AJS & Matchless Owners Club

Hi All,

I have a late model G15CS (it left the factory Oct 67 for sale in US as a 1968 model, this model was fitted with concentric carbs as standard. I have looked through the archives and several manuals and parts lists that I own (including Roy Bacons excellent resto book) and have and have found conflicting main jet sizes ranging from 220 to 270.

When I got the bike it had 260 but the plugs sooted up pretty quickly, I changed them for 230 and now it is not so bad. If possible I would like to know all the jet sizes and needle position please.

Thanks
Peter

The main jet only really has any effect above 3/4 throttle or so - below this most of the mixture variation is via the needle jet / cutaway.

Thanks Ian. Went for a run today, after 8 miles it popped back through the carbs, backfired and died…..(Guess where the tool roll was???) flooded the carbs kicked it several times and it started, ran for 4 or 5 miles and did exactly the same.
After flooding and kicking 20 times (ish) it started, ran for 500 yards and completely gave up the ghost. Had to get towed home by my Mrs in the car……tried bump starting whilst being towed, absolutely NOTHING!

I am in trouble because it has a Boyer Bransden electronic ignition (so tool roll probably wouldn't have helped) and I know exactly NOTHING about electronic ignitions………………… I guess I am going to have to learn.

Possable a flat battery.

I would start with the battery because that would recover a bit whilst the bike was not running which might explain the symptoms. However if that is ok I would go back to the plugs sooting up. Changing the main jet size will not have affected the performance on your ride out unless you were going above 3/4 throttle. On my much earlier G11CS I had similar problems, worked fine whilst thrasing it around outside London but as soon as I tootled back home through traffic at 30 and below it would soot up. (Air filter and monobloc carb so different set up maybe). I have largely but not completely tamed my problem by dropping the pilot jet down a size. Before I did that the slow running adjustment appeared to have no effect. I run my bike on the modern two star and wonder if the modern fuel mix is more likely to cause sooting up. (Stands back whilst people who actually know such things reply )

Current fuel with all its additives combusts more readily than the old "plain" petrol.
Hence you can often retard ignition timing to stop pinking with no loss of power.

Thanks for your help Guys.

The battery is not flat. I have taken the plugs out and now instead of one, both plugs have sooted up. (I haven't changed the jets yet)

I looked on the Boyer website help page and got some tips, I found that the plugs spark when I turn on the ignition but not when I turn it off which unless I misread it, it is supposed to do. Although it has sparks to both plugs when switching on the ignition, it will not spark when kicking over…..I even tried new plugs.

I use the more expensive unleaded fuel, I will fill up with standard fuel next time to see if that helps.

I have emailed the Boyer Helpline and will let you know what they suggest.

Peter

Have you checked to make sure the shaft is turning when kicking the bike over?

Peter , first things first .
The Boyer still uses the coils . should be 2 x 6V coils in series or 2 x 12 V in parallel
I'd do the following .

connect the power directly to the coils , the , make / break the connection to make sure the coils are firing correctly with the plugs out and earthed so you can see the spark . no need to kick the bike over for this test .
If you get a bright blue spark , then that side of the system is Ok and you can look at the Boyer side

another check is as follows :
Disconnect the wires from the ignition box that go to the stator plate. With the ignition on, touch these two wires together, making and breaking should produce a spark at the spark plugs. If sparks are present then the ignition box is most likely to be in good order, if none are present the box is faulty


if the coils are connected in series , then a dead coil will stop the bike

Other things that will cause you a problem , are bad ignition switch . if the volts drop too low or all together the boyer will cut out. I remember my P11 used to cut out after about 5 - 6 miles , turn the ignition on and off a few times and every thing was fine

Just thought if you are the Peter who came to the club last Wednesday in Sussex , send me a Pm and I'll come over and have a look one evening if you have the bike in a well lit garage .
Can't see where you are on your profile, but the carb problem sounds familiar from a conversation last week , but I only caught the tail end as was late at the meeting .

Peter

Thanks Guys.

I have had to go in for a knee operation so have not managed to check anything yet.

I will keep you posted.

Peter