G80S bogging down

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
markwhitelock
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Joined: Sat Sep 07, 2019 5:51 pm
Location: Hampshire UK

G80S bogging down

Post by markwhitelock »

My ‘56 G80 is all back in one piece, I've managed a couple of test rides up the road but it is bogging down around half throttle, it stops pulling. I've been trying to wind out the mixture screw ever so slightly but I'm not seeing much improvement. The carb slide looked a bit worn, but moves up and down freely enough. I have the recommended jets and needle setting still.

Would issues with the timing or the auto adv/ret cause similar symptoms? The bike happily idles and starts first or second kick, pulls away up to 1/4 throttle no problems.
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1608
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Location: ESSEX UK

Re: G80S bogging down

Post by 1608 »

Check the simple things first. Is the fuel getting through ok, filter on the carb banjo clear. Ensure the HT lead is not' tracking ' under load as you accelerate. Was timing set at full advance. If auto a/r then it may be sticking.
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Rob Harknett
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Re: G80S bogging down

Post by Rob Harknett »

People check carb and say its all OK but seem to forget the throttle slide cut away. Wrong slide cut away, bike will start OK and run, open the throttle it will die.
I once fitted a new slide I'd picked up. Never checked it. Bike started OK, slowly pulled away in 1st changed to 2nd. changed to 3rd opened up and it died.
Last edited by Rob Harknett on Mon Jun 29, 2020 1:49 pm, edited 1 time in total.
Mick D
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Location: Aberdeenshire

Re: G80S bogging down

Post by Mick D »

Hi

Half throttle is outside the range of influence of the mixture screw and fuel starvation is normally accompanied by erratic running.

Bogging down at half throttle sound more like poor timing or sticky ATD.

You have retracted the carburetter air slide, (choke), haven't you ;)

Regards Mick
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clive
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Re: G80S bogging down

Post by clive »

make sure you don't have dried polish/chrome cleaner blocking up the vent hole in your petrol tank cap. Not a problem for me as I rarely use it but I know it can cause fuel starvation.
clive
if it ain't broke don't fix
markwhitelock
Posts: 208
Joined: Sat Sep 07, 2019 5:51 pm
Location: Hampshire UK

Re: G80S bogging down

Post by markwhitelock »

Putting the choke on seems to make it run better, I will look at the mixture and needle position
markwhitelock
Posts: 208
Joined: Sat Sep 07, 2019 5:51 pm
Location: Hampshire UK

Re: G80S bogging down

Post by markwhitelock »

Newbee question....

Is the choke on or off when the cable is fully raised?! My mate is adamant that the choke is on when the lever is pushed forward and the slide lowered...
Mick D
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Location: Aberdeenshire

Re: G80S bogging down

Post by Mick D »

Yer mate is right

Choke is on when the cable is relaxed - normally lever forward
markwhitelock
Posts: 208
Joined: Sat Sep 07, 2019 5:51 pm
Location: Hampshire UK

Re: G80S bogging down

Post by markwhitelock »

:oops: Whoops. That's a bit embarrassing...

Do it seems the carb may be ok :rofl:
Mick D
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Re: G80S bogging down

Post by Mick D »

Every day's a school day ;)
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