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Engine running problems of first X country

engineerofsorts

Well Known Member
Haruko and I are 3/4 of our way on our first long cross country trip in N73HR--made it from Central Texas to Farmington New Mexico in three hops, obtaining 91 Octane unleaded from gas stations close to the airports. After adding 8 gallons here in Farmington, we had some engine problems--no problems at 4000 RPM runup, but at full throttle on takeoff, some incredibly rough running.

What is the collective wisdom of the VAF crew on this? Would bad/over-rated Mogas cause such grief? In the great state of texas, we ran on 93 Octane, and had 91 octane in our first two fill-up along the way, but now this rough stuff.

Staying the night in Farmington, hoping to resolve this tomorrow morning, so any ideas would be appreciated. My first default solution is to drain the gas out and run with 100LL whenever I'm really out and about.
 
Hmmmm - -

Have you removed the gascolator bowl recently ? Was the fuel ethanol 91 ? See anything in a fuel sample ? Sounds like it might be 'stuff' in the screen in the gascolator restricting flow.

Just some ideas.
 
Have you removed the gascolator bowl recently ? Was the fuel ethanol 91 ? See anything in a fuel sample ? Sounds like it might be 'stuff' in the screen in the gascolator restricting flow.

Just some ideas.

I inspected the gascolator after completing the production Acceptance Procs--about 20 filght hours ago. All my regular fuel has been labeled as "May contain up to 10% corn squeezings" Not sure about the NM gas
 
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More random ideas - -

Fuel Pressure readings stay the same ? Shut-off valve completely open ? If these things are ok, I would likely pull the carb bowls and look for 'sruff' or a float problem there. Tap the bowls with the handle of a screw-driver quickly to break them loose, and not hurt the gasket. Doesn't take long if you have done it before. Don't disconnect the cables, just work close to the engine. I check mine at each annual.

Another thing - do both mags give equal results when testing them ?
 
Ethanol free?

I'm not flying a Rotax, but I thought even the Rotax was suppose to be flying Ethanol Free Mogas.

I fly a Superior XP-O360 and I take off and land with 100LL (from one tank) and Cruise with 93 Octane ethanol free Mogas (from the other tank).

Get some ethanol free gas and you'll most likely solve your problem. I'd use 100LL before ethanol fuel.

Here is a web site to find ethanol gas in your area, they also have apps for your phone there.

http://pure-gas.org/
 
Any associated Dynon anomalies? Fuel pressure, fuel flow. Can you download to a laptop and check FP and FF function during problematic takeoff?

A check of the float bowls for trash just takes a few minutes.

IIRC Four Corners is a pretty long strip, albeit at high altitude, so a test hop shouldn't be too hairy.

Do you have the new style fuel pump? Old one gave me partial power loss on takeoff several times at about the 20-30 hour mark.

Make sure your ignition modules are solidly grounded to the intake manifold.

Nothin' like things going wrong a few hundred miles from home...

Jim
RV-12
 
Since I haven't flown yet, I haven't verified this, but there is suppose to be ethanol free gas just down the road from the airport KSAF (Santa Fe).

PHILLIPS 66
Honstein Oil Co. [505-471-1800]


There's also a Shell station within a mile. I believe most of our corn is 10%

If you make it into Santa Fe - give a call.

Bob

5 0 5 - 2 3 1 - 4 5 9 8
 
Had a talk with Jetguy

I spilled my heart out to JetGuy (John Albury), and he gave us several things to try:

1.) Pull out half of the gas and replace with 100LL.
2.) Do a few High-RPM engine run-ups, pulling the choke out in the process--thoughts being this might shake some crud out of the carbs.
3.) Fly earlier, when cooler.

I should have pulled the logs before leaving the airport so I would have a better record of whats happening...to tired to go do it tonight
 
I had the same problem after about 100hrs and it turned out to be a bad fuel pump. Look at the fuel pump dump tube and see if you have any fuel in it. I hope your issue is something else. FYI, I had the old style pump without the overboard dump tube and I only observed a small amount of gas in the weep hole so look closely.
-Bruce
 
Quite using MOGAS.....you can much of the time but some days.....it ends in tears.

Avgas is less likely to give you trouble. The price difference is not worth it.

In about 1-2 years you will have UL Avgas, and that will be even better. :) Bet patient.
 
Rob, mine is at 250 hrs. with a steady diet of 93 octane/10% Corn Squeezins with not a sputter. I get the corn likker at the same station all the time and they have tanks that are 3 years old. What about that fuel pump? New style/old style? Good luck!
 
Any chance of vapor lock? If problem goes away with the engine cold I'd think that a possibility. Fuel might be boiling at the altitude/temp combination where you experienced it. Quick fix would be a tank of avgas til you get home.
 
I am still betting on some contaminated fuel. We will know more when he pulls the gascolator and float bowls. The container used to transport the fuel could have some trash in it, as well as contaminated fuel at the source, we don't know what he used for a funnel either. Lets hope it is not a clogged finger strainer in the tank!
 
Just a thought, and to qualify my comments, I have zero exp. with Rotax. I don't know the first thing about them.

but. . . I looked up the ground elevation of Farmington, NM, 5506 ft. I would think you would have to lean a bit for a takeoff at that elevation. Can you do this with a Rotax?
 
Alton has a point. I've maintained a couple Diamond HK's up here and both had to have the drop rods in the carbs adjusted before they'd run right at altitude.
 
The Rotax 912 has auto compensating carbs with no manual mixture control.

The engine will run fine from sea level to 14500 (the highest I have gone) with no external adjustment.


My first action dealing with this problem would be check for contamination and then try some different fuel. The suggestion to drain and then add a large qty of 100LL is a good one.
You didn't by chance buy the fuel at ARCO or a convenience store did you?
 
That sounds like a choke problem.
Are you sure the choke was fully closed before applying takeoff power?
If the choke is applied, even a little, especially at that high altitude, a rough running engine would be a classic symptom.

JMTC,
Driftdown
 
That sounds like a choke problem.
Are you sure the choke was fully closed before applying takeoff power?
If the choke is applied, even a little, especially at that high altitude, a rough running engine would be a classic symptom.

JMTC,
Driftdown

I might disagree with this. If he had/has a typical fuel system/carb, that would be the case, but if the carbs are vacuum venturi, self compensating type, then it could be running lean if he got 10% (or more) ethanol. In this case the choke could be used to check the A/F mixture to see if it helps or hurts. It would actually help if he is already running lean.

Regardless, it still sound like some good diagnostics are in order. Hopefully we will hear good news soon.
 
I might disagree with this. If he had/has a typical fuel system/carb, that would be the case, but if the carbs are vacuum venturi, self compensating type, then it could be running lean if he got 10% (or more) ethanol. In this case the choke could be used to check the A/F mixture to see if it helps or hurts. It would actually help if he is already running lean.

Regardless, it still sound like some good diagnostics are in order. Hopefully we will hear good news soon.

Rotax specifically allows up to 10 % ethanol to be used in the 912. Because that is what is mostly available, Rotax flyers have been using it with success for quite a few years now.
If it is a fuel quality problem (strong possibility I think), it is likely to be because of contamination or poor fuel quality causing a fuel restriction ( gascolator screen) or vapor lock, not because the fuel has ethanol. (this guess would be based on the assumption that fuel pressure was near normal when the problem occurred)
 
I might disagree with this. If he had/has a typical fuel system/carb, that would be the case, but if the carbs are vacuum venturi, self compensating type, then it could be running lean if he got 10% (or more) ethanol. In this case the choke could be used to check the A/F mixture to see if it helps or hurts. It would actually help if he is already running lean.

Regardless, it still sound like some good diagnostics are in order. Hopefully we will hear good news soon.

Good points Bill.

That withstanding, since the carbs are self compensating though, adding choke would physically override that feature.

Would be interesting to see a test of using the choke on takeoff roll and climb out.

Anybody want to volunteer? :)
 
I'm with Scott - bad gas. If it was me, I'd drain half the tank and give it to one of the bystanders who, I'm sure, will be glad to get 10 free gallons for their car. Then refill the tank with 100LL.

Bob Bogash
N737G
 
Maybe not direct related but nice reading about carb/mixture problems :

See page 9 of the 2-2010 RVator:

 
Rotax specifically allows up to 10 % ethanol to be used in the 912. Because that is what is mostly available, Rotax flyers have been using it with success for quite a few years now.
If it is a fuel quality problem (strong possibility I think), it is likely to be because of contamination or poor fuel quality causing a fuel restriction ( gascolator screen) or vapor lock, not because the fuel has ethanol. (this guess would be based on the assumption that fuel pressure was near normal when the problem occurred)

I looked that up on Vans site and saw that 10% EtOH is allowed, so I figured that it was probably not pushing the A/F out of range and thus not the issue. The fact that it ran good at part throttle, but bad at full, is the best indication of bad fuel and misfires under higher pressures, or fuel flow. My comment was related to the post that stated increases in altitude will result in richer A/F, a fact not applicable to these Bing carbs. I should have updated my post, apologies.
 
An update

We got back to the Farmington airport at about 7:00 AM, and I started out by draining out about 8 gallons of Mogas and contributing it to the FBO's courtesy car fleet. We then took the -12 to the run up area, and everything ran just swell on the remaining pure Mogas, as it did for a fast taxi/hop down the runway. We then decided to do a few patterns, but, for a still unknown reason, the left main tire blew just as we were completing taxing. About five hours and lotsa bucks later, we had the tube replaced, and Haruko then did half a dozen touch and goes and full stops with no problems, all running on the Mogas. We then loaded filled up with 8 gallons of 100LL, packed up, and had the same grief as we had on Friday afternoon. After one aborted takeoff, back to the run up area, where were found we could maintain wide open throttle RPM with about one inch of choke. One more go-around due to an unlatched canopy (Doh!), and we were on our way. We had the expected long takeoff roll with high density altitude (don't have the numbers--downloaded the log and left it in the plane), and slow climb out, we put the choke back in at about 500 ft AGL, with no problems, climbing to 10500 on our way to Price, UT, where we waited out thunderstorms hovering over Price Canyon for about three hours before belatedly finishing out the epic journey at Provo airport.

General arm-waving conclusions
1.) Mayhaps not a function of the Mogas/Avgas debate--worked and failed with pure mogas and with a Mogas/Avgas mix.
2.) Mayhaps related to high afternoon temps/altitudes--smooth running in the cool mornings, rough running in the warm afternoons
3.) I'll be running with Avgas on the way home--waste much less time fetching Mogas from local gas stations, and get most of the flying done before afternoon heat sets in.
4.) I'll be checking the carb bowls/Gascolator bowl/screen for complete checking of the various theories presented in previous appends when I (hopefully successfully) return back to Austin (unless some RV-12/Rotax guru at Provo airport wants to get together in their hangar and play).
5.) Not sure what to say to those who say you can't have any choke with wide-open throttle--solved our problem
I'll post any further experiences, less arm-waving conclusions, etc as available.
 
We had an intermittent rough running problem on one of the Tecnam P2006T twins that we had sold as the UK Tecnam dealer.

On investigation, I found a tiny (2mm) flake of cork in one of the carb float bowls. My theory was that it had been nipped off the float bowl gasket when installed (we hadn't had the bowls off since the aircraft had been built and it was only 30 hours old).

There are two different types of float bowl gasket - the cork type and a slightly thicker sandwich type. I always try to fit the sandwich type now.

A Tecnam P2002-JF (single) that we took the maintenance on for suffered from severe rough running when carb heat was applied at high (cruise) power. Carb heat on this installation was from muffler warmed air as normally with Lycomings and Continentals. On this one I found neither float bowl gasket (cork type) had been seated correctly, they both had slight creases in them. Again, new gaskets fitted and no problems since.

Another P2002-JF had rough running at low rpm on the ground. This disappeared as soon as you got to half throttle or above and then suddenly the fault went when I was ground running. Fault never reoccurred and I think that was a foreign object blocking the slow running jet that eventually went through and out - never found anything.

When you have the float bowls off, check that the floats are floating equally as they should and aren't showing excessive wear where they occasionally contact the float chamber. Then make sure the float bowls and jet paths are absolutely clean.

As Van said in the RVator article, Rotax's are different to other aero engine and have their own set of snags and issues. That said, I have looked after many Rotax's for a couple of thousand hours in total and these carb issues, two (earlier spec) mechanical fuel pump failures and a number of (Honeywell) oil pressure sender failures are the only problems encountered. So don't think that they are unreliable!
 
The return trip--uneventful, more or less

Our return trip from Provo, UT, to Georgetown, Texas (Provo--> Green River -->Cortez --> Moriarty --> Andrews --> Georgetown) was uneventful but long--we experienced none of the engine problems we had on the way out of Farmington--running on Avgas--worst case for temps/density altitude was leaving Moriarty, NM, (OAT 90, DALT 9200), with the requisite slow climb out but no engine troubles. We had a very long final leg from Andrews to Georgetown due to headwinds, but enjoyed using the autopilot and staring at the Milky Way hovering over West Texas.

The only problem seemed to be in the mapping/GPS, which had us tunneling deep underground for the first 30 minutes of our flight out of Moriarty:

aa93a3db-04eb-470f-b93c-950698156380_zps78c2c711.jpg


The GPS position seemed normal, aside from being buried deep underground (but getting shallower as we climbed). After 30 minutes of flying, the map hiccuped a bit, then went up to about 1000 Ft below what our Ipad GPS was giving us, and slowly (over about an hour) got into basic agreement with the Ipad GPS, within the tolerances of WAAS-vs-non-WAAS GPS. At least the ADSB-based traffic seemed to show traffic buried deeper than we were.

So now that the engine problems don't seem repeatable, I'm wondering if we blew a booger out of one of the carbs, or what??? Looking at the logs, the engine speed dropped from the 5000 RPM-ish level down to about 2500-3000 RPM before we aborted takeoffs, running extremely rough, as if half the engine (hence one carb) was misbehaving. Throttling back to 4000 RPM, everything got smoother once again. Any theories/conclusions from me will betray the fact that I'm an Electrical Engineer, working on nano-acres of silicon, and not any sort of Mechanical Engineer).
 
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Back from vacation, late to the thread....

Carb bowl floats are a real MX issue with the 912 series, particularly with MoGas (tends to be dirtier than Avgas). Clean them and make sure the gaskets are good. Not sure what the manual suggests, but we did it every year.

Making sure the carbs are adjusted properly is the other big thing. Lots of guidance on that. Vent lines to the same spot, and the balance line connected.

TODR
 
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