I ran out to the airport to get some pictures of my throttle system and what did I find? NO AIRPLANE! Dang.
So I dug up some pictures from the build. It's a short rigid cable vernier push/pull throttle cable going through the firewall to a bellcrank that goes from the cable to the carbs on both sides. The bellcrank supports come off the cylinder head water exit on each side. Each end of the bellcrank is supported by a small sealed bearing. The connections from bellcrank to carb are a combination of threaded female rod and two rod ends. That's so I can adjust each strut's length. The idea was that once sync'd, nothing would move and the carbs would remain sync's forever. (Theoretically, of course.)
Details of the torsional spring install on the carburetor can be seen in Vans service bulletin 18-03-06.
Here's a link to the Vans SB. Link
Now for the $68 question, will VANs sell these springs to the general public or do you need an RV-12 serial number to get them?
Kitfox has a lighter spring. I put them on a couple days ago and it is MUCH better. Still have to crank a little friction on the throttle but 1,000,000 times better.
I’ll try this setup for a bit before deciding on the McFarlane throttle or just removing the springs altogether.
I'm pretty sure Van's will sell to a non-RV builder. Since they are here near me, I have bought quite a bit of stuff from them during my build.
Jim Ott
Portland, OR
Kitfox SS7 flying
Rotax 912ULS
My McFarlane throttle came with a set of lighter springs. Does the Vans Service Bulletin imply an issue with the McFarlane supplied springs?
- Gary
S7 SuperSport Tri-gear
w/Rotax 912, Oratex, Dynon
I have been using the McFarlane vernier throttle for 300 + hrs, with the McFarlane supplied lighter springs.
In 2015 when first installed with a new engine install, at the 25 hour engine inspection, I found a broken spring, McFarlane sent me a new set. They have been working since.
My throttle works great, smooth push , pull. l set the friction just so the vernier feature starts to work , never had creap of rpm at idle or on approach with it.
Back in 2015 when I talked with McFarlane , it was mentioned vibration as a big spring breaker, and I was asked if I had an RV12, we discussed the RV12 , seems they had quite a few of their carb springs break. They also said nicking the spring with pliers on install or such was a common reason for the spring to fail.
Kevin,
Kitfox Outback
912 ULS
Airmaster AP332CTFH-WWR70W
Summit Aircraft Wheel Skis
C-FOXW