summer wearing on....bike running worse

[Guest]

Been working on the bike for a year now. Had it running pretty well a few weeks ago. Replaced the rectifier and wired direct to the stator. Had a carb issue as soon as I put it back together. started missing in left cylinder after I reinstalled the carbs. Done everything I know to do to track down the issue with no success. Thought out might be the coil, so swapped them...now both sides are misfiring. Ran a direct line from pos to the coil before I swapped them. No difference.

Any ideas?

[oldrookie]

A bit more info...

Tested the igniter, seems to be okay. Both plugs fired correctly.

The left cylinder was initially the issue. Replaced the spark plugs and the spark plug boots.

The left plug was coming out sooty black. I reduced the air screw setting and seem to have the fouling out issue corrected.

Haven't done the coil relay mod yet, but did go straight from battery to the suspect coil as a test. Did not make any difference in how it was running.

Ohm test on both coils is good at the connectors and I think okay between the primary and the spark plug caps.

The issues with the spark began after I swapped in a used Shingden R/R and wired the stator directly to it. I also ran a fused link from the POS and NEG on the battery to the R/R.

First time I fired it up after that work I had a fuel leak from the left carb. Took the carbs off and cleaned the left carb (but did not do a full tear down.) The carb appeared spotless. Took it on a longish ride and discovered that left cylinder was not firing correctly. Can pull the plug wire and the bike will keep running. Pull the right off and leave the left on, stalls immediately.

I did get stranded after I did the R/R work, two connectors had failed to hold and the battery drained. Found those corrected that problem.

Seemed to run well except for some surging today, at least once I got into the higher rpms. Most of the misfiring is noticable at lower rpms.

[Big Rich]

I'm curious now too.......

Being that the airbox and exhaust are shared, I would look at the carbs (again) or the valves. You don't have a spare set of carbs, would you?

[oldrookie]

Hey, Big Rich!

Unfortunately no extra carbs.

I can half way understand one coil/sparkplug acting wonky, but I can't figure out why swapping the coil resulted in both acting up.

Looks like I'm staring another carb tear down in the face. I'm going to go back through all the connections in the new R/R wiring job

[Big Rich]

If you want to try any other parts, let me know. I have carbs, coils, ignitor, etc all laying around. Free of charge, of course.

How is the battery itself looking?

[oldrookie]

Generous offer. Thank you.

May get back to you once I think I've got it narrowed down. Right now I need to check everything I did to make sure it isn't as simple as a bad connection.

Did some reading today about surging and apparently some of the GS don't react well to vent tubes being placed incorrectly. Mine are coming off the carbs to the rear and hanging down behind the engine. I know your GR's are heavily modified, but do you remember how the vent tubes were configured in stock form?

The battery seems to be charging correctly. Was between 12.7 and 12.9 at each stop today. Carried my meter with me because I wanted to make sure the R/R was working correctly and not cooking the battery.

[Big Rich]

It should be in the service manual......but I believe they come up and rest on top of the airbox (between the rectangular snorkels).

Being that yours are on the motor, they may have melted?

[oldrookie]

Could hardly believe they were supposed to be over the airbox and terminating next to the battery (fumes near a primary source of spark makes no sense to me,) but you were correct. Manual says to route them over the airbox.

Rerouted them today. No melting evident, but no difference in how it is running either.

Stuck at work longer then anticipated, but will spent some quality time with it this evening.

[Super]

Hey oldrookie...just my 2 cents worth but...when you took off the left plug wire and the bike kept running sounds right, but when you pull the right plug wire and just run it on the left plug wire and it dies...make me think you've got a bad intermittent left coil. With the key word being intermittent.

Have you tried swapping coils yet? Try that. If it doesn't change anything then at least you can eliminate the coils as suspects. I've come to find that the more things I can eliminate from the equation, the better I can find the solution.

Good luck!

[Big Rich]

Aside from the coils, try swapping spark plugs as well. Might be a compounded problem (weak coil and bad plug).

If you do pull the carbs off again, you could try swapping the internals left to right. Maybe the problem will follow a jet?

[oldrookie]

The weirdness continues. I swapped the coils last night and didn't see much difference. Swapped the sparks tonight and it ran well. Same coil and plug that were struggling on the left side are fine on the right. The only symptom tonight was a bit of popping on decelleration.

Only other change was rerouting the carb vent pipes per your earlier post. Did have an issue getting the idle to settle down too.

[Big Rich]

Do the plug readings look identical from left to right? Both being the same "light tan" or whatever........

The problem with a floating idle makes me think air leak, and it could be leaking on one side.

[oldrookie]

The right side is tan-ish. The left side had been black and sooty until tonight when I swapped the plugs. Now it appears to be sort of gray.

I was beginning to think air leak too. I'll be checking the air box seal carefully, but the problem has been largely with left cylinder. What would account for just one cylinder having an issue? Wouldn't an airbox leak affect both cylinders?

The vent tube came off the left carb this morning while I was re-routing it over the air box, but got it back on.

The idle isn't hanging up, (maybe a little, not much though) just wants to idle low while running colder (say 5-8 minutes) and I had to adjust the idle up to keep it above 500 rpm. Set it at 1500 rpm.

Next stop sign, say another 5 minutes, the idle was at 3,000 rpm and I had to adjust it back down. Other than that it ran pretty smoothly-surging was gone.

[Big Rich]

The "swirling port induction" hose, carb mount, airbox to carb boot, choke, etc can all cause issued on one side.

But with the problems being on the left side and that plug being sooty, I don't think you have a carb issue. A weak spark can cause incomplete combustion (and a sooty plug). I haven't been paying much attention lately........when were your valves checked last?

[oldrookie]

Did them a year ago. Probably have less than 1500 miles on the bike since.

I did just notice that the choke is hanging up a bit. Not sure I got the spring assembly put back together correctly when I had the carbs out last week. That might account for running rich.

The former left side coil seems to be working correctly on the right side. I'll check all the air connections again.

Appreciate the advice, Big Rich.