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Which Prop for Break-in? MVVS 1.6 IFS Redhead

Old 11-12-2009, 04:35 AM
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cometravi
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Default Which Prop for Break-in? MVVS 1.6 IFS Redhead

Hi,

I have a 4 yr old redhead (never run) with a vlach ignition which i mounted on my CAP 232 with a Bisson Pitts muffler with the curved ends filed off. I have prepared 95 octane fuel with Motul 800 at 33:1 and have run 2 tanks (using a dubro 12oz/360ml tank) with a 16 x 8 APC prop on the ground. It will take to the air on sunday. I run it pretty rich (i think) for the first two tanks and got a run time of 15 mins at mid throttle.

Can i upscale the prop now since I believe it will be quite a while before the engine in truly run-in so which prop should I use for flying. 16 x 10, 17 x 8 or 18 x 6?

Also, The engine as not choking properly and needed my thumb on it so I have plugged the small hole on the choke to get better suction. Hope thats fine.

Also are the tuning instructions on your mvvs.nl forums for all types of Walbro carbs? Which carb is mine likely to have, the 481 or the 561? How do i identify?

The starting needle setting is as per the sheet in the box i think 2 turns for high and low needles. Is that ok for the first few gallons?

Thanks....
Old 11-12-2009, 05:06 AM
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pe reivers
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Default RE: Which Prop for Break-in? MVVS 1.6 IFS Redhead

Since this is an old type engine, there are a few things to do that greatly increase the life span of the connecting rod bearing.
1) Add one or two head shims (add 0.2 - 0.4mm). This will reduce compression ratio and will consequently bring the connecting rod bearing load into safe regions. With one extra shim, there is no power loss. With two extra shims, a little bit of power is lost (100 - 200 rpm), but engine handling becomes even sweeter, and fuel requirements are less critical.
2) The engine should be propped to allow 8000 rpm. Depending on exhaust system, that would be 16x10, 18x6 or 18x8 props
3) Use only the advised oils (see my web page www.mvvs.nl, left bar - petrol engines, scroll way down.
4) Use as good cooling as you can manage. See http://prme.nl/forum/viewtopic.php?t=148. Lack of proper cooling will ruin any high power engine.

Tuning the carb is typical for all WA/WT/WB Walbro carbs. Follow the method, and you will be fine. Do not tune the carb rich! There should be no 4-stroking in flight, and the plug should neither be black (too rich) nor white (too lean)
Also see teaching the Walbro to fly on my forum. It will save you a lot of in-flight tuning sorrows by providing a stable carb fuel reference pressure..
You can see the carb number imprinted on the carb body.
Old 11-17-2009, 03:32 AM
  #3  
cometravi
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Default RE: Which Prop for Break-in? MVVS 1.6 IFS Redhead

Thanks Pe.

Thats very informative.

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