Rotec TBI MK2 Advice for Aerovee

[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

[Bryan Cotton]

The fuel metering looks cool! Interested to hear how this works out.

[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.....

[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.