1957 M16 not running properly

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1957 M16 not running properly

Postby Plugsnpoints » Sat Nov 10, 2018 8:43 pm

Can anyone please advise me on how to sort a problem out. I have recently bought a late '57 M16 (alternator model). It had been laid up for almost 25 years when I bought it. I am just going through bits and pieces before I put a ticket on it.

The first thing I did was to drop the oil out of the tank and sump, and refill it with new straight 40.

I've been through all the electrics and fixed all the dodgy connections, it charges well (recent battery) and all the lights are now working as they should.


I took the 376 carb apart, and cleaned it with carb cleaner, and blew it all out with a compressor. It's spotless inside and out. I have also replaced the float needle as the old one was a bit aged shall we say.


However, it isn't running correctly, and hoped someone might be able to point me in the right direction. It starts easily, and when it warms up it's better but not quite right. Unless I'm really gentle with the throttle it wants to die on low revs, then it behaves itself and revs ok. In other words it doesn't want to pull smoothly, then it's away.

It points to fuel I guess? The pilot jet is clear, and the petrol is getting through ok. I also cleaned the tank out, and replaced all the pipes and both taps. Obviously it has fresh petrol.


I have replaced the points, condenser and plug, and double checked the ignition timing as per the book. I even went out to buy fag papers for the job!


I set the throttle stop and mixture by ear, and the plug isn't sooty or oily.

Today I put it all back together, fired it up in the garage (to annoy the neighbours!) and it's still not 100%. Once you get through the rough bit it's away.

I will fiddle again tomorrow, but any advice would be much appreciated in case I've missed anything. I thought if I asked you nicely someone on here might see the glaringly obvious! :D I dare say I'll sleep on in and it might come to me.

Thanks in advance.

Andy
Last edited by Plugsnpoints on Sun Nov 18, 2018 7:50 pm, edited 1 time in total.

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Re: 1957 M16 not running properly

Postby Expat » Sat Nov 10, 2018 10:33 pm

I’ll get in first then with the most common fixes, (just quoting from what I read here!), try a new spark plug. If that doesn’t fix it, clean the carb properly.

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Re: 1957 M16 not running properly

Postby Mick D » Sun Nov 11, 2018 8:08 am

Hi

It sounds like the pilot jet / orifice or pilot jet by pass orifice is blocked, see items 9, 7 and 8 below:

Mono X Section.png


Full document here:

http://amalcarb.co.uk/downloadfiles/ama ... d_Tips.pdf

If not the above, how much wear do you have between the throttle slide and the carb body?

Regards Mick
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Re: 1957 M16 not running properly

Postby Plugsnpoints » Sun Nov 11, 2018 8:20 am

Hi Mick, thanks for responding so quick. Just for the record I have gapped and fitted a brand new plug. The carb slide doesn't look bad at all, well within tolerances.

I will have the carb off later and have a peep at the bypass orifice, and blow it out. The pilot jet is clear. It could have a bit of crap somewhere as it's been standing so long.


Thanks again,


Andy

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Re: 1957 M16 not running properly

Postby SPRIDDLER » Sun Nov 11, 2018 9:39 am

As said, it sounds like typical Pilot jet blockage/restriction.
Does the engine respond when the jet screw is adjusted - e.g does it falter or speed up?
The typical setting for the Pilot jet screw is near enough one and a half turns out from closed (i.e. from screwed in).
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Re: 1957 M16 not running properly

Postby oldandsmelly » Sun Nov 11, 2018 9:40 am

I had a similar sounding problem on my G80. I found doing three things fixed it; sadly I wasn't very scientific about it and did all three at the same time so I don't know which one made the big difference. What I did was move to a hotter plug (champion N9), clear the bypass holes (mine were misaligned) and finally fit a smaller cutaway slide i.e. moving from a 3 1/2 to a 3.

My bike now runs cleanly on small throttle openings and picks up well when the throttle is opened.

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Re: 1957 M16 not running properly

Postby Rob Harknett » Sun Nov 11, 2018 11:27 am

Well worth double checking the carb parts and settings are correct. As mentioned. Correct Slide, needle position, sticking float needle, I found causes problems. Also main jet cleaning can leave blocked. View the jet hole. It should appear quite clear. If the hole is not clearly outlined, looks a bit misty, its got a bit of fluff in it.

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Re: 1957 M16 not running properly

Postby spookefoote1956 » Sun Nov 11, 2018 1:05 pm

Wynns carb cleaner. Magic
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Re: 1957 M16 not running properly

Postby 1608 » Sun Nov 11, 2018 1:28 pm

It does sound like the pilot jet/circuit, typical symptom is initial throttle opening being non responsive. An easily missed part of the system is the minute drilling in the throat of the carb body directly above the pilot jet and situated just cylinder side of the slide. I appreciate you say you cleaned the carb, but this can sometimes dislodge further debris so worth a second look. Does the bike start easily from hot and cold.

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Re: 1957 M16 not running properly

Postby Plugsnpoints » Sun Nov 11, 2018 2:13 pm

I've just spent all morning on it.

I thought I'd got it sorted when I found the pilot jet partially blocked. Maybe it is still a bit of crap in the carb body. I gently poked a piece of brass wire brush strand where I could, sprayed carb cleaner It fired up up then revved ok. Then it didn't! I've taken the carb off twice, blown it out again. Reset the points gap at 15 thou, set the plug gap at 21 thou according to the book. I also put the needle back to where it was, as I had moved it to position 3. I have double checked the float isn't sticking.


It starts easily hot and cold. Now it won't pick up at all. It dies when the throttle is opened and now and again spits a flame out of the bell mouth. It ticks over nicely though!


Time to walk away from it (it's nice not being a sole form of transport these days!) and have ago another day.


Thanks everyone for your help. I have studied all the replies.

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