Hot Starting

Information relating to the Matchless G12 or AJS Model 31 650cc twin
MalcW
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Hot Starting

Post by MalcW »

Hi

I went out on a run with some friends yesterday. Starting from cold in the garage was fine, as was the start after a 10-ish mile run and a break for about an hour for a Toby breakfast. Then another 30 or so miles for a coffee stop. Again, no problem in starting afterwards. On the way home, one of the other bikes had a very minor problem; for the couple of minutes that took to get sorted mine sat ticking over sweetly, then ran fine the rest of the way home. No more that 10 minutes after getting there, I realised I needed to pop back out. Would the bike start again? No chance! I obviously upset it by not doing something exactly right, and that was it. I did check for sparks, which were fine, and I only had the magneto professionally rebuilt about 1000 miles ago, so I'm reasonably confident in that. Any tips, to avoid future embarassment, and possible leg damage?

Malc
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Rob Harknett
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Re: Hot Starting

Post by Rob Harknett »

Is this the 1960 31? If you have a good spark at the plug, the bike should start. All it needs is petrol. Don't fear the worst. Quick check. Just take the bottom nut off the carb mixing chamber. Look to see you have nothing in the nut like a water bubble and no muck. Turn the petrol tap on and flood it. If petrol flow is OK Check the float has not stuck.
Andy51
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Re: Hot Starting

Post by Andy51 »

Hi, don't know much about twins but is the carb insulated from heat? I had a a G80 years ago that had a metal spacer twixt carb and cylinder head, with only the thin gaskets for insulation. All the others
I have known had the Tufnell spacer - is something similar available for twins? If it starts easily once it cools down, that may be your problem. Andy
MalcW
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Re: Hot Starting

Post by MalcW »

Hi Chaps

Thanks for the replies so far.

Rob, that's definitely worth checking, though it seems strange that it was running very sweetly up to the point of turning it off. Andy, it does have a tufnell, or similar, spacer. I must admit I did wonder about the possibility of a vapour lock or similar affecting the fuelling once it was turned off, was hot, and with no airflow or vibration to help. Rob's suggestion might well clear that.

Malc
bitza
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Re: Hot Starting

Post by bitza »

Check fuel thro the carb , crap in pilot jet, vent hole in tank filler cap, if it's a magneto possible condenser, do the simple checks first.
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1608
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Re: Hot Starting

Post by 1608 »

Twin should have a 1/4" tufnel spacer. One cause of difficult hot starting is too rich mixture.
Mick D
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Re: Hot Starting

Post by Mick D »

Hi

Have you tried starting it since it has cooled down? Did it start?

You say you have sparks, did you check the plugs? were they wet or dry?

Regards Mick
oldandsmelly
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Re: Hot Starting

Post by oldandsmelly »

My Model 31 starts brilliant stone cold or hot but can sometimes be a tricksy piglet when it's somewhere in-between. For me, it's definitely fuel related. Opening both petrol taps and closing the air lever seems to help but I've come to accept the occasional embarrassment when out riding with mates that if left for just the wrong amount of time I'll need to give the kickstart lever a lot of work. When it does fire up, it goes fine as if there was no need to fuss.
MalcW
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Re: Hot Starting

Post by MalcW »

Hi

Mick, the plugs weren't wet as such, but I didn't expect them to be, as they were far to hot to touch without gloves. They did smell a bit petrolly (I don't think that's a real word) though. It has certainly started well since then.

Bruce, I might try the two taps/choke trick, to see what happens. I am coming round to the decision that the bike was tired, was tucked back up in the garage and just didn't want to go back out. Laziness, basically.

Malc
Mick D
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Re: Hot Starting

Post by Mick D »

Hi Malc

If it's starting OK now I think you just hit that 'difficult' point - when mine is reluctant to fire I find the slightest tickle gets it going.

Regards Mick
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