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Old 03-14-2006, 06:03 AM
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Default MVVS 45IRS/MG


My MVVS 45 primes very hard when the tubing is empty of gas. She needs more or less 40-50 flips with choke closed and throttle open.
I changed the tubing and double checked the tank with no effect. The gas tubing length is less than 6 in and there is no air leakage.
Do I need to shield the small hole in the choke disk?
Since I have run only a couple of tanks through this engine I use the included oil at the recomended 30:1 mix.
Using a Bisson muffler with all buffling removed I get 6760 RPM on a Menz 22x8 on the second tank.
This is approx. 4.1Hp according ThrustHP (more than 1Hp less from the listed power).
How much improvement should I expect while the engine breaks in and going to 40:1 mix?
Is this big lack of power cause of the Bisson muffler ?



Old 03-14-2006, 07:18 AM
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Default RE: MVVS 45IRS/MG


The rated power of this engine is stated with the #3204 canister silencer, which will give you a noticeable RPM improvement, over your current Bisson muffler.

The Walbro carburettor on this engine is equipped with its own internal fuel pump.

The pump nipple is the one, which is closest to and needs to be connected to the nipple on the crankcase.

The pump operates irrespective of the choke position and it should be is enough, to rock the prop back and forth, in a wide arc (no flipping), to bring fuel into the carburettor.

Make sure this happens on your engine.

After fuel reaches the carburettor, the engine is capable of starting within just a couple of flips.
Old 03-14-2006, 09:25 AM
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Default RE: MVVS 45IRS/MG

Thanks for your answer,

In how many "arc" flips should I expect to have all tubing filled with gas? A friend of mine told me that his DA pumps from dry in less than 3-4 flips.
In my MVVS this is not the case for sure.
And another question : How can I avoid the rich moment when throttling the engine from full, down to idle. In another thread about Walbro carbs I read
that this caused by fuel dripping from the carb high speed jets when throttling the engine down. I also read that this won't happent if the Walbro
is equipped with a check valve in the high speed jet. This "rich" moment last many seconds (10-20) in my engine making the idle unreliable.
How can I minimize this effect ?

Old 03-14-2006, 03:22 PM
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Default RE: MVVS 45IRS/MG

It helps to get the fuel up to the pump, if you also close the little hole in the choke plate. Also it helps, if you supply a little pressure to the tank. (blow on the vent line)
This is a Walbro issue, not MVVS. Clean the carb well, and re-fit. Do not tighten the central cover bolt much, because that will cause the pump petal valves to curl up.

About tuning the carb, a lot of bed time stories are told as stuffing for the forae. I found,[link=] this way works best, and is quick to adjust[/link].

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