How to baffle the Rocketman?

[Guest]

OK so life is not so rosie in Rocket-Land....but I'm sure not terminal.....
Just got my bike ('82 GS850L) back from the mechanic again, and can't really figure out why a cold cylinder/header moves from place to place randomly. Two weeks ago, cylinder 4 gave out, then switched to #3; back to #4, and today to #1! I've had the carbs removed 5 times now. Rebuilt from scratch twice. Screens checked out clean; needle valves fine; slides work great; no holes or leaks in diaphragms; carbs synched twice; vacuum perfect; compression perfect. Just replaced Fuel petcock with OEM from Suzuki and new vacuum and fuel lines. Absolutley no intake or exhaust leaks of any kind. You know the rest of the history: new plugs, wires, caps, coils, pickup, etc, etc. Virtually eliminated all electrical & ignition possibilities by replacing every component. Thought it might be a fuel issue so replaced petcock as advised. Getting plenty of good, strong spark in all 4 cylinders; dropped 4 carb bowls, and getting plenty of fuel into each. Plugs are between tan and white, and mixture finally seems right-not too wet, not too dry. Just doesn't seem to be firing in one cylinder, randomly changing which one. The dead cylinder isn't cold to the touch, but all other 3 headers will burn my skin instantly, and the dead one is basically luke warm. Why then after I pick the bike up and go ride home for 1/2 hour at a steady non-stop 60-70 mph, do I end up driving on 3 cylinders the first time I come to a stop? Running on choke has no effect, nor does switching petcock from run to reserve or prime (for a short time). Acceleration is a little piggy on 3 cylinders until I get back up to speed, and then she smooths out again until I come to the next stop. No stalling at stops, but definitely that "idling on 3 cylinders crappy feeeling and sound). Then I bring it back to the mechanic, he does some more stuff, says its fine, come pick it up, and on the way home, I'm riding on 3 different cylinders? This is too weird, and the mechanic is a reputable old timer, who's not even charging me for all these repeat visits, and is making it his mission to find the cause of my problems. I hate to ask you guys again for the BILLIONTH time, but any ideas? I've done everything you've suggested between June and last week (within reason). Looking forward to your responses (again)..........
Larry

[SqDancerLynn1]

I would put some SEA FOAM cleaner in the gas tank & ride it 20-25 miles & recheck it. If you still have problems take a close look at the intake boots & O-rings

[txironhead]

I'd replace ALL of the wiring related to the coils, and sand the coil mounting spots until they're shiny. If that doesn't work, there's always a good priest......

[49er]

A good priest is hard to find. I agree with Lynn. Recheck your intake boots and airbox for air leaks. By the sound of it, you've got several leaks. An ignition fault is unlikely to cause a cylinder to run cold at idle, and then run correctly higher in the rev range.

[txironhead]

I agree a good priest is hard to find, just like an honest lawyer.

When all else fails, put one of those ride bells on it and your problems will be solved.

Are you sure you don't have a stray Harley part mucking things up? Does it ever sit close enough to a Harley to pick up a virus?

Maybe some Theraflu in the tank.....

[Mike Curtis]

I had basically the same problem it would switch from cylinder 2 & 4 while messing with it I noticed a pick up in RPM's by moving #4 plug wire the cure was the connector at the coil to the wiring harness was very loose and when I moved the plug wire it would make contact and run on all four and when I went riding the vibrations was loosen the connector.

[Rocketman]

Coil connections will be reverified, but I'm almost sure its not the problem. Sea Foam in the tank couldn't hurt, but I've been through dozens of tanks of gas since the bike came out of storage in June, had the tank almost empty when we replaced the petcock, and had the carbs taken apart and cleaned on several occassions, so any crap should have been blown out by now, but certainly worth a try. Intake boots and airbox were sprayed with WD40 and absolutley no change in RPM's. Confusion is, if it was always the same cylinder might be able to narrow it down. Jumping from cylinder to cylinder is the confusing part. Priests and bells will not help at this point, and I think we've about used up all of them on this site just this riding season alone!

[Dave8338]

Rocketman: Are the o-rings and or intake boots original or have they been replaced? It sounds like you have an air leak somewhere. This pattern of fire/misfire brings back some very testy memories to say the least. I tried the WD-40 and had no luck with it. Though it may not be suggested, I found mine with starting fluid and the spray tip and straw from the WD-40 can. I would give it another complete check from air box cover to the head, all connections, fittings, clamps, sync screws, ect. I'm sure you know the routine by now.

If the electricals all check out and there are no air leaks, you have ruled out two of the three necessities and it can only be a fuel issue, ie. idle circuit. Though I never got the T-shirt, I've been there.

[Rocketman]

I really appreciate your advice. The boots on the air box side and the engine side and o-rings are original but are in nice pliable condition. Even if there was an air leak (which I've already checked numerous times) , I can't imagine how this would cause an inermittent combustion problem that migrates randomly from one cylinder to the other. It seems to me, it would constantly affect the one cylinder with the leaky boot, not all 4 randomly. Same holds true for the idle circuit; assuming the carbs have been torn down and rebuilt and cleaned numerous times, including blowing compressed air through the fuel line to almost force fuel injection into the carbs, and blowing out any specks of residual crap, and then cleaned out again, why the heck does the cold header keep moving form one place to another? It's odd that I never have any wet plugs either. You would think after riding for a while on 3 cylinders, that the 4th non-running cylinder would be soaked, but its not. And its not like I'm dropping a cylinder only at idle when I stop; its just that's the time I notice it, and on acceleration after that.

[txironhead]

You've probably already checked this, but are you sure that your calibration inlets on the carb boots are sealing properly?

[Dave8338]

I know what you mean...It just doesn't seem right, lack of a wet plug. When I was working through this problem, the "warm to the touch pipe" was too warm to be caused by heat transfer, but not even close to the others that were firing at the time. I concluded that, and could hear from time to time, the weak cylinder fire slightly, sometimes a pop in the exhaust or slight increase in the RPM's for just a split second. This would explain the "DRY" plug mystery (at least in my mind).

These bikes seem to be set to run on the least possible fuel mixture with the stock jets, needle settings and filter box, as was their mission when they had to beat the emissions standards set back in the late seventies and early eighties. It also explains the excellent fuel economy that a stock GS has. Any deviation in the air/fuel mixture seems to send these bikes into tail spin, leaving their owners frustrated and eventually, the bikes get put at the back of the garrage, waiting for one of the lucky few to discover them. I consider myself lucky to now own a 6500 mile bone stock one!

You may want to bump the jet needles one notch up. I had to do this to get the 650 to run flawlessly without having a slight, very slight flat spot in the midrange. If your pilot jets are stock, or stock size, I'd try the jet needle bump up. Though the idle circuit is seperate, in theory, they all work together to keep things in check. Just a few thoughts...

Dave

[Dave8338]

As a side note, the fact that your plug reads are always dry, suggests that you're fuel mixture to the cylinders is right on the edge of lean.

[Billyboy]

"The power of CHRIST compells you!"

[Tarbash 27]

Have you done a compression test on this bike or any valve adjustments?

[REDDY]

The only variables in this story are IGN and FUEL. Something is MOVING. I had the same problem with my hot rod VW. It turned out to be IGN. The electronic ign (replaces points) was intermittant. I fought this SOB for two months before I finally went back to the old points. Problem solved. The dry plugs were what kept throwing me off. Apparently I was getting enough spark to keep the plugs dry but not enough to run properly.
The needle jets are also suspect. There is a lot of room for trash to move about in there.