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Rough Running Rotax Finally Solved

todehnal

Well Known Member
This ongoing problem has plagued me for over 2 years, and 200 hrs of flight time. Near the end, the spark plugs were lasting less then 10 hrs and oil changes were done at 20 hrs, which was as black as coal by then. I rebuilt the carbs twice myself and had Lockwood do them 3 times. I drained and flushed the fuel system twice, and Lockwood did it twice.
Each time the carbs were done, and the plugs were changed, I would have a few hours of a perfectly running engine. We knew that it was fuel, but could not end the nightmare. I came close to replacing both carbs, but in retrospect, that would only have resulted in a smooth running engine "for a little while".
This Spring I flew the airplane down to Lockwood Aviation in hopes of a fresh eyes solution. The first thing Joe, the shop manager did was to ask Phil Lockwood to test fly my airplane. After a thorough preflight, which included a fuel sumping that entailed taking several samples, and pouring them into a clear, funnel shaped collector for a detailed look for debris, Phil would not fly the airplane. Following that, Joe had his staff clean the fuel system. Again Phil did his preflight and flew my RV-12. He was quite complimentary about the airplane.
Before flying back home, I decided to have Lockwood comply with the 5 year Rotax rubber change, after which Joe asked Phil to fly my airplane. Again, Phil did a thorough preflight, and again he rejected the fuel samples. He walked back into the shop and told Joe to pull the fuel tank. Admittedly, no one was excited about it but, Phil is the boss, so they complied. Upon draining and flushing the tank, very tiny particles continued to be flushed from the tank, which were being collected into a white 5 gallon bucket. It was determined that is must be Proseal deteriorating, which was finer than confection sugar and had a light sand color. Being 1,000 miles from my home shop, a new tank was ordered from Vans and installed. Problem solved.
In summary:
Only fresh 93 octane ethanol free auto fuel has been used in the airplane, which now has 550 hrs on it.
Each time service was done such as carb clean and/or spark plugs changed it would run great, "for a little while"
Sumping using the normal sump tool revealed no debris.
During one of the carb rebuilds at Lockwood, Joe had his staff run my carbs on his test engine which caused them to rebuild them twice before he was satisfied with the test run. The only problem was that after I installed them, it only ran great "for a little while".
This was an expensive and frustrating problem and I now have about 100hrs on it since the fix that Phil Lockwood identified. To this day I have no idea why my Proseal continued to deteriorate, but I am done with that tank.
There is much more to the story, such as, I have posted many many times on this site and the Rotax site, looking for a solution, but this is the short version. Also, I greatly appreciate everyone's help in trying to solve this problem This forum is fantastic!!
All in all, I love my RV-12..............Tom
 
Has Van's expressed any interest in looking at the tank to help understand what might be going on, in case other classic RV12's start experiencing similar issues?
 
I still have the tank. I kept it, thinking that I may open it up some day. I would be glad to send it to Vans for a detailed internal inspection. I was extremely careful when mixing my Proseal. I even kept a samples to verify drying and hardness. The only mistake that I made that may have caused the deterioration was to store the remaining Proseal in the refrigerator, and then I used that to perform the tank modification that came out some time later. As I recall, that Proseal was almost 2 years old. But again, I used a sample to ensure that it cured properly. That is the only thing that I can think of, and I did not develop any tank leaks. Perhaps that is the big reason for the short shelf life, which I understand can be extended by refrigeration.
As far as the filter goes, I did not detect Proseal there, in fact very little debris has been captured in the fuel sump. These particles are so fine that the screen would have had no effect. I'm just glad that it is over......Tom
 
Hard to believe anything gets through gascolator screen. I run 93E10 Mogas and pour directly into tank with no filtering. I find a few particles once in a while when sumping gascolator, but have never found debris in either float bowl.
 
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... After a thorough preflight, which included a fuel sumping that entailed taking several samples, and pouring them into a clear, funnel shaped collector for a detailed look for debris, Phil would not fly the airplane.

...

Again, Phil did a thorough preflight, and again he rejected the fuel samples. He walked back into the shop and told Joe to pull the fuel tank. Admittedly, no one was excited about it but, Phil is the boss, so they complied. Upon draining and flushing the tank, very tiny particles continued to be flushed from the tank, which were being collected into a white 5 gallon bucket. It was determined that is must be Proseal deteriorating, which was finer than confection sugar and had a light sand color. ...
Phil's been around a while - smart guy. Glad you found the problem. It's a failure mode that I would not have suspected, particularly due to the color of the particles.

I would expect that Van's or perhaps the proseal manufacturer would be interested in your old fuel tank - if for no other reason than as a cautionary tale.
 
If particles from the tank or anywhere else upstream made it to the carburetor bowl you should be looking at the gascolator, see if it is assembled correctly, or has a missing or bent screen, etc. Nothing of any significance should be able to make it through to the bowls.

If contamination is getting through it is just a matter of time before you have another problem, maybe it won't be tank sealant but something in the gas that makes its way into your tank.
 
I'm sure that I was sumping out minute particles that I did not notice. These particles were indescribably tiny. The key to the detection of the debris was that Phil uses a standard sump in conjunction with his funnel shaped clear receptacle that allows him to collect several sump samples that will concentrate any particles, making them more evident. Still, not easy to see. And yes, when disassembling the gascolator, I would flush out what looked like a tiny dab of mud, but I never expected it to get through to the carbs, I do sump much more carefully now and have found zero fuel contamination of any kind. Hind site, I should have figured it out a long time ago. Thanks for the comments. Sump carefully guys...........
 
There is no doubt that I have been complacent with the sumping task. I have a hangared airplane, my own indoor fuel farm, with an electric fuel pump and final filter, and the fuel is also filtered going into the tank. I just don't get fuel contamination. So, yes, I do a cursory sump with a primary check for water (never had any) and I probably didn't look that closely for tiny debris. That has changed. I am much more attentive during the sumping process.
 
One last comment. I have removed the float bowls many, many times and have never seen any debris in them. That is one area that I examine carefully.
 
... Upon draining and flushing the tank, very tiny particles continued to be flushed from the tank, which were being collected into a white 5 gallon bucket. It was determined that is must be Proseal deteriorating, which was finer than confection sugar and had a light sand color. Being 1,000 miles from my home shop, a new tank was ordered from Vans and installed. Problem solved.

I had a similar problem in my RV-6A (Quickbuild tanks) ~20 years ago. I added a very fine Purloator 806 fuel filter to one tank, and ran alcohol-free 93 octane fuel in that tank. Multiple times the filter became clogged with a very fine "dust" that interrupted fuel flow. I decided it must be Proseal deteriorating in the presence of the auto fuel, and quit using auto fuel. Problem solved.

I envy folks who are able to run autogas without issues. But after my bad experience, I've stayed with 100LL.
 
I had a similar problem in my RV-6A (Quickbuild tanks) ~20 years ago. I added a very fine Purloator 806 fuel filter to one tank, and ran alcohol-free 93 octane fuel in that tank. Multiple times the filter became clogged with a very fine "dust" that interrupted fuel flow. I decided it must be Proseal deteriorating in the presence of the auto fuel, and quit using auto fuel. Problem solved.
...

From here:

https://www.aircraftspruce.com/catalog/appages/ps890.php

Proseal Technical Data Sheet said:
Resistance to other fluids - Excellent resistance to water, alcohols, petroleum-base and synthetic lubricating oils, and petroleum-base hydraulic fluids.

Seems strange that proseal would not be able to handle auto fuel. Perhaps there is something else in there that's deteriorating? Gaskets? Fuel float?
 
Been using ethanol free mogas for 14 years now. No Proseal issues so far. 35 micron filters before the pumps, nothing evident there.
 
I would think, with all the aircraft built using Proseal, that this could be chalked up to a bad batch. I’ve got a fellow SLING owner who had a similar experience, who had his tank rebuilt. In his case, he found white gunk in his carb bowls after aborting a takeoff with a ruff engine. The onset was quick after a normal RunUp.
 
Our fine filter on the iS is an 8 micron filter, so would likely be captured by it. But by the time the iS was released, Van’s had gone away from ProSeal and over to their Flamemaster sealant, so it shouldn’t be an issue for us iS guys anyway.
 
Like Ross, I use 10% ethanol car gas almost exclusively. In almost 13 years and over 1200 hours I’ve never had anything in my gas samples or on the gascolator screen. Seems odd. Are you sure it’s Proseal? A friend who had an RV-12 had some thread sealant on his gascolator screen. They can look similar as small particles.
 
Like Ross, I use 10% ethanol car gas almost exclusively. In almost 13 years and over 1200 hours I’ve never had anything in my gas samples or on the gascolator screen. Seems odd. Are you sure it’s Proseal? A friend who had an RV-12 had some thread sealant on his gascolator screen. They can look similar as small particles.

I have the same experience. In the past 3 years I have put 3200 gallons of E10 through my 912ULS. Nothing on the screen or in the bowls (checked at 100 hrs), carbs have not been serviced, they run smooth, stay in balance, still average 4.3 GPH.
 
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