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Convert Marz 2.5 diesel to RC?

Old 10-10-2009, 10:53 AM
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Mavi91
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Default Convert Marz 2.5 diesel to RC?

I have a new Marz 2.5 diesel and have seen an online video showing a conversion using an OS FP .15 carb. See the video [link=http://www.youtube.com/user/olikliolik#p/u/2/14twyJPWrCk]HERE[/link]. Since I have the OS carb on hand, I thought I'd try the conversion once I have broken in the engine in its current UC configuration. So, I'm looking for some advice.

I found good info about the Marz, including mechanical drawings [link=http://www.modelenginenews.org/ad/marz.html]HERE[/link] . The UC venturi tube can be removed and I propose to make a replacement on my mini-lathe with the outer end dimensioned to allow mounting of the OS carb. The replacement tube would have a straight-through bore so that the venturi effect would come from the carburetor. Since the engine will run on suction, I suspect that it may be necessary for me to make an insert for the carb intake to reduce the venturi . (Alternately, I'll use an OS .10 carb, if I can find one.) The existing needle valve assembly on the Marz would be replaced by a simple draw bar feeding through a notch on the outside of the replacement tube. I have the Aussie "muffler conversion" version of the Marz and I do intend to turn the collar upside down and run with the exhaust ports open as there is no muffler rule or problem with disturbing neighbors at the flying field I use.

As a somewhat more exotic question, I was wondering if the increased length of the induction path (~ 1 Cm) of my proposed RC conversion would be likely to have a negative tuning effect on engine performance?

I'd especially like to hear from anyone who has done an RC conversion of the Marz 2.5, or from people who have attempted UC to RC conversion of any diesel. I did successfully convert a .061 (1 cc) UC Norvel to RC using an ASP .061 carb, although I'm still fiddling around with the tuning in the hope of getting a lower reliable idle.

Thanks
Old 10-10-2009, 11:16 AM
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Dan Vincent
 
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Default RE: Convert Marz 2.5 diesel to RC?

I adapted an OS Pet .09 carb to a brand new Russian MK-17 diesel. It started easily and I was able to get it down to 2600 RPM on the very first run on a 9-3 prop. I don't know what it will do after the engine is broken-in. It responded very well to throttle changes.

The best thing is that I modified the carb, not the engine, so it can be restored to new factory condition.

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Old 10-10-2009, 12:11 PM
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Mavi91
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Default RE: Convert Marz 2.5 diesel to RC?

Dan,

From the pictures it looks like you retained the original needle valve and just use the carb body as a sort of incoming air valve. Is that correct?

George
Old 10-10-2009, 12:54 PM
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gkamysz
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Default RE: Convert Marz 2.5 diesel to RC?

Changing the length of the intake tract will have no effect on tuning. They are not sized at a length that is tuned now. Your thoughts on venturi size are spot on, but if you have to reduce it substantially it seems to effect the air bleed system. Another carb to consider is the Enya .09. I used one on an MVVS 1.5D I purchased as CL and it worked great. Venturi for the Enya carb .09 is ~3.7mm while the OS .10 FP is 3.9 or so. Subtract the spraybar size and it's pretty close to the area of the stock 3mm venturi. If it runs fine with a stock .15 FP carb, then you probably only need to verify that it draws fuel well enough with the nose up for flying.
Old 10-10-2009, 03:15 PM
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Dan Vincent
 
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Default RE: Convert Marz 2.5 diesel to RC?

George,

Yes, the original MK-17 holds the carb in place and the venturi diameter must be just about right as it works very well.

I got the idea from Stu Richmond as he used to have a MVVS carb on an MK-17 and would crank it up at shows to show how easy it started.
Old 10-10-2009, 04:46 PM
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Default RE: Convert Marz 2.5 diesel to RC?


ORIGINAL: Mavi91
From the pictures it looks like you retained the original needle valve and just use the carb body as a sort of incoming air valve. Is that correct?

George
George,

That's how carbs worked on the Pet .09. To convert from CL to RC, you would remove the spraybar, install the carb in the intake, line up the holes, and replace the original spraybar.

George
Old 10-11-2009, 09:39 PM
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Default RE: Convert Marz 2.5 diesel to RC?


ORIGINAL: Dan Vincent
I adapted an OS Pet .09 carb to a brand new Russian MK-17 diesel. It started easily and I was able to get it down to 2600 RPM on the very first run on a 9-3 prop. I don't know what it will do after the engine is broken-in. It responded very well to throttle changes.
The attached software will give you an idea that 2600 rpm is already quite low enough for any practical purposes.
I fly a slow vintage model powered with a Taifun Zyklon 2.5cc engine and an 11x4 prop, which gives 7400 rpm max and throttles down to 2800 rpm.
At this low rpm, the prop is already acting as an airbrake.
To use the software, you must first change its extension back to .zip from the .txt

Happy flying;
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Jg14399.txt (276.9 KB, 35 views)

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