Thorp Air Command - T18.net

I have a Ellison TBI on a VW conversion that has had a couple recalls by Ellison in the late 1980's and early 90's, O ring failure was part of the problem. They no longer support the small unit that could be used on 65 to 85 HP engines.
Ed Torberr

Okay, I'll play Devil's Advocate. I don't know anything about Rotec, but Ellison has a page dedicated to Service Bulletins. Even the pathetic, POSA style slide carb from Sonex has such a page.

The Ellison is an elegant solution to the problem, but I don't know how well they work in practice. I believe this style of carb was used in race car engines for decades (before fuel injection took over). The M-S is, of course, very well proven.

Okay, I went and looked at Rotec's site, and they do have a page for Advisories. On their installation page, they do recommend a primer: "a cockpit mounted TBI primer lever is highly recommended as it could be used to save your bacon should vapour lock or some other fuel starvation anomaly ever occur." They do not, as you point out, note one "anomaly" might be their failure to properly clean out the unit at the factory.

Their suggestion to use the mags to kill the engine is a bit scary.

Problems with sticking on slide carbs is common. Makers have tried various coatings to try to solve this. AeroVee sells a beefy lever quadrant to try to help you over come the high forces. Oh, dear.

The Ellison seems to be the only slide carb for airplanes which has a decent reputation. They are not cheap, and their design includes a proper idle cut off. Still, I'd only consider it if the carb location allowed for a linkage to actuate the (sometimes stiff) slide. I wonder if any slide carb has been built with roller bearings on the slide?

“The Ellison is an elegant solution to the problem, but I don't know how well they work in practice. I believe this style of carb was used in race car engines for decades (before fuel injection took over). The M-S is, of course, very well proven.”

FYI – I have had an Ellison EFS-4 on my 180hp O-320E2D for approximately 16 years and 700 hrs of flight time. It has provided excellent performance and I am very happy with the unit and the customer support. It was my solution for obtaining less drag in the lower cowling caused by an M-S hanging from the bottom of the oil sump. I directed the ram air in and into a plenum that fed into a rear mount oil sump. I have never experienced a “sticking” slide plate or any other anomaly. I did send it in two years ago for an upgrade and had all wear-parts replaced (Teflon slide plates, etc). I’m happy enough with it that I found another one with 20 hours on it and will put it on the Pitts S-1C that’s somewhere down on the To-Do list.

I looked over the notes on my old computer and find I am guilty of guilt by association. I thought I recalled reading of a sticking Ellison slide, but I can find no note of this. Some part of my (aging) brain had lumped them in with all the crummy slide carbs on the market. My apologies to Ellison!

David Read's T-18 has a non-standard carb installation which cleaned things up nicely.

A quick look around the web with google suggests an Ellison installation takes more trial and error than with a carb, but the people who get it right like their Ellisons.

Karl

I see the Keihin motorcycle carbs use rollers. They are an interesting design, using a float instead of a diaphragm regulator, and they have an accelerator pump. I can't see any advantage to this design over the M-S. The Ellison at least offers simplicity, not that an M-S carb is complicated.