Aghh, these bloody carbs! Cylinders 3 & 4 are running really rich, plugs very sooty. So I'm trying to adjust the carb on this side to lean it out. I'm following the procedure on http://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=7767&p=139237&hilit=leak#p139237 However when I disconnect the wire to the cut off pilot jet on the left side carb nothing happens. The solenoid is 'clicking'. When I disconnect the right hand side carb's the revs drop nicely. I'd expect the left carb to do the same, but there's no change. I've swapped the pilot solenoids from left to right but the left still doesn't change so I don't think it's a problem with the solenoids themselves. I think this might explain why the mixture screw isn't doing anything, it's almost like this side is getting petrol from somewhere else, a leak maybe? The other symptom that points me towards this is when the 'idle circuit' is turned on, the revs rise, but again the mixture screw on the idle circuit has no effect even if screwed all the way in or out. I'm pretty sure I don't have any air-leaks on the manifolds/rubbers as I've re-sealed the manifolds and checked everything with oxy-acetylene gas and the idle doesn't move. I think there was a slight manifold sealing problem on cylinders 1&2 but I've sorted this, and if it was an air-leak then surely it's be running lean? Basics: valves, points & timing are all spot on, I've even done a compression test and all ok. Tearing my hair out now!!
Check the pump jet is there, little brass tube that you can see in the top of the carb near the butterfly, they tend to fall out and cause overfueling
I can't give you a full answer for this. There are several somewhat unfathomable guides out there which I've nevr mastered, but what you need to know is that the carbs have individual idle controls and also a central idle system. The idea is you get them roughly right with the throttle stop screws then fine tune with the screw on the top of the left hand carb. If you give them too much throttle they will idle directly through the main carb bodies and nothing you do to the top screw will affect the running speed. I'm assuming it's the big screw you're turning - this is the idle speed. You can't adjust the mixture on the main carb bodies. That's only possible by altering the jets. The idle circuit mixture can be adjusted but if you're getting sooty plugs on one side only I'd be suspicious of the choke units.
Agreed it sounds like throttle stop screw is too far in. Disconnect the linkages and set again? You can set mixtures for each carb as well as the idle circuit Andy, the screws are facing backwards, outside edge near the base of each carb.
Thanks for the advise. I've stripped it down ( again) to double check the pump jet tube wasn't loose and this time I double checked the float needle valve. There's a big lump of muck in it so it must have been sticking open causing it to flood slightly. Right, off to fit it and follow the tuning procedure, yet again!! I'm going a bit deaf from leaning over the engine to fiddle with the screws. Wish I'd got an engine hatch too as my back aches!
Great feeling when you find a problem and fix it, even better when it doesn't involve having to spend any money on parts.
