Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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tippi11
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Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by tippi11 »

Hello all,
I have to come back to the topic “can a faulty capacitor affect affect spark quality" dated Jun 17.
I changed the capacitor but still face the same problem: it fires once or twice after I didn’t touch the bike for hours/nights (you can really hear that the engine wants to run, but misses something after a few revs). Kick-starting again for several times leaves the engine dead. I can reproduce this situation every day. The carb intake portion is quite wet from fuel, so is the needle guide and throttle valve/slide. Is it possible that the fuel level in the float chamber is too high and as a result the engine suffers from a far too rich mixture after a few revs? I believe the spark plug is wet, but it is hard to identify for sure. My theory is that the fuel (wet carb intake) evaporates over hours or night time and then, for the very first kick-start after this break, the mixture is good enough to fire for milliseconds.
What do you think? Thank you very much, Peter
56G80S
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by 56G80S »

HI Peter

At the risk of being irritating (as ever) your earlier post says it's a G3 but it's not safe to assume that it has the usual carb. It would probably be helpful to know which carb is fitted. This could help people to give instructions on checking the float level, if that's appropriate.

In the earlier post there are several suggestions made but it would be useful to know which ones you followed up on and which ones you didn't.

Good luck.

JohnnyB
SPRIDDLER
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by SPRIDDLER »

You've probably already done so but my first and really simple step would be to fit a new sparkling plug, Champion N5C preferably.
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Which taken at the flood............'
tippi11
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by tippi11 »

Hello,
I am sorry that I have missed to provide this info: carb is a Amal Monobloc 376/5, all jets and throttle valve according to manual. Regarding suggestions: Replaced the capacitor and checked the sr1 magneto internal wiring as well as the HT lead and yes, I have a spark (spark plug removed from head); same mystery when I temporarily used the spark plug from my Enfield. I am on the way to the garage to check ignition timing again. There is an automatic advance/retard unit fitted which seems to be okay (no previous problems start and drive situtions). I think/hope this unit will not influence ignition timing during kick-start since it is at very low revs.
Regards, Peter
Mick D
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by Mick D »

Hi

It does sound like your carb could be flooding - if you turn on the fuel and leave the bike on the centre stand does fuel drip out of the bellmouth after a little while? if so you have a leaking float valve or a stuck/punctured float which need attention.

Regards Mick
Groily
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by Groily »

Carb problems don't usually stop an engine dead while it's running, the way you described it at the beginning of the original thread, unless something actually comes adrift (like the main jet unscrews, the needle clip drops off, the float gets jammed down, or something). But they certainly can cause starting trouble, no doubt about that. So I agree with Mick you need to check the carb to be sure it's all where it's meant to be, the pilot jet isn't bunged up and that the float needle is working properly to maintain a reasonably correct level. (And the air slide (choke) is working correctly if one is fitted.)

If you hadn't had that 'failure to continue' I'd certainly agree the carb was the most likely cause of all this (given that you have had sparks apparently all along) . . . but I'm wavering a bit.
If carb checks throw up no visible fault, then I think you are quite right to be checking the basic ignition timing hasn't slipped. It can happen. Slippage there, even if the auto advance unit seems to be properly on its taper, would quite possibly cause the odd 'crash bang' you describe as you try to persuade it to go, and would also - ref my bafflement as to why the thing died when it was running well - stop the engine dead in its tracks on the road as it happened.

But hey, there are always a good few maybes with these things, so it has to be a case of 'one thing at a time' until you find what's gone pearshaped!
tippi11
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Re: Ongoing start problems (re topic can a faulty capacitor affect spark quality)

Post by tippi11 »

Mick D and Groily,
Thank you very much - I will follow your suggestions tomorrow or on Monday, please stay with me ...
Regards, Peter
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