Ellery V-Twin 100cc Design & Build

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Beautiful work!!!!
Might say that a diaphragm carb can only get fuel by the impulses working the pump side of carb. If you can pull fuel through that carb then your needle/seat is leaking
Is that two 100cc cylinders or 100 between the two?
Its 50cc per cylinder. (well 49cc swept volume actually, but 100cc sounds better than 98cc :) )
Stroke 39mm
Bore 40mm
Compression ratio 8.5
Fantastic ! A most impressive snow blower. !
Do you plan on making plans available?
The wt40 carb seems to be un available, darn.
thanks. yes thinking of how I can best do this. It would be nice to gets some funds so I can start the next one.
Wonderful engine!

The Walbro carb used on the GF40 is the WT-1024. It's unlikely you'd find one anywhere other than an OS dealer. Walbro will design a carb for a specific application if you can fund it, as OS and Saito have done. With some effort, one can track down a suitable carb, though Walbro doesn't make it easy. In the past their site was more searchable. Four strokes really like an accelerator pump in the carb. The trick is finding a carb model which is currently available with the specs required and there is no resource which lists venturi size and other features.

Might say that a diaphragm carb can only get fuel by the impulses working the pump side of carb. If you can pull fuel through that carb then your needle/seat is leaking

This is not how a Walbro works. If there is venturi suction, the diaphragm opens the inlet needle. Obviously, suction also has to be great enough to pull fuel through the inactive pump. I would not try to fly a model with the carb setup like this, and certainly needle settings will change if the pump is working. It's working, seems quite well, as the carb is probably on the smaller side for the displacement.
I really struggled and got lost looking for a suitable carb. Was ideally looking for a WT-225 which is what the Kolm engines use, but could not source. Decided to try my luck with the GF40.

Still playing with the setup and have only managed to run it for a few more minutes as I need to be a bit respectful to my neighbors with the noise.
With the 26x10 prop, the range was 1300-4800 rpm which i'm pretty happy with without making any adjustments to the carb needles.

If i'm happy enough to put it in a plane I will likely use a pump which is common in commercial models (Kolm/Valach) of this type. That should at least provide a neutral pressure on the postivie side and let the engine suck what it needs.

For now I need to find somewhere remote that I can test and play with it (once lockdown finishes).
I also plan on trying a 24x10 prop.
Over the weekend I got her running again (sorry no video this time). I ran a 24x10 prop and it was comfortably pulling 5500rpm. The low end is still pretty lumping and it does not yet sit well below 1300rpm.
Still some breaking in to do, but have now stripped her down for inspection. A satisfying feeling seeing all the parts laid out.
Sorry for reviving an old post. @cbooth if you are still there, can you mention what kind of ignition system you used for this engine? And generally how is the engine getting on, particularly if it saw 'air' time!

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