Rotec MKII TBI

[SonexN76ET]

I have posted a few pictures below to help those who may be installing a Rotec TBI Mk2. I CAN NOT YET ENDORSE this product because I have not done enough testing of it yet. Rotec's directions are not as good as those of the AeroInjector. The AeroInjector technical support from Sonex is far superior.

Here is a picture from the front looking to the back of my Rotec TBI MK II. It shows both the mixture and the throttle cables. This picture shows the throttle with a cable from Aircraft Spruce which was not strong enough. I have replaced it with one from Steinjager that has a tough plastic outerwall over the metal cable sleeve. The throttle on the Rotec TBI MkII is extremely stiff. Rotec claims it will improve (get less stiff) with time.



And here is from the front looking at the mixture cable:

[SonexN76ET]

Here is a view from the side. The fuel line has an AN4 fuel/vapor return line on a T fitting along with the 6AN fuel line. I have a Facet fuel pump. The Rotec TBI will run without the pump on but you have to have at least two gallons in the tank to create sufficient fuel pressure without the pump on.

[SonexN76ET]

Here is a picture of the primer lever and the mount for the push pull cable for the throttle.



Jake

[fastj22]

Jake,
No air filter?

[SonexN76ET]

I have not included pictures of the air filter in these series of photos. I can take some photos with my air straightener, air filter, carb heat, and induction plenum installed later in the week.

[SonexN76ET]

Here is a picture of my Rotec installation with the air cleaner and the intake plenum. Carb heat comes in on the other side of the plenum. There is a flap that cuts out the ram air when you apply carb heat. The filter is a larger size K&N. It is E-3221.

I still have not completed my testing.

Some initial observations:The AeroInjector has better instructions. The tech support from Sonex is far superior in my experience. I also believe that Rotec made the tolerances too tight on the MKII TBI which make the throttle extremely stiff.

The keys to tuning the Rotec TBI are to have smooth incoming airflow, setting the idle mixture screw, setting a mechanical throttle stop at the appropriate setting, and setting full rich stops on the cockpit mixture control (mine will not run at the full rich setting at full throttle and required installing a stop.



Jake

[lpaaruule]

Hi Jake,

A friend of mine with a Zodiac 601 couldn't get his Jabiru 3300 with Rotec TBI to run at full throttle, and initially put in a throttle stop. We ended up enlarging many of the holes in the spray bar from 0.3mm to 0.35mm (IIRC) with a small drill in a pin vice. Now his engine runs great at full throttle. We determined he was running way to lean at full throttle because his fuel flow was only 6.5 gal/hour according to his flow meter. Now it's about 10 gal/hour at full rich. This was a last resort after adjusting the idle mixture screw to no avail.

I have a first gen Rotec TBI that was included with a Jabiru 3300 I bought from another builder. I remembered you commenting that you put an oops fitting on your tank in case you wanted to install a vapor return line. I'm very interested in doing the same thing, but hopefully I won't need to used an oops fitting. I'm also considering removing the mechanical fuel pump from the engine (per Sonex instructions) and using an electric fuel pump. I've heard of the mechanical fuel pump actually heating the fuel because it's mounted right on the engine. Besides, the plumbing could be simpler that way, and there would be less unpressurized fuel than by opting to used the mechanical fuel pump.

My thought is that I'd mount the fuel pump fuel pump on the firewall right before the gascolator. That way the fuel in the gascolator would be pressurized. I'm also thinking about putting a flow meter between the regulator and the TBI and either insulating it or using a blast tube to cool it. The fuel line upstream of the regulator would have a T-fitting that would have a vapor return line connected to it.

So I sort of have a plan, but I have to figure out which holes on the fuel tank I'm going to need to use, and for what. I'm thinking the top sight glass fitting would be good for the vapor return.

Any suggestions are appreciated.

Paul

BTW, my friend with the Zodiac also had a lot of frustration getting good tech support from Rotec. He politely confronted them about it at Oshkosh this year. He ended up sending all email questions to both tech support, and tech support's wife. He has received more "timely" responses.

[wolfpack3]

I have a Rotec carb for sale. I'm asking $600.S/H included in the US. It is not a MKII. Excellent condition only used 10 hours. pictures upon request I have decided to go with a float bowl carb instead.
Please PM me if interested.

[SonexN76ET]

Paul,

If you search this site with the keyword Rotec you will see that most of the people using Rotecs on a Sonex have a Jabiru. Most of the Jabiru users have positive comments about the Rotec TBI. There were very few photos of Rotecs on non turbo Aerovee engines for me to use in my planning.

Tony Spicer is currently building a Panther with a Rotec Mk I TBI on a Jabiru. He has some excellent photos on line of his very professional looking setup. I copied his air straightener which is thin honeycomb aluminum sandwiched between an aluminum frame that mounts on the intake mouth of the TBI.

As far as the fuel pump goes, I mounted mine in the cockpit on the firewall to protect it from heat and to be able to keep an eye on it. I could not figure a way to mount it on the firewall on the engine side. With the Facet fuel pump you are also required to have a fuel filter before the pump. I am still trying to figure out the best way to squeeze one in.

I looked at your builders log, you have a good looking aircraft under construction.

Jake

[SonexN76ET]

Here is a picture of an air straightener similar to the one I made for my Rotec TBI.



The grid itself is 1/2 inch thick.

A word of caution: One of the other builders has reported that they talked to Rotec about using ram air with a TBI at Oshkosh. He said that Rotec now recommends against using ram air. The Rotec website still references the use of ram air. So, what the Rotec technical support is saying is in conflict with the information on their website.

Ellison Fluid Systems (which the Rotec TBI copied) says that ram air can be used but you have to have a good induction system design for it to work. So please be careful.