Misfire on a gt750L

[oldbiker]

So there I was, overtaking a lorry on the M1 when there was a drop in power. So I passed the lorry ok and continued to the next exit nr Leicester.
Drawing to a stop, the bike was running fine. Good stable tickover. No unusual noises. I start off again and a pronounced hesitation on one or more of the cylinders.
Anyway, I crept home and thought it would be a simple matter to fix...............

New set of plugs made no difference.
Switched the coils & plug caps for a known good set. No difference. Still the same misfire.

Took it for a short run and pulled the plug caps off one at a time. It turned out to be the r/h cylinder with the fault. At least it ran ok on the other 2 cylinders

At home, checked the points. And the r/h points were stiff. Changed the r/h points with a spare nos one........ set up the timing and went for a quick run............ no difference. Still the same misfire. But still idles fine.

Decided to go thru the pain for taking the carbs off. No split in the rubber of the rh carb. It looks clean with no bits in the float bowl.

I also checked if there is a continuity issue somewhere from the r/h points to the coils, but sofar it "seems ok". Zero resistance from the pints to the upper wiring loom.

Before I pull the r/h carb apart further, I thought I would ask if there is anything else worth checking??.

I have had this bike years and It's been fine for most of the time.

Ta
OB

[mick 63]

Hi OB , could it be a condenser ? or maybe still a points issue on the pot ? , mine did the same went on 1 pot on a run back from wales got me home on 2 pots , it would tickover nice but as soon as i set off it was missing and went on to 2 pots , a new set of points cured it , cheers Mick.

[teazer]

test for spark on the right pot before stripping the carbs. You could use a strobe type timing light and see if it has a steady flash. Or take the plug out and lay it on the head ( the bike's, not yours...) and see if it sparks when you fire the bike up. If not, remove the plug cap and cut the HT lead back by 1/4 inch and lay that against the motor and see if it now sparks when the motor spins over.

if you still have no sign of electrical life, it's time to check all the electrical connectors and wires to see what's wrong. It might be a corroded terminal or broken wire.

On the other hand, yes minister, if you have signs of steady electrical activity, then move to plan B and strip the carbs.

[oldbiker]

Hi OB , could it be a condenser ?

Yup, It turned out to be the condenser. Late last night I realised it's the only thing not changed. So I took one off the gt550. Its the same part number and today put it on the gt750. Bingo.

Not had a condenser fail before on any bike. Cheap to fix. And there was me thinking its a spark plug gone duff.

Ta
Nairb

[mick 63]

Glad you got to the bottom of it .