2 Stroke Engine Tune

[Pickygit]

This is my first attempt using a 2 Stoke petrol engine (DLE35RA) and is mounted in a 1/5 scale Spitfire. I've managed to set up the engine OK with the cowl off and can run indefinately with little or no '4-stoking' at any throttle setting. However, when the cowl is fitted, (only approx. 15mm of the head protrudes from the bottom of the opening in the cowl through which the Pitts style exhaust is also exiting) I have a running problem. The engine starts and runs for about 1.5 minutes at around 1/3rd. throttle and then wants to die. Only tickling the throttle and choke will keep it going before it stops altogether. Of course, it's geting a bit warm in there but the engine doesn't appear to be seizing as I can freel rotate the engine after its stopped. Any advice would be welcome.

Edited By Pickygit on 18/08/2017 16:07:33

[Brian Cooper]

Yup, I had EXACTLY the same problem with a DLE35RA and a big Seagull Spitfire. The engine will also be impossible to start after it has become hot and will only start again after it has cooled down.

The problem is caused by the position of the rear exhaust. When the engine is inverted, the heat from the silencer goes straight up and into the (rear) carb . . and it doesn't like hot air.

The solution is to fit a solid heat shield between the silencer and the carb. A piece of thin plywood covered with tin foil works well on mine. . After that, you need to make the exit holes in the cowl bigger to get the exhaust heat away faster. .. An extra "trick" on my Spitfire was to fit a funnel shaped air intake to the cowl which directed (blasted) fresh, cold air straight into the area where the carb's intake lives. I positioned the (funnel) intake under the exhaust stubs on the cowl so it hardly shows. The duct looks a bit like one of the exhaust stubs but facing the other way so it can scoop air into it.

Basically, the idea is to keep hot air away from the carb, and blast fresh air into it.

B.C.

[TartanMac]

You might be getting a super charged type effect where the wash of air going into the cowl is pressurizing the cowl and making the engine lean. Hence you need to pump the throttle to keep it going or give it choke. Set the engine slightly rich on the low and high then fit cowl. You will just need to get to know the mixture offset you need through experience as your cowl is unique to your plane. I don't think you have a mechanical problem by the sound of it if you can achieve a good running setup without the cowl. It sounds like it is the change in atmospheric pressure inside the cowl that is throwing it off.

I just read the post above this sounds like a more likely problem to be honest never thought of temp of air

Edited By TartanMac on 18/08/2017 16:50:08

[Pickygit]

Guys, thank you for your responses. Brian - you describe my restarting problem very well also. I have included a picture of my cowl installation. Is it possible for you to show your 'funnel intake' installation please?

[Cuban8]

Would exhaust wrap from car spares shops be of use?

[Brian Cooper]

Here is a pic of the "scoop" to scavenge air and blast it towards the carb. Paint it to blend in and it won't show.... and it works beautifully.

The exhaust stubs on this model were also drilled out to help get hot air out of the carb area

B.C.

[Pickygit]

Thanks Brian. Looks like I've a few hurdles to jump!

[cymaz]

An excellent read! Not wanting to hijack the thread...I've the exact opposite! In the air the EME120 goes rich! I will post another thread. Any ideas most welcome?