Rotec MKII TBI

[fastj22]

I set mixture about ½ way for takeoff. Anything richer and it runs like crap.

John, Can you confirm your full rich position is at the full rich of the TBI's capability? (so when you say 1/2 mixture.. you mean 1/2 on the TBI itself?) If not.. where (approximately) do you set your full rich cockpit stop relative to the TBI's stop?

10 GPH on climb out at WOT with EGTs in the 1200s (much more than I saw with the Aerocarb)
I see 5 and 6 going a bit lean at WOT and pulling back throttle a bit brings them even with the others. (over carbing?)

I had intended to install a boost fuel pump, but decided to try with just the gravity feed. Its working fine with gravity only.

Just put another 2 hours on mine. I recently recalibrated my fuel system and found I was getting 25 GPH through the fuel feed disconnected from the carb.

You get 25 GPH fuel flow with your gravity feed system and no pumps (the engine driven pump is not installed in your setup also.. correct?)??! Very impressive. You quoted some in-flight fuel flow numbers.. do you have a fuel flow transducer? what kind? Was it in the flow path for your hanger calibration? If i could have gotten those kinds of flows, i never would have installed the pumps. Although, per Rotec, it shouldn't make a difference...


I must say i am jealous.. the performance you are getting is absolutely what i was hoping for!

I did not limit my mixture control per the Rotec instructions. It swings the mixture lever of the Rotec the full arc. So when I say I'm at half mixture, the arm is mid way in the throw. If I go full rich, meaning the spray bar is turned to maximum fuel sucking, the engine runs like crap, too rich. Leaning it for takeoff required I pull it mid range. This took some trial and error to figure out where the best setting was for takeoff. I'm also at 7000ft MSL so your results will vary.

on the disconnected flow, I have a Red Cube transducer. when I disconnect the fuel line from the carb and hang it into a gas can and open the valve, I see 25 GPH, that is through the gascolator, no boost, full tank. I verified it with the EFIS and just by timing it. It does drop a bit near the end of the tank, but always over 20 GPH. All my lines and fittings are AN6.

Still think you have a dodgy regulator.

[SonexN76ET]

Here is a video of my Rotec TBI cutting out while accelerating during an attempted touch and go. You can hear the engine cutting out shortly after I start accelerating. The plane had already begun to lift off. After it cuts out, I pull the throttle back and abort the touch and go. This was on a day with gusty winds and a 9 knot crosswind.

I do not have a fuel flow transducer so I do not know the fuel flow at this time. In a subsequent attempt, I had richened the idle mixture but had the same result. It has not yet occurred during a regular takeoff roll, only during touch and go attempts. I believe this is due to one of three things:

1) Too much ram air too fast while accelerating
2) Too lean of mixture at the spraybar (mixture lever leaned too far)
3) Over carburation where the throttle slide needs to be restricted

My next step will be to restrict the incoming ram air.

I have not been able to replicate this with ground runs.

Before my next flight I may slightly retard the throttle slide and try a slightly richer mixture on the mixture lever for the spray bar.

I only share this so others can learn from my experiences. I am not slamming any product or company.

Thanks,

Jake

https://youtu.be/G45AEPfAwQU

[142YX]

Thanks for posting that video, Jake. Below is the video of my failed takeoff attempt (sorry the audio from my mic is so bad).

In your video, it sounds like you get up to a high RPM and the engine dwells there pretty happy for a few seconds before it just abruptly quits. Was there any adjustment made at all to either throttle or mixture after you got to top RPM? Very similar to what happened to me.. a few seconds at 2800 RPM with no inputs made whatsoever, then it quits.



https://youtu.be/TLcTzYc9-iM

Rotec got back to me with some basic troubleshooting steps:

Hi Nick sorry for the late reply, this time of year here is extremely hectic!

The first test I would do would be to make sure the TBI metering regulator is not passing fuel when the engine is off.

To do this depress the fuel primer button located in the center of the TBI regulator cover, with the throttle wide open and fuel pump on the fuel should pour out. When you let go the primer button the fuel should stop, may be a few drips here and there but should stop fairly quickly.

If after you let go the primmer button fuel continues to flow liberally then the regulator is not shutting off and may need attention.

I can send you out a refined flow valve we have been working on.

Also to get a nice clean idle you may need to adjust the small Allen screw located on the side of the TBI, this set the idle mixture only.

Also air inlet is extremely important, a good base line would be to ground run the engine with the filter and or ducts disconnected. Just for a quick test.

The reg spring length wont matter.

I didn't suspect any problem with the regulator (as far as it's ability to seal, because pressure held when the engine was not running) but i re-performed this test anyway. The primer button did function as expected - flowing liberally when depressed and stopping immediately when released. I noted that the carb leaks (drips) at a slow rate with the boost pump on now.. didn't do that before that i remember or noticed. I sent another email back to Rotec and got the following response:

I would advise you send the TBI back to us and lets take a look and see why its so rich.

I suspect it’s a metering problem.

We will take care of it.

Please print a copy of this email and include it with the TBI.

I appreciate the support from Rotec.. just seems like they are very busy. I fear that i won't fly again before the end of the year, at least, though. :cry:


Then i tried another engine run, this time with the idle adjust set back at the factory position. The engine started right up, and i noticed 4~6 is GPH at 1200 RPM.. which sounds wrong yet again. When i brought the throttle back to idle it quit (to be expected because i was trying to reset the idle setting).. but then i could not get the engine to light up over the nest 45 minutes worth of trying. It's possible i flooded it.. but that has never happened before. Killed the battery pretty good so i had to stop for a charge. Going to try to get it running one more time.. and then i will likely be sending it back to Rotec.


This is a picture of my metering tube. Does this look right to other people with 40mm bore TBI's? The holes point out (into the incoming airstream) when full lean. As best i can tell from other photos i find on the internet.. this is the correct orientation for a Rotec TBI (but opposite compared to the old Ellison patent) but i am getting pretty desperate to figure out what is gong on here so i figured i would ask. Also, do the holes look like the same pattern as everyone else? (i don't have a larger model meter tube in mine)?

[fastj22]

Yes, orientation and pattern look identical to mine.

[SonexN76ET]

Nick,

On my video of the Rotec TBI when the engine cuts out it is after it has achieved full power for a few seconds. I did not make any throttle changes or mixture changes. I am thinking that my induction system is the cause. I am in the process of redoing the air intake plumbing.

By the way, it looks like Rotec has updated their website with enhanced documentation.

Your video seems to show a result very similar to what I encountered. Not fun!

It will be interesting to find out what is causing your metering issue.

Be safe with your testing!

Jake

[WaiexN143NM]

Hi Nick and Jake,
Hope u guys get it figured out soon. John Gillis and myself have had good luck with our Rotec TBI. In fact I recommended to john to get one. We are using gravity feed , no gascolactor, red cube fuel flow inline. Carb heat box with flow straightner, and a filter much larger than the stock sonex one.

Off topic, Avery tools is closing. Always enjoyed seeing Bob and Judy at Oshkosh at their booth. Visit their web site before Dec 15 if u need something. WWW.Averytools.com

Great cowling fasteners are available from WWW.Skybolt.com. Not cheap but stainless and great quality.

Happy Holidays to the Sonex Family.

WaiexN143NM
Michael Radtke

[WaiexN143NM]

Hi all,
One correction to previous post, pls change we to I , as I describe my Tbi set up.

Nick , don't forget when priming, to fully open the throttle, to fully expose the spray bar. If u don't then priming won't occur.

WaiexN143NM

[onex28]

I need to find a 90 degree female 1/4 NPT to 6AN male for a fuel line connection, preferably AL. So far the only thing I've found is a metal male 1/4NPT to female 1/4 NPT swivel hydraulic hose adapter, (internal pipe swivel adapter) which I could use. It has a 5000 PSI rating. Anyone have a source for an Al fitting? Just assuming that a hydraulic fitting would also work on a fuel line. Am I wrong?

David W

[fastj22]

I need to find a 90 degree female 1/4 NPT to 6AN male for a fuel line connection, preferably AL. So far the only thing I've found is a metal male 1/4NPT to female 1/4 NPT swivel hydraulic hose adapter, (internal pipe swivel adapter) which I could use. It has a 5000 PSI rating. Anyone have a source for an Al fitting? Just assuming that a hydraulic fitting would also work on a fuel line. Am I wrong?

David W

Have you checked performance racing or Jeggs? They have most AN fittings you might need.

[onex28]

Hi John

I think I've exhausted all the sources on the Internet and it looks like my remaining choice is an Eaton Aeroquip 1/4 NPT street elbow and adapt from that. I found several 6an to NPT elbows but they were the wrong sex. I also discovered that NPT and NPSM are not compatible unless you use an O ring in the NPSM.

Didn't find what I wanted but I leaned something so no loss.

David W