Cutting out!

Scenario!

Bike runs great, ticks over 1000rpm ish when coming to a stop ie lights, sit for a minute or two at tickover waiting for green, open throttle to set off and it cuts out almost as soon as the slide lifts.(But not every time) It'll start again easy enough but am I too weak on the pilot side? Single 32mm Mk1 concentric(New) (Air screw is 7/8 out ) Main is a 260, needle Jet is a 106, and the needle is on the middle groove. Plugs look good and the bike performs lovely just the wee cutting out issue any idea's?

Hi Willy
What slide are you using? I would guess from your settings a 3 1/2 ? you may need to go to a 3 slide, I am guessing it's week just at the bottom end.
JohnT

willy mac said:

(Air screw is 7/8 out )

Click to expand...

Have you checked the fuel level/float height?

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels

JohnTy said:

Hi Willy
What slide are you using? I would guess from your settings a 3 1/2 ? you may need to go to a 3 slide, I am guessing it's week just at the bottom end.
JohnT

Click to expand...

Hi John, I did have a 3.5 in but the the tickover when coming to a stop wasn't so good so it now has a 3 in with the choke slide fixed in place. I'll maybe try another wee adjustment on the air screw!

L.A.B. said:

willy mac said:

(Air screw is 7/8 out )

Click to expand...

Have you checked the fuel level/float height?

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels

Click to expand...

Hi Lab

That was something I looked at when I was having the problem with it cutting out when rolling to a stop, It was a brand new carb and the level was at 6mm below the lip of the bowl so that was duly fettled to the recommended 2mm.

willy mac said:

L.A.B. said:

willy mac said:

(Air screw is 7/8 out )

Click to expand...

Have you checked the fuel level/float height?

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels

Click to expand...

It was a brand new carb and the level was at 6mm below the lip of the bowl so that was duly fettled to the recommended 2mm.

Click to expand...

Fuel level or float level?

The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.

Click to expand...

The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.

Click to expand...

[/quote]

Hi Lab

Me thinks I might have got me metric and me imperial measurements mixed up DOH! But saying that It's not flooding and seem to run fine as is, would the fuel height cause the cutting out as described?

willy mac said:

Me thinks I might have got me metric and me imperial measurements mixed up DOH! But saying that It's not flooding and seem to run fine as is, would the fuel height cause the cutting out as described?

Click to expand...

It's difficult to say for definite, but from what you've said, it seems you made a significant alteration to the float height, so perhaps it would be worth a re-check taking into consideration there is no recommend float height setting any more, only fuel level?

L.A.B. said:

willy mac said:

Me thinks I might have got me metric and me imperial measurements mixed up DOH! But saying that It's not flooding and seem to run fine as is, would the fuel height cause the cutting out as described?

Click to expand...

It's difficult to say for definite, but from what you've said, it seems you made a significant alteration to the float height, so perhaps it would be worth a re-check taking into consideration there is no recommend float height setting any more, only fuel level?

Click to expand...

These wee snippits are worth there weight in gold, I've been out today and it's not done it once I think I'll leave for the time being "if it aint broke don't fix it"!

willy mac said:

Scenario!

Bike runs great, ticks over 1000rpm ish when coming to a stop ie lights, sit for a minute or two at tickover waiting for green, open throttle to set off and it cuts out almost as soon as the slide lifts.(But not every time) It'll start again easy enough but am I too weak on the pilot side? Single 32mm Mk1 concentric(New) (Air screw is 7/8 out ) Main is a 260, needle Jet is a 106, and the needle is on the middle groove. Plugs look good and the bike performs lovely just the wee cutting out issue any idea's?

Click to expand...

Have you tried enrichening the idle? Have you cleaned and VERIFIED flow through the idle passages?

This is the exact problem I am experiencing with my 75 MKIII (new to me since January, weather hasn't allowed riding until the last 2 weeks) It will idle flawlessly at about 1000 rpm, but when ridden and approaching a stop with clutch pulled in, will often die. It's easy to restart, but doesn't seem to want to return to a steady idle after running.
First thought was clutch dragging, but adjusted that with no change. Doesn't matter if bike has been running for a few minutes or an hour- same situation. Re adjusted the air screws, installed in-line fuel filters, dumped out each bowl. Would really like to find a fix for this or some ideas before I remove the carbs and stat from scratch. It's a pain in the rear to artificially hold the idle up in traffic stops.

concours said:

willy mac said:

Scenario!

Bike runs great, ticks over 1000rpm ish when coming to a stop ie lights, sit for a minute or two at tickover waiting for green, open throttle to set off and it cuts out almost as soon as the slide lifts.(But not every time) It'll start again easy enough but am I too weak on the pilot side? Single 32mm Mk1 concentric(New) (Air screw is 7/8 out ) Main is a 260, needle Jet is a 106, and the needle is on the middle groove. Plugs look good and the bike performs lovely just the wee cutting out issue any idea's?

Click to expand...

Have you tried enrichening the idle? Have you cleaned and VERIFIED flow through the idle passages?

Click to expand...

Hi Fella
When I was investigating the "cutting out when rolling to a stop problem" and found the float level setting wrong the pilot air passages were cleaned and blown through with carb cleaner and air, like I said in my previous post It never missed a beat yesterday so I'll play with it again if it starts acting up!