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Cutting out conundrum

Submitted by tony_wood on Tue, 13/06/2023
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Heavy Twins

Hi. I went out for a ride on my 99 today  and twice I had the engine cut out on me. Both times it happened when I turned 90 degrees right from a T junction and then almost immediately (after about 5 metres) turned 90 degrees left (quite low speed and almost no throttle). On turning left the engine just stopped, (within about 3 metres of making the left turn). The bike started immediately again with just a short prod of the kickstart. I don’t get that cutting out if I reverse the directions, i.e. a 90 degree left turn followed almost immediately by a 90 degree right turn. My carb is a modern Amal Monobloc with less than 1000 miles use. I’ve ruled out electrics as I can swing the handlebars fully right then left with the engine on tickover and there’s no hesitation or cutting out.
It’s been a very hot day today - could that be something affecting the carb, or maybe it’s the fuel sloshing back across to to the left side of the float chamber when I turn left? I’m really puzzled by this one - anyone got any ideas ?

Thanks

Regards

Tony

Submitted by jonathan_newton on Tue, 13/06/2023

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which  in our world means electrical!!!  If it was  carb it would not be so closely linked, "cause and  effect" wise.  Do you have a kill switch on the bars? check for wiring issues related to bar  movement.   Have  you done a static  test by  moving  bars side to side with engine running?  or  try  leaning the bike over while running,  (two of you recommended).

 

Intersting.

 

J

Submitted by tony_wood on Tue, 13/06/2023

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Hi Jonathan. Thanks for your ideas. I don’t have a kill switch. I’ve done the ‘bars side to side’ bit with the engine running and the engine doesn’t falter. The problem ’feels’ like it should be electrical but I can’t find anything likely to cause it.

Regards

Tony

Submitted by alan_osborn on Tue, 13/06/2023

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The ignition wires go round the head stock. Try hot wiring the ignition see if this overcomes the issue. There is no handlebar kill switch as I assume we are talking coil ignition 18D2.

Submitted by tony_wood on Tue, 13/06/2023

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Hi Al. Thanks for your comments. It’s a Boyer dual output coil connected to a  Pazon Surefire electronic ignition. I rode over 110 miles today over a wide variety of roads and only experienced the problem on two very similar junctions. Those two junctions were the only two where I had to do a ‘right-left flip flop’.

Regards

Tony

Submitted by robert_tuck on Wed, 14/06/2023

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Thats an entertaining clown machine !!. Does the Pazon utilize the old distributor ? , Is there a lot of end float (axial clearance ) on the shaft?. What sort of ignition switch ?, Heavy bunch of keys flopping around?.  Knee down cornering  allowing heavy  WD dispatch riders coat tails to cover carb intake !!.

Submitted by tony_wood on Wed, 14/06/2023

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Thanks guys. Robert, I’ve got a magneto replacement ‘bean can’  housing the Pazon stator with a manual magneto sprocket. Lucas ignition switch (new) with only one key in it (no dangling bunch of keys). No overcoat - it was 27 degrees yesterday!

Neil, the Boyer twin output coil was approved by Pazon for use with their ignition units.

I’ll check the wiring around the headstock, as recommended. However, the bike has now done 500 miles since rebuild over all sorts of roads without any problems. If I had a wiring problem I thought I might have had an issue before, but maybe it’s a newly broken wire, although the handlebars weren’t turned that far to the left when the engine cut out. Also my loom goes round the lefthand side of the headstock, so it would be at very low stretch when the bars are turned left.

Regards

Tony

Submitted by mikael_ridderstad on Wed, 14/06/2023

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Everybody else has suggested an ignition problem. So it is likely a fuel problem. You said almost no throttle. The fast change of direction changed carb fuel level substantially. At small throttle opening, very little fuel is consumed so a change in fuel level will affect air/fuel mixture more. Possibly so rich or lean that engine stalls.

Edit: Could be dependant on your riding style. If you have more or less bike leaning angle than you have..

Submitted by jonathan_newton on Wed, 14/06/2023

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Still thinking on the electrical route although Mikael's points are valid also.  if is a "flip flop"  situation you may want to look at other parts of the loom that can move under inertia. 

Battery box, do you have an inline fuse holder that is floating in there,  conductors exiting the battery box grounding out on tinware either by insulation "nick" or bullet connector exposed at  a crucial position.

Wiring under tank is trapped, weight of fuel putting pressure on and breaking down the  insulation, are the coils spade connected or eyebolts, any movement anywhere? 

But as in my first post, when we all think its electrical,  and as Mr. A. O. has  guided us, ...  its probably Carb.

 Good  hunting

J

Submitted by barry_carson1 on Wed, 14/06/2023

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hello ,

are there any indicators fitted to the bike, drawing to much power. or creating a temporary short when turning

 

barry

Submitted by tony_wood on Thu, 15/06/2023

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Hi Barry. Thanks for your idea - that’s a very interesting suggestion. I do have indicators - they’re low power LED ones but they are bar end with the wiring running through the handlebars into the headlamp (exiting the bars between the clamps via a rubber grommet). I’ll check the wiring for a short circuit possibility.

Thanks again

Regards

Tony

Submitted by jonathan_newton on Thu, 15/06/2023

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... the power source to the indicators and go for a ride.  Probably just go for a ride and see if  you can repeat the error THEN disconnect the power source and re run the route...

 

J

Submitted by alan_osborn on Thu, 15/06/2023

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Ask your self-was you using the indicators when the engine 'stop' happened? If it is a short then it will blow the fuse. There has not been any mention of such. So A O assumes there is no fuse. OR the engine 'stop' is not a short of the battery to earth, but more likely a broken feed. I did say 'hot wire' the ignition which could show/cover up the fault.

But of course this will turn out to be carburation!! But again as been said a carb fault should cough and sputter as it fails. An instant stop-no blown fuses or lights going out would 'say' an open circuit in the ignition?

Submitted by tony_wood on Thu, 15/06/2023

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Hi Al. Thanks for that. The indicators are fused and that fuse didn’t blow so I guess that means it wasn’t a short in the indicator circuit - thanks for reminding me about that fuse. I’ll look for an intermittent open circuit. I can’t get the engine to cut out when the bike is on the main stand so I guess that I need to revisit the route on which the failure occurred so that I can recreate the exact conditions.

Regards

Tony

Submitted by barry_carson1 on Thu, 15/06/2023

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hello

faulty brake light curcuit.  then again i suppose you could count that out if its fused also.

 

barry

 



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