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Airflow Performance Hot Start tips?
Greetings,
I continue to struggle with hot starts, even though the Airflow Performance system has a purge valve that's supposed to make this easier. Cold starts are great, never more than a couple revolutions before it's running, but hot starts are hit and miss, and recently more miss than hit. When it won't start, there's no firing at all, which leaves me thinking it's either flooded, or has no fuel at all. If anything, I think I might not be giving it enough gas, likely compensating for all the horror stories you hear about hot starts on injected engines. My question is how many seconds of priming action do you give when the engine is thoroughly hot, and has been shut down for 15 min or so? When cold, I give it a count of 5, but hot I try to use no more than 1 second. Unless I hear otherwise, the next attempt will be with about 3 seconds, or maybe 5 seconds like when it's cold. Is it possible that the purging is just so good at cooling the lines and eliminating vapor that I don't need to be so concerned about flooding? Hopefully I won't have to start looking for a carburetor :-) Thanks, Rusty |
No Prime
On the IO-375 in my Sportsman with the AFP system (no purge valve) I never primed it hot. Hot procedure was:
Throttle cracked open Mixture Idle Cutoff (ICO) Key to Start When engine fires slowly move the mixture control toward full rich It always started very easily hot or cold. It is very easy to get too much fuel in the system. |
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PURGE VALVE
Hey Rusty:
Remember you have the purge valve installed - or your post suggests this. If I can recall what Don said about this: for a hot start, purge valve open/ICO position, and flush system with boost pump until cool fuel is in place. I would add that you should be starting from the tank that has the return line to it so no fuel sprays on the ground from your vent system. No fuel will go into the engine, or on the ground - when purging. This assumes that you have the system installed correctly. Once you purge (Bonanza owners use 60sec of boost run time - you might get away with less) you can tickle the system with a bit of fresh fuel with the purge valve closed/set to run position - not too much tho - then try to start with the mixture rich, and the throttle set at about 1000RPM. Another option is to swap out to an SDS system, which will lighten your wallet substantially. Starts like your car - quite amazing. Seriously, the purge setup is very good, but it sounds like you are not using it as designed, again assuming that it is installed correctly. A quick call to Don will get you straightened out, no matter what is going on. Good luck! |
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You are most likely idling at shutdown, which is a happy place for both the mixture and throttle. Just use the bypass valve to shut the engine down, not the mixture. For restart, with the bypass still open, turn on the boost pump while you get buckled in, boot up the EFIS etc. Throttle and mixture still where you had them at shutdown. Now start cranking and slowly close the bypass. Boost pump off after start. This is what I used in my 10-----worked well for me. |
Do you have electronic ignition?
We have PMags and when we switched to automotive spark plugs, our hot start problems disappeared. TIFWIW. |
After shut down, the fuel in the lines between the injector and the spider boils. The expansion causes this fuel to be pushed into the intake area of the cylinder head, leaving a very rich mixture once you start cranking.
I have no purge valve, but my procedure is Throttle cracked as normal, mixture rich and boost pump for 1 second. This refills the injector lines with fuel and adds a bit more fuel to the intake area. Then mixture to ICO and crank. Once it begins to catch (usually 5 seconds or so), move to full rich on the mixture. It usually keeps running, but sometimes doesn't. Next start effort, if it didn't catch, is throttle cracked and mixture rich with no priming and it will start in a blade or two. Larry |
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Thanks to all for the comments. The checklist that came with the plane had another procedure that left the purge valve in the run position during start, but then moved mixture from cutoff to rich. I had the official procedure with me yesterday as well, moving the purge from off to run while cranking. I tried that yesterday, but perhaps the damage was already done by then. Next time out, I'll try to official procedure, without any prime, and see if that makes a difference. I'll just have to make a practice of letting the plane sit a few minutes at the hangar, then hot starting for practice. Maybe I should put Don's number on my starting checklist :-) Thankfully the plane has two PC680 batteries, though I'd like to cut that down to a single lithium at some point. I need to learn how to crank it with only one battery first :-) Thanks, Rusty |
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Thanks, Rusty |
I've also found that getting the start process down pat (both hot and cold) using the Airflow Performance FI with purge valve has been a struggle using their recommendations.
For me this has been working great: Throttle halfway, Mixture rich, Purge valve ICO. Run the boost pump 30 seconds. Watch the fuel pressure come up and boost pump off. Purge Valve to Run, Throttle in about 1/4" in from Idle. (Basically this works the same for both hot/cold starts. You are just getting the cooler fuel to circulate up to the distribution spider.) For cold starts: Run the boost pump about 5 seconds on/off to prime. Turn the key. (I found that originally I wasn't letting the boost pump run enough here, especially when it is cooler outside). For hot starts: Mixture ICO. Turn the key. Slowly advance Mixture to rich. Be prepared to give the Throttle a push after it starts, and/or toggle the boost pump to make sure the fuel gets pushed into the cylinders. Sometimes here if the initial start doesn't take, give it full throttle while cranking. I'm still trying different techniques to get this fool proof. |
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