G5 Running Rich

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
starfield181
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Joined: Wed Aug 18, 2010 11:56 am
Location: WILTSHIRE UK

G5 Running Rich

Post by starfield181 »

Got my newly acquired G5 MoT'd this week and took it out for its first ride. Mostly things went well, no undue noises from engine or gearbox, all the gears select and stay selected, steered fine and the brakes worked adequately. Actually the tester was quite complimentary about the brakes and the bike as a whole.

The down side is that the bike is running far to rich and its seems to be worst (or at least most obvious) just off tickover. Slowing down you can feel the engine hesitating and pulling away again it hiccups slightly unless you give it a handful. All in all not the most comfortable bike to ride slowly but when pulling hard up hills and suchlike its fine. Setting a reliable tickover is also virtually impossible.

The picture below shows just how wet the exhaust is. It does not burn any oil (no blue smoke anyway) but sometimes it emits black smoke when picking up but not once revving steadily. I have dismantled the carb and everything looks ok, all jets are per the book, slide is correct cutaway and the needle is in the middle notch. I checked the float to make sure it was not puncture and the carb does not flood if the fuel is left on when stationary. I checked the timing and I am pretty sure its correct though once in a while it does kick back when starting.

For the moment I have run out of ideas; wish now I had kept the M14 a bit longer because I could have tried a carb swap. I guess it could be too high a fuel level but not sure how you measure or adjust that with a monobloc. I also keep thinking of that mantra which states that 90% of carb problems are electrical though I don't see how that applies to this problem.

Suggestions welcome

Peter
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Rangy65
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Re: G5 Running Rich

Post by Rangy65 »

Hi i had a similar issue when i first built my G5. As it was my first british bike i got mixed up with the choke so to eliminate this i took air slide out

Sooty running and black smoke poor acceleration fixed.

I then learnt how to set the carb up and which way round the air lever worked!

Sounds simple but when you don't know you don't know.

Might be worth checking.

Cheers
Steve
SPRIDDLER
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Re: G5 Running Rich

Post by SPRIDDLER »

starfield181 wrote:The down side is that the bike is running far to rich and its seems to be worst (or at least most obvious) just off tickover. Slowing down you can feel the engine hesitating and pulling away again it hiccups slightly unless you give it a handful. All in all not the most comfortable bike to ride slowly but when pulling hard up hills and suchlike its fine. Setting a reliable tickover is also virtually impossible.
Sounds like an over-rich pilot jet. The needle should be about 1 and a 1/2 turns open.

You can check the float level by removing the pilot jet cover and attaching a piece of transparent tube from it to beside the float chamber cover. The fuel level (tank tap 'On') should be in line with the dot at the AMAL logo cast on the float chamber cover.
'There is a tide in the affairs of men
Which taken at the flood............'
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Ozmadman
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Re: G5 Running Rich

Post by Ozmadman »

No worries about getting rid of the M14 as the carb is a different bore anyway.

When you dismantled the carb did you remove the jet block? And if you did did you fit a new genuine gasket? If you get a leak there fuel will flood he engine. I couldn't get a reliable tick over on mine due to throttle slide wear.

Eventually I got the carb overhauled by Martyn Bratby who bored the carb body and fitted a brass sleeve to the slide amongst other things(new brass needle valve and not the viton ones which kept sticking for me, re-tapped thread for the jet block retaining screw and new screw supplied, re threaded the carb body top and supplied a slightly oversize threaded ring (all needles and jets were already new before I sent it, blasted the carb body back to its original grey colour and refaced the flange where it bolts to the intake) well worth the £70 as it now runs and ticks over like a Swiss watch
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
starfield181
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Joined: Wed Aug 18, 2010 11:56 am
Location: WILTSHIRE UK

Re: G5 Running Rich

Post by starfield181 »

No nearer a solution as yet. I checked the fuel height in the float chamber today by connecting a piece of clear pipe to the pilot jet. The level was spot on the pimple on the side cover at rest with fuel turned on. I have yet to strip the carb completely - a task for later in the week when I can get the bike on the lift to make it a more comfortable job. However I have previously checked the pilot jet (25), the main jet (220), the slide (3 1/2) and needle position (middle). No air cleaner is fitted so a blocked filter is not to blame.

Must say I am tempted to go for one of the Wassel concentric clones. Does anyone have any experience of fitting one to a G5 or similar bikes and what size would be best? A 28mm is slightly too small (but probably best) and a 30mm a bit too large against a target size of 1 1/8" (28.5mm).

PeterF
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ajscomboman
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Re: G5 Running Rich

Post by ajscomboman »

Don't waste your time and money on a Wassell carb. The parts service had a few in stock when they first came out and every one was returned as they were rubbish!
starfield181
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Re: G5 Running Rich

Post by starfield181 »

That's useful to know, better concentrate on sorting the Monobloc then. My friend rode the 250CSR over yesterday. Starts first kick and ticks over like a swiss watch - makes you want to spit!

PeterF
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Ozmadman
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Re: G5 Running Rich

Post by Ozmadman »

I would still contact Martin Bratby, not the quickest but 1st class work and generally under half the price of a new carb which have inconsistent quality problems from what I hear. From what I understand, if the jet block gasket has gone/leaks then the fuel would enter the engine without having to go into the float bowl first so the level could still be correct, someone will correct this if that is the wrong assumption??

Martin Bratby, on 01543 572583, or mobile 0777 2169524

Martin Bratby
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Huntington
Cannock
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
starfield181
Posts: 114
Joined: Wed Aug 18, 2010 11:56 am
Location: WILTSHIRE UK

Re: G5 Running Rich

Post by starfield181 »

I'll certainly consider sending the carb to Martrin Bratby if needs be. However, I have now stripped it down (though not to the point of removing the jet block) and I think I found the problem. The pilot jet was not fully screwed into the body. My fault because I could not find a suitable screwdriver to work in situ when I replaced it recently with a new one. After reassembly I took the bike for a test run and it is much much better. The tailpipe is no longer wet and it will trickle along on low throttle settings in top/3rd gear without drama.

The tickover is still not as sweet as I would like. It seems to slow down and almost stall then pick up again when ticking over on the centre stand. However, on the road the tickover is reliable enough for general riding so that is just what I am going to do - ride it and see if I like it.

Thanks for help.

PeterF
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Ozmadman
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Re: G5 Running Rich

Post by Ozmadman »

Well done!! before I had my carb my tick over was like that and I put it down to a worn slide as you could actually hear it rattling at tick over. Still not sure if that was it but no problems after the carb rebuild
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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