Pilot jet

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Pilot jet

Postby ChrisTheChippy » Fri Aug 10, 2018 10:35 pm

Hi all
Sorry but another carb question . Ajs model 31 CSR. Just trying to set up the carb as bike won't tick over revs great but won't tick over . I have just replaced the float needle as the old one was sticking and the carb seemed to be running out of fuel and coming to a sudden halt even with the throttle held open . I have yet to test this as I ran out of time before it got dark tonight .( No lights in workshop )
I would like to know approx setting for the pilot and throttle screw's so
I have a starting point to set carb up . Can't seem to find any info on this . Lots of carburettor articles but they mainly refer to disassembly and rebuild of carbs not settings. Same thing in the manuel I have. I guess I could play around all day with it but life is just too short !
Cheers Chris

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Re: Pilot jet

Postby Rob Harknett » Fri Aug 10, 2018 10:43 pm

Not much to set, just needle in correct notch and adjust slide stop in slide closed position. Adjust air screw, screw it in, maybe out a couple of turns continue till it runs smoothly , When its warmed up, final screw adjust so in ticks over. Don't always expect the old bike to tick over very slowly without cutting out.

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Re: Pilot jet

Postby PeterJCorby » Fri Aug 10, 2018 11:40 pm

Finally one I can answer... from the AMAL carb web site...

(1) Screw out the throttle adjusting screw until the engine
runs slower and begins to falter, then screw pilot air adjusting screw in or out to make engine
run regularly and faster. (2) Now gently lower the throttle adjusting screw until the engine runs
slower and just begins to falter, adjust the pilor air adjusting screw to get best slow running:
If this 2nd adjustment makes the engine run too fast, go over the job again.

Wish I had your problem as mine idles beaut but will not rev.

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Re: Pilot jet

Postby Rob Harknett » Sat Aug 11, 2018 9:52 am

Chris, check the main jet is really clear. Sometimes you may see it as clear, or does the hole look a bit misty? It needs to seen as a clear hole. Also check the throttle slid is the correct cut a way number. You probably have the needle position set OK. Also check the throttle has fully opened. It should rise up out of sight. Just little things that can catch you out, worth double checking, that have caught me out.

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Re: Pilot jet

Postby ChrisTheChippy » Sat Aug 11, 2018 10:34 am

Thank you for all your quick replies.
Don't know why I can't always find this info myself but I guess im not that great with technology willing to learn though.
Rob thanks for the extra tips re jet etc even though I have cleaned carburettor really well it's definitely worth another check .
I actually have some free time today so intend to have a few blissful hours fiddling around with the bike . I am actually looking forward to this free time when I can escape from things. My dad has been very ill lately and the pressure of juggling everything has been tremendous. This hobby of ours is sometimes a great help.
I will update if I make any progress today bike hadn't run for 22 years so I've been gradually getting it ready for the first start . I must admit I am really pleased with the way it runs apart from no tickover . Bike had a full engine rebuild in the 80s including crank regrind and balance . Hardly done any milage since then . Can't wait to get her on the road .
Best regards
Chris

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Re: Pilot jet

Postby SPRIDDLER » Sat Aug 11, 2018 11:01 am

Very therapeutic, fiddling with the old bikes (mostly!).

As already mentioned above, start with screwing the Pilot screw in until it's fully closed. Don't force it or you may damage its seat, then open it about one and a half turns and start twiddling with it from that point.
The throttle stop (tickover) screw setting is not critical. I set it at a bit too high a tickover speed for convenience so that the engine doesn't keep stalling whilst I'm fiddling with the Pilot screw to obtain a good steady tickover. Once finished you can adjust the throttle stop screw to obtain your preferred tickover speed.
Have a look at this tuning guide and its associated pages:
http://www.hitchcocksmotorcycles.com/mo ... to-tune-up
Last edited by SPRIDDLER on Sat Aug 11, 2018 11:20 am, edited 2 times in total.
I poke badgers with spoons.

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Re: Pilot jet

Postby ChrisTheChippy » Sat Aug 11, 2018 11:11 am

Thanks spriddler
Will do
Cheers Chris

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Re: Pilot jet

Postby ChrisTheChippy » Sat Aug 11, 2018 9:41 pm

Hi all
Well that was a waste of time . Lots of checks lots of fiddling around and still no tickover . I have checked all jet sizes slide etc all standard size and clear and clean . Only thing I did notice is that the needle jet is very slightly bent. It is set on the right notch though. I might renew it but I'm not sure that would stop the bike ticking over .
I'm going to take carb off again and carefully recheck everything .
If I find everything correct and clean I will look elsewhere for the problem maybe start with new plugs check points gap and ignition timing etc.
Got me puzzled atm bike does not start too great either takes about 10 kicks and I'm beginning to learn it's individual starting procedure .
I will update when I next get time to work on the bike .
Cheers Chris

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Re: Pilot jet

Postby clive » Sun Aug 12, 2018 10:21 am

Tickover and starting problems can be caused by air leaks around the carb. Points worth double checking 1. Is the top securing ring cross threaded or not turned fully home? often difficult to do properly if the tank is on and the carb has not been removed. 2 have you got a choke cable fitted? if not you need to seal up the hole where the cable enters the carb. 3 is the carb flat at the flange, they are frequently distorted from uneven tightening. 4 is the rubber seal round the flange still flexible and projecting from the face of the flange when the carb is off? they often go hard.
Final point reading that the bike has stood many years is that gradual evaporation of the fuel if a tap was left open can cause deposits to be left. The tickover works because a mixture of air and fuel, managed by the air screw, enters the airflow into the engine via a very small hole at the bottom of the throat of the carb between the slide and flange. If this is blocked you will never get a tickover. Don't poke use an airline to check its ok. The air supply is though the small holes at the front of the carb.
clive
if it ain't broke don't fix

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Re: Pilot jet

Postby Duncan » Sun Aug 12, 2018 10:35 am

I could add 5. if this is a rebuilt engine was the manifold attached before the heads were torqued down to ensure the head(s)/manifold joint aligns?

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