Older twin 3W's and induction problems

[norm68]

For anyone out there who has experienced unrelenting problems with their motor going from fine straight n level to super rich (spluttering and even quitting) when thrown to knife edge or inverted, and have ruled out everything else (ignition, air leaks, air pressure in cowl problems, fuel supply, etc, etc), then I might have something that could be the answer you've been looking for.

I found that my reed chamber on the old style 3W 85 twin suffered from fuel accumulation (puddling) when run upright and when the engine is tipped over, the excess fuel is dumped straight into the crank/cylinders and the engine runs like a pig, eventually clearing but spluttering and sometimes quitting first.

My remedy was to make a boot which fits over the reed cage and fills the gap between the cage and the crank case housing. It has transformed the engine and now it is rock steady in all attitudes. I'm betting the early 3W twins had a bit of a flaw in the induction design which allowed this fuel to pool.

More info is at the following thread http://www.rcuniverse.com/forum/m_51..._5/key_/tm.htm

I really hope this is of interest as it has been a very annoying problem which I'm very pleased to see the back of.

Cheers.

[xtreem3d]

if it doesn't hold up to heat and gas is it a piece that you could possibly machine out of aluminum (or something else)? great work BTW !!!!!

[snap a saurus]

Was the performance affected in other words did you loose any power?

[plane]

Snap, my guess would be you'd actually pick up a little power. The 2 stroke guys call it packing the crankcase, which basically means you have less volume inside the crankcase so more fresh gas charge goes to the cylinders.

BTW Norm, great thinking on this one! My guess it'd work on all bottom induction motors.

[norm68]

Thanks heaps for the encouragement guys.

No loss in power at all. I might be imagining it but there seems to be a small improvement in throttle response. The fuel air mix has no choice but to get where it's intended without too much fussing about; that's what my X-Ray vision's telling me anyway... So far after 20 flights the boot is showing no sign of stress and I'm loving every minute of it.

An aluminium version is a good idea. I'm not nearby a CNC mill though to give it a try. I wonder if a metal boot would have any ill effect due to heat conduction. I think the thermal insulating properties of the sealer-based boot may be advantageous but I'm not basing that on anything other than a feeling.

I'm going to make a cleaner, more respectable mould and make a small quantity for people to try.

Later, N.

[norm68]

Have now done 35 flights and the boot is still in original condition. The engine is rock solid. What a difference going from an absolute pig where my trust and respect for the unit was hovering around zero, to now where I just can't do a thing wrong by it no matter how hard I try (hehe).

I'm going to make some more to pass around in the near future.