RE: MVVS Twins
Following on from my last post, here are notes Bill Vail sent to another enquirer about sorting the twin, which he kindly made available to me. I post them here for all to read:
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"It's funny how these threads go. I posted a picture of my collection of toy engines and I've received 3 e-mails asking about the MVVS 1.20!
My 1.20T did NOT run well as shipped. I would not have considered the engine flyable. The carb the engine shipped with would not pump enough fuel and while it would run, it was very close to full goose lean even with the needles back all the way out. Further, one cylinder ran considerably leaner and much hotter than the other. One cylinder ran nearly 100F hotter and of course the colder cylinder was prone to flaming out.
I contacted friend, genius, and hobbyist the late Jim Cline. He recommended the carb pictured. It has proven to be near perfect solution. The carb runs perfectly and the only reason I say near perfect is that the linkage to the throttle is not very handy and will require some work to setup.
As for one cylinder running leaner, he recommended placing a small piece of brass between the carb and reed cage bent such that it deflected some of the incoming fuel charge towards the lean (hot) cylinder. I had NO expectation that such a simple solution would work. It took some tinkering/trial and error but it worked better than I could have dreamed.
At this point I should mention, I've never flown this engine. I did all my tests while it was strapped to the test bench. I removed the engine running extremely well and had every intention of building something that would showcase its looks but the holding pattern over my building bench is large and I haven't gotten around to it - yet (12 years ago)! I did keep notes of my running though.
Dec 1999 - Air temp 70F
Mufflers -Bisson twins
Plugs - Fox IB
Fuel - 8% nitro, Klotz synthetic, and castor.
Prop - APC 15x8, 8,800rpm with solid 1,500rpm idle
RT cylinder 265F, LT cylinder 255F max. (typical - RT210,LT200 at plug)
While it took me several enjoyable days and a fair bit of fuel to get this engine sorted out, all credit goes to Jim. In this ARF/E world, I miss folks like him. Sometimes it's easy to back off sharing what took me days to discover and then I remember Jim who would share everything he'd learned over a lifetime and ask for nothing more than to let 'em know how it went. The bit about modifying the airflow with a bit of brass was genius and he shared it without a second though. I've used it on other twins since and NEVER heard of, or seen reference to, this simple mod anywhere else. If you choose to pass this tip on, please reference Jim.
Let me know how it goes!"
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