What next.

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
mikeydpippin
Member
Posts: 1102
Joined: Tue Jan 15, 2008 4:18 pm
Location: SOMERSET UK

What next.

Post by mikeydpippin »

Went for a long ride on my 1958 G3ls alternator 350cc 12v today, and after a short run I noticed I started to lose power and just managed to get home.
Checked spark at plug, this was intermittent, and not too good.
Removed lead from points to coil and connected a temp lead from this connection at coil and earthed and had a good spark at plug ( coil okay?) put a temp cable either side of coil and connected to bulb, and after pushing down kickstart the light went on and off.
Changed plug no difference, but did notice spark was weak and sometimetimes had disappeared.
Should I be looking at changing the points and condenser?
Fuel is getting to the plug. Ok.
Not starting still.
Battery full,
I,m guessing coil ok,
plug ok ( as tried a few)
Cleaned points.
Any ideas welcome, was running well before, all I,ve done is refitted the exhaust into cylinder head as it had pulled out.
Had full power for a couple of miles, then started to die slowly.
Carb jets clean.
Thanks in advance.
Mike
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: What next.

Post by Rob Harknett »

You have tried a few plugs?? Does that mean new plugs ? If it means old plugs cleaned then that could be your problem. Cleaning plugs made in the last 40 approx years do not have a glazed central electrode, cleaning damages them so they quickly contaminate.
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: What next.

Post by Mick D »

Hi

I assume from your description that the bike still won't start, even when cold.

First thoughts would be to check the choke lever hasn't rattled closed / slide is still operated by the lever, check nothing is loose or has moved in the points, (back plate / cam etc), confirm ignition timing is correct, confirm valve clearances, replace HT lead / plug cap, replace the capacitor.

Regards Mick
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: What next.

Post by Rob Harknett »

If the bike were a 2 stroke the exhaust could be almost totally blocked. So you would have had to be burning a lot of oil if your exhaust is blocked.
Reynard24
Member
Posts: 362
Joined: Mon Dec 16, 2013 2:27 pm
Location: CAMBRIDGESHIRE UK

Re: What next.

Post by Reynard24 »

I had a not dissimilar problem with my alternator G3 recently when I tried to start it after the winter lay-up. The bike appeared to have a good spark but would not start and would only spit back through the carb and occasionally give an almighty back fire in the exhaust. I checked timing (fully advanced and retarded), cleaned the carb and ensured all jets and drillings were clear, checked tappet clearances replaced the plug, plug cap, coil and condenser each in turn all with the same result.
In desperation I gave up on the methodical approach and replaced the points and condenser with brand new items and checked the spark again - all looked much the same as before but I thought that I might as well see if it would start and to my utter surprise the damned thing started first kick and has continued to do so. 50 miles yesterday without a hitch. Bloody old bikes!
mikeydpippin
Member
Posts: 1102
Joined: Tue Jan 15, 2008 4:18 pm
Location: SOMERSET UK

Re: What next.

Post by mikeydpippin »

Reynard24 wrote:cleaned
Unbelievable, me too,v removed and replaced exhaust system, no blockages, kicked it over and it started, prefer to know why, probably attention seeking lol.
I did notice the exhaust pipe has been cut off inside the silencer only about 3" of holed pipe inside, would that cause some back pressure and the exhaust to keep blowing out of the cylinder head.
I,ve got a nice tight fit in the head since I swaged the end, and fitted with eap5 paste.
Will try her up the road later.
Mike
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: What next.

Post by Rob Harknett »

After a lay up mags get condensation, that needs a good warm up to dry them out. Points need to be cleaned and dry.
mikeydpippin
Member
Posts: 1102
Joined: Tue Jan 15, 2008 4:18 pm
Location: SOMERSET UK

Re: What next.

Post by mikeydpippin »

Took her for a run rode really well for a couple of miles, then here we go again pulling back on acceleration slowly getting worse.
Looks a good seal in exhaust to cylinder head, thought that a slight air leak on that join may be happening.
Jets all clean on carb.
New plug.
Mike
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: What next.

Post by Mick D »

Hi

So it's fair to assume it's heat related.

Capacitor breaking down - valve clearances wrong - starting to seize, what's the oil return like? - mixture too rich, what colour is the plug?

Regards Mick
User avatar
dave16mct
Member
Posts: 3234
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: What next.

Post by dave16mct »

Could be the petrol tap filter in the tank mostly blocked. just enough fuel can get through for a few miles, then it begins to starve. Could also be the breather hole in the fuel cap.
dave.
Locked