can fire, even weakly or not all the time, and leave no carbon on at least the outer rim of the plug. We all know a cylinder can run so lean that the insulator can stay white and clean looking, but no carbon anywhere? Defies logic. A cylinder not firing WOULD pass raw fuel through and the plug would stay new looking, but you would have to smell and see fuel out the exhaust too. You would also get some good, irregular backfiring because some of the excess fuel would "stick" to the header walls and eventually fire, causing the backfire.
And of course, the bike would run bad.

[Scud]

Thanks Keith, I guess I will have closer look at the boots and maybe tear into the carb again (hate doin that..) then let you all know what I find out.

By the way...what would a compression test tell me about this condition in the #1 cylinder?

Scud

[KEITH KRAUSE]

If a compression test shows low compression at #1, then combustion will be poor in that cylinder. Poor combustion means the mixture won't be exploding correctly and you lose power in that cylinder.
I still think that with some firing (you say the pipe warms up) that there would be at least a little carbon, but I suppose it's possible that all the raw, unburned fuel passing through could "scour" the plug and keep it looking clean/new? Very poor compression could cause this.

[Scud]

Keith, there was what looked like a very slight discoloration and I mean very slight around the rim with a few light brown spots. When I removed the plug there was a slight fuel smell.

Scud

[Anonymous]

Your problem comes from one of three issues. Some have already been explored some.

First - No spark. Swap 1&4 and see if problem moves to #4 (already done) but also remove #1 plug and then put it in cap and hold electrode about 1/16" away from cylinder. Turn engine over and observe spark jump. If you see one, move to step #2.

Second. No Fuel. I think you have BS34 Mikunis on your bike? I think these have a screw on the bowl that opens the drain. Back screw out and see if there is gas in the bowl. I think you have already done this so if there is gas, go to step #3.

Third. NO COMPRESSION - This can be caused by either bent or very burned valves, a holed piston or a broken ring. Whichever is the case will require disassembly of the top end for further assessment of the problem. Buy a press fit compression gauge from an autoparts store. They are about $30. Warm engine. Remove Plugs. Hold gauge so that rubber tip seats in plug hole and turn engine over with throttle held WIDE OPEN. If you don't hold throttle open, compression readings will be lower than they should. You may need to crank engine several times. Once you have the max reading, do other cylinders, in turn. A cylinder with the bad things I covered will have close to zero compression, depending on which one and how bad. With no compression, there will be no combustion.

Oh yeah, as far as rich and lean. Rich air/fuel mixtures will leave carbon deposits in your combustion chamber. They will form on the piston crown as well as the valves. Eventually the valves will have seat problems and any pinging will cause the valves to pit where carbon deposits have formed. Too rich is BAD. Lean causes more complete but much hotter combustion. Too hot and you will run into a gamut of problems.

Which discolor pipes? Well, most GS bikes use either factory or OEM 4 into 1 pipes that are single walled mild steel that is chromed. ANY air/fuel mixture and the pipes will eventually discolor in the header area. Lean will cause the discoloration faster because of the greater heat. Some bluing is normal and bluing comes after the pipes get a slight gold tinge. If bluing continues more than a foot down the pipes, this is an indication of lean.

[Scud]

George,

Thanks so much for the in depth diagnosis/problem solving text. I will look into a compression tester tomorrow ( I live in Droggs, Idaho...one auto parts store..may have to go to Rexburg and get one).

I will look for spark with the plug removed.

I did drain fuel bowl and it has gas, same amount as others actually.

None of my pipes are blue or gold, they are all still silver, no discoloration at all..hmm. I have the factory exhaust.

Thanks again,

Scud

[Scud]

I took a digital photo of the #1 plug and would like to post it for all to see but I do not know how to do it, anyone care to tell me so I can share this phenomenon?

Thanks in advance,

Scud

[steve4mc]

Yes but she runs good.

I keep coming back to your comment that she runs good. If you were getting no gas such that No 1 wasn't firing, it would drastically affect your performance. The same with no spark or weak spark. If it purrs at idle, does it still have all the power it should have? Personally, I would give my left you-know-what for a plug that looks new after 200 miles. Mine foul so bad, I end up putting new ones in after 500 miles. Maybe You should be content and ride like the wind.

[Scud]

Steve,

You know what? you are right, I should be content, but......I am a perfectionist unfortunately. I am worried about holing a piston but my exhaust pipes still look like new and she indeed purrs, in fact she fires right up after one-half a second after the starter button has been pushed, no choke when it is 90 degrees outside and with choke when it is colder outside. Sounds normal and like a dream does'nt it.

Then why does one plug look like new and the others tan or slightly on the dark side???? and should I be a worry wart about this.

I so wish to put this photo on this website...someone let me know the way and I will shed a lot of light on this subject for all to see.

Scud