MVVS 77 issues
I'm looking for help to diagnose, and then solve, two issues with my MVVS 77.
Have been breaking in a brand new MVVS 77, on test stand, test stand screwed tightly to solid deck, zero nitromethane, just 20% castor and methanol. Jtec pitts muffler.
Have run it with an 1, OS#8 plug, 2.the plug supplied with the engine and 3. the plug supplied with a differrent MVVS 77 I had. Now have run 1/3 of a gallon thru engine. Running to full throttle awhile, than down to reliable idle, then repeat. Reliable idle now about 2400 rpm, with little exhaust smoke; smokes up a cloud from about 6K to WOT, about 10K. Running APC 13 x 6, balanced to a fair thee well, tip to tip and across the hub.
Fuel line pinching indicates low needle is spot on, and high end is still a few clicks rich. Idle to WOT quite smooth, only slight hesitations. Generally smooth running EXCEPT around 2,800 rpm where it vibrates big time.
It displays the same strong vibrating with all three plugs, and with a 13 x 8 Zinger Pro, 12 x 6 Zinger Pro and 13 x 6 Zinger.
I can think of no other glow engine I have used that displays such serious vibration. I do hear what sounds like possible pre-ignition.
Oh, the weather has been between 60 and 75 degrees F, 50 -70% humidity, 1,500 feet ASL.
Hope there is a fix, thanks.