nowinkk

I wonder what's the proper size propeller to use on the spe 40. Mine was a wooden 18x6 which seemed too small in pitch.

outahand

Im using a 20x8 and the engine runs good with. I know it will run better soon as I get this walbro wt540 on.

nowinkk

My spe 40 engine coughed during the flight with the 18x6 onboard. Did it mean engine was tuned too rich or the prop was undersized? I may try out my other prop which is a Master Airscrew 18x10 fibre filled.

outahand

Its hard to say because that could be ignition, carb, spark plug or bad gas. I would put a big blade tune the carb in with a tac and see what happens. The engine makes the power if its tuned right.

nowinkk

Thanks for the advice.

I would go ahead and fix up the 18x10 first for another flight before tuning the carb and see how it performs. Anyway, I am still running in my engine (till now hardly 1 gallon of fuel had gone through) and leaning out the carb wouldnt be so soon, I guess.

Jake Ruddy

My Feedback: (40)

Yes that is a problem... that's not a safe way to run an engine

No he probably wont have them on hand... he hasn't worked on them for awhile now... it's also more to it than that. He also balances the crank. It's a bit of a process... but I know he's backed up right now so it would take a bit of time.

Jake Ruddy

My Feedback: (40)

You should tune your carb from before the first flight... it's important to get your mixure right so you are not building up carbon or running lean. 18x10 is a better prop for this engine... 20x8 - 21x8 is more for a 46.

nowinkk

Yes, the carb was tuned richer on running in, isn't it that way?



Sorry, the word more lean should be replaced by richer..a typo

NM2K

My Feedback: (14)

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You cannot run a gasoline fueled/spark ignition equipped two-stroke engine too lean. It will just quit. Running rich is one glow habit that should remain with glow engines. It has no place in gas/spark two-stroke airplane engines.

Running lean in a glow engine advances the "spark", so to speak. This does not occur in a gas fueled/spark engine.

Running the spark too far advanced/too much compression will kill (hole a piston) in a gas/spark engine, but not running the mixture too lean. It just won't run.


Ed

Jake Ruddy

My Feedback: (40)

That is just plain wrong If an engine is set too lean it runs hot and hurts the engine.

A gas 2 stroke engine will run lean all day long so I don't know where you get this idea from. All you have to do is pull verticle and you can hear an engine that is too lean sag. That same engine can be flown all day long without a problem even though it's set lean. However it won't last long because it's burning up inside.

I also fail to see what the mixture has to do with timing.. but maybe I am not following your example.

outahand

Hey there I put that 540 wt walbro carb on my spe 40 and the rpm went up 100 I dont know I will have to play with it Do you think going from a 340 to 540 should make a big change like 500rpm? Also what kind of rpm range is all your 40 gas engines running at and what size prop? I tried to call Scott and I left a mesage but never got a call back like the customer service. I went out to my park out here and two guys came both crashed within 2 muinets lol it was a great show.

NM2K

My Feedback: (14)

All two-strokes cough occasionally, glow or ignition. I've always wondered why folks get upset over an "occasional" cough or sputter. More than something occasional warrants investigation.


Ed Cregger

nowinkk

After changing from a 18x6 to a 18x10 prop and leaning out 1/8 turn of the H needle, the spe 40 doesnt cough at high rpm, only occasionally at low rpm.

gpar

outahand:
The wt-340 venturi is 7.94 mm. and the wt-540 venturi is 13.49 mm.
So with such a big difference in size you must expect a big change in rpm , maybe 1000 more

First check this link to make sure your black plastic piece between the carb and the engine is right:

http://www.rcuniverse.com/forum/m_34..._WT-540/tm.htm



Then try closing down slowly the hi needle using a tachometer and let us know what you got.

NM2K

My Feedback: (14)

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You are confusing glow engines with spark/gasoline engines. Completely different animals. The glow rules mostly do not apply to gasoline engines.

Mixture controls the timing (ignition point) in a glow engine. Running too lean in a glow engine advances the timing and causes preignition, eventually leading to detonation, which damages the engine.

Gasoline engines' timing is controlled by the ignition timing. If you deprive a gasoline engine of cooling air, you can damage it in a similar manner as a glow engine tuned too lean, which can also be damaged by a lack of cooling air.

You have come a long way in the short time you have been involved in model flying, but you need to bone up on the differences between glow and gas. I wish I could get a reprint of Gordon Jenning's "Two-Stroke Tuner's Handbook". They have been out of print for a while, but they can still be found. I stumbled upon that book in the Seventies and loaned my copy to a friend. Don't have the friend or the book anymore (he passed, sadly).

One more thing, when a gas engine sags in the vertical, it is because it is not up to the task at hand, not necessarily because it is lean. It does sound just like a glow engine going lean.

Don't feel bad. There are fellows like Ralph Cunningham and Dick Hanson that make me feel like a beginner in gas engines.


Ed Cregger

gpar

ed :
If I undestood you correctly we should not worry to tune a gas engine "too lean" to get the maximum rpm, because the engine wont start and so we never can damage the engine or get a dead stick because the setup was "too lean".
Is that right ?

seagull extra

My Feedback: (12)

Ed you are incorrect with your statement that you can not hurt a gasoline ign. 2 stroke by running lean.

NM2K

My Feedback: (14)

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How large is your fuel tank? TIA


Ed Cregger

NM2K

My Feedback: (14)

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Well, it is okay to have differing opinions. I know I'm right on this one because of the excellent teachers I have had over the years. However, I'm still ready to listen to your explanation as to why I am wrong. I'm still capable of learning something new - even at age 60. <G>

Please proceed...


Ed Cregger

NM2K

My Feedback: (14)

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I never said that it wouldn't start.

If you choke the engine sufficiently, the engine will start because of the fuel already in the engine. Carburetors do nothing until the engine is turning over and air is flowing through them. Starting has to do with sufficient prime in the engine to get it going. Needles can be removed and the engine will still start.

I can remove the carb from any engine (you can too) and get it to start. All I need is a squirt bottle with some fuel in it so I can inject the fuel into the engine. The engine will then start, if there is sufficient fuel and it isn't flooded.

Glow engines, because of the type of fuel they use and the characteristics (stoichimetric ratio) of the fuel necessary for a successful burn, will run under conditions that would shut down a gasoline engine. Gasoline is much more demanding of everything being "just right" in order for the engine to run. This is one of the reasons I say that you can't hurt a two-stroke, gasoline fueled, spark ignition engine of the type commonly used in model airplanes by running the mixture too lean. The engine simply will not run, whereas its glow counterpart is quite capable of destroying itself.


Ed Cregger

karolh

Lesson 101 complete.

Karol

gpar

If the setup is too lean the engine runs for about 1 minute or 45 seconds and quits.
The time it needs to get too hot. I perfomed this test

altavillan

My Feedback: (1)

I see you guys have found a use for the engine. And as I've mentioned about all it's good for. Engine cooking experiments. Hopefully far away from spectators.