VB600 starting issues

[MarkO]

Gents

VB600 has always been a bit of a swine to start so looking for illumination. Essentially it is a 1951 (I think!) alloy head in a rigid rear 1946 frame but with teles at the front with a 276 carb. It should be an easy starter, but has always given bother starting when cold. First kick start when hot. It runs very well otherwise. In the light of which, over the past few weeks I have done the following...

Cleaned out the carb. Blown and poked through all orifices, especially idle passageways. All seemed well.
Carefully re-timed it. Sounds fine.
Done valve clearances. All seem OK.
New non resistant plug cap.
New Lodge plug - the 3 electrode thing - pretty sure it is the right Lodge plug. Do we prefer other plug makes perhaps?
Fresh oil.
Cleaned HT pick up at mag end.
Cleaned contacts and reset gap.

Starting drill is as follows

Open petcock. Wait a few seconds for carb to fill
Tickle carb.
Raise ex. lifter.
Give a few kicks to prime carb.
Air valve to about 1/2 closed. I do fiddle about a bit with it but it seems to make little difference.
Close ex lifter.
Find TDC.
Set to about 1/3 retard.
Open lifter and take over TDC.
Close lifter and kick hard.
Sometimes also give it a bit of throttle on the final kick.

Repeat many times......

It often catches then dies, and often huffs through the carb.

Couple of things

It feels as if there is too much resistance when kicking with the lifter closed. Far more so that with other similar bikes and this is supposed to be a low compression SV! One thought is that I am not generating enough rotation to get the mag to spark. What causes this resistance? It definitely reduces when kicking the bike when hot. I don't have a particularly weak foot either. It does get a damn good kick! Too much retard/advance perhaps? Flooding?

Secondly, I am fiddling about with the pilot air screw. On other bikes, where this is set does make a wee bit of difference to starting. At present it is 1 and 1/2 out...

Thoughts welcome

Cheers
Mark

[simon.holyfield]

What do we know about the magneto's rebuild history?

[MarkO]

Mag - According to PO, rebuilt a couple of years before I got it @ 2014 or so. I have had mag problems on other bikes showing either no spark or a very weak one when bare HT lead is about 5mm from the block. VB looks OK from this regard

[SteveShone]

How much are you tickling the carb? Since getting two Ariels recently - one a 1937 500 OHV the second a 51 (52 spec) VB600 (the ex-Sam Larkman 260,000 mile one) I have found that they are both particularly prone to flooding unlike my other bikes. Curiously the chap that restored it, the late Arthur Hodgkins made repeated mention in his diary of the rebuild to always having difficulty starting it. I can only put this down to the slight downdraught of the carb. Any excess fuel must run straight down the inlet manifold. In fact I do not use the choke at all on my other bikes - they seem happy getting a good gobfull of juice and a firm prod to be away.
I think Ive cracked it now with the Ariels by tickling the carb for no more that a second or two once it's had time to fill, fully close the choke (closing it half way is pointless as the slide won't drop below the level of the throttle slide so will have no effect on air flow), leave the throttle closed or very nearly closed, ease it over compression as tyouve described, and usually they'll both fire up first kick.
Perhaps your 'few priming kicks' are helping to flood the engine - Ive only found that necessary on my 1926 AJS and 1916 Triumph H but their carbs are a lot differrent.

Steve

[Roger Gwynn]

The problem is unlikely to be the mag if it is starting well when hot unless you are re-starting straight after stopping. If it is reluctant to start when left for 5 minutes when hot then you have mag trouble.
I agree that priming kicks are unlikely to help.
I find that all my Ariels require slightly different starting techniques that will alter slightly after a rebuild so do try full throttle, no throttle, a little throttle. Rarely do I find retarding the ignition or choke helpful but they can help.
Check the fuel level in the carb, should be just level with the top of the big nut on the bottom of the mixing chamber.
Mixture screw adjustment is about right.
Is the jet block tight in the body or does it fall out?
Keep looking, don't give up 'cos when they work they are great to ride.

[Mick D]

Hi

I'd suggest doing your 'priming' kicks before you tickle the carb, you may be expelling all the rich, (tickled), fuel during your priming. I don't use the air slide at all until the engine fires, then I adjust to a point where the engine is happy to self sustain without blipping the throttle, then open in stages as the engine warms up, (no longer than a couple of minutes).

Increased resistance when cold will be due to the oil being more viscous, (sticky), and the running clearances in the engine being generally smaller when cold, nothing to worry about.

Regards Mick

[MarkO]

Gents

My thanks for all the useful replies

Agreed about the mag. I think it is OK.....
Choke - it does not seem to make much difference where it is. I'll try fully closed as a starting point.
I'll experiment with not using priming kicks and giving it no tickle or hardly any.
Jet block is tight

Agreed that it is a fine machine when riding. A continuous 50+ mph in top up a long steep hill yesterday.

Just for my education please. How does the fuel level in the carb affect things? ....and if it does need adjusting how is that achieved?

[simon.holyfield]

Basically the higher the float is, the more easily fuel is drawn from the needle jet. Therefore, the higher the fuel level, the richer the mixture will be.

Assuming you float is not leaking and that it's correctly fitted to the needle, you can lower the fuel level a little with a thicker washer above the float bowl banjo. I use a Dowty washer on my W/NG.

Incidentally, on my W/NG using the choke on anything but the coldest days will prevent it starting; it needs the briefest of tickles. Any more will prevent it starting, but get the technique right and it's a first kick starter every time. I don't use priming kicks.

[MarkO]

Simon

Thanks for the illumination. One more thing if I may. I does invariably fire up very briefly - a couple of bangs - then dies. Any idea what causes this....choke setting? More tickle/fuel needed?

[Mick D]

Hi

If you are getting a couple of bangs and then nothing it sounds like it's fuel limiting. Go with what you're doing and try increasing the throttle opening, (I use about 1/8th), or increase the tickle time, (you are tickling until fuel is evident at the tickler aren't you?). If it fires with an 1/8th open throttle, try to sustain it by opening the throttle a little.

Regards Mick