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MVVS 1.20 with long pipe

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Old 02-03-2006, 07:55 AM
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Default MVVS 1.20 with long pipe

I got this used 1.20 with a long pipe and an OS carb and I am told it is strong and smooth-- It has great compression. My question is there is a fitting in the back plate with a small screw going into the fitting. Is this something that was added (maybe for a pump) after the fact since I noticed the pipe has no pressure fitting--which may explain the fitting. Also, where should I put the pressure fitting? On the pipe or the header? One final thing, What is a good prop for this combo, which is going on an "Icepoint" sport pattern plane.
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Old 02-03-2006, 08:56 AM
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Default RE: MVVS 1.20 with long pipe

AJF,


I have not seen such an engine yet, nor have I seen its 1.44 sibling.
They are said to be a bit problematic to set up.

Maybe PĂ© Reivers could add more info on it.

It does have two piston+cylinder sets, from the very successful #3090 GFS/R 10.0 cc (.61 cid) engine.
Induction balance and reliability are not one of its fortés, however.
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Old 02-03-2006, 12:33 PM
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Default RE: MVVS 1.20 with long pipe

Thanks for the insight. This is the single cylinder model (in case you were refering to the Twin). I guessed there have been some issues because of the expensive OS carb that has been added. Any other thoughts!
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Old 02-03-2006, 01:20 PM
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Default RE: MVVS 1.20 with long pipe

AJF,


I was referring to the twin...

A 1.20 single was not produced in my time...
The smallest big single is now the 1.60 (26 cc) and previously it was the 1.50.

Can you please post a digiphoto of your engine?


The new carburettors MVVS uses are much better than the older ones.
Some customers of mine substituted new #3216 and #3219 carburettors, on their OS and clone engines, because they were running too rich in the mid-range.

They needed shim stock wrapped around the spigot, to make the 13 mm MVVS fit the 0.5" carburettor hole in the crankcase.


As for the normal R/C carburettor for the larger singles; it requires fuel to be fed under some pressure.

Using a fuel pump is recommended (preferable to exhaust pressure) and this crankcase pressure fitting is used to supply pulsed pressure to the pump. This pressure tap is also needed for the optional Walbro carburettor, on these engines.
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Old 02-03-2006, 06:40 PM
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Default RE: MVVS 1.20 with long pipe

http://www.rcuniverse.com/market/item.cfm?itemId=164448

Here is the engine-- with picture-- that I bought
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Old 02-04-2006, 12:09 AM
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Default RE: MVVS 1.20 with long pipe

AJF,


This engine is clearly the predecessor of the later 1.50.

It is supposed to be an ABC (the 1.50 is) and has the same angled ports as the 1.50.


This engine has probably been run, with the pressure tap powering a pump.
The OS 7D is a suction carburettor, which would probably get enough pressure from the exhaust, if the fuel tank is small enough and is located very snuggly behind the engine.

...If your plane's fuel tank is situated on the C/G, you must use a fuel pump (Perry VP-30) and use that pressure nipple to power it.
(I cannot see it in the photos, BTW).

The original MVVS header for the 1.50, had a pressure nipple welded on the header.

This would not be ideal, but would offer a positive average pressure. You can try that, but don't even bother if the model has a C/G tank.


The proper prop for this engine would depend on the application, but the load class would be that of a 17x6.
On a model designed for the F3A pattern, I would suggest something in the vicinity of a 15x10.

You should be getting around 8,500 RPM. If you are seeing more, or less RPM, use an appropriately larger, or smaller prop.


The engine was sold to you by a merchant.
I doubt he had the time to actually run this engine (with over 2,400 ads placed in 3.5 years).

But with only positive feed-back, he's probably selling reasonably good items.
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Old 02-04-2006, 08:47 AM
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Default RE: MVVS 1.20 with long pipe

You have been a great help. Thanks a lot. My thoughts are in line with you.

Here in the US the only kick against MVVS that I have ever heard is the carbs--or else fuel distribution for whatever reason. So I am thinking that somebody had enough confidence to spend $70 in a modification carb to get things running right.

As for the merchant, I have bought a few things from Jerry before and if he says that it runs and idles well, I believe him. Looking at his rating-- and past experience- I don't think he would lie to me. We shall see. Thanks again for all the help.
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