rough running above idle

[tucsonchris]

This problem appeared suddenly and really has me stumped.

I can't get the throttle above idle without severe roughness. If I add choke I can get it smoothly up to 2800 or so, but without the choke, I can't move my throttle above 2000 with out the engine running rough and quitting. It idles fine after warmup any where from 1600 -1800.

I had 1.5 smooth running hours before all this on my brand new 912S. I was preparing to do a pneumatic balance, so I started from scratch and redid my mechanical sync first. Then I redid it 5 more times to be sure my throttle levers were moving in unison. They are. They also reach their Hi speed stops at the same time.

Like I said, this is a brand new engine that ran great out of the box initially. My mag check even at idle had consistent, but not fatal, drops on both sides. EGT'S go up fast and hover around 1000. All other readings nominal.

This just isn't feeling like out of balance carbs--but I hope someone has some ideas.

Tucson Chris

[wadeg]

Double check and make sure your chokes are closed. I have had some problems with the chokes not closing all of the way. In fact, I have wired my chokes so they are always closed. Don't seem to need them to start up.

[DesertFox4]

Chris, I also would check to make sure both "chokes" are returning to full off position after start. That can raise havoc with things. If you don't find this to be the problem give me a call.

[Dorsal]

Chris,
Just to be thorough check the thread "help" or "I think I soiled my Carburetor", I kinda hope your problem is unrelated but the symptoms sound familiar.

[tucsonchris]

Problem solved.

Thanks for the feedback everyone. My new, "alcohol resistant" tanks were dissolving. It's on to 100LL for the duration---

[Dorsal]

Chris, can you give some details as to what you experienced? this is a troubling area and the more information we all have the better.

[DanB]

Problem solved.

Thanks for the feedback everyone. My new, "alcohol resistant" tanks were dissolving. It's on to 100LL for the duration---

Chris, Very sorry to hear you are having this problem. Are you getting the brown sticky stuff in the carbs? Where did the "alcohol resistant" tanks come from? When you get the time, keep us in the loop as it helps others from going down the same road. Hang in there.

[tucsonchris]

Yes, brown and sticky. The tanks are the latest tanks that come with the Super Sport. I can stick a screwdriver down into the bottom of the tanks and it is obvious the material has softened and begun to dissolve. I only had gas in the tanks for about 3 weeks. Still have yet to do my first flight. Maybe Tucson area gas has a more corrosive formula, or otherwise I suspect every new kit out the door would have this same problem. My kit was produced in 2007.

[Dorsal]

Chris, thanks for sharing, sounds very familiar. My concern is a possible difference between residual stuff on the inside of the tank being released and the tank itself dissolving. My experience was that my tanks where slightly sticky inside before any fuel was put in them. I then ran auto fuel which sent the sticky into the system and completely fouled my carbs. After rinsing the tanks with acetone the insides where smooth and hard and remained so after rinsing with auto gas. I have since been running 100LL so can't comment on further effects of auto gas on the tanks.
Thoughts comments?

[tucsonchris]

I've already rebuilt the carbs. And BTW Gumout spray dissolves the resins lightening quick, so you don't need to brush or scrape anything. As per Steve's recommendation, I rinsed and sloshed my tanks with some avgas, then drained. I'm a little nervous about a hole bunch of acetone sloshing around my paint job. I'm going to let the tanks air out, and in my experience, the tank will harden in a few days. But the tank fiberglass was definitely dissolving. It was not leftover residue. The insides of my tanks were just as hard as the outsides when new.

Interestingly, I had a similar experience with an old Norton motorcycle I was restoring. The tank was circa 1967 fiberglass, but it had lived in a no-ethanol zone its whole life. As soon as I got it home and put E-10 into it, it started to dissolve. You could scrape the resin out of the tank like it was hardened butter. but if you let it dry out it would harden back up again. Eventually I decide to recoat the inside with the new Vinyl Ester Resin (ironically the same material the new KF tanks are made from, I'm told) and it worked fine. To test the compatibility of the VER with E-10 I cast a block of it and submerged it in gas for 3 months and found no noticeable softening. Now maybe gas down here has changed since then and the VER materials are no longer resistant. Don't know.