Condensor issue...?

[Alan G]

My VH500 will not run properly. It starts but will not pick up revs cleanly and is not rideable the way it is. I thought it was carb related, but even a new replacement has not changed how it responds.

So.... if it has fuel and air, and has compression, but doesn't run correctly it must be the ignition.

Is there a simple way to check out the condensor and/or the magneto? I do also have a BSA A10 and a Matchless G5 that I could swap parts on if they were compatible- but I certainly don't want to end up with three non working bikes...

Most obvious first step to me would be to swap the condesor from one of my other bikes and see if that fixes things. Is that something I can do? Are they compatible? Any risk involved (such as frying a good condenser? )

[Mick D]

Hi

It sounds more like a timing issue in that the timing isn't advancing as the revs rise. Does your bike have manual or auto advance, is it free to operate, does it operate?

What magneto is fitted? the symptoms you describe are unlikely to be caused by a dodgy condenser.

Regards Mick

[Roger Gwynn]

If the mag has not been re-wound in living memory I would advise doing that anyway, which will include replacing the condenser. An old mag may give a healthy spark in the air but on a warm engine under compression it can be a different matter. My mag packed up this year but would still start and run well for 2-3 miles, then became increasingly erratic until it refused to move. Usual condenser symptoms are weak spark, sparking at the points and a reluctance to start when warm. I agree with Mick, the problem is more likely ignition timing or possibly valve timing. Always look at the last job you did, the operator is the biggest nut on the bike.

[Alan G]

The last job was head off, carb off strip and clean, new pushrod seals and back together again. So I agree - bit of a coincidence for it to be electrical when it was OK before the strip down.

but... what could I have messed up? I assumed I had somehow damaged the carb, although I cannot see how. But fitted a new carb which should be very close to spot on - accepting some fine tuning may be required expecting everything to be fine again.

The ignition timing seems fine - with a manual advance/retard lever on full advance it can kick back trying to start, retarded slightly it starts easily.
If the valves were miles out, and too tight, it wouldn't start easily.... surely?

Could the pushrods be binding on the new seals or something that stops the valves timing correctly when revs rise...? seems unlikely, didn't notice anything when reassembling.

The reason I had the head off was a massive oil leak - oil everywhere after riding - and it turned out to be coming from a pushrod seal. I repeatedly used brake cleaner to remove the excess oil and am wondering if this has allowed oil to migrate into the electrical components resulting in what I now have. But it starts easily....

[Julian Murphy]

I dont think that the condenser in a magneto is a readily changeable item, compared to a condenser in a coil and points sparked engine.

I believe its 'buried' in the windings.

I could be wrong though. Just ask the wife

[Mick D]

Hi

Is the engine just not accelerating when you open the throttle, is the timing fully advanced when it does this?

Are there any other symptoms, spitting back, will accelerate slowly, etc.

Regards Mick

[Alan G]

engine starts with a couple of kicks
engine running - at tickover all sounds well.
open the throttle it dies and stops.
open the throttle slowly and carefully the revs will build - but this is so slow and careful that it would be impossible to ride away.
no spitting back. Can't accelerate away as getting rolling would be a challenge.

Is there anyway to test the magneto/condenser (condensor?) in situ?

There is no battery connected - but I understand it is not needed with a magneto.

[Roger Gwynn]

Do you have compression? You should be able to stand on the kick starter and the engine to slowly turn. The condenser is inside the armature. battery not needed. Certainly sounds like compression or carb problem, less likely to be carb as you have tried a different one and I assume the symptoms didn't change.

[will_curry]

Being something of a miser, I'd try the plug cap first, followed by the plug itself.

If this doesn't sort things out you need a spark tester. I have a small length of
clear petrol pipe with HT lead pushed in both ends until the leads almost touch.
Connect one bit of HT lead to the mag and the other to the plug. As long as the
gap isn't too big the spark will jump the gap and be visible. Start the bike and there
should be a jolly firework display of sparks in the pipe. Open the throttle. If the
sparks stop the mag is the likely culprit. If it is the mag you'll need an expert
to sort it if it isn't the pickup or the points.

[Alan G]

Thanks Will - excellent idea. It has had a new plug and cap - but I can make fireworks display tube and see what happens.

Roger - yes, plenty compression... and yes, does feel like a carb problem, but.....