Hello to all you controlline engine experts out there!

In case you missed my last post, I have just finished rebuilding a rather old (and abused) Fox 36 BB engine. I'm running it in on a 28% mix (approx 7.5% nitro) with 10% unleaded petrol added. - Eases cold starts allegedly!

Running in on a 10*6 prop on about 3 turns of the needle valve, occasionally 'blipping' it by pinching the fuelpipe.
All is well except for the spraybar (or so I think).

When the engine is running a small amount of fuel gets sucked out of the carb by the propellor. Why bother about such a small thing I hear you ask?

So upon inspection of my PAW249, I discovered that the main jet (one in both casrs) in the spraybar was facing forwards. Yes yoy guessed it, the Fox spraybar jet was facing the opposite way towards the cylinder!

Ritated the spraybar and fired it up, but this has made little difference.

Is there a correct way to fit these single jet spraybars, or is it simply due to that rather radical slanted fox carb?

Any feedback on this would be greatly appreciated.

Over the years I have come to point the hole(s) in the spray bar slightly forward of the main flow of the air down the venturi passage in this way the air and fuel mix is more finely atomized as it enters the block and therefore less likely to bubble up out of the passage due to prop vacuum!

Phil Spillman
 

I read an article about nitro fuel on RCM&E recently which states petrol has a flash point of -45·C, methanol 11·C and nitromethane 43·C.

Whilst using a higher nitro content fuel (10%+) a petrol additive isn't really necessary, although if using fuel with a lower nitro content (up to 5%) adding 10% petrol does seem to make a difference. There is little chance of engine damage and one big adventage is there's much less chance of internal corrosion.

I've been using this to run-in my Fox 36X on cold mornings as an experiment with great success! - It's also a good way of topping-up half gallon fuel containers too, just remember to make up the oil content lost after adding petrol!

Definately one to try (especially for you Canadians up there with all that snow and ice!!!).

     You might also try adding naptha (lighter fluid), ether, acetone, or propylene oxide.  Any of these will help in keeping a marginal plug lit, as well as in cold weather starting.  Supertigre mentioned adding 1% acetone to glo fuel in engine manuals from the 60's.  By all means, keep a squirt can of lighter fluid in your box for the winter months, for priming.

Is there a correct way to fit these single jet spraybars, or is it simply due to that rather radical slanted fox carb?

I believe that 15º below the horizon (this is when you view the intake straight down) is the correct place for maximum suction and although this is a small sweet spot to aim for at least it gives you a start point. (Rotate the spray bar so that the jet just disappears from view and it will be very close.)

Placing a jet forward or back seems to make little difference but I like to rotate to the back because the engine almost always tractors forward in use and the angled slipstream may influence where the real 'down' angle of the venturi will be.

Thanks.