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912 ULS Carb Throttle Springs?

J

Jcurry

Well Known Member
Hello,
I ordered 2 carburetor o'haul kits. The kits came with non painted and different style throttle springs than I have. I called them and asked if they have the red and blue style springs that I have? They said no that it is a "Van's" thing. Are the Rotax springs in the kit acceptable to use? What is the purpose of the red and blue springs in comparison to stock Rotax springs?
Thanks in advance for the education.

Jack
 
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The purpose is to bring your throttle to full throttle if a cable breaks so you theoretically get to an airport at full power (well at least 1/2 the engine will be full power ;) I think we have gone thru 4 iterations of throttle springs. In reality the whole concept was really designed for open cowling setups which is Rotax roots. Sorta like safety wiring the air filters. Pretty sure they aren't going aware on Rv12.
 
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Jcurry said:
I ordered 2 carburetor o'haul kits. The kits came with non painted and different style throttle springs than I have. I called them and asked if they have the red and blue style springs that I have? They said no that it is a "Van's" thing. Are the Rotax springs in the kit acceptable to use? What is the purpose of the red and blue springs in comparison to stock Rotax springs?
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I think SB 14-07-23 and SB 14-09-10 got rid of the red and blue McFarlane springs. The current springs as per SB 18-03-06 are quite a bit different and look like this...

1740175804343.png
 
For many hours/years I was happy with the McFarlane springs albeit they seemed a bit on the overly powerful side. FYI, I use the old-style non-vernier type of throttle. I now have installed Van's torsional-style springs i/a/w Van's SB 18-03-06 and I am very happy with them.
 
I have both the torsion spring and the extension spring on my throttle arms. Keeping the cable taught aids in carb synchronization...
 
The SPRING-00002-L/R-1 torsion style throttle springs were developed to solve the high failure rate of the extension springs - we (Van's) seen the extension springs breaking or missing in less than 10 hours flight time. We (Van's) never had a report of a broken torsion spring after they were released.

The -1 torsion springs were engineered to apply the same amount of force as Van's SPRING-00002, which is less tension than the McFarland and Rotax springs, to help prevent throttle creep caused by the original higher tension springs.
 
rk2436 said:
The McFarlane springs work just fine. Vans went way overboard with the different spring SB’s imo.
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For those that weren’t around earlier in the evolution of the RV 12…

The springs that are supplied on the carburetors from the Rotax factory are quite stiff and most RV – 12 pilots found it difficult to find a throttle friction setting that allowed them to easily adjust the throttle, but not have it creep on its own.

So Vans started supplying lighter springs produced by McFarlane. At some point, those springs started failing because of vibration induced fatigue. Vans even worked with McFarlane for a while trying to find a spring design that would survive more than one or 200 hours.
At some point with no success, we gave up and designed our own spring, which is what is in used by most ULS RV-12 owners and is the part that was linked in a previous post.
 
Piper J3 said:
I have both the torsion spring and the extension spring on my throttle arms. Keeping the cable taught aids in carb synchronization...
Click to expand...
Yes, keeping those cables tight is critical to carb sync, and in my experience none of these springs have enough tension to really do it well. I hadn't considered using both. I'm convinced this is why so many people struggle with sync and make claims like "you're almost never going to be in sync at all throttle settings". My sync is perfect, at all throttle settings, and never needs fiddling. Instead if using ever stronger springs, I achieve this procedurally by always advancing the throttle beyond where I want it, so I can pull it back a smidge. Uniformity guaranteed. I do it for start up, warm up, run-up, cruise, and sync testing of course.
 
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