Saving Old Seagulls

Hi,

I have returned to a Seagull after years of disloyalty with a couple of small Suzuki's. I have a great 40 featherweight which had a dead ignition, but swapped it out for a Wipac mk4 with recoil and it's all good now. Still on a 10:1 carb. I have noticed that the needle screw is not level with the top of the brass barrel, but screwed some way in. I was just wondering how to 'tune' the carb (if such a thing is even possible with such a basic design) for optimal starting and running?

Many thanks in expectation!

The Seagull repair hand book says to "Turn needle adjuster until it is flush with the top of the piston."

On newer (mkII equipped forty plus) Villiers carbs,the adjusting screw at the top of the throttle valve piston is screwed way in. This screw is supposed to be flush with the top of the piston.

No 2 needle - 25:1 (may be marked 2 & 1/2' or have no marking)
No 3 needle - 10:1

Screwing the adjusting screw a tad more than 3 turns down may cure excessive 4-stroking.

If choke is needed for more than the first half minute or so screwing it out again a bit at a time may help. Thus unscrewing produces a richer mixture and vice-versa.

If the engine 4-strokes (other than when lightly loaded) wind it down.

Many thanks for that - very helpful.

The featherweight starts a treat - literally first pull from cold. I have noticed that when you turn the fuel off, it strokes faster on the last 30 seconds of fuel. So maybe it is 4 stroking when the fuel is on, and as the fuel starts to run out, the mixture weakens and it 2 strokes? Currently screw is at the top, so maybe I will turn it down a little?

Leave it be.... It is not broken, so don't try to fix it!
If you run it too lean you will kill it!!!

My earlier post was a somewhat edited collection of the salient points from historical threads on the forum concerning Villiers carbs.

Here's a definition of four-stroking by someone else:

"Two-stroke engines rely on effective scavenging in order to operate correctly. This clears out the combustion exhaust gases from the previous cycle and allows refilling with a clean mix of air and fuel.
If scavenging falters, the mixture of unburnable exhaust gas with the new mixture may produce an overall charge that fails to ignite correctly. Only when this charge is further diluted, by pumping through a second volume of clean mixture, does it become inflammable again. The engine thus begins to 'fire-and-miss' every second cycle (every four strokes), rather than correctly on every cycle."

You seem happy with how the thing runs generally - are you sure it is four-stroking? The description above doesn't sound like a engine that starts and runs easily.

Yep, I think I will leave it be. It just is so willing to start and run. Best featherweight I have ever had!