VB600 starting issues

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MarkO
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VB600 starting issues

Post by MarkO »

Blasted thing refuses to start! It is superb when running, but to get it going imperilled my knee and it has now gone on strike. Long story short, there is no spark at the plug when cranked over and when plug is on the block. Not even a glimmer of a spark.

Checked points - set them at 12 thou, pulled them and cleaned them up - they looked fine anyways. Checked everything over - looks fine
Checked HT lead - fine, checked and cleaned pick up/slip ring - also fine. Vey clean ring actually, Brass very good.
Swapped plug - no joy
Checked earths - all good.
Checked for loose wires - can't see anything.

I suspect the mag. It has never started that well and it may have died overnight. The bike is a numb old thing and surely there is not much to go wrong here?

That said, is there anything stupid I could have done when fiddling about with points etc. as above?

Thoughts most welcome. Mag is now off, and I have a pal who can check it out - to eliminate it at least.
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paul.jameson
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Re: VB600 starting issues

Post by paul.jameson »

Take the outer point off by unscrewing the screw which holds it on. Check that the screw underneath it has not come loose so as to hold the points open. This happened to me last year after goodness knows how many thousand trouble free miles beforehand.
Assuming that is ok, replace the point and remove the earth brush to check that it isn't sticking. Its worth wiping the brass ring which the earth brush contacts with clean rag on the end of a rod whilst rotating the armature.
Take off the mag pickup and clean the slip ring inside with a piece of clean rag held in place with your little finger. Rotate the armature gently using the other hand. Your finger will tell you if there is life in the mag! If there is, check the mag pickup brush is free and that the pickup isn't cracked.

If there is no life in the mag, send it for a full overhaul. I use Tony Cooper for this in the UK.
Paul Jameson
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ian williams
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Re: VB600 starting issues

Post by ian williams »

hi Mark ,
when i had trouble with my NH and MO1 magneto i found that the spring on the end of the advance/retard cable was missing and the cam ring wouldnt go back and forth very easily of its own accord thus the advance and retard didnt work properly .
another problem i found was that the points used to close up and i eventually found that the thread holding the inner half of the points in the alloy block was stripped and i couldnt tighten and lock it up , which then meant the points would sloce up pretty much no sooner than id got it going again .

the thread used in the alloy block holding one half of the points in is same as is used in the uk mains wall light and switch etc socket boxes for the screws that hold the covers on , i think 3.5mmx0.6mm , i used one of the brass threaded bosses to adapt to fit and press and loctite into my alloy block and also countersunk and peened it at rear so it held in place when the points locking nut is tightened , i did a little bit of lathe work on the brass boss just to give it a bit of a lip at one end so i could press it in from the back of the alloy block and i drilled the alloy block out to a size suitable for the brass boss but i also put a slight countersink in back of alloy block [only small countersink just to stop the brass from pulling through when points locknut etc is tightened up .

i think the magneto does need a decent grounding connection to the frame though and some frames that are heavily painted may not make contact , i think the mag has a lug for a ground wire connection but many are not fitted with a ground wire , im not sure whether this affects the spark ability of mag though .

one thing to do with a magneto is dont use resistor plugs or caps with them as they dont produce enough energy to operate with them proberly .
for NGK caps its the "long ones" that are resistor caps , the short ones are not .
you probably dont use ngk plug caps but thought id mention about not using any resistor type plugs and caps .

i find it easy to start my NH by just bringing it up to top dead on kickstart and then let it just go past top dead on the decompressor and then you can swing the engine over so easily without much effort , a stark contrast to trying to kick my AJS twin over .

when i start engine i just move my advance lever to full retard and then move it about half advance which is pretty much in line with centre lin of handlebar and with a bit of throttle on kicking it over it usually goes with a kick or two .

i do remember being a plonker one day though and taking the chrome cover off the magneto when i tried starting it and i couldnt get a spark , then i noticed the covers spring arm hanging down and touching the points block , i did lift it up before trying to kick it over but it flooped down and i didnt see it .

hopefully youll find the issue out and it will be sorted .
cheers
ian
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dave.owen
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Re: VB600 starting issues

Post by dave.owen »

Are you sure the carb is working on the pilot circuit, worth stripping and cleaning .
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MarkO
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Re: VB600 starting issues

Post by MarkO »

Gents

Thanks for all the useful replies. The lack of spark turned out to be a poor connection from the HT lead to the little brass chinese hat embedded within the pick up at the mag. The central core wire was just touching (or not) the hat as opposed to being threaded through it and the strands being bent back/soldered. There is now a spark, and testing on a magneto rig with an oscillator, it now appears to be pretty strong, uniform and consistent.

That said, it is still a bit of a swine to start. Timing was redone as the mag was off - so I'm happy with that, I'll also change the plug again. Pretty sure I did the pilot circuit but I'll give it another go. Carb cleaned out not long ago. It wants to go - I get a couple of chuffs and it then dies. Fuel issue perhaps?
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paul.jameson
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Re: VB600 starting issues

Post by paul.jameson »

It will need a tiny bit of throttle as you kick it over to get enough mixture into the cylinder to keep it going.
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simon.holyfield
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Re: VB600 starting issues

Post by simon.holyfield »

dave.owen wrote: Thu May 30, 2024 4:52 pm Are you sure the carb is working on the pilot circuit, worth stripping and cleaning .
Dave
The carb isn't new is it Mark? Our chum Lee Mallabone has had another example of a poorly drilled idle circuit recently.
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Simes

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Re: VB600 starting issues

Post by MarkO »

Yes - I have tried all manner of throttle and A/R settings on start. It does burst into life - eventually, but seems it to be a fine line between starting it and flooding it. One thing I have noticed is that if it does not start after a few kicks, the resistance to the kick start is increased. It then becomes even more difficult as I don't think I am then getting the mag spinning fast enough to generate a decent spark. Is this resistance indicative of flooding? I've also changed the plug to a new NGK B5ES - no discernible difference.

Another thing I have noticed is that the tickler was not allowing fuel through. It was not pressing down on top of the float, thence pushing down the needle and allowing fuel into the carb proper. This would also seem to suggest the float position on the needle was not quite right, even though the small hole in the tangs was located correctly on the needle groove. I simply bent them downwards a little which effectively raises the float up very slightly. Not sure whether this is the cause of my starting woes.....It was definitely getting fuel though regardless.

Carb is original and correct - Amal 276??? can't remember, but a pretty numb thing. I removed the pilot screw and blew it out with comp. air. I have not pulled the carb though. If I recall right, it has a very small pilot outlet hole in the body which can get blocked - though fairly sure it was fine not too long ago. I may pull the carb and take a look....
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paul.jameson
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Re: VB600 starting issues

Post by paul.jameson »

For a magneto ignition bike you need 18 thou gap at the spark plug rather then the 25 thou they are usually set to. You should not use a suppressor cap to connect the HT lead to the spark plug and the HT lead itself needs to be a copper wire one. A final thought is that if you use a non-suppressed plug cap it is quite easy for the screw which goes into the lead to fail to contact the copper wire core of the lead, or to make poor contact. After fitting non-suppressed caps to my plug leads I always check the connection using a multi-meter.
Paul Jameson
35 LG (project), 37 RH500, 52 ex ISDT KHA, 54 KH(A), 75 Healey 1000/4.
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
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MarkO
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Re: VB600 starting issues

Post by MarkO »

Hi Paul

Yes - plug set to 18 thou - I think that came from the workshop manual. No suppressor cap fitted and the cap is a decent new NGK screwed well into the core of the HT lead. I don't think it is now the mag/spark giving rise to starting problems. I did the tappets last night - inlet was slightly open but not by much. Next will be the carb perhaps.

It still wants to go. After a good kick, the engine either chuffs or fires once or twice then dies. Fiddling with throttle and A/R doesn't seem to make much difference.
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