Engine will not idle

[Neil21]

Hello all,

I am starting to tear my hair out not that there's much left anyway, I have recently rebuilt my 1952 gold flash plunger and engine but I cannot get it to idle no matter what I do.

I have ultrasonicly cleaned the carb twice run through all of the holes/channels with a set of jet needle's and fitted a new pilot jet but still no idle.

I have noticed now that the throttle stop screw is not touching the slide inside the carburettor, is this pointing to a worn slide or am I missing something silly.

Thanks for any advice Neil.

[Swarfcut]

 Idle adjustment is by means of a just off the vertical screw in the side of the earlier AMAL Carbs. Screwing this in raises the throttle slide, and allows the tick over to be set. Worth taking the top off the carb and seeing if the screw is visible in the throttle body, and the state of the throttle slide. As always, worn, "modified" or incorrect parts can cause these conundrums. 276 Carb has a remote float, screw and locknut  to adjust. Later Monobloc Carb has a screw and spring, adjuster is prone to seizure.

 Bike should tick over as the throttle is closed, if it then fades out as the cable slackens off, then that points to a simple slide adjustment which can not be effected for some reason.  Idle mixture also needs to be at a basic setting, plenty on the Forum to guide procedure.

 Swarfy.

[muskrat]

G'day Neil.
You don't say what carb you have. Does it run OK above idle?
I ran the original 276 for a few years on my 51 A7. Got sick of it leaking so threw a concentric on (pre internet).
Cheers

[KiwiGF]

Hello all,

I am starting to tear my hair out not that there's much left anyway, I have recently rebuilt my 1952 gold flash plunger and engine but I cannot get it to idle no matter what I do.

I have ultrasonicly cleaned the carb twice run through all of the holes/channels with a set of jet needle's and fitted a new pilot jet but still no idle.

I have noticed now that the throttle stop screw is not touching the slide inside the carburettor, is this pointing to a worn slide or am I missing something silly.

Thanks for any advice Neil.

Yes it does point towards a worn slide, new carb is best solution to that HOWEVER you need to rule out other sources of air “leaking” into the inlet eg check inlet manifold o ring (or gasket) taping it off temporarily is easy way to do that (carb bodies/flanges are often warped but can be fixed), throttle and choke cable entry points (noting the choke cable is often not used so blanked off), obviously there should be nothing wrong in the carb eg all jets present especially in the idle circuit.

[limeyrob]

Do tell us which carb.  The idle circuits get so blocked that even ultrasonic will not clear it, especially if its a Concentric.

[Neil21]

Hi sorry I didn't think about that,
It's an Amal monobloc 376.

Thanks Neil.

[limeyrob]

Get hold of Service sheet 708, its on the web, and look at the idle circuit, its on the 3rd page, and make sure you can blow through every passageway.  I had the same problem with my Concentric and nothing short of a drill would shift the rock hard deposits.  Monobloc should be easier.  This doesn't rule out a worn slide, but if the idle circuit is blocked your a fighting a loosing battle.

[Colsbeeza]

Hi Neil,
Some jet cleaning and measuring stuff I did a few years ago may help you.

https://www.a7a10.net/forum/index.php?topic=14024.msg115943#msg115943

Col