Misfire

The GT was brought out to play today, it passed it's MOT on nasty old tyres
with no issues, however it seems to find being legal an issue and has taken
on a misfire on No2 cylinder (pulling the leads off one by one proves this)
the thing is it starts and sounds great but misses when it warms up, pulling
the choke partly out helps and it will then pick up a bit, I am guessing
that it is crap from the tank when it got low that is the culprit, however I
do remember something about enrichening the fuel mixture will hide ignition
issues, but on one cylinder?

Is this a carbs off again or does anyone have any other ideas?

/d

 

It's the inlet manifold. It's old, it's rotten, it's died. The others will
follow. Replace them as a set, and you'll appreciate what the bike used to
be.

 

Although IME a misfire is usually ignition but I'd guess its an airleak
on number 2.

When you say "carbs off _again_ ", what did you do last time?

However this doesn't totally rule out ignition. A failing (when hot)
coil would affect 2+4 (I'm assuming its the normal jap two coil system)
so that's more unlikely.

Try swapping the leads on 2 and 4 over. Does the fault move to No. 4?.
If so look at the lead and cap. Does swapping the plug with another
cylinder have an effect?

 

The bike has a low millage (<21,000) but had stood for over 10 years and had
only been started once in that time so it took a lot of cleaning to get it
started, it seems to be getting better with use and runs well to 3,500 RPM,
then misses, if you pull the choke out slightly it is OK to maybe 5,000 RPM,
after that it is a dog. As it warms up over 10 or 15 miles the idle speeds
up to >2,250 and it smells hot, so I will check the plugs for colour and I
will be swapping leads and coils over to see if I can move the problem,
however I am beggining to think it is a combination of blocked jets and
balence. If that fails I will replace the inlet stubs even though they look
good

The major issue for me is we are of for a European domination tour (well
Jutland and Germany) in 5 weeks and a dead SOB in the wilds of Europe is
never good........

/d