? Rich Running

[RoyC]

Hmmmm. As per a different thread, mine came home on the back of a rope the other week. The problem very clearly seemed to be fuel starvation on mine – I didn’t even pull the plugs to look. Found what I take to be some kind of rubber gland had swollen up in my lever type taps. I’ve re-established flow – drilled one out a bit, replaced the worst one with a brass lever type which simply works on a taper (I think). Not bothered to attempt a restart since though.

Not sure why fuel starvation would make the plugs sooty.

Could it be the dreaded ethanol at work ?

[Black Sheep]

Sounds awfully like a sticky float. With ethanol, some floats expand and catch against the float chamber cover causing intermittent flooding. Have a really good look at the float and float needle - even get new ones. It may well do the trick. 

[Zander]

After the engine rebuild I've found that to get it running in a half decent fashion, it has been necessary to raise the needle the maximum amount to stop it spitting and spluttering at about 25mph.  I've been through the procedure of doing it one notch at a time and then testing it, but this is the best setting so far.   The plugs have always (well, since I've owned the bike) been black / sooty and they still are.  The only thing I've changed on the carb is fitting a new needle jet to stop it eight stroking on the over-run, and that has worked.  Although the last test run was the best so far, I'm not comfortable with the "extreme" setting of the needle.  Any ideas, folks?

[mugwump]

Sounds like very weak or fuel starvation. Presuming its a 389 monobloc have you got the correct slide, needle should be marked 'D'. Check for air leak at the flange. Is the carb flange buckled. Is there a steady flow of fuel. I have always removed the filter is the tap as they tend to block and and can be a messy road side fix. Much easier to clean the banjo filter. Good luck

[Zander]

Thanks, John. It's a 376 carb, and I've ordered a new slide with a smaller cutaway to experiment.  I've had the taps out and the filters were clean, and I checked that the flange is flat. There's also a bias spacer fitted.  As it seems to be running ok at the moment, I'll continue the rides round the block for the time being and see how it goes.

[Triton Thrasher]

After the engine rebuild I've found that to get it running in a half decent fashion, it has been necessary to raise the needle the maximum amount to stop it spitting and spluttering at about 25mph.  I've been through the procedure of doing it one notch at a time and then testing it, but this is the best setting so far.   The plugs have always (well, since I've owned the bike) been black / sooty and they still are.  The only thing I've changed on the carb is fitting a new needle jet to stop it eight stroking on the over-run, and that has worked.  Although the last test run was the best so far, I'm not comfortable with the "extreme" setting of the needle.  Any ideas, folks?

At the sort of throttle position I equate with 25 mph, a richer slide as suggested, or bigger needle jet (if they make bigger ones for the Monobloc), may work better than raising the needle.  Raising the needle may make it too rich at a bigger throttle opening, when you're going fairly fast on the road.

On a twin Concentric setup on another make of 650 twin, I fitted bigger needle jets while chasing an off-overrun hesitation.  The bigger jets caused obvious richness at around 1/8 throttle, but a change from 3 to 3.5 slides, with the bigger needle jet, has the bike running pretty good.

[Zander]

Thanks, TT - advice noted and stored for use in near future.