AJS & Matchless Owners Club

Hi, Can anybody help with this ? I can't get my G5 to start easily or run smoothly. I've dismantled the carburettor, cleaned it thoroughly, set the needle at the centre notch and reassembled with all new washers setting the pilot jet air screw at a nominal 1 1/2 turns out. I've set the ignition timing as prescribed with piston at 1/4 inch BTDC and bob weights held open (using trick offered by the ever helpful John Bolton) and points just opening. It will start with choke (briefly) and run, but not smoothly and tends to cut out and the plug then looks wet as thought I've flooded it. One thing I have fitted is an air cleaner and I'm wondering if that is causing a problem. The bike came to me as a non runner with just a small bell housing on the carb.
Any ideas please before I go mad !?
Cheers, John

Carb float setting maybe? Dependent on carb type, can you test with short piece of transparent pipe?
There'll be an article explaining somewhere I'm sure.

Or maybe it's just sticky

Your story sounds familiar. 3 yrs ago I bought a G5 none runner with a claimed head gasket problem, in a way it was. I first of all replaced the carb which was for a 500cc bike and oversized. Took the head off and fitted new gasket "nipping up" the bolt next to head oil feed, which had been recut to M8 helicoil. The engine would run but not for long and oil was getting into the cylinder. I wont dribble on about a long list of things I tried in a fruitless quest to find the problem, crankcase oil, porous wall etc. You will find the whole story of you search vigo, oil in cylinder.
Anyway I had to seek help, a blow to my pride indeed. The head was not out of true and did not need skimming. After the copper gasket was correctly annealed and the 5th bolt pulled up more than nip up the bike is running great and has done 270mls.
So if you think it's oil in the cylinder and not fuel..........

Thanks Andy, I'm quite sure the carb float is OK, but I'll check it anyway.

Thanks vigo, but the plug is wet with fuel and I'm not seeing any smoke at all from the exhaust due to oil in the cylinder.

bike63 wrote: ↑Mon May 29, 2023 11:08 am It will start with choke (briefly) and run, but not smoothly and tends to cut out and the plug then looks wet as thought I've flooded it. One thing I have fitted is an air cleaner and I'm wondering if that is causing a problem.

What sort of filter is it? If it's just a coarse wire mesh/grille type for posing at the caff and preventing small children from getting sucked in it probably isn't the filter causing the problem but manuals specify a smaller main jet for carbs fitted with the more restrictive felt or dense wire wool filters.

The bike came to me as a non runner with just a small bell housing on the carb.

Although the main jet doesn't do much until above half throttle a filter will restrict all air flow and richen the mixture at all throttle settings. it's easy enough to check by trying it with the filter removed.

Thanks Spriddler, obvious I suppose and I should have thought of it ... have removed the filter and it runs a lot better and starts more easily from hot.

John

bike63 wrote: ↑Sun Jun 04, 2023 11:15 am Thanks Spriddler, obvious I suppose and I should have thought of it ... .

Happens to most/all of us, John, when trying to sort issues and we are too close to the wood to see the trees.
Fingers crossed.