Hello, I am doing up an old 360 and it idles at 2000 rpm. I have tried adjusting both the mixture and the slow running screws - both have no effect at all. The carburettor diaphrams have been checked and the gaskets between the carb and the inlet manifold have been replaced. Still it idles at 2000 rpm!

Is this likely to be a problem with the carb or with the electronic ignition (renix) and if so can a renix unit from a 340 be swapped into a 360??

Carb, for sure.

Hmm...have you checked the throttle position at idle? It could be the throttle offset cam for the choke being mis-adjusted...a semi-famous fault with these carbs.

cheers

James

Many thanks indeed but I am still not clear about the details. Could you possibly point the relevant things out to me on this piccy....??

The throttle position is an easy one - just look down the barrels, and see if the throttle plates are closed.

The fast-idle screw isn't visible on that pic, but a nifty bit of digicam work later...



cheers

James

Hello again. Many thanks indeed. I have always been confused by the fast idle screw. On other cars I only ever have to adjust the slow idle screw. I don't have my Haynes manual to hand, but does it explain how to adjust fast idle?!?! Or to put it more bluntly, what exactly is fast idle?!?!? I am sorry that I am asking you to spell it all out, but there ain't much hope of me getting an answer from anyone else who I know. I am sure it will all make sense one day.

The engine has to run slightly faster when cold to remain smooth. To do this, the choke richens the mixture, but more subtly also opens the primary throttle slightly. This degree of opening is dictated by the fast idle speed screw, and it is this adjustment which alters the engine speed on-choke. For a while mine was set very high (2500+ to make progress), which I then tweaked down. You ought to be able to make good progress without forward-firing with 1200-1300rpm fast-idle from stone cold.

Regarding your problem, one possibility is that the fast idle screw (or the associated mechanism) has been adjusted to the point where it intereferes with the slow idle speed. If it has, you'll see the throttle open very slightly. Having said that, it may be too subtle for a visual inspection - my twin carbs suffer from this!

cheers

James

Sorry James, I think it was my fault. I had not put the carbie back together properly! There's a plastic knob/pivot that is supposed to fit into a slot in the cam that is operated by the choke cable and I hadn't got the two to fit together, despite warnings in the Haynes manual. I think the choke flap was stuck at the wrong angle! Now I am making some progress - idle speed is lower and can be adjusted at last.

Glad to hear you've been making some progress. The most sensible explanations can make no sense in the heat of the moment with the thing screaming away at you (I had a 4000rpm idle at one point!) - as I've been finding out recently with my twin carbs!

cheers

James

All seems fine now. I tried to set the mixture by using one of the colourtune devices (i.e. transparent spark plug) by turning the mixture screw and trying to find the point where the flame goes from blue to yellow. Alas, could not find the point - it stayed blue from one end of the screw's movement to the other. Hence, did it by weakening the mixture until the engine sounded happy.

Is it just me.... but the design of the carbie i.e. the mixture screw being both out of sight and almost out of reach at the bottom of a deep hole and having to work in the dark to see the colour of the flame does make life a little awkward.

Yes, it is annoying - in fact it's a fairly rubbish carb full stop. The improvement I found in quality of carburation moving to the ADDHEs was huge, and that isn't purely due to them being sidedrafts. It's a nice setup for economy as it's such a tiny carb, but drivability is compromised. If I were keeping mine, I'd have probably sourced a Weber alternative.

cheers

James