Vapour carbs

[Quadra]

I'm thinking to powering a couple of I.C. engines using bubble or vapour carbs. My concern is flashback into fuel tanks. In pictures of engines I've seen with vapour carbs, I haven't noticed any flashback arresters except for one engine.

The question is, is it a potential problem and should I be concerned? Fuel would be Aspen 4T.

John

[Jasonb]

I've run a few engines on one of Nck Rowland's (RMC Engines) vapour carb and not had a problem, the low vacuum when the engine sucks in may not open a flashback device.

Not sure how well Aspen will work, Nick suggests pump petrol over Colmans as it is not volatile enough to give off sufficient vapour.

[AVTUR]

Many years ago I attended a talk given by a motorcyclist with experience of riding a bike with a surface carburettor (I assume that this is the same as a vapour carburettor). I remember three things:
The fuel had to be much more volatile than pump petrol. The fuel of choice, and at the time it could be bought fully taxed, was petroleum thinners used for impact type glues.
Fires were frequent particularly when the bike fell over. This did not seem to concern the speaker.
The engine went far better when riding along a bumpy road.

I am sure all this is of little use.

AVTUR

[Dave Otto]

In full sized practice, the antique stationary engines that I'm familiar whit always used a flame arrestor, check valve, or combination of both.
On my Pacific engine I replicated an original flame arrestor from a patent drawing. Starting on post 312. https://www.modelenginemaker.com/index.php/topic,1326.310.html
I guess the chance of a flashback and explosion can always exist, so anything that can be done to help prevent that might not be a bad idea.

Dave
 

[Jasonb]

What size engines were you thinking of using the carbs /tanks on? Dave's engine is quite a bit larger than the 7/8" and 24mm bore engines I have been using them on which will affect the scale of the arrestors etc and how much flame there is to open a valve.

I've also got a larger kit to build that has a vapouriser that heats the paraffin but again no check valves on that.

<a href="https://www.youtube.com/watch?v=4MdSeVslvig" target="_blank">http://www.youtube.com/watch?v=4MdSeVslvig</a>

[Quadra]

Jasonb ,

The two engines I thought of fitting vapour carbs to are the Karl Benz and Thomas engines both from Torsten Schur Germany. They have bores 30 and 28mm respectively.

John