Old fart bike conked out

[daytona-supersport]

Well it finally happened. Riding my 1950 350 Matchless in the pishing rain on Saturday and it was going great, stomking along really nicely. Stopped of at Thrapston services after a run to Bedford, thinking I'll just top off the tank and head off to a café at Wansford for some fodder. Topped up the tank, went in to pay, came out, went to start the bike and zip, nothing, diddly squat. I was stunned, this puppy normally goes if you so much as give it a funny look and half a kick. It is super reliable.
OK, it must be poorly. So out with the plug, fine, big fat spark from the Lucas competition mag. Hmm, OK, fuel, plug not wet so drop out the main and pilot jets. Nope, both clear and clean. Just to be sure, I checked the tappet clearances just to be certain that all was correct, a bit tight so a quick adjust, only a tad. Good compression. SO, Fuel - check, Compression - check, Sparks - check. All good.
The sodding thing won't go. A couple of guys, (one a Matchless owner), double checked my work and they agreed all good.
In the end I gave up and called home for a lift to fetch my trailer. After a trip by car back home to get the trailer, then fetching the bike in the pishing rain, I was pissed of and soggy. Not a clue as to the problem was with the bike.

Sunday morning I went into the garage to start pulling things apart to find what the hell was going on. Or rather not going on. Gave the bike an investigative kick. The bloody thing started first kick. Ah, maybe it only happens when the motor is good and hot. So went out for a ride in traffic. Stopped, started fine. Then went for a good thrash, well as good as a 350 old bike can be thrashed. stopped, started fine.
Current state is that the bike is running great. I did just to be sure check the carb, jets, tappets and sparks again and found nothing wrong.

Come on guys, I know some of you are in the trade and well past your yoof. Have you ever come across this before? Any ideas what the heck is going on?
I have my own thoughts but would be interested to hear yours. The carb is an Amal Monoblock with open short bell mouth, Mag is Lucas Wader Comp version. Ignition timing checked, manual A/R. Only recent work was a rebore, but this was some time and about 200 miles ago. Loads of compression, You can stand on the kick start.

The bike is the one in my picture / avatar thingy.

[Scott_rider]

Does it have a battery? If so, maybe it has a dodgy 'earth' ?

[daytona-supersport]

Does it have a battery? If so, maybe it has a dodgy 'earth' ?

Nope. Wrong answer. Battery not needed as the bike runs a separate magneto. For an alternator bike you would be in the right ball park though.

The clue I think is in the first and final paragraphs. But I could well be wrong. I often am.

[halfpint]

water .in some where and your thoughts ,electric problem was there a spark at the road side ?.water in the float bowl!

[viince]

probably was pi--ed of at going out in the rain :whistle:
should treat the old ones with more respect :laugh: (thumbs)

cheers vince

[Paul_XRV750]

Fuel tap?

[sohoeasy]

Some years ago,my old man was trying to bump me on my Norton 500 for the start of a club race at Brands.I missed the start of the race and after a load of head shratchin' I discovered he's forgotten to remove a rag from the bell mouth. If your bike was fine then nothing at all,could it have maybe been big old autumn leaf lodged in the bell mouth that my have just blown out once the bike had dried out ?

[daytona-supersport]

water .in some where and your thoughts ,electric problem was there a spark at the road side ?.water in the float bowl!

No water showing in the carb, the float bowl empties when the main jet cover is removed on the Monoblock carb. Plenty of fuel gushing out when the tap is opened with the carb jet cover removed. Float checked and operating fine. Nothing blocking the carb.

Got to admit that you guys are coming up with good answers. Not quite in line with my ideas but getting there.

Hi Vince. The old fart bikes get ridden as intended, I have no respect for their age and expect them to have improved with time. :unsure:

[catcitrus]

One thing you didn't mention was whether the fuel was getting through to the float bowl? Also I take it that the cut out button was not earthing as you had a good spark? I've had an odd problem with a monoblock where the brass insert for the float needle was "loose"--and moved occasionally cutting off the fuel supply. Additionally is the slip ring smooth and not stepped--when worn a kickback can break the brushes off. I suppose its also worth checking that the brush is free in its holder and making good contact.
To sum up it sounds like a fuel problem--float needle or tank breather/cap. If rain had been getting in the tank and then down the fuel line (it sits at the bottom of the tank) it can flow through in globs and once collected in the bottom of the float bowl will stop it dead . Years ago I had an MZ 250 and in the poring rain would stop every 50 miles or so--out with the screwdriver, drain the float bowl--and away again. Let us know the "fix".

[viince]

Hi Vince. The old fart bikes get ridden as intended, I have no respect for their age and expect them to have improved with time. :unsure:

my sentiments exactly (thumbs)
my trident has had what needs doing
and now it is going to get used rain or shine/salt :sick:

cheers vince (thumbs)