I have a Webra Speed 50 on my Sig Something Extra. I can't get it to quit sagging. I also coughs some. I sent it in to Webra. They put in new front bearing and piston and sleeve. It runs better but still cuts out. Just can't depend on it. I am running Sig 10% and a OS 8 glow plug. Could it be something about my tank? Any ideas?

Thannks

The Webra .40 - .50 Speed/GT series engines are designed to run at high rpm. Loading them down with much more than a 10x6 prop is asking for trouble.

Yes, it could be that your fuel tank is foaming the fuel from engine vibration. The only real solution is to balance everything as well as you can and then make sure that the fuel tank is not touching the sides of the airframe or the firewall directly. This includes the brass fuel tank lines too. I realize that tank space is limited in the Something Extra.

These are standard things to check. There are others if you perform these things and still have trouble.

In fact, the very FIRST thing I would do is to check for loose screws on the engine. Good luck.

I am not trying to start an arguement but I know for a fact that the Webras run just as well loaded down. We have Webra 50s running 12.25x3.75 props on three different funfly's and all perform excellent on 15% fuel so the choice of prop is not the problem here.

We had one of our Webras doing the same thing and all it took to fix it was properly adjusting the low speed needle. Webras are extremely sensitive to the setting of the low speed needle. If it is to lean it will cause the engine to die and if it is too rich it will cause poor tranistion in the midrange. This is the price you pay for high performance. At least they seem to not need any adjustment for a while once are set right. It took me three tanks of fuel to get my last Webra correctly set and has been a gem ever since. Also there is no need to run the expensive #8 plugs in these engines they like the cheaper A3 plugs just as well.

Hi!
The .40-,50 Webra is not any differnt than any other two and twostroke engine ! they could swing any prop, large and small, without problem...just set your needle accordingly!
I´have run the webra .40 GT in my Q-500 pylonracers for many years and most pyloncompetitors in sweden use this engine as it is by far the most powerfull engine of all .40 twostrokes on the market (we use only 10x6 props and FAI fuel in Q-500 pylon).
The Webra trottles exeptionaly well and rews at 14000 on a Graupner 10x6 prop, a lfew hundred rpm less with a APC.
The Webra .40 is equiped with a Rossi 3 and I think the .50 Webra also use this plug.
It might be that you run to much nitro that you have a problem...these engines are made to run on no or low nitro blends as nitro in central Europe are hard to obtain. Here in Sweden it is no problem to get it as dragracing is very popular....but it costs 13$ for 1 liter though.!!

Regards!
Jan K
Sweden

Actually, Webra engines ARE different than other two-stroke engines. That's why they cost so much here in the USA.

Yes, you can put a large prop on it and tune accordingly, but you might as well have bought two or three el cheapo engines instead of the Webra, because the Webra is timed and ported to produce its best horsepower while revving up.

A Fun Fly/3D prop isn't really loading down the Webra all that much. Loading it down to me is swinging an 11x7 to an 11x8 prop. Yet, I know there are those that do exactly that. They pay their money and it is their right to waste a perfectly good engine.

When people post questions, I assume that they know how to adjust the mixture screws, so I gloss over that and look at other mechanical possibilities. If someone is so stupid that they complain about how an engine runs before tuning the problem away...