Zenith Aircraft Builders and Flyers
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Rotec TBI Carburetor
I am running a Rotec TBI on my FlyCorvair engine in my Cruzer. When I initially picked it up, I couldn't find any photos or help with linkages, etc so this is what I came up with.
The throttle bracket on the carb itself is cut from a piece of 2.5" square tubing. It mounts via the two rear main mounting bolts and 3 of the diaphragm bolts on the carb. I am running a single pilot-side throttle only. The bellcrank came from summit racing. I had to machine the push/pull link to connect it to the throttle slide. There is a small safety spring attached at the front connecting to the air box. If the bell crank or anything fails, it will pull the throttle full open.
The airbox is my own design, roughly based on the popular van's airbox utilizing a round K&N air filter. The carb heat is a combo carb heat/cabin heat design like WW recommends. Carb heat works fine, we'll see if it is enough to heat the cabin.
The mixture cable attaches to the block using two of the rear oil pan bolts. I'll have to get some photos of that.
Anyway, I hope this is helpful to some folks looking to use the Rotec. My plane isn't flying yet, but I have broken the engine in and done some taxi testing with this setup, it works flawlessly thus far.
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rotec TBI carb corvair.jpg, 290 KB -
rotec tbi air filter corvair.jpg, 263 KB
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rotec TBI carb heat corvair.jpg, 284 KB
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Replies to This Discussion
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Permalink Reply by Jonathon Payne on
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Does TBI need carb heat?
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Permalink Reply by Peter Eiberger on
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You aren't likely to get carb ice, but you can get manifold ice on any engine with a "cold" manifold. In the first photo, you can see the condensation on the manifold from the drop in temperature. That was idling on an 80 degree day.
Cold manifold = Continental, Corvair, VW, etc
Hot manifold = Lycoming (basically full time carb heat)
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Permalink Reply by Ramesh Nori on
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Hi Peter - Have you looked in to James Weasemen's cowling kit for Corvair engine ? Also is your Corvair engine from WW ?
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Yes its a FlyCorvair/SPA engine. I am using the FlyCorvair nose bowl, but I built my own cowling and baffles. I wasn't a fan of the square intake and flat bottom look. I have a NACA duct in the nose bowl below the spinner that feeds into my airbox.
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Permalink Reply by Paul Saccani on
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Peter, that looks like you have handled the linkages quite well. Just double check that there is no sideways movement on the mixture, as that can result in a fatigue failure. The part with the arm on just falls off and the spray bar stays at whatever position it was in.
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What do you mean by "sideways movement" on the mixture? I am using an A-750 vernier control with a heim joint that pushes/pulls straight inline with the mixture arm, so there shouldn't be any side-load like you are speaking about.
Here is another angle (sort of) after I re-indexed the arm for the mixture stop.
For those that don't know, the Rotec (by design) can supply far more fuel than needed, so you have to limit the travel of the mixture arm. I'm not going to re-type the manufacturer instructions, so hit their website if you want to know more.
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G’day Peter, so as we look at your latest picture, in-out is the push-pull operating as it should, sideways is in the same axis as the bolt holding the rod end onto the mixture arm. The range of movement available via the control should also not allow contact by the mixture arm with the stop pin, as that puts an off axis load on the connection. The failure point is internal, where the sleeve on the mixture bar joins a threaded end. I don’t have photos of failed parts to hand at the moment. The nice thing is, if it does fail, it stays where it was set. The failures I have seen where at a mixture rich enough to allow for landing. Being aware of the potential problem, you may be able to identify it and mitigate it if it ever happens when you are LOP in the cruise at 10,000 feet. There is the priming system which could help, but if you identify it, you could simply maintain height until you get where you are going and do a spiral descent and glide approach. But as I said, your installation looks good.
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A couple of quick updates:
I removed the (boost) fuel pump entirely.
- The fuel pump isn't needed in my application at all, I had it as a boost pump for startup etc
- I also have small header tanks
- The drastic change in fuel pressure from gravity feed to 6psi would change the mixture
- using the 2.5psi Facet pump (40163) would be a better choice for a boost pump
I removed the Earl's 35 micron fuel filter as it was hard to purge air from mounted horizontally.
I replaced the 100 micron screen in the Usher gascolator with a 35 micron screen (from McMaster Carr).
Overall, my fuel system and checklists got simpler and I am happy with the results.
- The fuel pump isn't needed in my application at all, I had it as a boost pump for startup etc
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Permalink Reply by Bryan Walstrom on
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Sent you a "Friend Request" on here. Can't message you "PM anyway" until accepted. I wanted to ask you to give me a call. Thanks.
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Permalink Reply by charlie rosenzweig on
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Peter thank you for posting all these pics. For a new builder it is very helpful!
As far as your tac welded exhausr pipes, curious, what is the metal you are using? Also what did you use to cut those ends with, the intersection looks excellent.
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I used a hole-saw in my mill to make the notches for fit-up. Material is 304 stainless. I tacked them together with the MIG and then went back and TIG welded them (back purged). The graphite gaskets require a turned "funnel" for each stack to mate up, which I made on my lathe.
Needless to say, the exhaust WW sells is an excellent value and should be your primary choice.
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Looks great thank you.
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