1950 VB trouble starting

[bevanclark]

Hi folks,
I'm hoping for some troubleshooting guidance as I am not an expert.
Background:
- type 6 ("dripper") carb.
- magneto was professionally rebuilt after being flooded with oil when the return pump failed.
- I have done around 300 miles since then without any problems at all - starting 1st kick, even after having been sitting for a week or two.
- today however was different. Started 2nd kick, rode approx 20 miles to a cafe, bike running perfectly. Day was pretty warm - around 26 C.
- 1/2 hour later, when I went to leave, it was extremely difficult to get running. I initially thought I had flooded it, because it has always been a bit susceptable to this when doing a hot start. But spark plug looked nice and clean and was not wet AT ALL, despite petrol dripping from the bottom of the carb.
- eventually got it to fire up after much kicking, but it would not idle. Rode the 20 miles home at 50 mph with no issues at all. Idled perfectly when I got home. Still a very warm day.
- waited 20 minutes then tried to start it - no joy at all - would not go.

What I have done:
- stripped carb completely - no obvious blockages, pilot/idle circuit seems clear, but it is now soaking in carb cleaner just in case.
- kicked it over in the darkened garage - appears to be a good, healthy spark (albeit that the engine and magneto were then fairly cool).

Obviously, I have yet to reassemble the carb and see if all is well, but I suspect it may still not be.
Also: the carb nuts were a little loose, but the carb seemed well attached. I have just blued the carb flange and found that it is not that flat, so am lapping it - see image.

Would appreciate any guidance/advice on the best next steps.

Cheers,
Bevan

[Brian_Walker]

Had a similar problem with monobloc on my VCH, when I stopped the the carby was bleeding fuel into the engine, a change of a fresh plug and it started straight away. After that I would turn off the the fuel tap whenever I stopped, and problem went away. I now have my GP fitted again with remote float bowl fitted as was easier to set float level with my 13" inlet tract (valve to main jet) I assume you a a 279 or something similar and it may have a bleeding float valve so try the fresh plug next time and see if it starts it may confirm the problem the problem.

[charles.bulloch]

Possibly the magneto needs a new condenser.

[Roger Gwynn]

Typical magneto condenser problem. When your guy fixed it after it flooded with oil I expect that all he did was strip it and clean it as it had already been rebuilt. You don't give a year of your VB, if pre war you may have lost the magnetism during the cleaning of your mag as I have on my SB. The carb flange is flat enough to seal and better than most. If you have other machines try swapping mags, carbs etc it is larger a process of elimination.

[will_curry]

Do you have a heat insulating spacer between the carb and the inlet?

Modern fuels don't seem to like being warmed which is what happens when
you stop after a decent run. Heat from the engine is conducted back into
the carb and the bike won't start until things cool right down again.

Once the magneto gets really poorly the bike will start to cut out at low revs
when the throttle is opened quickly.

[bevanclark]

Thanks for the replies folks.
I was really hoping it was not the magneto at fault. It cost me a lot of money to have it rewound and fitted with a new condenser etc about 5 years ago; then had to be stripped again afer the oil soaking as i said (amazingly, the bike kept running perfectly at the time, even though oil was coming out the points cover !).

It does seem odd that the spark plug was not wet, which is why I wondered if it may have an air leak at the carb flange. Anyway, it is now pretty flat.

There is no room for a spacer, let alone an air filter unfortunately - see attached picture of the bike.

I guess I'll refit things and see if it will behave itself. I do have an MO1L on my 650 Panther which I could swap in I guess, but I was intending to go away on a road trip shortly, so not keen to disable it, but we'll see.

Thanks for your help.
Cheers,
Bevan

[will_curry]

These heat insulators don't have to be that thick - 1/8" phenolic insulator will make a big
difference. Things are obviously getting pretty hot seeing the colour of the exhaust pipe.

That said, it's a very tidy bike.

[bevanclark]

ok thanks. Where might I be able to buy a suitable spacer ? Not sure there'd be anywhere here in N.Z.

I've done almost 3000 miles since importing the bike - the pipe was that colour when i got it and doesn't seem to be worsening, however, you are right of course, that the old girl does run pretty hot ! That's my bike on the cover of Cheval .

I guess I'll swap the mag if all else fails - only takes around 2 min to remove the Panther one (without affecting the timing) since it has an oldham coupling) but the Ariel's one is a bit more of a faff obviously.

Cheers,
Bevan

[will_curry]

It will be worth asking Draganfly I suppose.

I believe the insulators were original fitments on Norton Commandos and late 60's onwards Triumph twins.

Mine came from a local motorcycle dealer many years ago, now long gone unfortunately.

[paul.jameson]

My Red Hunter's mag was rebuilt about 5 years ago and over that time, starting became a little more difficult, then a little more difficult still, etc. Eventually, I took the points out, cleaned them, tightened everything up, set the points to the correct gap then cleaned up the joint between mag pickup and HT lead. Result: Much easier starting, consistently.