Hi There,

Wierd issue. When driving my 1944 m20 runs fine for a while. ON the wa home on a long slow sloping hil the bike will suddenly shut off as if it ran out of gas. Pull over tickle the gas a few times and starts right up. However in a few minutes on the next hill same thing happens. Check the spark plug at home (included pic) and it seems like the bike is running the correct temp. Have the old original 276 carb on it though. Any ideas please?

https://picasaweb.google.com/115674442219018009194/BsaSparkPlug?authkey=Gv1sRgCND8woW4vanwGw&feat=directlink

email (option): jeff@infinitymedspa.com

also if I replace the carb since half of it is stripped. Can you recommend a newer carb that is cheaper/ or will run better than a new 276 from amal?

email (option): jeff@infinitymedspa.com

If the carb is ok, it should run fine on it, if it runs fine most of the time on the present carburettor I'd suspect the lining in the tank, it may be breaking up (if it has one fitted) and it may cover the tap and cause fuel starvation

email (option): davmax@ntlworld.com

HI,
I would agree with Dave and suspect a fuel feed problem.
I think tickling the carb probably doesn't actually do much. If you sat with the bike and let the carb fill up itself you would get the same effect.
Best thing to do is pull the petrol pipe off at the tap and see what the fuel flow is like.
If weak and weedy then that will be it.
On the flat you are not pulling the revs so it will keep going, but on a hill opening the throttle uses up what is left in the float bowl.
Regards
Clive

email (option): cliveandjo@lineone.net

Have you checked your Winged Tank Top Cap???
If its screwed to tight when the bike is hot will tend to pressure up the tank.
Well does on mine,its original and the tanks not lined.
Even with air hole clear, i tend to back off the wing nut on the tank a turn to allow plenty venting.
Next time you try your bike check your fuel tank wing nut unscrew it a little after a run see if you hear any venting of air...creates pressure vacuum.
Mine does this. Tend to keep it backed off a turn to half a turn.
Some heat comes off these engines and travels upwards to gas tank etc.
Try this,,,,,it happened to me fuel starvation.
If its tight when the heat expands everything also air vent to fuel tank Cap screw.
Open your taps see if there is good flow,if no flow,air hole in tank cap..inspect.
Back off a turn fuel flow.
Strip and check your Tank Cap.

Hi Jeff, it's interesting that you say the bike suddenly shuts down. If it was fuel starvation, I'd expect to hear it pop and cough a few times as the mixture leans. Also, that spark plug looks too black to me. If the engine shuts down suddenly, I'd suspect an ignition problem (maybe something earthing your plug or plug lead or something). I'd certainly try another plug. It might be that the plug is weak and won't run very well under load. Also, do you get the same problem with both fuel taps open?

email (option): dannydefazio@sumpmagazine.com

We've been through this before, but spark plug "reading" is useless unless done in a particular way, i.e., suddenly cut off power to the plug while going on a slight uphill with the throttle wide open. The latter two conditions are easy to satisfy. But cutting off power to the plug on a magneto engine is not that easy. What most end up doing is to simply lift the exhaust valve until the motor stops. This will not give you an accurate reading because it will "soot up" the plug between the time you lift the valve and the time the motor stops. It looks like that's what happenned to this plug. Otherwise, if you've done it correctly, it looks like your mixture is too rich.

Clive: Do you mean there are many times when you ride the M20 at less than full throttle? Amazing! Mine basically has two positions: full on or full off. There just isn't much I can do with, say, 8 horsepower instead of 11 (yes, I know, it's supposed to be 12).

email (option): jonny.rudge@verizon.net

Don't talk down the M20 John..it has a rippling 13 BHP.. ...Ian

email (option): ian@wright52.plus.com

there is more brake horse power in most car startermotors now day

email (option): roger.beck@node6.com

You can do a plug chop fairly easily if you just run the bike with the HT lead resting loose on the plug. On the move, either knock it off with piece of wood, or use your (gloved) hand if you're brave enough. If not, tie a small piece of wood to the (fairly loose) HT lead using a foot of string or something and throw it over the tank on the left side down by your leg. That'll jerk the lead off and cut the power without any risk of a shock. Might need a couple of tries.

Or you can rig up a wire from the HT lead (or plug top) and tie it around your boot or something. Touch that to the engine case and earth it. As long as the current has somewhere better to go, it won't bother you too much. Simple.

email (option): dannydefazio@sumpmagazine.com

These bikes run hot....
Go the simple route first and tick off the obvious.
First check your "Winged Tank Cap" is venting and venting good.
Thats what happened to mine go for a while spurt then stop.
Some quick checks .....tickle of fuel from both taps cracked the Tank Top heard the air rush problem solved,Lack of venting from the cap.
Been ok since just dont over tighten the fuel cap back it off half turn.

I will check the flow tonight. But I am running both taps open.

email (option): jeff@infinitymedspa.com

email (option): jeff@infinitymedspa.com

Have you got a tuffnol spacer between the cylinder and the carb? It is best practice to have one.
Have you made sure the carb flange boltes are tight so there is no air leak causing a weak mixture? An air leah there can cause all sorts of problems

email (option): gasboy@btinternet .com

Jeff, you perhaps need to work out how the hill climbing is involved. Is it just angle? Or load? Or both. I'd prop up the front of the bike and run it for a while with the top of the float chamber removed so I can see if the fuel is flowing, etc. But as I said in an earlier post, if the fuel was being restricted, it should pop and bang as the mixture becomes increasingly lean. Hence my feeling that the problem lies elsewhere. Which means you have to go back to basics and check all the obvious things before thinking laterally. I'd certainly start by changing the plug and see if the problem persists. It might be that the plug won't work under load and breaks down (a common problem). A stopped engine for a few seconds/minutes might be enough to cool the plug to a workable level, especially with a fresh charge of air and fuel.

email (option): dannydefazio@sumpmagazine.com

Danny your a thrill seeker!!
Telling the guy to pull HT cable while driving the bike!
Be a fine ground for the earth,or if you have irregular heart beat..that soon put it back into sink! Or cause an accident!
Though check the obvious,Plug and Fuel supply wing the Fuel tank cap off open both taps slacken the bango on the float if good supply of juice comes out? Yes? No ?
No? you have shit in the tank and your fuel tap filters are gummed up,tank lining check not braking down?
Rule out the Tank Wing Cap that its venting ok especially when motor is hot.
That caught me out!

Graemeyboy, personally I wouldn't even bother pulling the plug lead. I don't think that's going to get anyone anywhere. If the carburation is set up as per the manual, it's unlikely there will be much there to worry about. In any case, the problem seems to happen on hills - but that, I suspect, means under load.

It probably isn't fuel starvation (for the reasons I gave earlier: no popping or banging), so it has to be the plug (assuming it runs okay the rest of the time). But I'd check the timing and points just to rule that out.

I'd go straight for the plug. But if you have to pull it on the move, just be inventive. I can think of various ways to do it without getting zapped. Or get the wife on the back and ask her to help you out. Just make sure she's holding onto the grab rail and not you.

email (option): dannydefazio@sumpmagazine.com

Maybe yours does, Ian. Believe me, when I say mine has 11, I'm talking it UP.

email (option): jonny.rudge@verizon.net

Yeah, it may be a matter of "back to basics." This may not be a fuel problem, the "tickling" may only be giving the plug time to cool off. Is the plug the right heat range? Sorry for being so basic!

email (option): jonny.rudge@verizon.net

i am assuming that pulling the plug lead off is to stop the engine without using the valve lifter if this is the case would not stalling in top gear do the same thing

email (option): roger.beck@node6.com

Roger, not sure what you mean by "stalling in top gear". Just remember to pull in the clutch when the HT lead comes off - and make sure no one is behind you.

email (option): dannydefazio:sumpmagazine.com

ie when stationary putting it into top gear with your foot hard on the rear brake and with no throttle let the clutch slowly and the engine should stop as it is to higher gear to pull away in but i think you want to stop the engine as you are moving along sorry if i confused the issue roger

email (option): roger.beck@node6.com

Thanks Roger, I understand what "stalling" means. I just wondered if you had some other devilish high-speed idea in mind.

email (option): dannydefazio:sumpmagazine.com

email (option): jeff@infinitymedspa.com

A grea idea, but it starts back up immediately. However I have to hold the throttle open as if it is flooded and it starts right up. Whereas a normal start up for me is tckle the carb and catch the throttle as it starts.

email (option): jeff@infinitymedspa.com

Danny DeFazio

Graemeyboy, personally I wouldn't even bother pulling the plug lead. I don't think that's going to get anyone anywhere. If the carburation is set up as per the manual, it's unlikely there will be much there to worry about. In any case, the problem seems to happen on hills - but that, I suspect, means under load.

It probably isn't fuel starvation (for the reasons I gave earlier: no popping or banging), so it has to be the plug (assuming it runs okay the rest of the time). But I'd check the timing and points just to rule that out.

I'd go straight for the plug. But if you have to pull it on the move, just be inventive. I can think of various ways to do it without getting zapped. Or get the wife on the back and ask her to help you out. Just make sure she's holding onto the grab rail and not you.

email (option): jeff@infinitymedspa.com

Jeff, I guess you just have to check everything. Plug, Points. Timing. Carburation. Can't suggest further. But remember; M20s generally have a lot of latitude. They're not usually that sensitive. Therefore, if something is wrong, it's usually significantly wrong.

However, all the "significant events" in a motorcycle engine usually revolve around small measurements (plug gap, points gap, jet size, tappet adjustment, etc). Look for blockages (in the fuel line and the air bleed holes in the carb); look for a sticking carb float; look for a "holed" carb float; look for loose leads and a weak plug, and so on.

Sometimes you just have to live with the problem for a while. The answer often creeps up on you. That's how it works for me, anyway.

Good luck.

email (option): dannydefazio:sumpmagazine.com