cylinder and head for walkerjet paramotor

[aquatix]

When you've finished flying for the day can you run the carb dry? it maybe when you put your motor in a warmer environment the pressure change in the tank is forcing fuel through the carb in to the engine.

What ratio are you running at 30-1? I run mine at 50-1 with fully synthetic and no problems.

Tank is vented so no issues over pressure change, and there is no leak through from carb - even when applying a steady positive pressure on fuel line. Can't run it dry without fitting a quick release coupling, and I prefer to keep things simple to avoid problems.

Engine is usually down to tickover for at least 20 seconds before landing, so very little fuel being drawn through and any excess oil / mixture should be expelled during the normal combustion cycle. No traces of excess oil in exhaust when disassembled to re-grease the joints at regular intervals.

I run the manufacturer spec 3% (33.3:1 in old money ) although Kobra said it was safe to go down to 2.5% (40:1). Not sure I would want to drop to 2% (50:1) even though I use a full synthetic oil and Simonini only specify a semi-synthetic for use with the Evo engine. My view is a higher quality oil can't hurt it and the "bottom end" certainly seems to be getting well oiled and things would be great if the engine wasn't inverted.

Reason for keeping the recommended oil mix is the CHT gauge shows the engine will hit maximum allowed temperature during a sustained fast climb. If it wasn't fouling the plug I'd normally be happy with that amount of oil remaining in the engine casing, as at least it offers some protection during cold starts.

PS - just seen your post Barry ..... if I can't pinpoint any other problems I'll consider a dry break, since it was standard practice on my outboards. Where did you get yours from ? Are all your other problems (particularly exhaust) sorted now ?

[bendmeroundthehedge]

>Posted this a while back.

> > "People believe that the oil just rushes right through a two-stroke

> along with the fuel, but that just isn't

> > so. The engine is lubricated by the residual oil that builds up in

> the crankcase. All the oil in the fuel does is replenish this oil. It

> can take an hour or more for the oil migration through a two-stroke to

> result in complete oil exchange.

> > What happens to the oil in your fuel when it goes into the engine?

> While the oil is still suspended in the liquid petrol, it cannot

> lubricate anything. It has about as much lubricity at that point as

> straight petrol. When the petrol enters the engine, it evaporates,

> dropping the oil out of suspension. Now that the oil is free, it can

> lubricate the engine.

> > The best way to determine if you are running enough oil is to check

> the level of the residual oil in the crankcase. When you are using a

> sufficient amount of oil in your mix to thoroughly coat and lubricate

> all of the moving parts, then after the engine is shut down and sits,

> enough oil will drain down into the crankcase to form a small puddle of

> residual oil at the bottom. After a major stripdown rebuilders

> > pour oil into the crankcase.

> > The oil eventually makes it into the combustion chamber, where it is

> either burned, or passes out the exhaust. If the combustion chamber

> temps are too low, such as in an engine that is jetted too rich, the oil

> doesn't burn completely. Instead, some of it hardens into deposits in

> the combustion chamber. The rest becomes the dreaded "spooge". The key

> to all of this working in harmony is to jet lean enough to achieve a

> high enough combustion chamber temperature to burn the oil, but also

> still be able to supply enough oil to protect the engine."

> >

None of the above process begins until the engine is at working temperature,

Until then oil flows straight out with the petrol.

Also the amount of oil each engine uses varies. A small engine or one that is thrashed will use more.

A Large engine used with mechanical sympathy will use less.

The Manufacture gives oil % for worst case scenario.

Most of the oil will settle in the piston in an inverted but not all, hence your oily plug.

[aquatix]

All the above is perfectly true, but would seem to make it a common issue for all owners of inverted engines. Never had the problem with my F200 or Simonini mini2+, just the Evo motor. Perhaps this motor is best suited to installations with spark plug on top ?

Engine temps certainly aren't cold and it isn't jetted too rich (manufacturers spec). There is never any exhaust smoke or oily residue on prop after a long flight, which might suggest a surplus % of oil that could be reduced.

It takes a good few days for this residual oil to work down to the plug so not sure that 20 seconds of running the carb dry would make much difference. Might try a different brand of oil, or maybe just accept it as the price for having a well oiled engine......