AJS & Matchless Owners Club

I've had similar problems with 2 new Monoblocks fitted to 2 different bikes. On my 16s after failed start attempts the plug was usually very wet. If it started ok it would sometimes cough and splutter when accelerating. When taking the plug out after the run it was usually very sooty. I stripped and cleaned the carb several times and also checked the fuel level in the float chamber. The penny dropped one day when the carb flooded as soon as I turned the fuel tap on. A circular mark on the float chamber gasket showed that the bush on the float pivot shaft was too long and was restricting the free movement of the float. Once I removed a few thou from the bush the problem was resolved.

The symptoms with my BSA A50 were very similar and the cause the same.

Andy E wrote: .... penny dropped one day when the carb flooded as soon as I turned the fuel tap on. A circular mark on the float chamber gasket showed that the bush on the float pivot shaft was too long and was restricting the free movement of the float. Once I removed a few thou from the bush the problem was resolved.

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That's interesting A.

I've never had the carb flood, but the sooting up and wetness sound just like mine ..

Try and get out there tomorrow and have a look-see..

Thanks

Andy E wrote:The penny dropped one day when the carb flooded as soon as I turned the fuel tap on. A circular mark on the float chamber gasket showed that the bush on the float pivot shaft was too long and was restricting the free movement of the float. Once I removed a few thou from the bush the problem was resolved.

The symptoms with my BSA A50 were very similar and the cause the same.

checked this out today .. no evidence of anything similar .. in fact, with the carb off the bike if it is tilted you can hear the float flop from one position to the other, and with a different tilt you can hear the bush move on the shaft ..

Earlier, as I said, I put in new needle and jets from Burlen .. I have checked them all for correct marking and all are ok except for the needle jet which is marked 1065 , not 106 .. the old needle jet is 106.. can anyone confirm that 1065 is ok? .. the old jet does appear heavily worn, so no point in putting it back..

Now wondering if the air supplies to the pilot jet may be in some way obstructed .. certainly I am not sure that that tick over can be adjusted to as slow as it should be //

Hi

I'm sure I've seen that the 1065 needle jet, (original fit), is no longer available and 106 is supplied as the nearest alternate.

Regards Mick

Mick D wrote:Hi

I'm sure I've seen that the 1065 needle jet, (original fit), is no longer available and 106 is supplied as the nearest alternate.

Regards Mick

Hi M ..

My recently bought (last September) needle jet is 1065 .. I have a feeling that at the time 106 wasn't available and 1065 was the alternative ..

Looking on Burlen's site now it shows both ..

I have a new needle 'C'.

I understand the the jet size is a direct relation to the max through 'flow' so 1065 will be a bigger bore than 160, so enriching the mixture, but by how much? .. should I lower the needle 1 notch? .. or buy a 160 jet?

Have to admit, I'm getting out of my depth

If the needle currently resides in a slot where it could be lowered (i.e. any one but the end one) then I would certainly try dropping it a notch and see how it goes and then, if still very rich and there's another slot, drop it again and have another go. After all, that's what the multiple slots are for .... Do make sure you don't (literally) over-cook it and get it too lean though!

When I first got my little Beeza and found that it had the wrong carb and completely wrong jets fitted, dropping the needle two notches did at least allow the engine to work and run throughout the range and it was still running rich but it got the bike going and now I have, following a call to Surrey Cycles and purchase of, what seems to be the perfect combination of jets and needle for the odd ball concoction. I asked what did I need and Mike(?) sent them to me and it worked perfectly first time.

Alan

Decided to start again from basics ..

I have ordered a 106 needle jet from Burlen .. then all jets and the needle will be new and correct .. now need to make sure that both pilot jet air supply drillings are clear, then to reinstall carb and see what the result is ..

Sorry, back again ...

All previous done and checked except lowering the needle .. all new bits ,, jets and needle .. fuel level checked

Still running rich as far as I can tell, not having been out on the machine ..

Warmed up on the centre stand and tick over adjusted .. and puffs of black smoke when ticking over leaving it ticking for a while .. it starts to intermittently 8 stroke (I think .. )

Reading various literature I found a comment that if the jet block washer isn't pristine, fuel can leak past and richen the mixture .. I've tried to remove the jet block to check the washer with no success .. (I did remove the screw .. 376-070) ..

I am reluctant to lower the needle (just one of those things) but I think that will be my next move, though with lockdown, being unable to show it what a road looks like, I will put that off for a while ..

again, if it is so rich at tickover, is the needle likely to be involved, or can I expect it to be very rich at tickover?

Perhaps I ought to get my pushbike out again ..

Taid wrote:if it is so rich at tickover, is the needle likely to be involved,

Hi

Not in my opinion.

Where is your air screw set?

Does your choke slide fully retract? can you raise it further by pulling up on the outer?

Regards Mick

Taid wrote: Warmed up on the centre stand and tick over adjusted .. and puffs of black smoke when ticking over leaving it ticking for a while .. it starts to intermittently 8 stroke (I think .. )............ if it is so rich at tickover, is the needle likely to be involved, or can I expect it to be very rich at tickover?

Do you get any response when adjusting the pilot jet? It's primarily the pilot jet (and to a lesser extent the slide cutaway) which supplies fuel at tickover and up to maybe half throttle after which the main jet becomes involved. The pilot screw adjusts the amount of air being supplied, not the fuel. If the engine doesn't show much response to pilot screw adjustment it's likely that the very narrow pilot drillings are obstructed. The 'normal' setting for the pilot screw is about one and a half turns 'out'.

Check, as best you can, the drillings 7, 8 and 9 by forcing aerosol WD40 or brake or carb cleaner through........