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Sorry , got distracted. Whats the answer.?


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Originally Posted by koan58
"Have you got chokes fitted? If not, have you plugged the cable inlets ,? "

This has been asked twice recently. Can we eliminate this possibility?

Oops, sorry... Chokes are fitted and are "off" (up all the way).


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Does putting the choke On make any difference?


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Originally Posted by gavin eisler
Maybe a coincidence, 2,500 rpm is about the break even point for Alternator output matching ignition power draw, 90 % of carb faults are electrical.

Can't see this being the problem
If the alternator was not working at all the bike should start & run quite fine .Lots of time we have had a member on a ride with a dead alternator running total loss & swapping his battery with another bike when it ran flat.

The other alternative is a dead battery with the bike running 100% on the alternator
However when this happens the engine usually will not start.
Once again been in the situation where a bike had no battery or a blown fuse so whould die the instant the alternator output fell.

The third case is an alternator wired backwards to the battery
However in that case the bike should run fine off the battery at low revs then the fuse would blow when the alternator cut in .


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Originally Posted by gavin eisler
Maybe a coincidence, 2,500 rpm is about the break even point for Alternator output matching ignition power draw, 90 % of carb faults are electrical.
Oddly enough it's also the point at which a Pazon will start to crap out if the supply voltage falls below about 11V. I always check voltages before blaming carburetors. Perhaps we are chasing the wrong wild water fowl?


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The Pazon will go much lower than that David, although it’s not something you want to try and achieve.


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I think we need to know???
Will it run at low rpm with a bit of throttle juggling?
or to put it another way
Is it just at low/closed throttle that it will not run?


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Try screwing the air screw most of the way in, say 1/8 turn from seated. It should idle very rich, if not the pilot jet is too small


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Originally Posted by Andy Higham
I think we need to know???
Will it run at low rpm with a bit of throttle juggling?
or to put it another way
Is it just at low/closed throttle that it will not run?

\Andy,
How many A65L's will do 2500 rpm with the throttle down all the way ?


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Mine did last year, I had some self modified slides which I put in because the slide position was too rich (I shaved them to be equal to #4, which I would have changed once I knew it was correct or not) I couldn’t get the bike to slow down much below that, I eventually said sod it and ordered some slides, the same phenomenon didn’t happen and it ticks over nicely. Compare my modified on to the other and you’d never know.

Maybe try a new set of slides.


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Originally Posted by Andy Higham
I think we need to know???
Will it run at low rpm with a bit of throttle juggling?
or to put it another way
Is it just at low/closed throttle that it will not run?

Right, will not run with the throttle low/closed. That's why I didn't mention RPM right out, only later to reinforce what I meant by "will not idle". Yes, you must hold the throttle open for it to start and run - I don't know how far; the throttle is not indexed, but I would estimate about 1/3 open. The moment you let go of the throttle, the engine dies.

The most obvious explanation for this symptom is a clogged idle circuit, but we did not find a clog. I'm now waiting to hear from my son regarding further inspection and cleaning and the next test. Unlike me, he has a job, a family, and two other motorcycles, so he's not at the BSA every day.


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Yes,
Something is definitely wrong
With no needle jet at all you should be able to get 1500- 2000 rpm, just on the idle circut alone
Liquise with a totally blocked off pilot jet you should be able to get the mbike idleing down to around 600 rpm on the needle jet alone

the more I think about this the more it sounds like an ignition stuck on full advance.

The problem there is of course on full advance you can not kick start the engine.


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After 3 pages of posts, surly this question has been posted, but do you have the correct main needles (2 rings around the top) with the correct jet holders? I once put together a bunch of parts to make a B44; it would run up and down the street as long as I held the throttle open, but would die when throttle was closed exactly as you describe. Put in the correct 2 ring needle and it solved the problem.

Maybe measure the length of the needles to make sure they are correct - - I get 2.4945" for the 3 ring and 2.669" for the 2 ring needle.

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Tom

Last edited by koncretekid; 07/05/20 11:10 am.

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Good information Tom, I will pass this on. When I looked at the needles, I was looking for a letter and so didn't notice the rings. Being brand new carbs, it's less likely that they have the wrong parts in them, but as you say, the symptom does match what you experienced to a tee, and we as yet have found no clog in the idle circuits.

Trevor, I could see the spark retarding and advancing with the strobe light.


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