Solex Twin Barrel Carb fault

[WeisBier]

Hi my 79 520 straight 6 M20 engine has the Solex twin Barrel Carb.

It idle's high when warmed up. When you start the car initially it runs at 1000
rpm. Once warmed up it could idle at 2000 rpm for the rest of the journey.

On other journeys it will idle at 1500 or 1300 or 1700. Once warmed up it will stay at one of those rpm's.

Would anyone some info on why this is happening? I have used carb cleaner on the moving parts and slightly back off the bolt that drives the throttle linkage. but still high idle.





Overhead view Choke flap open



Overhead view Choke flap closed



View Looking towards windscreen

[socalfiver]

Has the car been sitting, or is it a daily driver? Has it recently been running properly? 2000rpm is extremely high.

Is the choke plate opening completely upon warmup? Seems like perhaps the idle mixture and choke settings need to be adjusted. Warm the car up, and use the idle mixture screw to attain a proper idle speed (850-950rpm?). Let the car get cold overnight, and reset the choke with the engine cool.

Also, you should thoroughly clean this carb inside and out. Clean the throttle and choke plates with liberal amounts of carb cleaner and a cloth. The plate edges and mating surfaces must be clean to ensure smooth, even running.
Hopefully spray cleaner will work. If not, consider a carb overhaul, as it looks to have been a while since it was cleaned and rebuilt.

[WeisBier]

I think the car did sit for a while before I bought it.

Have been using quite regularly, I swap between the golf,635 and 520 on a weekly basis.

NO the choke plate seems not to move much. I am after buying a autodata book that covers the 620 M20 engine and it shows how to set the idle speed and choke for the Solex Carb. Will have a go over the next few days and try cleaning it.

Thanks.

The Haynes manual is not great for the adjustment of the solex carb.

[WeisBier]

Just I though I would update about Solex 4a1 Carb.

The Main reason why the rev's would increase to 2000 when the car is fully warmed up was:


The TN Starter Valve or its called Auxilary bypass valve. Its a mechanical valve thats opens and closes with the heat of coolant ciculating around it. This valve allow extra air into the engine even when the butterfly valves are closed.

So the valve is open when the coolant is hot and closes when cold, The gap can be adjusted with a screwdriver. mine seem to be stuck. Luckily a I bought a second hand 4a1 Merc carb on ebay. And its valve worked fine when tested in a hot bowl of water. Put it into the car, Idle speed problem resolved.