Lumpy idle

[Dickie]

Anyone have any ideas how I can solve a lumpy idle. Car runs well but feels like it might be slightly down on one plug. 1972 carb model Solex 36/40.
Replaced the following. 
1) New plugs
2) New wires
3) New 123 electronic ignition
5) Valve points adjusted .007
6) Timing set static
7) Carb refurbished - but I did notice the injection pipe (5) is quite loose. Ie: able to twist with little effort and not locked in place. Should it be ? Could this be the issue?
Any ideas?

Edited October 28, 2022 by Dickie

[John76]

Ilde jet clean?

Do you see any fuel dribbling into the primary during the rough idle?

If so, check the float level and condition of the plastic float (rots and sinks from alcohol in fuel).

Check for any vacuum leaks.  Causes lumpy idle but goes away as RPMs increase.

John

[Dickie]

Thanks John I bought a new float and will install and try. Do get occasional fuel leak after shut off. Very occasional. Will try to identify vacuum leaks I read spraying carb cleaner around the pipes to see whether engine tone changes. Just worried about fire. Cheers great help!

[Mike Self]

11 hours ago, Dickie said:

but I did notice the injection pipe (5) is quite loose.

That's the outlet for your accelerator pump, which doesn't function at idle--at least it isn't supposed to! You might try staking it in place; just make sure it squirts directly into the carb throat, not to the edge of the venturi.  

 

Those 1 barrel Solex carbs have a very smooth idle--wish my Weber 32/36 was as smooth--so something is the matter.  Presume you do have your idle speed set at about 800 rpm, and you've adjusted the mixture screw.  If that doesn't help, you either have gas dribbling in--enriching the mixture--or a vacuum leak that is leaning out the mixture.

 

mike

[Hans]

Did it ever idle well for you? Anything changed since then? What timing curve have you got in the 123? Have you adjusted timing?

[Dickie]

Thanks John I bought a new float and will install and try. Do get occasional fuel leak after shut off. Very occasional. Will try to identify vacuum leaks I read spraying carb cleaner around the pipes to see whether engine tone changes. Just worried about fire. Cheers great help!

 

 

Thanks guys. Interesting point Mike about the injection pipe. Now you mentioned it, I ran the engine with the air filter off. Stopped the engine and saw evidence of fuel still pumping from the injection pipe into the Venturi for a few seconds after engine off. I am not an engineer but could this be the issue- over fuelling at low revs? Maybe pointing to float? 

[John76]

You might also check the condition of the pump diaphragm (#14).

Replace if cracked or brittle.

 

[Dickie]

Replaced the accelerator pump diaphragm as part of the carb refreshment 

Edited October 30, 2022 by Dickie

[Mike Self]

15 hours ago, Dickie said:

Will try to identify vacuum leaks I read spraying carb cleaner around the pipes to see whether engine tone changes.

Another way to do this is to use an unlit propane torch, turned low and held near potential vacuum leak locations.  

 

mike