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Engine basics => Engine set up tips => Topic started by: CharlesF on June 12, 2007, 09:43:30 AM

Title: Johnson & Fox questions
Post by: CharlesF on June 12, 2007, 09:43:30 AM

Hi

I have two questions:

1) I have a Johnson 35S in my Thunderbird. Tank is uniflow. Fuel is 25% castor, 5% nitromethane, 70% methanol. Prop is 10 x 5 Zinger wood. My problem is, the motor won't two-speed. It just seems to run at constant speed, either slow and rich or fast when leaner. Same speed on insides, outsides and inverted. WILL the 35S do a two-speed run? It's 35 years since I last ran a Johnson 35 in a Thunderbird, but very vague memories tell me that that motor gave a good two-speed run, peaking in manouvres. That altitude though was around 6000' ASL - but now it's more like 100' ASL.

I was flying this morning, but stopped after 4 flights because it was getting very windy indeed.

2) I bought a new ABC picton/liner for my Fox 35. I favour running it in a few minutes at a time fast and rich on a 9 x 6. Would the experts agree? Fuel same as above. I had two gallons made up for me yesterday.

As a comment, I also bought a new HOT plug from the fuel people (Model Technics) and put it in my Torpedo 19 greenhead. Now, it does not sag when I take the battery off  :)

Charles
Canterbury
UK

Title: Re: Johnson & Fox questions
Post by: Dick Fowler on June 13, 2007, 05:34:23 PM

Hi Charles, I'll throw my two cents in on this. The Johnson should do a very nice 4-2-4 break. The fact that it runs consistent is a blessing but the engine might need more engine load. Try using a bit more prop like a 10" X 6P or an 11" X 5P. Most stunt motors won't break unless they see some load increase. The large prop will put more load during maneuvers and it should then break.

I would not run an ABC engine too rich during break-in.  I like the idea of 2 minute runs but I also like to hear the engines stuttering between two  and four stroke during the run.

Title: Re: Johnson & Fox questions
Post by: wmiii on June 13, 2007, 08:51:13 PM

 That's how I remember my .35S running, constant speed, just what we seem to be asking for from current engines.

 Walter

Title: Re: Johnson & Fox questions
Post by: CharlesF on June 14, 2007, 04:40:42 AM

Hi

Jim Ivey, who worked with Hi Johnson says they just run at a constant speed - that's what they are supposed to do!

So that's OK

Thanks guys  :)

Charles