Follow-Up
We also have been experienceing a fuel smell on take off and sometimes during flight. I posted on another thread what I was experiencing.
We have only ever ran 91 auto gas. It does have ethanol in the fuel.
http://www.vansairforce.com/community/showthread.php?t=114065
We have around 50 hours on our -12 and have experienced this exact problem. In October we replaced the old style fuel pump with the new one (just as a pre-caution). About a month ago we did a takeoff and the engine went very rough right after adding take-off power and then could not replicate it again. Then a couple of weeks ago it was happening on the ground almost every time power was added. Did the "mag check" and found that it did not change anything. So we pulled the carbs and replaced all the suspect parts everyone has talked about here. We started it up and did lots of full power run ups and everything appeared to be great so we took off and flew around. I did notice the fuel pressure dropped a little when climbing, something I had not noticed before. So, over the airport (probably should have tried this on the ground first:roll eyes I pulled the fuse of the electric fuel pump. I have done this many times and typically the fuel pressure drops a few psi and then comes right up. This time it dropped to .1 psi and the engine started missing. It came back to life after I put the fuse back in and we landed. On the ground I pulled the fuse again and it did the same thing. Went to about .1psi but this time the engine kept running and didn't go rough.
We have a new mechanical pump coming and will update everyone on what we find. We may check the float adjustment as well.
Everyone may want to try this test on the ground and see if there was a bad batch of the new style fuel pumps out there.
The other thing we cannot figure out is the fuel smell on takeoff during this time. We never had it until these past few flights and can sometimes see a little fuel in the aluminum catch under the carbs. If the mechanical pump is bad, why would that cause fuel to come out of the carb. It does not look like anything has come out of the overflow tube on the mechanical pump.
I will update after the new pump is added and more checks are carried out.
I should have mentioned that I smelled fuel each time and also found fuel in the catch basin below the carb during this time.
So, here is the followup to this issue.
I installed the second "new" fuel pump and ran the engine on the ground with and without the electric fuel pump on and the plane ran great with no significant loss in fuel pressure. So I took the plane up, smelled fuel on takeoff, and once in the air saw the fuel pressure fluctuate and pulled the electric fuel pump fuse over the airport and the fuel pressure dropped to almost 0 and the engine started cutting out. Installing the fuse and the engine came to life.
I went to Oshkosh and talked to everyone I could about what could be going on. The symptoms were:
- Rough engine when full power was added, sometimes
- Smelling fuel on takeoff and sometimes in cruise
- Fuel pressure would drop to almost 0 when the electric fuel pump fuse was pulled, sometimes.
The hard thing with this problem is that it was not consistent.
At Oshkosh I came away with two main thoughts. The Rotax guys said it sounds like the hose that recirculates the fuel may not have the restrictor in it. And almost everyone else thought it was the carbs.
I took
EVERYTHING apart when I cam home from Oshkosh. I disassembled every fuel line from the tank to the intake manifold. I totally disassembled the carbs and looked for any piece of dust. I blew out every line. I verified the restrictor was in place on the return fuel line.
I did cut the overflow line that comes from the back side of the mechanical pump, up about 2". There were some that thought it might be the issue. I ruled it out since I could replicate the fuel pressure drop when only running on the mechanical pump on the ground. The thought was that if this line is in low pressure during flight it may cause problems with the diaphragm.
The gascolator screen was clean, I even ordered a new electric fuel pump but they both tested exactly the same so I reinstalled the old electric pump. (remember, there are only 50 hours on the plane)
After reassembling everything, I ran the plane on the ground for awhile and it ran perfect with and without the electric fuel pump on.
I decided to go fly and did not smell any fuel on takeoff and the fuel pressure with both pumps on was around 5.1-5.2 and with only the mechanical pump was around 4.7. For now I am calling it fixed but need to put a few more hours on it before I claim victory.
The problem of course is I have no idea what root cause was.
If I were to hypothesis what the problem is, I would probably point to the carbs. I know there was fuel coming out somewhere, probably the clear tube on the side of the carb. I can't imagine why a carb problem would cause the fuel pressure to drop to almost 0 psi when the electric fuel pump was turned off though.
Hopefully everything continues to run good. I will keep you all updated if I learn any more.
Since this is a new flying design then from time to time more things will be found out about it. Posting it here will help keep the problems in a loose data base for others who follow. It will also provide some feed back to Vans through Scott. 
