AJS & Matchless Owners Club

Hi I have a problem with my ajs 650 csr . Year 1961. Just want to throw it out there and maybe some fresh thinking will help.
The problem is the the bike runs fantastic until the engine gets up to temperature then it will misfire for about 10 seconds and cut out. Typically this is just enough time for me to get some distance from home !! I have to sit and wait until the engine cools then start off homewards .
I have replaced all the usual suspects, condenser, coils,plug leads,plugs etc. Getting to the stage of running out of ideas . Fuel flow is good and it has always been a first or second kick starter.
I am now beginning to suspect the oil tap cut out as its fitted with an oil tap that cuts the ignition unless it's turned on.
Electrics are not my strong point ( beyond basic ) so my question is would it be possible to leave the oil tap in the on position and remove the wiring to the ignition switch in effect turning it into a manual tap?
If the problem then persists at least I could eliminate it from the process.
Has anyone else had this problem?

I reckon you'll have to join the wires. You can check by seeing if one of the plugs sparkles.

Have you checked the fuel flow by tickling a carb immediately after it has cut out?
Have you checked for sparks immediately after it has cut out? Take a spare plug to check quickly as the ones in the engine will most likely be too hot to remove - as it's coil ignition and not magneto you won't have to kick it over vigorously.
If the oil tap is O.K. the ammeter needle will kick/deflect as you ease the engine over with the ignition turned on.

My 61 G12 used to do that too usually leaving me fuming at the local supermarket or petrol pumps, a magneto problem with my bike but if yours has coils ?

Ive had ignition switch with high resistance cause similar issue . low voltage to the coil
happened every cold start until switch was replaced
you could test this with a meter (voltage to coil )

Thanks all for your replies. My bike is unusual in that it was converted to a distributor in place of the mag sometime back in the 80s . It still retains the dynamo.
I have done the roadside fuel test and all fine so I'm pretty sure it's not a fueling issue. Hadnt thought to take a spare plug with me and do a roadside spark test . I'm usually too fed up to think straight and all I can think about is how am I getting home.
I usually get it home and try something else. I have been doing one thing at a time so I can eliminate potential problems in a logical manner.
It was late last night that I noticed intermittent sparks with what was a new coil . Tried a spare coil and sparks returned. I thought great ive cracked it ! Went out for a ride and same result . Misfire for 10 secs then cut out as soon as engine was hot . Bike was running great as usual. I was too fed up to hang around and let it cool so I ended up pushing the bike home . When I got back checked spark and intermittent again . Went home totally fed up . Woke up at 4am and thought it's the oil tap cut out . That's the only thing I haven't checked.
Tomorrow evening if life doesn't get in the way I'm going to disconnect the oil tap switch. See what happens. Hence my question. It cant do any harm I've tried every other bl###y thing.

The reason why it's bugging me so much is it brings back memories of a norton commando I had in the late seventies. I would go out miles on that it it went like a bat out of hell and started great from cold but just sometimes it would refuse to start after a run . I would be kicking away for ages and absolutely nothing. If I then left it and tried again sometimes after 10 mins sometimes half an hour later it would start first kick . I tried everything with that bike to get it reliable and in the end I had to admit defeat . I sold it and instantly regretted it. No Internet in those days and couldn't afford to put it into the shop for repair. I can feel the same frustration with this bike but armed with a little bit more knowledge it works get sold.

Just a thought. Are you using the choke correctly. Remember it's the opposite to a car choke. Lever pushed in is choke on and pull lever back when warmed up.

After you've eliminated the Oil tap switch I would try condenser, I've seen quite a few of them fail when hot only to spark back into life when cooled down. Most of the failures I've seen seem to short out putting the points side of the coil to earth when warmed up, so your points cant break the circuit.
Having said that I've just had a faulty one that failed constant open circuit and it was ok low revs but misfired as soon as the revs increased. (Magneto)
Think your doing best approach, try one thing at a time then you make slow progress, but know what's fixed it.

Thanks les and shaun.
Les I am definitely using the choke correctly but thank you for pointing that out doesn't hurt to be reminded.
Shaun I have already renewed condenser and nearly all the electrical items.
The only things left are the oil tap cut out switch and the dvr2 regulator that's why I'm suspicious of the switch .
I will let you know how I get on. Had a day when I haven't even looked at the bike so it will be with renewed enthusiasm because I was getting a bit frustrated with this.

Sorry senior moment, do remember reading that on phone now you mention it!
Maybe provide temp wire for coil & points direct and try. That would eliminate all switches and wiring?

shaunstaples wrote: ↑Mon Jul 03, 2023 12:40 am Maybe provide temp wire for coil & points direct and try. That would eliminate all switches and wiring?

Good plan!
But given those symptoms, I'd also pay heed to Shaun's point about the new condenser - traditional rolled paper ones have been known to degrade 'on the shelf' so are no good 'from new'. If you have another one handy, off something that is known to work maybe, then it's worth the few minutes' effort to swap it out so you can eliminate that too.