Idle W/NG

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simon.holyfield
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Idle W/NG

Postby simon.holyfield » Wed Aug 07, 2019 9:13 am

Folks,

I need a few pointers. I've recently installed a 275 in my W/NG, a completely standard carburetter in every respect, and in very good condition. It runs and idles well.

The problem I have with it is that when I come to a standstill after a run, it often dies. If i can keep it going, the idle is at a good speed and I wouldn't want to increase it. Idle screw is about 2-2 1/2 turns out.

What makes it die?
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG, '78 CX500
http://ariel-square-four.blogspot.com

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brenton.roy
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Re: Idle W/NG

Postby brenton.roy » Wed Aug 07, 2019 10:43 am

Hi Simes, 20 questions..
Does it die immediately when you stop, or after a period of time?
Is the idle set by a cable length adjuster or via the stop screw on the carb body?
If the latter, how much cable free play? Is free play affected by turning the handlebars?
Does the slide easily drop to the bottom of its travel - not loose and catching sideways or a bit tight?
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

Mick D
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Re: Idle W/NG

Postby Mick D » Wed Aug 07, 2019 11:47 am

Hi

I'd be tempted to increase the idle mixture strength and adjust the revs back down with the throttle stop - sounds like it's a bit weak.

Regards Mick

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Re: Idle W/NG

Postby john.whiting » Wed Aug 07, 2019 12:34 pm

Symptoms of a worn spot in the carb at idle...........idle is always the worst spot for wear ,as the suction puts a lot of load on the slide initial movement in the carb body.

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simon.holyfield
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Re: Idle W/NG

Postby simon.holyfield » Wed Aug 07, 2019 3:10 pm

Throttle slide is good - for once, I have a very good body and slide.

I think the ignition timing is questionable - it seems fine on full advance, but runs very fast. Secondly, I have the throttle stop wound almost all the way in which seems wrong. It must be a year since I looked at the timing.

Another thing which points in this direction is that on anything other than full advance, there is a lot of banging in the exhaust on the overrun. Sounds like it it too retarded to me, so I will do some investigating and report back.

Now, just to amuse you, I was parked outside my barber's earlier. He asked me where I was going, and I was heading off for an hours ride or so. He asked whether it would get all that way without breaking down. I told him that in my experience most roadside breakdowns were instigated by the rider messing something up or not paying attention when in the workshop.

Forty minutes later, I spluttered to a halt thinking the carb was flooding. This is what I found:

IMG_20190807_125329.jpg


I've wiped a lot of egg off my face since I've had old bikes!
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG, '78 CX500
http://ariel-square-four.blogspot.com

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Steven.Carter
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Re: Idle W/NG

Postby Steven.Carter » Wed Aug 07, 2019 3:14 pm

Your carb disassembling itself, :D

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simon.holyfield
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Re: Idle W/NG

Postby simon.holyfield » Wed Aug 07, 2019 5:21 pm

Steven.Carter wrote:Your carb disassembling itself, :D


Quite. Last year I had another egg on face moment, witnessed by another biker who had stopped - I found the main jet sitting in the bottom of the jet cover/bottom bolt. I'd changed the jet and failed to screw it in properly...
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG, '78 CX500
http://ariel-square-four.blogspot.com

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simon.holyfield
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Re: Idle W/NG

Postby simon.holyfield » Wed Aug 07, 2019 5:24 pm

Here's a real question:

when I set the ignition timing after the magneto was refurbed by Tony Cooper, I believe I set the timing to 3/8" BTDC per the March 1941 instruction manual i have here on my desk.

Looking it up again today I noticed that the workshop manual, which has no date but must be post 1944 (it has the later wiring in it), tells you to set it 1/2" BTDC.

What do you guys do?
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG, '78 CX500
http://ariel-square-four.blogspot.com

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simon.holyfield
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Re: Idle W/NG

Postby simon.holyfield » Wed Aug 07, 2019 5:26 pm

brenton.roy wrote:Hi Simes, 20 questions..
Does it die immediately when you stop, or after a period of time?
Is the idle set by a cable length adjuster or via the stop screw on the carb body?
If the latter, how much cable free play? Is free play affected by turning the handlebars?
Does the slide easily drop to the bottom of its travel - not loose and catching sideways or a bit tight?


It dies slowly - when I have come to a halt it will have died within 10 seconds. The throttle stops on the screw, and still stops on the screw with the handlebars at both extremes. It's nice and loose, though your question prompted me to look and I realized the choke lever allows the air valve to drop maybe 1/4" from fully open.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG, '78 CX500
http://ariel-square-four.blogspot.com

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brenton.roy
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Re: Idle W/NG

Postby brenton.roy » Wed Aug 07, 2019 11:41 pm

The symptoms are unusual for an ignition issue, which probably wouldn't wait for you to pull over and park..
Timing wise, you would want retarded timing at idle, so amount of advance isn't so likely.
They could point to either running out of fuel or something expanding when warm and affecting mixture. Did you say it was backfiring on the over run?
Also, the vibration of the running engine can keep things like the needle and seat / carb float moving and open.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.


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