S51 problem...

Hello everybody!
First of all, excuse me for writing in english, unfortunately I speak no german...
I have an S51 here in Greece and trying to solve my problem, I had no luck in local forums, so I decided to write to you, simson experts!

Well, I bought this 1985 S51 2 years ago with a 2-kanal 60ccm cylinder and piston installed and 16mm BVF carb, it was well-maintained and perfectly functioning, but a little rusty, so I decided to completely unrust and paint it myself and here is how it looks now...

Well, which is my problem?
After I reassembled it, freshly painted, without having touched the motor at all, it does not keep idle when it gets hot... it starts up cold fine with choke and it keeps idling normally, but after 2-3 minutes, it loses its rpms and it goes off...
On the road it goes fine, but only in high rpms, it has a v-max of 65-70km/h but when I release the throttle it sounds like if it was switched off, and when I pull the clutch lever the engine stops...
The only thing I did after I reassembled it was cleaning the carb and setting it up as advised.
I have bought so far another brand new, 19er BVF and a 6-kanal 60ccm cylinder and piston, I tried swapping to see the results but they remain the same!

Here is my setup and what I have tried so far, I hope for your advice... please answer with any ideas even in german and I will try to understand with google translate!

-Clean tank, fresh fuel and gas filter installed
-Clean carbs, both 16er and 19er BVFs, the second is brand new, properly jetted and set up as recommended, without any modifications! Choke seems to function well.
-Clean and flawless both 60er 2-kanal and 6-kanal cylinders, heads pistons and rings.
-Brand new original-type air filter installed
-Brand new spark plugs and cable, tried both NGK B8HS and B7HS and they give fine blue spark.
-Freshlhy burnt and clean original 28mm exhaust

I have tried all possible combinations with air-screws on both carbs, the best result I can get is what I describe, and it happens within the range of 1-2 turns open, as recommended.
The floaters are set to 28-32.5mm recommended, the jet needle was tested in all positions. Also the idle screw is set correctly and all carb settings are being made with the engine warmed up. As far as I play with the throttle everything seems fine, but when I release it, the engine goes off and when I try to restart, it starts only with full throttle, giving few rpms just to keep the engine alive, and after a little time the rpms are getting higher, as they should... the same occurs without air-filter connected, and even with the exhaust removed.
Seems like the engine is flooding with fuel after a little time, regardless of which carb setting I use... the carbs (both) also seem not to provide enough air, in any air-screw position... another wird thing I noticed, when I remove the rubber pipe which connects to the air-filter box, the hole is flooded with fued, like if the carbs are spitting the fuel backwards, instead of spraying it inti the cylinder.

I suspect that it might be an electrical problem, or the problem is INSIDE the crankcase (a mechanic that checked it, though he doesn't know much about simsons, said it looks to be good, both the rod an the crankshaft, and there are not any "odd" noises from inside the engine) and I am searching in wrong direction, my S51 is an 6v with contact breakers (not electronic), and I have touched nothing about them since I bought it (I haven't done more than 1000-1500km since then), when it functioned perfectly...

Could you please give me any suggestions???
I thank you all in advance and send my regards from sunny Greece...

Zitat von gelbraum;2839808

it looks like a typical carb problem. clean it again (especially all nozzles)... what happens when the engine is hot and you pull the choke? you have built the right carb nozzles on the right place in the carb? sorry for my terrible english...

First of all thanks for taking the time to reply, your english is just fine and surely better than mine!!
Well, when I pull the choke lever on hot engline, it stops, no matter how high are the revs... BUT... I just remembered that when the choke cable broke once, I replaced it with a new one, but since it seemed to me VERY loose, I cut it off about 1cm in length... now it appears to fit and function perfectly, but perhaps it remains slightly open and gives some extra-air into the carb...

I will check it and I will tell you!!
Perhaps it remains slightly open and gives some extra-air into the carb...

Thank you all for your kind replies, I suspect (and hope) that it might finally be a gas and/or choke cable problem, I will get myself a pair of brand-new ones, check and tell you!!

As for 6v unterbrecher zundung and special spark-plug, cable and high-voltage connector, I see what you mean, but it was working fine before, with the very same setup!
Hope this is not such problem, I shall keep you informed!

Well, after a looooong time, I decided to spare a couple of hours to do some testing on my S51, and yes, finally it was the choke cable!
It had been broken long ago and I replaced the cable inside with another piece I measured and cut my own, but since the old one seemed to me a bit loose, I made it 5-6mm shorter, and it seemed tight and fit...
...but, as I realized, the choke was remaining slightly open, thus the big problem that occured!
Now the S51 is up and running fine, with 19mm carb and 2-kanal 60ccm cylinder! I will try next to install the 6-kanal cylinder and piston, to see what happens!
Thank you all for your precious advice!