Suspect carburetter

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

Post by vigo »

The packer between carb and head according to diagram, should have o ring head side with flat surface mating to second o ring recessed in carb. I found the packer the other way round with flat side to head and an amal gasket fitted. This left o ring to o ring onto carb. 2 different number o rings. Additional to that a piece of the packer is broken off (see pic).
So now a dead period while I get Amal spares.
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clanger9
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Re: Suspect carburetter

Post by clanger9 »

Have you checked the float level? This is the first thing you should check on an Amal - it's easy to accidentally change it when the fuel pipe union is removed...
1989 Moto Morini Dart 350
1993 Ducati 750SS
vigo
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Re: Suspect carburetter

Post by vigo »

Hi Paul, I did look at the float level which I understand is given by the small pimple on the outside cover. There is a "tide mark" on the float which I assumed (bad word I know) is where the fuel reaches. But when I get this spacer sorted, I'm trying to repair it, and get it assembled properly then I'll check the float again.
What's the best way on a mono? I've done concentric but not this animal.
Mike

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clanger9
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Re: Suspect carburetter

Post by clanger9 »

Take the cover off the idle jet, stick a bit of clear plastic pipe over the jet & hold the other end of the pipe against the float cover.
Fuel should settle at the 'pip'. It's important that it's spot on, otherwise you've got no chance of the carb working properly.
Problem is that the level is set by the washer under the fuel union & this often gets changed...
1989 Moto Morini Dart 350
1993 Ducati 750SS
vigo
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Re: Suspect carburetter

Post by vigo »

WellI trued up the carb face and put the spacer the right way round. O rings to flat face. Then using plastic tube checked the float level, it was spot on. Put the fresh plug in and bingo, started and ticked over like it never has. Air slide off inside a minute and responded to throttle.
I set off up a steep hill engine responded to revs but then started to hesitate (miss). Over the top of the hill and got worse until cut out, would not fire up again. Pushed up the hill and back down home. Bump started weakly and seemed to just hang on with rapid throttle movement but then cut out.
What happened to my lovely tickover, could the float needle be sticking? Fuel starvation is my bet what do you gents think?
Mike
Mick D
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Re: Suspect carburetter

Post by Mick D »

vigo wrote:What happened to my lovely tickover,
Hi

My guess would be crud in the pilot jet

Regards Mick
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clanger9
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Re: Suspect carburetter

Post by clanger9 »

Good, it looks like the carb is spot on. Seems more like fuel starvation. Check for muck in the tank and float bowl. Could also be a blocked fuel tap.
What does the flow look like from end of the feed pipe?

Another fun Amal feature is if the little spacer is missing off the float pivot shaft. If that's missing, the float will stick occasionally.
1989 Moto Morini Dart 350
1993 Ducati 750SS
vigo
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Re: Suspect carburetter

Post by vigo »

I did all fuel checks, the jets were clear and despite the fact the float needle is the standard light plastic one, works ok. Plenty of fuel is getting through and pours from pilot jet cover nut when removed. I think the carb and fuel to carb is ok and I have another theory, oil is messing up the burn once pressure is reached. Why? well black eng oil weeps from exhaust to head joint, there is some blue smoke when running but not too much.
Started 1st time, choke off and over 2 to 3 minutes idling gets worse and any attempt to open throttle must be done gently. These symptoms only after engine warm, when cold starting I could raise the revs but all gets progressively worse until engine dies and tries but will not restart. I think if I try tomorrow it will start then same again. Some of my earlier forum entries were oil across head gasket and loss of compression but I did all to resolve that and there is good compression.
I'm a bit stuffed here in Germany with limited resources maybe I'll need to trailer back to UK for some help.
vigo
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Re: Suspect carburetter

Post by vigo »

Just returned from my G5 stress break with some spares in my pocket and renewed determination. Fitted a new viton float needle and changed condenser. Checked again points gap, plug gap, timing and carb float level. I also put back in the 30 pilot jet replacing the correct 25.
Choke, tickle, throttle and starts. No smoke, allow to warm up keeping fast tickover. Slowly choke off over a couple of mins. Still holding fast tickover.
Now here's the thing, if I let the revs drop closer to a tickover then open the throttle the motor will try to die, in fact it seems more likely the warmer it gets. There is also some hunting when holding fast tickover, could that just be backlash in this "hightech" ign system.
I have the book spec 220 main,106 needle but 30 pilot.
Do I need to raise needle, currently on middle?

I tried to confirm which 389 I have and could only find 4 66 which is a spring number. When the carb was off I could have measured it.

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Mick D
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Re: Suspect carburetter

Post by Mick D »

vigo wrote: if I let the revs drop closer to a tickover then open the throttle the motor will try to die
Hi

That's indicative of the pilot bypass being obstructed or possibly a sticky ATD

Regards Mick
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