No spark(?) over 2k RMP

[maciek336]

Hello!

I've joined the GS-tribe a few weeks ago and as a new owner, decided to make some standard maintenance - oil, filters, plugs, carb cleaning and syncing. Yesterday I went for a ride and something strange happened - suddenly it lost about half the power. Aaaand it came back again. And so on. There was about 5s of nonworking and one sec of working all the way back to home (luckily only about 5km). My guess is that the spark is going missing (after it ran for a while at home I noticed dark petrol-smelling liquid blowing off an exhaust after said no-spark periods). Have you ever had an issue like this? My guesses are:
-signal generator malfunctioning after it gets hot;
-one of the coils came loose
-wires from/to coils came loose

I would really appreciate any help!

[J_Walker]

hmmm? switch sparkplugs see if that fixes anything, or "moves it around" do the easiest things first.

[mr72]

-signal generator malfunctioning after it gets hot;
-one of the coils came loose
-wires from/to coils came loose

Logically speaking, none of these issues manifest at 2K rpm and heal below 2K rpm.

You sure it's RPMs and not load or throttle related? Does it run above 2K rpm on the center stand in neutral?

How do you get underway at all if it won't run above 2K rpm?

Maybe clarify the problem here.

However I'd say the problem, whatever it turns out the symptom is, is most likely low float level and you are running out of fuel under load. The next most likely is for whatever reason the slides are not coming up (at least one carb) maybe due to damage to the diaphragm or some carb assembly error that results in the slide not coming up so you never can open the main jet. My money is on one of these two issues and not ignition.

[maciek336]

@mr72, that totally makes sense. It didn't stall over 2k, one of the cylinders was working intermittently, thats why I was able to make it back. I'll check fuel levels after the ride tommorow. Maybe I failed to aknowledge that I broken/misadjusted something and searched for fault anywhere else. That would also explain why it idled fine, but after increasing RPM/load it was starving for fuel and why it needed some time to develop. I'll report tommorow, thanks

[maciek336]

I just checked, float level in right carb is about 1,5-2mm lower than in left one (left one is spot on - on level with gasket). I'll rectify it now and check if it helped my issue.

[mr72]

Doubt that's it. While you have it apart, I'd suggest taking the tops off of the carbs and verify the diaphragms are in perfect condition and the slides move up and down as expected.

It's fairly easy to get the needle, spring, circlip, etc. installed in the wrong order or get the spring mangled up a little bit and screw it up. It's also easy to get the top of the carb put on in a way that pinches the diaphragm. It's super easy to get carb cleaner on the diaphragm and make holes in it or melt part of it. It's also very easy to lose one or both of the tiny o-rings that go beneath the vacuum ports on the diaphragm covers or not put the caps back on them and wind up with a debilitating vacuum leak (on Mk1 carbs...). Any of these things would cause something like the behavior you describe.

[maciek336]

Thanks for the tips. I've checked everything and it seems fine. I've also enriched the mixture (turned the screw out 1/2 turns and moved the needle one notch up) because tips of the plugs were too pale. Fuel levels are now equal. I'll take it for a spin tomorrow and report back

[maciek336]

oooooookay, after yesterday's fixes everything seems fine Today I rode for twice if not trice as long as two days ago and everything seemed in perfect order. Acceleration was smooth across whole rev range and idle was stable at ~1200 RPM. Maybe I've dun goofed before and reassembled carbs the wrong way. I've also applied some percussive maintenance to coils and signal generator's connections - just in case. Anyways, thanks for help!

[mr72]

Probably was the low float causing the problem. Could be that in the process of disassembling to fix you also fixed some other things just by redoing the reassembly. It's useless to try and pinpoint what the cause was when it's a solved problem .