Zenith carb question

Hi, had my 72 SWB 2.25 Petrol for a week or so now. Not been able to go out in it yet as the brakes were non existent, but now they’re sorted I’ve move to trying to work out why it’s running rich, and sooty. Below is a photo of the carb.

Does anyone know if the choke/strangler flap should be more upright/open than it is, with the choke fully pushed in? The sectional diagram suggests it should be fully open.

If so, would it being like this mean air is sufficiently restricted to cause it to be overly rich?
Planning on replacing the choke cable and using a direct air filter at the weekend, along with usual points, cap, leads and plugs being checked. Also tappets will be checked too. Might do one thing at a time, starting with the choke, but thought I’d ask here first to get advice from those with experience.

Thanks

yes it should be vertical at the angle it is it will reduce air flow so enrich the fuel

looks like choke cable stuck,if that doesnt work ,the rubber o ring in the carb could be leaking ,letting excess fuel into manifolds or just general old zenith heat distortion on jet block

The choke flap on my zenith is exactly the same as yours. Mine doesn't run rich though, well, not anymore. Have you set the mixture screw as per the book? It might need a quarter to half a turn extra one way or the other. It is a balancing act between the mixture screw setting and the tickover setting on the throttle stop screw on the carb linkage. The throat of your carb looks pretty black which suggest to me it has been back firing or the filter is filthy.

Col

Thanks. The choke cable is pretty tight, and generally ineffective. I have bought a new one but haven’t changed it yet. Haven’t touched anything on the engine yet as I was just pondering what to start on. Col, you’re right, it’s pretty filthy in the photos there. I’m thinking that I need to remove and thoroughly clean it. I’m going to add an air filter directly to the carb bypassing the oil one.

after reading quite a few threads on running rich, it’ll probably end up with a new carb....

I have replaced the oil bath filter for a modern one that just attaches to the top of the carb. The oil baths were designed to work in dusty fields and dirt roads and were very affective but for modern road use they are over the top. You will notice more noise with a modern filter though. Have you taken the mixture screw out and checked to make sure the end is ok, mine was bent. I assume you are using lead replacement additive in your petrol.

Col

Hi, yes, additive in fuel, but can’t be sure previous owner was.
Haven’t took mixture screw out yet. Apparently it has been rebuilt. I’ll fiddle over the weekend.

Going to check everything. One concern is the excess oil in sump. That can’t be good. Hope it’s just oil.

I’ll report back.. thanks again

sadly rebuild doesnt mean its been done properly, worth checking it over

Hi, update.

had a mess about in a spare hour this morning. Replaced choke cable and now opens the flap fully. New filter, and leaned the mixture screw somewhat. Turned about five turns in, then backed off a couple of turns.

started and settled the idle once warmed up and choke off. Seems a little better but belches black smoke on blipping the throttle still.

So, decided to loosen dizzy, run engine and turn it a little. Engine sounded “better” at one point so tightened it up. Beltch of smoke now 80% better!! And probably as good as to be expected... anyway I’ll wait for the new electronic one to tinker further.... but looks promising.

There could be a lot of junk in the exhaust that needs burning out.. it might clear up further as you use it