Running problems

[tomo]

I guess this should be posted in the technical section, but not sure under which heading it would go. Took Gessie 2 out for a spin a couple of weeks back, bike was running great so must admit the last few miles I opened her up for a bit of "spirited riding". On the way back she started to run a bit rough, felt like maybe one pot was not firing. Next day fired her up again and still running rough, checked the pipes and nos 1 & 3 were cold, 2 & 4 hot. Checked the spark plugs and they did spark ok, if maybe a tad weak. Cleaned them up and fired the bike up again and seemed to be ok now, went for a short ride and all was well. Few days later tried to start her up and she was a pig, eventually fired up but running rough again although all the pipes warmed up. Strange thing though, when the starter button pressed, noticed the front LH indicator glowed. Tried to start her again tonight and same thing, she fired up but ran rough and eventually cut out. Bit puzzled, my first thoughts were maybe a coil out, maybe a condensor for pots 1 & 3, but seems to be firing on all 4, just rough as hell. Wondered about fuel too, if maybe a sticking float would be a possible culprit. The glowing indicator maybe couple of worn wires touching somewhere ?. Did wonder about timing which I have`nt had the chance to check yet. Could thrashing the bike have caused the cam chain to jump a tooth if maybe the tensioner was not functioning. The bike is a 1978 GS750. Not had the chance to check too much yet, bloody cold outside and my garage lights have decided to take a Christmas break !. Any thoughts or suggestions appreciated as unsure where to start looking first !.

[salty_monk]

You seem to be looking in all the right places.... Did you check the HT leads? Sometimes they crack and "leak" spark to the head. Are they stock? I had it with some Dyna that had worked a bit loose from the coil once. You couldn't see it. When it got hot they would drop the cylinder and eventually spark eroded the terminal...

Maybe also have some funky Earth stuff going on... both the ignition circuit for coils & the indicators are powered off the Orange or Orange white from memory and that bike doesn't have many fuses so maybe something going on there.

Most fuel issues are electrical once the carbs have been sorted out (or so says experience here). Good luck!

[Redman]

Hum, with mention of weak ignition, a possible suspect could be charging voltage. So check voltage at battery at mid-rpms.
But you didnt say anything about slow cranking, so maybe voltage okay at battery, so also check voltage at the coils (org/wht wire & ground.)

[tomo]

Thanks guys, I will check those leads and earths. Think the charging system is ok as battery ok and she cranks over fast. Hopefully will put on my detective`s hat and take a look this week-end if I can sort out the garage lights first, also got a leak in the roof now too !. Before I got married I would have just wheeled the bike into the house, but those days are long gone !

[Hanlon]

I would swing the other direction actually in my own way. I have had float valve assemblies stick and it was causing a misfire, and I had clogged caburetor parts and cleaned up all gaskets and whatnot. That may actually help, especially if you know its firing and you have spark. Goodluck.