Guest rocketdriver Posted June 9, 2011 Posted June 9, 2011 We had a good day today trying out our KR 2 19 - 7814 All fairly straight forward ... a brake issue caused by improper adjustment .. that was easy fixed. We did a series of taxi runs, staring with some quiet circles around the tarmac to check out the slow speed handling ... a little pussy cat! The we got a little bolder and took her out onto the runway and ran her down the tarmac a bit quicker ....still a pussy cat, but needing to be a bit quicker on the rudder, especially with a slightly gusty cross wind. Then we went for some tail up runs and found a bit of a problem .... every time (almost) that I lifted the tail, the engine cut out. See the attached sequence of photos taken by a camera we setup to take photos every 5 seconds for just this sort of issue .... the resolution is a bit fuzzy to reduce the size, but on the originals you can read the instruments fairly well too .... From the indications on the mixture indicator (the row of LEDs top centre of the panel (lean =red to the left, rich orange to the right)) the mixture goes lean as the tail comes up and then the engine stops, all in less than 15 seconds ...... this is just one of several sequences we recorded all much the same ... Would appreciate any wisdom as she ain't gonna fly 'till I find out why .... and fix it!
Guest ozzie Posted June 9, 2011 Posted June 9, 2011 Hmm what engine? but off chance i'd might lean toward incorrect float level and or poor fuel pressure.
facthunter Posted June 9, 2011 Posted June 9, 2011 Not much point in guessing. Unhook your fuel feed pipe near the carb. lift the tail and see whether you get air ot nothing at all and then trace your fuel run back to the tank. Are you running a booster pump? So far you get the most unusual fuel problem award. Nev
Guest rocketdriver Posted June 9, 2011 Posted June 9, 2011 Hi Hmm what engine? but off chance i'd might lean toward incorrect float level and or poor fuel pressure. Ozzie. Ita an Ea81 subaru with a Holley carb. We have new twin fuel pumps in parallel with a fuel rteturn to the tank using restrictors as supplied with the pumps ..... I think the fuel pressure is likely to be ok as the pumps are said to supply 3 to 4 psi which is what the holley book says the carby needs and we tested the fuel flow to be something over twice that required for full power operation .... and the problem only happens as the attitude changes ... at least I think so. I did try it with one and with two pumps on and with carby heat on / off. No diff ..... It could be float level I guess .... perhaps tomorrow we should do a full power static run in the level attitude and see if the engine runs ok. If it does, then the problem will be to do with the attitude changing ... maybe altering the float chamber level in a transient way? Now I know why I was so pleased when carbies disapeared from road cars! cheers RD
Guest rocketdriver Posted June 9, 2011 Posted June 9, 2011 Not much point in guessing. Unhook your fuel feed pipe near the carb. lift the tail and see whether you get air ot nothing at all and then trace your fuel run back to the tank. Are you running a booster pump? So far you get the most unusual fuel problem award. Nev Hi Nev We have two electric pumps and a see through filter located quite close to the carby Normally we can see the turbulence as the fuel goes through this filter, (not in flight) but I'm not sure if we checked this with the tail up ...... will look tomorrow .... good thought., Thank you. RE the most unusual fuel problem award, thank you, but I would rather not have the award or the problem! Cheers RD
facthunter Posted June 10, 2011 Posted June 10, 2011 Check fuel line is not being kinked anywhere. Could it be related to stick position rather than pitch attitude? The level of the carbs should not be that fussy. If it was the acceleration on T/O would be a consideration also. Needs to be sorted, thoroughly...Nev
Tomo Posted June 10, 2011 Posted June 10, 2011 How's the fuel suction in the tank? Like Nev said the carby shouldn't be that sensitive! Unless the carby has been touched previously, I think your problem is somewhere else - ie, fuel supply. By the way, does it stop like you've switched the key off, or does it hesitate?
Yenn Posted June 10, 2011 Posted June 10, 2011 Could something in the tank be moving across the inlet, when the tail come up. I would definitely try a fuel flow test with the tail raised. I was once stopped in a car by an ignition coil that was loose and moving, it shorted out on acceleration, then came back on.
Guest rocketdriver Posted June 10, 2011 Posted June 10, 2011 Hi everyone, and thanks for the assist .... Turned out to be the fuel return line. When we replaced the pumps, we got restrictors for the fuel return line with each pump. I put both restrictors in series in the return line andd thought, "that'll be ok" but it wasn't. It always looked like a lot of fuel being returned to the tank .... So today, we tied her down to my car and did a power run. Sure enough, the engine died when I lfted the tail ... after about 15 seconds. ...(Tomo, when we were out doing hi speed tail up taxi runs, it felt like it just stopped, but on the pad, after about 120 seconds with the tail up, it faded away over a 5 second or so time period). Luckily, I could get hold of the fuel return line inside the tank with my multigrips, so I gave them a loving squeeze until the flow back into the tank was more of a squirt than a stream. figured that would be enough to get risd of any vaporisation in hot weather, and would at the same time increase pressure and fuel availabilty at the carby. Problem fixed ... on the pad and on the runway!
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