Matchless G9 won't idle

Henry Gonsalves · Post by **Henry Gonsalves** » Fri Jun 03, 2011 11:53 pm

Hi Guys. my Matchless G9 Twin 1959 will not idle when warm. (Monobloc carb) It spits and cuts out even after 5 miles. When run at a fast tickover, 500 rpm. it slows up and wants to cut out and when I open up slightly it spits back through the carb. I have checked the timing 3/8"BTDC with rotor advanced pos. rechecked the tappets (.008 thou) Checked for air leaks at joint face. Its not a patch on my 1953 model which still runs like new.
Any suggestions please.

TommoT · Post by **TommoT** » Sat Jun 04, 2011 8:06 am

Make sure that all air passages are clear, in particular the one for the idle circuit. Be aware that when you turn the idle screw in, you reduce the amount of air, making idle mixture richer, and vice versa. The spitting back you experience when opening the throttle indicates that the idle mixture is too weak, confirmed by the inability to idle. Also the cutaway on the air throttle/slide controls the mixture in the transition phase from idle to main circuit. You may need a slide with a smaller cutaway to enrichen the mixture in this phase. A #3½ cutaway is standard, but conditions may vary. I found I needed a #4 cutaway to compensate for the airfilter I fitted. All you'll ever need to know about setting up Amal carburettors can be found on: www.hitchcocksmotorcycles.co.uk and go to the Amal section. Excellent diagrams and tuning procedures.Edited by - TommoT on 04 Jun 2011 07:09:03 AM

rex.webb · Post by **rex.webb** » Sat Jun 04, 2011 8:39 am

Great that "HITCHOCKS" site wish i had seen it earlier .Well as i say
"Your Never to old to learn somthing NEW"
RIDE with CARE and LIVE LONG to ENJOY your BIKES

Rob Harknett · Post by **Rob Harknett** » Sat Jun 04, 2011 1:14 pm

Our old bikes were not that fussy were they Rex, I seem to recall Basils old prewar AJS was running OK minus its float chamber top on a Jampot rally run. When my little 36/22 AJS could not decide if it was a 2 or 8 stroke, she got back to camp OK, & told me what was wrong. All I had to do was remove the bottom nut, the jets fell out.

Henry Gonsalves · Post by **Henry Gonsalves** » Sat Jun 04, 2011 3:52 pm

Thanks, TommoT, I will give it a try.

rex.webb · Post by **rex.webb** » Sat Jun 04, 2011 7:54 pm

HI ROB !
Must get the 1937 AJS 350 out asap and get an MOT.
I have 4 bikes MOT,d now so saving for another one.
Why my AJS flooded when the float chamber top was put on ???? I do not know. Must prepair myself for more "MICKY TAKING " if it still has to be so.
RIDE with CARE and LIVE LONG to ENJOY your BIKEX.

Henry Gonsalves · Post by **Henry Gonsalves** » Sat Jun 04, 2011 10:17 pm

Found the problem. Removed the carb again, total dismantle job. On close examination I found that the air screw was radiused on the end like something I have never seen. So I ground the screw on the same angle but only to reduce the radius to 20 thou. Assembled the carb and it started first kick and ticks over just acceptable OK. the screw is only a temp. job till I order one from Kettering.
Thanks for reading my post. H.G.

wilko · Post by **wilko** » Sun Jun 05, 2011 1:00 am

Did you remove and clean the idle jet which hides under the little hex cap? This is usually the culprit, easily blocked.

1608 · Post by **1608** » Sun Jun 05, 2011 11:34 am

I can't for the life of me see how the air screw became so rounded off as to effect the mixture, i think you probably inadvertantly cleared a blockage, well done anyway.

SPRIDDLER · Post by **SPRIDDLER** » Sun Jun 05, 2011 6:06 pm

quote:
like something I have never seen.

That takes a bit of imagination. Now none of us can't see it either.
If I never see another rounded pilot screw it'll be a week too soon.