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Need help with MVVS 77


Old 09-15-2015, 01:38 PM
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Default Need help with MVVS 77

I can't seem to get reliable idle and smooth transition...only one or the other.

MVVS 77 (old style but "new" needle and spray bar). FAI fuel (no nitro, 20%castor). K&B 1L or 1S plug. 13/6 Zinger prop. Have 1/3 gallon fuel through it broken in as recommended in other posts here.
Starts like a charm. 10k+rpm top end no problem. Needle valve settings: high speed out 1.7 turns (manual says to start at 1.5 to 2 turns out from closed). The low speed needle is 1.4mm out from closed. (Manual says to start at 1.2mm out which I did). The fuel nipple on the spray bar is parallel to the crankshaft (i.e., "level").

By adjusting the low speed needle valve, I can get an idle speed of about 3700rpm. However, transition is rough to impossible...too rich, even tho full throttle is spot on. Leaning the low speed needle to get smooth transition ruins idle. It will simply die below about 4700rpm.

I found that leaving the glow plug driver on did not help. I see MVVS recommends a Novarossi C6s plug, which some sites describe as a cold plug. Could this be part of the problem? I believe K&B 1L or 1S are "medium".

One other matter about this engine stands out: It is frugal on the glow fuel, like no other 2 stroke glow I have ever run, more frugal than the old black head Webra 60s. Yet I don't believe I am running it lean. The smell of castor is in the air and the blue smoke is visible. I am running it a bit rich I believe.

If this were a Super Tigre, I would adjust the spray bar position to lean the midrange. Will that help with the MVVS?

Your suggestions are welcome. At this point I do not want to trust my airplane with this engine.
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