Poor starting when hot

[Muzzleloader]

Hi.

My 1962 650cc Gold Flash is very  difficult to start when hot and the kill switch will only cut out one cylinder. Have Checked cut out switch, wiring and magneto end cap and centre connection.

Starts cold easily and runs really smooth and plenty of power with no misfiring.

Comments greatly appreciated

Muzz

[muskrat]

G'day Muzz, long time no see.
I'm no xpert on magies but that sounds very strange only cutting out one side. Could you be getting pre-ignition on one side making it "run on"? Could be a combination of timing/fuel & bias.
Cheers.
ps: Give us a clue as to here your located.

[Muzzleloader]

Location Herefordshire uk

[trevinoz]

Have a look at the earthing brush for the stopping problem.
The hot starting issue could very well be a failing capacitor.

[muskrat]

G'day Muzz.
Thanks mate, you now have a flag.
Trev is most likely right but why would it only cut one side?
Cheers

[Muzzleloader]

Thanks for the replies.  I have checked the carbon brush and continuity is good. I think an overhaul  of the magneto is a good starting point.  Will update at some point.
Ride safe wherever you are located

Muzz

[Triton Thrasher]

Did you really check the earth brush and not the kill switch brush?

Some earth brushes are under a screwed-on holder, like this:

[trevinoz]

I have had engines only cutting one cylinder.
It was the earth brush, maybe it was only contacting the armature in a limited area.
Usually the armatures have a distinct hollow in one spot which needs to be machined out.

[muskrat]

G'day Fellas.
I remember my first problem with the A7 back in '81. She would start and run great but I couldn't stop her. Never had a Lucas magged bike before. Lucky the local library had a Lucas book. Yep that brush was gone.
Cheers

[Worty]

Just to pick up this thread.

My Flash has become a pig to start when hot.  Fine when cold with no issues, but doesn't take too long to start spitting and backfiring on right hand pot.  Took 40 mins to get it started when I filled up, but then ran ok for the next 100m with a few spitting and hesitancy moments.  Was one moment when I thought it might pack up altogether, but it ran through it and I got home fine (didn't stop).  Am I in for a maggy rebuild (hasn't been done since I owned it and I don't know if it's ever been done)?  Earth brush looks fine, plugs and leads are fine - what do you all reckon?

One other quick question, what size are the front spindle clamp bolts and the mudguard studs on the lower fork leg.

Cheers all.

[Triton Thrasher]

Have you already seen to all the service items?

[muskrat]

G'day worty.
As TT suggests 1st give it all a good service.
Tappet clearance is the first thing I'd check. Then carb mixture, cold likes a rich mix hot doesn't. Then it's the maggy.
Cheers

[Worty]

Cheers guys.

So, plugs new, HT leads new with no frayed ends, earth brush and pickups cleaned and good condition, slip ring cleaned, points contact cleaned and dressed with correct gap.

Tappets have just been adjusted, I run 10 on inlet and 16 exhaust for max power (according to the handbook).

It does run a tad rich, always has and hasn't played up until now. 

I'm really keen on keeping right on top of everything I can think of.  Past posts have suggested fuel evaporation in the carb, but I did tickle it a bit with this in mind.  I guess this wouldn't make it spit and backfire occasionally when on the road.  It does generally seem better at higher speeds.

It was a very hot day here, around 30C and I'd just given it a 60m blast??  Funny how it fired up after 40 mins and even ticked over nicely.

[muskrat]

G'day worty.
Give it another two thou on the inlet.
Cheers

[Worty]

Cheers Musky - so 12 and 16 - what'll that do performance wise?