Sooty plugs

[a101960]

I have not ridden my bike for a few days. Yesterday I went for a ride and it started first kick from cold, however when I stopped after about fifteen miles or so it was reluctant to restart. When I returned home I checked the plugs and they were very sooty. That has never happened before. Does anyone have any suggestions as to what might have caused this? carb is a monobloc 389, and the petrol in the tank is Tesco 99 octane (The petrol that I always use). Could the float or float needle be at fault here?

John

[alanp]

Assuming that all was well previously, the first thing I'd check would be to see if the float is free and there is no possibilty that it can jam against the lower rib of the chamber due to a small distortion of the float causing unreliable petrol levels. Maybe as a result of an increase in Ethanol in the Tesco petrol? Been there and had to rub down the contact point on the float.
The only other time she wouldn't restart after that mileage run, she was too hot just after a rebuild and too tight as a result.

[Brigadista]

I have the same problem (plunger A7). I've lowered the carb needle to the lowest position but it's still running very rich. I aim to dismantle the carb again and check the state of the needle. I've been told that they are subject to more wear with unleaded fuel. If that isn't the problem, then maybe I'll play around with the jet, though I am very wary of this, as running lean does much more damage.

[gold33]

G'Day John,

That was the first symptom of what turned out to be a disintegrating fibre drive gear on my magneto.
Went from starting first kick to 3rd to 5 or so over a few hundred miles. The first time it gave me grief I pulled the plugs, sooty!
I tried fuel additives, retarded the timing but no answers. Went well once running with an occassional tinny electrical type sound right up until it stopped dead at 70 MPH on the freeway into Sydney

[cus]

G'day John,
If it's happened all of a sudden, maybe have a look at your air intake filter, could need a new element.
My bike always runs a bit rich, it used to run really rich but I dropped the pilot jet down to a 105 I think it was,
the next one down from standard, made a big diff., I use B7es plugs & run 98% fuel, timing 11/32, carby 389,

regards, Cus

[nagrod]

Hi John - I am really shooting from the hip here and my monobloc is on the bike and currently mummified for the winter or I would check first, but my thinking is that there must be a main air bleed, and if this is plugged or blocked somehow it could result in rich running. You can probe the air passages with some material that is softer than the carb body or better yet back flush it with compressed air. I would check all the air passages as the idle system could be a culprit also. Good Luck

Rick