Suspect carburetter

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
vigo
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Suspect carburetter

Post by vigo »

This 1960 G5 was the winter project 19/20 non starter. Engine top end, gearbox then ignition needed attention. It has run but not very well so I moved on to the carb. All the jets where wrong, correct fitted and rebuild using good info from "real classic" August.
I have a great spark, at the right time (checked many times),good compression, but I get only an occasional response.
When initially taking the 389 monobloc apart there was no gasket under the jet block (jb) which is said to be very important. So I fitted what I had a fibre washer 1.84mm thick. The jb seemed to sit a little high in the carb inlet,
Does anyone know how thick this jb gasket should be, I'm inclined to think paper thin?
Being in Germany the turnround time for spares is long.
There is evidence of fuel, maybe too much and black wet deposits form in the carb.
I know I really need a new carb it's certainly done some service. I'm only left with the float level to check then stumped!
Any advice gents is appreciated.
Mike

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dave16mct
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Re: Suspect carburetter

Post by dave16mct »

The gasket under the jetblock is just a paper ring made from gasket paper. You get one in a carb gasket set but easy to make.
Dave.
vigo
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Re: Suspect carburetter

Post by vigo »

Thanks Dave I thought it might be paper. Time to raid the kitchen for some baking paper Don't laugh it's flight of the pheonix here in Germany.
vigo
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Re: Suspect carburetter

Post by vigo »

Put the carb back together, I think I had a murmer from the engine, ran it down the hill, nothing. Changed to my second plug and it ran for about 3 secs. a degree of success. From then on spitting back or kick back. Doesn't this point to weekness? There was originally a 30 pilot which I standardised with a 25 and a huge 470 main which I changed for 220 standard.

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dave16mct
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Re: Suspect carburetter

Post by dave16mct »

Have you cleaned the pilot jet and airways?
Dave.
vigo
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Re: Suspect carburetter

Post by vigo »

Yes, pilot jet is new and have cleared all the airways twice. I think I'll adjust the air screw and maybe even try the bigger 30 jet back in one at a time.
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dave16mct
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Re: Suspect carburetter

Post by dave16mct »

Have you got a good spark?
vigo
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Re: Suspect carburetter

Post by vigo »

So I put the 30 pilot back in and adjusted the air screw, air slide closed and started. I could even give a bit of throttle, lots of smoke but wouldn't keep running. From then on with closed throttle it would try to start but not pick up.
I seem to be making ground and am convinced it's the carb. There is a "burgess triumph" silencer fitted and the pipe has been dented to fit under the footrest, I wonder if that could have an effect? May explain why there was a 470 main jet fitted. Enough for today.
ChrisTheChippy
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Re: Suspect carburetter

Post by ChrisTheChippy »

Probably not what you want to hear at this stage but make sure your ignition timing is absolutely spot on . In my experience these lightweight bikes are very sensitive to correct ignition timing . My G2 had similar symptoms and turned out ignition timing was off . After days of buggering about with everything else a small adjustment and it fired second kick after 20 years of standing .
I have no doubt that your carb needs attention from the sound of it but if you get the jetting near enough you should be getting more response than you currently are .
Hope this helps and you get it sorted I will be interested to know what the problem is .
Regards Chris
vigo
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Re: Suspect carburetter

Post by vigo »

Thanks Chris, any tips appreciated. All the ignition is new except points. Yesterday bike started but wont stay running.I've set and checked the timing again and again. With the 470 main jet which was in the carb I did at least go up and down the road. Now the correct 220 jet is fitted it wont play. I will lift the needle a notch and if that doesn't work I'm going to put the 470 jet back in to see what happens.
I'm not one to be beaten but if all fails I think I'll get the carb back to uk for a carb magician to go over.
Mike
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