History repeating itself on my 2.2 engine trouble


Senior Member
Latest update on my Subaru issues:

Once I got everything back together, and did my first runup on the ground, I discovered the engine would only achieve 4400 rpms, not the 5300 I had been achieving previously. Called the sub guy, and he suggested I put the original throttle body back on, as the engine may not be compatible with the 2.5 one(they look identical, don't know how anyone knows the difference).

Finally got back up there, and spent a couple of hours switching out the throttle bodies. Jim had worked me through how to set the TPS sensor, which took me a while to get good readings there.

Took the gyro outside, did my trial runup, no change in maximum rpms!!!!!! I then took a degree of pitch out of the prop, and tried again. Same result! And, to add insult to injury, discovered the alternator had failed. Had to jump start the gyro to pull it back inside.

When I was discussing my problems with my NAPA buddy, who said the alternator was covered under warranty(yahoo!!!) he suggested my problem sounded like a plugged exhaust.

I really hated to break open my Supertrapp, since I had no experience doing so, but today was really warm here, so the deed got done. Guess what???

Yep, it was plugged almost solid with fiberglass fluff!!!! Not sure how it ran at all, since I could hardly see any open slits in the baffles. There's really nothing to the Supertrapps, construction-wise, and they're easy to remove, disassemble, and put back together. I removed all the fiberglass before reassembly.

Did a trial run with the exhaust wide open, and as soon as the rpms hit 5300, shut it down. Let it cool a little, then re-installed the baffles. Wire-tied everything, and did another runup. It was headed for 5700 rpms when I shut it down. Not sure how far away from full throttle I was, but didn't want to find out how much more rpms it would gain.

Added two degrees of pitch to the prop, and tested again. Seeing about 5400rpm max now, which may still be too much in the air. But, daylight was almost gone, so called it a day.

Now I have to wait for the alternator to arrive, and for decent weather again, for the next tests. This time of year, good days for working on the gyro, and testing things, are few and far between. We're scheduled for snow and much colder weather for the rest of this week.

The bad thing is, I wasted a lot of time and effort avoiding messing with that Supertrapp, for being afraid of working on it. The good news is, my engine is now ready for flight, and I didn't have to pay for another mechanic trip, or to replace a bad alternator. Gotta love those NAPA guys for their lifetime warranty on their alternators.

One other note: If you're using a Supertrapp, take it apart and pull that fiberglass out of it! To my amateur eye, it appears the only reason the fiberglass is in those things is to keep the exhaust heat from frying the exposed ends of the little socket head bolts that hold the baffles in place. I'd much rather buy a new baffle set every two years or so than deal with the frustration of lack of engine rpms. Just my two cent's worth.


Gyroplane CFI
Hello Mark,

Glad you found your problem.

The socket head cap screws are stainless and the plate the thread into is also stainless.

In my experience it is important to use anti seize compound on the threads or they will gall.

I feel the fiberglass is there to dampen the high notes and give the exhaust a less annoying tone. In my experience it usually burns out quickly so removing it first shouldn’t hurt anything but people’s ears. We used to use ceramic wool instead of fiberglass. Super Traps were not designed to run on an exhaust system that short.

We used to have the Super Traps come apart all the time on motorcycles. The early ones had a stud and ¼ 20 nut that held things together with a spring. It worked better than the screws. Don’t over tighten the screws or you squash the plates and then the gap closes up.

If the plates come apart and go through the prop it could cause some damage.

I am not a Super Trap enthusiast, they do flow a lot of air.

Thank you, Vance
I am glad your troubles are coming to an end.. It's about time you get to fly that thing. =)
Thank you for posting your experiance.... I really like the simplicity of my carb and this is just another reason to not change it out for EFI.


Senior Member

Your explanation for the fiberglass is probably true. Also started to overtighten the baffle bolts, then realized that would be a problem, so you were right about that, too.

I know a lot of people are not fond of the Supertrapps. This issue with the fiberglass disintegration seems to be a sporadic problem with our use for them, and unfortunately, I'm one of the statistics. The Supertrapp exam is part of my preflight, so hopefully I can catch a baffle crack before it becomes a flying disc.


Thanks for the congratulations. Some people prefer the simplicity of the carb setups, but I'm more afraid of carb ice, so opted for EFI. Although the EFI part has been a real pain for me, if I never experience carb ice, it'll be worth it, in my mind. And again, I'm the statistic rather than the norm for EFI conversion. There are probably hundreds of guys out there who've had no issues with their EFI systems, compared to my experience with it.

Although I'd never dream of tackling a project like Vance's in a million years, all this EFI and Supertrapp trouble has made me a better powerplant mechanic than I ever thought possible. And each experience likes this that has a happy ending makes me less afraid of tackling other flight related projects.


Senior Member
Latest update on my Subaru issues:

One other note: If you're using a Supertrapp, take it apart and pull that fiberglass out of it! To my amateur eye, it appears the only reason the fiberglass is in those things is to keep the exhaust heat from frying the exposed ends of the little socket head bolts that hold the baffles in place. I'd much rather buy a new baffle set every two years or so than deal with the frustration of lack of engine rpms. Just my two cent's worth.
KennyJ state the same thing over 4 years ago as he had the "fluff" dropping to the bottom and nearly cause an engine out.
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Platinum Member
Mark, I'm glad to hear you are getting her going properly ! Sorry to hear about the snow & cold, though.

Do you have any pics of your exhaust ?

I removed the insulation from my Supertrapp before I even started it !

Let me see if I have any pics of my exhaust handy.


Geeez Mark what a great experience in troubleshooting an engine. By the time you get to fly that thing again it'll be time for your BFR again... LOLOLOL


Senior Member

I remember Ken's problems with the fluff, that's why I figured that was going to be the cause of my power loss, too.


No pictures, other than the installed system. As usual, both of our cameras were still sitting on the desk at home. And I really wanted to take pictures of the innards for everyone, but wasn't willing to lose an hour to do so. Sorry.


With thoughts like yours, who needs enemies? I do have to admit, it was beginning to feel like it might be all winter getting it sorted out. Cold and I don't get along any more, and I'm pretty sure the sub mechanic isn't interested in working in a cold, dirt floor hangar over the winter, either.

Once in a while, though, you do get lucky.

Hey, how are you coming along with the new house, and the new gyro? Keep hoping to hear you've gotten it airborne. If you could use a day of help from someone who's getting pretty good with Subaru's, I know just the guy for you. He is retired, and won't be flying as much in the cold. Bet he'd be willing to return a favor for you. Call if you're interested, I'm serious.


Senior Member
OK, yesterday the stars all aligned themselves, and I managed to commit aviation again.

It was a raw 38 degree day, lots of humidity, totally cloudy, and a northeast wind at about 8-10mph, but I decided it wasn't going to get any warmer than that for a while. Did a real thorough preflight, and pulled her outside.

Had to clean the blades, which isn't fun on a raw winter day, let me tell you. Fired the thing up, and taxied around the other side of the hangar so I wasn't in the wind so much. Have not put the doors on yet this year, and won't until I get another flight in. After about 10 minutes of warmup, the temps were in the right spot for takeoff.

Pulled out to the end of the runway, and started my spinup. With the headwind, things wound up pretty quickly. Started my takeoff roll, released the prerotator, and let the wind take over. Next thing I knew, I was airborne!

Only lasted two tight circuits, due to the cold, but noticed a lot of differences from my last flight before she broke down on me:

First, the acceleration when I push the throttle forward after getting the nose down again, was scary. Didn't take anywhere near as long as it used to, with the blocked exhaust.

Second, broke ground in about 800-900 feet, which I've never been able to do in similar conditions.

Next, can't believe how loud the engine is now. No more stealth mode in the air, I can't remember being in any gyro that was louder in flight. Thought something was wrong, but all the gauges looked good, hadn't felt anything fall off, and I was still gaining altitude.

At altitude, and back over the runway again, started noticing other differences. Absolutely no stick shake, and no noticeable cabin hop. At 60mph cruise, was maintaining altitude at 4200-4300rpm, way lower than before.

Next thing I noticed was the coolant temp. 138 degrees! Not good to run like this! Checked my digital read against my manual gauge, they were pretty close, so it was reading right. I was now committed to another circuit by now, so just relaxed and enjoyed the last 5 minutes of flying for the day.

The landing wasn't the prettiest, but got her stopped in about 15 feet. Taxied up to the hangar, and put her away.

Wanted to check the radiator right away, so did so. The exit hose was cool, and the entrance hose was warm. The right third of the radiator was warm, and the rest was cool. Once I had landed, and was taxiing back, the temps came back to my normal 180-190 degree readings.

I've had this radiator issue since the get-go, and changing thermostats made no difference in this phenomena. So, after discussing it with Mark Knight, I'm going to block part of the radiator on my next flight. I really wanted a much smaller radiator than is on there, but it was the cheapest and lightest one I found at the time. Being so close to the prop, and so wide, it must be way oversized for my use.

Regarding the noise from the engine, don't want to continue flying with the gyro that noisy. Besides irking my runway neighbors, it's unsettling to me in flight. I'm going to buy another set of guts for the Supertrapp, and try it again. Obviously, this next time, I'm going to pay a lot of attention to that exhaust on my post flight inspections! Vance, your statement about the fiberglass softening the exhaust note was right on the money, so pat yourself on the back!!!

All in all, it felt great to be airborne again, and was worth every minute of freezing my extremities off for about an hour.

Chris, here's a couple pictures of my exhaust. It's the same system Mark Knight uses on his 2.5. I believe the tubes are 30" long, which is what someone in the business who knows recommended Mark use. He's had absolutely no trouble with his exhaust, in probably 300 hours of flight time on that engine.


Mark- Its good to see you in the air again. You deserve a long steady run of flying now...and I am betting you will.

Merry Christmas and the best of 2010 to you and Cathy.



Senior Member
Seems like we could find something besides the Supertrap that was half quit. Or a way to quit the Supertrap without the fluf.