Carburettor set up - Help!

[Tyre Smoke]

My Trabant is giving me a challenge.

It's a very simple single carb, butterfly opening with an air correction screw for mixture adjustment and a side choke lever that seems to add more fuel.

I bought a brand new carburettor for her as the old one was quite worn. Apparently it came set up and ready to go. But we all know that might be lies, right?

Anyway she was a pig to start from cold, like flatten the battery churning her over. Tried all sorts of techniques, full choke no throttle, no choke, half choke and throttle, you name it. Had to resort to a squirt of Easy Start every time. At this point I should say the air mixture screw was exactly two turns out.

I got her fully warmed up by going for a run, not great pulling power, but it is only a 595cc 30hp two stroke. She was also dying out on tickover. Back home and I started unscrewing the mixture screw, revs immediately increased and she settled into smooth (as far as a two stroke does) idle. Mixture screw now five turns out.

Starts from cold easily with half choke and no throttle. Pulls really well and no smoke from exhaust when fully warm, except under load. The thing is, she's only doing 18mpg. I reckon it should be approaching double that. Also queuing to get fuel last night ticking over nicely, she was very reluctant to rev cleanly to move forward. A bit of rev, clouds of blue smoke and she cleaned her throat and was fine.

I'm also not being anal about the two stroke mix, I have a conversation card telling me how much per litre for 33:1 or 50:1 mix so if it says 460ml of oil in the tank she gets 'about' that. If anything slightly over. I gauge the amount from the markings on the side of the 5 litre can in the boot. For what it's worth it's fully mineral oil.

So, running too rich? Over oiling?

Anyone know much about air cooled two strokes?

[paintman]

My experience is from years ago with old motorbikes & current with two outboards, a 4hp & a 135hp.

Too much oil in premix & you'll get lots of smoke & likely plug fouling which might create a whisker on the plug between the electrodes which will stop the spark.

Put far too much in & it might not run at all.

You give two mixes. What is it supposed to have?

Any airleaks?

Edited by paintman on Tuesday 27th July 11:26

[Tyre Smoke]

No airleaks and it's supposed to be 40:1 but...

The original manual says 50:1 but the club says 40:1 and 33:1 for motorway runs. So anywhere in between I guess!

I suspect the mix is OK, it's doing what it's supposed to, smoking on start up then no smoke at all cruising along, a bit on hills or under load. I think this is a fuel mixture (too rich) rather than oil/petrol mix.

[paintman]

Does the butterfly need to be ever so slightly open for idling & if it's fully shut you're not getting sufficient fuel in?
But it's working because the mix is excessively rich?

Quick google suggests that there are pattern Trabant carbs on the market which are crap.

I'm guessing you've already seen this & the other posts on the trabant forums: https://www.trabantforums.com/forum/trabant-tech-f...

[Tyre Smoke]

Absolutely. The carb was from a well respected Trabant spares supplier in Germany. It's not a dodgy one. And although the build quality is hardly Dellorto or Weber, it's a vast improvement on what came off.