The Changes Made

page created: May 19, 2000 last edit oct 17 2000 (in blue)

Hi Ted,
Report update. Sorry for the metric data (1 inch is 25.4 mm) 

Flew Sunday with mid range still a tad rich. Engine tended to flamed out when going leaner  (This went away with more run-in time)
Today, modified the throttle drum translation groove some more by 0.3mm, because turning in the low end needle 1/4 turn (0.3 mm), cured the mid-range, but spoiled the low end. (added: This is a good test to check the angles in the translation groove) (The dog-leg angle is now reversed.)

Preliminary test runs after final mods gave me the same mid-range setting as the high end. I.e. Rich high end now gives rich mid range and vice versa. All with a slightly rich low end. When I pinch the fuel line at idle, RPM goes up a bit before the engine dies. Throttle response is smooth, with only the slightest 4-stroking in maintained mid-range. Prop Menz 18x8 Wood. 

Summary of my mods so far: 

1) Added pump/regulator assy (Walbro Zenoah G23) , fitted beside motor 
2) Added exhaust pressure line to steel Walbro back plate (regulating membrane) 
3) Modified the throttle drum translating groove as per drum translation table below. 

(Note: This adjustment of the translation depends on production tolerances in individual engine parts, and is best done after initial running of the engine)

(added: all new dog-legged carbs run well with this form)

Table of the throttle drum translation stroke (in mm) related  to throttle settings

Mod 1 was a straightening of the groove
Mod 2 resulted in a slightly reversed L-shape

(See CAD drawings of all the carb mods)

The distance between throttle bore and groove, now is reduced to 2.7mm at the idle location. 
The translation for the first part of the barrel rotation is 0.3 mm less than for the last part of the rotation.
This prevents the excessive richening of the mixture that I experienced before, and the required excessive tweaking towards lean of both the low and high end needle which may cause flame-outs.. 
I would be much obliged If you could measure the drum translations in your engines (from fully open to just fully closed) 
Test flights will follow this week-end if the weather co-operates. 

Pé, 


Monday, November 08
Subject: Test flights G20/23

Hi Ted, 

Had a chance to flight-test the last mods to the carb (1.9mm stroke inverted L-shape) yesterday. Cool weather occasional a bit rain, cross wind. 

Idle setting slightly rich, high end slightly rich, (running just a bit unsteady). 
Excellent throttle response, except when accelerating from extended 1/3rd throttle, when the engine would still tend to load up and go a bit rich. In this case, as with a touch and go, the engine briefly clears it's lungs before winding up. Very stable in all flight positions, instant throttle response in normal flight. 

I think, if I adjust the low end leaner, it will improve a bit more, but the engine is still breaking-in, so I must go slowly in this leaning process. If I add glow to 3/8 throttle and below, all throttle response is perfect without the slightest hiccup. Time to start plug experiments; currently use an OS-F 

pé

Hello Pé
Glad to hear you're still having luck. I have found that the new engines are coming with a smaller venturi and 2 outlet holes in the muffler. I will measure the new carb as soon as I have a chance. 

Regards...Ted

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