Rotec TBI MK2 Advice for Aerovee
Posted: Wed Aug 09, 2023 3:46 pm
by DBrown
I bought a Rotec TBI @ OSH a couple weeks ago and I am looking for some input from those of you that have installed one on an aerovee
Did you install carb heat?
Have you gotten carb ice with it?
did you install a Fuel pump? or was gravity enough?
What did you do for the intake flange adapter & air filter?
What kind of primer setup?
I was under the impression (told by Rotec) that this would be a relatively simple swap by changing the throttle cable & installing a primer lever.
but if I have to build a Intake adapter, add carb heat, a fuel pump, return line, a primer control, swap control cables & throttle quadrant, I may just stick with the little red slider for now.
I’ve scoured the forums and the Google for a couple days and haven’t come up with much conclusive data, or many examples of MK2 TBI Aerovee installs.
And advice and pictures would be appreciated, I’m trying to get more input & ideas before I start making parts.
Thanks in advance
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Thu Aug 10, 2023 4:56 pm
by Arjay
Fred installed the Rotec on our legacy Sonex, with aerovee, last year. No carb heat. Never had icing. If you have ice, you can shake/scrape it off using the throttle back and forth. (look at how the throttle works in the tbi. It’s like a scraper). No air cleaner. (a little dust never hurt anyone, and we don’t get a lot here in the southland). No fuel pump. Gravity is enough. We had to custom make new throttle and primer linkages. That was a big job. We did run a small gas vapor return line back to a tee on top of the fuel filler and rerouted the fuel vent line down to outlet out the bottom. This replaced the stock fuel vent that was sticking up facing forward from the top. Since then we have had no “burp” issues. Although we have not yet tried serious aerobatics, we have tried high g turns and it seems to run just fine throughout.
One problem that stumped us for a while was that we couldn’t get it to run consistently when first installed. Turns out the diaphragm in the pressure regulator did not have a proper vent hole in it for ambient air. This was a bugger to find. Had to tear it all apart and figure that one out. Apparently, it was due to an assembly error (the wrong diaphragm installed). We fixed it by drilling the correct hole in the diaphragm. I suggest you check yours before installing it. So much easier that way.
I don’t know how to post pictures, so none here.
Ron, legacy Sonex td with aerovee, here in North GA
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Mon Aug 14, 2023 8:37 am
by DBrown
Thanks for the input Arjay, I appreciate it
I didn’t know anything about a regulator vent hole? This is the first I’ve heard of it. I don’t see anything in the instruction manual.
I spoke to Rotec over the weekend and they confirmed that you pretty much have to build an intake adapter He also sent pics of one he builds out of fiberglass & he said most people do a scat hose adapter to a remote filter. Seems easy enough but the instruction manual says (uses standard 4 bolt aviation flange for easy installation) They must be talking about the other carb’s with flanges on both sides because I have looked everywhere! Automotive, aviation, diesel, go carts, McMaster Carr & nothing off the shelf fits this flange. The fact that they make their own from fiberglass confirms to me that they are not a standard size.
Why they don’t offer any way to attach a standard air filter or a scat hose or anything to this TBI is just mind boggling to me! (or throttle & primer brackets) They obviously have the CNC mills, I built an adapter cad/cam file in Fusion 360 in 10 minutes…why would they not do this? Why is the manufacturer making these out of fiberglass? makes zero logical sense to me.
(sorry rant over)
As a hobby machinist; making the Flange, & brackets for throttle & primer should be a non issue, It’s just more time and hassle than I was expecting. I was hoping for a quick install but I guess it’s going on the shelf until December when I start the condition inspection. There’s too much flying left this summer to tear it apart now.
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Tue Aug 15, 2023 12:02 pm
by Arjay
The regulator vent hole was supposed to be in the diaphragm of the regulator that is attached to the TBi body to begin with, but it was not there. We had to drill it. There is nothing in the instructions about it because the absence of the hole was a manufacturing defect in assembling the TBI, not a normal condition. (I assume the diaphragm model without the hole was used on prior regulator models, possibly used in the older regulator model that was separate from the TBI. I assume during assembly of our TBI in the Rotec factory the assembler installed the wrong diaphragm for that model TBI. They are the same except for the hole).
As I recall we had to acquire an adaptor flange from somewhere other than Rotec to get the TBI to mate up to the intake manifold.
Yes, it was all more of a hassle than we expected also. Hopefully, it will all be worth it in time.
Ron
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Tue Aug 15, 2023 7:38 pm
by BRS
This talk of the MK2 is peaking my interest.
How much different does the Aerovee run with the MK2?
Is the MK2 much taller (wider?) than the AeroInjector?
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Wed Aug 16, 2023 10:59 am
by Arjay
Brock:
Our engine runs smoother and gets maybe 100 more static rpm (3250 at wot for takeoff). Also, where the aerocarb would not allow aerobatics on our bird, the Rotec will (supposedly-we haven’t tried it fully, yet). A major difference is that the mixture control will not cut off the engine at idle. Another major difference is that the Rotec has a primer, which is a great safety factor, as it can help keep the engine running if something else goes bad in the tbi.
I think the Rotec is a little larger than the aerocarb, but still easily fit our engine.
Good luck with it. Please let us know how it works out.
Ron
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Wed Aug 16, 2023 11:21 am
by Bryan Cotton
For what it’s worth, I’m one of the several/many people doing aerobatics with the Aerocarb. No issues but I do need to lean it before pulling significant Gs. If I don’t, it bogs down but recovers afterwards.
That static RPM sounds great!
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Tue Aug 22, 2023 8:46 am
by DBrown
The only reason I am eventually going to the Rotec is for aerobatics, I’m not knocking the Aeroinjector, once I got it set up and tuned properly it does fine, 3150 static, runs smooth at idle (once warm) and no burping (after installing a burp tube) but while doing aerobatic testing it’s made me pucker more than a few times and turned off in spins twice. I agree with Bryan that leaning it out helps, but for me it still coughs quite a bit under minimal G loads.
If I wasn’t doing Acro, I would just keep the Aeroinjector.
I have built a bracket that incorporates the throttle and primer in one piece, I’m going to have the flange I made in Fusion 360 cut by a local CNC shop to fit a standard 3" SCAT hose for a remote K&N filter. and install it all in November when doing the condition inspection
I appreciate all the input!
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Tue Aug 22, 2023 9:13 am
by Bryan Cotton
Interesting. It did take me a while to figure out how to keep the Aerocarb happy when doing acro:
- don’t go to idle in spins
- before a loop, lean aggressively - pull back until it stumbles and go just a little richer
But otherwise I am happy with its acro performance.
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Sat Sep 23, 2023 11:20 am
by BRS
Here is another MK2 question.
I’m trying to even out my CHT’s, the right two (cyls 3&4) always run warmer. It’s common for me to see 80 deg difference between #1 & #4. Though I still manage to keep #4 at around 380 deg. Since the CHT’s corespond to higher EGT’s it’s looking like uneven fuel distribution on the R2300 & AeroInjector.
Q. Has anyone noticed more even fuel distribution (even EGT’s) after going to the MK2?
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Fri Oct 27, 2023 11:54 pm
by BRS
The MK2 was too interesting for me to pass up. It seems to fit the bill as far as solutions and features. Most interesting is more even fuel distribution as well as a dedicated idle circuit. So after several weeks and not a small amount of $ I’m well on the road of swapping the red for the gold.
Dimensionally, Looks like the fuel inlet is the only fit question. I’ll have to try the cowl on to make sure the fitting clears.
I like how the fuel is pulled from up to 46 holes vs one. Should help even out the EGS’s thus the CHT’s.
zoom in close and look at all those holes in the Rotec
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Sat Oct 28, 2023 10:50 am
by Bryan Cotton
The fuel metering looks cool! Interested to hear how this works out.
Re: Rotec TBI MK2 Advice for Aerovee
Posted: Thu Nov 02, 2023 11:26 pm
by BRS
As I work on installing the Rotec MKII TBI there is a learning curve. Here is one clever mod that I came up with then confirmed with a call to the factory.
My sonex uses standard push/pull controls (not the sonex reversing quadrant) some head scratching to get the mixture to travel correctly (push-rich/pull-lean) was in order. The MKII was reverse from what I needed. The mixture is controlled by a spray bar (see previously posted images) that can move 360 deg except for a external pinned stop. From the factory the bar rotates CW as seen in the fuzzy picture to go from rich → lean. In other words, the spray bar holes are at 6 o’clock (same pictured side perspective) for rich then moves to 3 o’clock for lean. But if the bar could continue rotating in the same direction then the holes would eventually be at the 12 o’clock position which would also be Rich. So rich can be at 6 or 12 o’clock and lean only at 3 o’clock (facing the incoming air stream). The external stop arm is pinned (roll pin) to the spay bar to fix the relationship. By tapping out the roll-pin and drilling the shaft at 90 deg then the stop lever can be mounted in such a way to allow the spray bar to move from 3 to 12 instead of 6 to 3 o’clock. This reverses the cable action so that my standard push-rich control now works. The factory would have done this for me if I had asked before them sending it. What we don’t know…
First Impressions: Rotec TBI MK2
Posted: Mon Nov 20, 2023 1:12 am
by BRS
After getting the OOPS fitting sorted, and the MKII finally installed and tuned, I got to go for a short RTS flight yesterday. Here are my first impressions.
Easiest TBI to tune and get running (compared to AeroInjector and Revflow) hands down. Basically this was done in two steps (these are my steps not any official advice). Warm the engine, at idle determine if it rich or lean, adjust the idle screw and try again. I think after 3 iterations I had it where it was idling nicely at about 850 rpm. Although the main mixture does not control the idle circuit it does affect it slightly so I set idle at full lean, and when I set mixture to rich the idle increases slightly. Second, adjust the mixture linkage so that it hits the stop at the point of your determined full rich fuel flow. Mine is currently slightly rich at 8gph WOT on takeoff. That’s all there was to it. The second step is needed since the the MKII can flow way more fuel than our little engines can handle.
Different but easy to adapt to: With the separate idle circuit the engine will run while at full-lean (mine anyway) up to about 2000 rpm before getting rough. So I found my self taxiing at full lean - weird eh? It has Rich-Lean positions but not really an ICO (idle cut off) thus some modified proceedures are needed. To Kill the engine I find it most elegant to set the engine to Idle and Lean then briskly advance the throttle. The engine rpm starts to rise but then quits as it leans out. Leaning in flight is a nice linear control from rich to lean with no surprises unlike the afore mentioned tbi’s that use a supply line valve to reduce fuel flow. Also the MKII does a nice job keeping the mixture constant without the need of swapping (guess work) out needles. The manual explains something important. If you kill the engine inflight for leaning too agresively, just pushing in the mixture may not start the engine. Instead the engine must be retarded to idle then the mixture advanced and the throttle returned to cruise. Read the manual for a good explanation.
The installation manual is a good concise tool for setup and tuning. A must read, in advance, if you are considering this TBI. Keep in mind to (per my last post) that when ordering, there may be customizable configurations which might help your installation so DO call ahead. Mine arrived with the throttle designed for a 'bulkhead" push-pull cable but I already had a more common bayonet type push-pull cable. Not sure if they have this option.
Well, that’s all for now. I still need to make a filter manifold as my flight was done filterless. Thinking of 3D printing what I need.