Hot start problem
in 912 / 914 Technical Questions
9 years ago
I have a 912ULS in my Van's RV-12. It first flew June 10 and has about 45 hours on it. It has been run exclusively on 93 octane Ethanol auto fuel. The engine runs great. Starts great cold. Starts great hot if I start it right after shutting down. If I let it sit for 10 - 15 minutes or so, though, it starts with difficulty. Usually initially fires pretty much OK but with a LOT of vibration for 20-30 seconds or so. During that 20-30 seconds or so I can keep it going by playing with the throttle then it smooths out and runs normally. The left EGT ran cooler than the right EGT until a minute or so after the engine smoothed out. It seems to be quite consistent - it's happened pretty much the same way every time I've tried to start it after letting it sit for 10-15 minutes or so. I haven't done done that very many times, though, so the sample size is pretty small.
I've tried various throttle positions from the 1/8" suggested in the POH, to full closed to full open and in between, all without success. The 1/8" open is the best - that's the only way I can get to to start at all. I've previously changed the original floats out for the new ones and, actually, have had to replace one of those new ones recently as well. The carbs were balanced recently when I replaced the float.
I took a video of my last try: https://youtu.be/VlJ4isGpqRc. For some reason I can't get YouTube to show the actual video but you can hear the sound. Sounds like my grandfather's old 2 cylinder John Deere :(. It smoothes out at about the 30 second point.
Vapor lock comes to mind but this is a standard, unmodified RV-12 installation and I haven't heard of this problem over in VAF.
There's definitely something going on but I'm not sure how to shoot & correct the problem ...
I've tried various throttle positions from the 1/8" suggested in the POH, to full closed to full open and in between, all without success. The 1/8" open is the best - that's the only way I can get to to start at all. I've previously changed the original floats out for the new ones and, actually, have had to replace one of those new ones recently as well. The carbs were balanced recently when I replaced the float.
I took a video of my last try: https://youtu.be/VlJ4isGpqRc. For some reason I can't get YouTube to show the actual video but you can hear the sound. Sounds like my grandfather's old 2 cylinder John Deere :(. It smoothes out at about the 30 second point.
Vapor lock comes to mind but this is a standard, unmodified RV-12 installation and I haven't heard of this problem over in VAF.
There's definitely something going on but I'm not sure how to shoot & correct the problem ...
