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fuel problem

Since it appears appropriate to now "think out of the box": Is your tachometer accurately reflecting engine RPM? Are you hearing and feeling these power reductions or are you just observing changes in the tachometer reading? It wouldn't be the first time that the ROTAX/SV tachometer connection was a bit erratic.
 
its the new vented tank

the vent line terminates near the base of the filler neck, but the return line terminates right next to the fuel output on the bottom of the tank

The return line continues inside of the fuel tank and actually terminates pointing upward into the bottom of the fuel filler neck - at least that is the original design with vented cap. I'm pretty sure the return line is still routed the same way. So maybe you can look down the filler neck and verify that fuel is actually returning to the tank unimpeded. That would be good to know in your case...

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Jim - of course now I understand what you mean, yes I will check that tomorrow.

David - yes its the engine note change that really gets your attention and you can hear it stumbling with a bit of vibration, but I would have said the vibration is minor.

Its more of a concern of is this going to become something else....
 
Is it possible that one of the ignition modules is going back into "soft start" mode randomly? Would not hurt ruling that out.
Alex
 
I just did some testing on my fuels lines and ran fuel for 5 mins at each point

Before mechanical fuel pump
28 gph displayed on gauge
I filled 2.4 gallons in 5 mins

Outlet of mech pump (21.4 gph displayed on gauge)
I filled 1.75gallons in 5mins

Left carb at union
(15.8 on gph displayed on gauge)
I filled 1.25 gallons in 5 mins

(I can confirm my fuel cube is accurate !)

I also check my spark plugs, all slightly off white

I check the integrity of my spark plug leads and connectors alll good.

I scoped down the fuel filler neck and I see a good spray on the return line.

I also check that I got no difference between running for 5 mins with hose off at mechanical pump and fuel cap on and off and there is no difference
 
I just did some testing on my fuels lines and ran fuel for 5 mins at each point

Before mechanical fuel pump
28 gph displayed on gauge
I filled 2.4 gallons in 5 mins

Outlet of mech pump (21.4 gph displayed on gauge)
I filled 1.75gallons in 5mins

Left carb at union
(15.8 on gph displayed on gauge)
I filled 1.25 gallons in 5 mins

The PAP requires "at least" 1 gal in 180 seconds from the output from the gascolator.

As an aside I was finishing my "annual" and noticed one float was sinking/ borderline - and during the run-up, fuel was leaking from that carb. Another sinker - new ones are 100/pair. Hopefully that will be it.
 
I'm pretty certain I have solved it, but I need to do a flight test and it is too hot here right now (120F). But I will report back
 
When I cleaned the carb out I hadn't unscrewed the jet that is located in the fuel bowl. I unscrewed that jet and cleaned it and then blew out the area it screws into and I saw something black fly away... assembled the carb and tested on the ground (I had been able to replicate consistently) I couldn't get the issue to return and the engine seemed to remain cooler after an extended period of WOT on the ground. I have tested it three times now and it appears to have gone. haven't had a chance to test in air as it's been way too hot here
 
You got that right Julian! A couple of years ago I was giving a familiarization flight to a guy who wanted to ferry an RV-12. I try to do all me checks except run up during taxi so I can into the air in hot weather with some margin on CHT and oil T, but with a pilot unfamiliar with the RV-12 we took longer on the ground. During climbout in 115F heat we picked up both CHT alarms and an Oil T alarm. Had to land right away and also picked up an avionics alarm "Temperature Out of Limits". Now I don't fly if it's above 110F

Rich
 
Well, I had my first experience with what appears to be vapor lock today. My plane has been out service for about 7 weeks while I was on vacation and then having my carbs overhauled. It's been over 100F here in AZ for much of that time. I was concerned that my fuel would be affected and I think it was.

I put a switch on my electric fuel pump and shut it off except for takeoff and landing. I was at 5000 feet with an OAT of 79F when my fuel pressure went to about 1 psi and I got a high fuel flow spike. Turning on the electric pump brought everything back to normal in a few seconds. When I shut off the pump again everything was fine for about a minute and then the issues repeated. I did this a couple of times with as much as two or three minutes with the electric pump off before the symptoms reappeared.

I think I'll fill up with AVGAS and make a habit of fresh bought auto gas in the summer months.
 
If you have been following the threads… It is highly recommended to run the electric fuel pump for all ground and flight operations. In other words – do not shut off the electric fuel pump. Van’s designed the control circuit so that the electric fuel pump cannot be shut off. There is a reason for this and it is to prevent vapor lock.
 
Jim,

The reason I put a switch in is because I am concerned that if the mechanical pump fails I won't know until the electric pump fails too, and there is no backup in that case. I understand the design premis, I just don't agree with it.

Rich
 
Why object to having cool (ambient temp) fuel recirculate through fuel distribution system in a hot enclosed cowling especially in a climate like in the southwest? EMS will warn if combined fuel pressure falls below normal green arc value indicating one of the pumps not producing pressure.

You can lead a horse to water, but you can?t make it drink?
 
Turn on master switch. Listen for electric pump. Check fuel pressure on EFIS.
Start engine. Look for fuel pressure increase on EFIS.
Go fly. The chances of both pumps failing during that flight are slim.
After landing, download EFIS data to USB flash drive.
At home later, analyze data using MS Excel. Check pressures and temps and etc.
 
Expanding upon what Joe said:

1) Turn on the Master Switch, listen for the electric fuel pump clicking and slowing down as system Fuel Pressure (FP) builds up, and look for @ 3 psi on the FP gauge. If the airplane is heat-soaked, let the electric fuel pump run for awhile (a minute or two) to allow cooler fuel from the fuel tank circulate through the fuel lines.

2) Start the engine and verify that the FP gauge is now showing @ 5 psi (i.e., reflecting the additional pressure of the now working engine-driven fuel pump).

3) During run-up, verify that FP remains @ 5 psi. If you want to double-check the fuel pump system, momentarily pull out the FP circuit breaker and verify that the FP is @ 3 psi with the engine-driven pump alone. Typically, I do not see any reason to do this if the FP is @ 5 psi.

4) In-flight, visually monitor the FP gauge as you would other engine instruments. The SV/Garmin units provide an additional visual/aural warning if FP drops.

5) After landing, shut-down the engine and listen for the clicking of the electric fuel pump before you turn off the Master.

The "full-time" electric fuel pump as installed in a standard RV-12 keeps cool fuel circulating, helps to avoid vapor lock, is not likely to be forgotten, and apparently has a relatively long service life. Others may prefer a switch-controllable electric fuel pump ala many low-wing airplanes -- I prefer the Van's factory set-up. As a critical flight item, I carry a spare electric pump with pre-attached electrical connectors and AN fittings -- just in case. ;)
 
Jim,

Your assumption that one pump failure will bring in the fuel pressure alarm is incorrect. I have been operating with a switched fuel pump for 5 years and see only a couple of tenths of a psi difference when I switch the electric pump on and off. As I said I just believe the scenario of losing the electric pump when the mechanical has failed is much worse than having to flip a switch in cruise if I experience vapor lock. Coupled with the operating experience of one vapor lock in 5 years (with old fuel) the approach I use seems sound.

A wise horse will check what's in the water and then decide whether to drink it.

Rich
 
Jim/Rich --

I agree that the loss of one of the two fuel pumps in-flight will likely not cause a "Yellow or Red" FP warning indication on the SV/Garmin and that the resultant loss in FP may be slight (in my RV-12, I do see a noticeable slight reduction in FP psi when I disable the electric pump in-flight) -- good points. I guess it all comes down to whether or not the pilot concurs with the benefits of Van's "full-time" electric pump use design philosophy versus a "use-it-when-you-want-it" philosophy. It is a question of whether or not one thinks the "full-time" electric pump will live a long and happy service life versus occasional switch-activated use. Suum Cuique

-- David

ps -- I will admit that I wonder how many cycles the FP fuse receptacle will tolerate over time since I remove/reinsert the FP fuse at least once every 28 days for data updates. ;)
 
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What about scenario where you re-start a hot engine, perhaps in a hot climate, and do not switch electric fuel pump on until ready for flight... Suppose fuel has boiled in supply lines and maybe even carb float bowls because under-cowl temps are very high and fuel system is heat-soaked.

What if you take off and engine stumbles at this very critical phase of flight?
 
Jim,

I'm not saying that one should never use the electric fuel pump if it's on a switch. I certainly agree that if the pilot thinks vapor lock is a strong possibility it should be on. I am glad to have experienced it and seen the immediate benefit the electric pump provided when I turned it on. I now know what a vapor lock scenario looks like which is also useful.

Rich
 
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