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pitts_pilot(at)bellsouth.
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 Posted: Mon Feb 12, 2007 5:54 pm Post subject: I've sworn off purge valve installations |
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Panama wrote:
| Quote: | I am sorry to get into this dog fight a little late, but, I do not understand. My engine definately is hard to start and hard to keep running at idle during hot weather. I run an IO-360 (180 hp) Bendix FI system.
On taxi to and back from the runway on a hot day I get some pretty violent engine surges, settles down with boost pump on. It can take 30-40 revolutions to start the engine. Before I installed the purge valve, one time during a hotstart I had to take the cowl off and wait 90 minutes for engine cool down! I have even been supervised by Don Rivera himself during engine startup. My current solution; don't fly in hot weather
If this is not vapor lock, then what is it? .
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I'm going to stick my neck out and say it's a worn out fuel pump ..... or maybe the pump cam on the camshaft. If the engine is running, then there's a constant flow of 'cooler' fuel and it can't absorb enough heat to cause it to vaporize. Take a look at the idle mechanical pump fuel pressure VS. the pressure with the boost pump on.
Let us know what you find.
Linn
do not archive
[quote]
You guys really got me confused
Bob
| Quote: | I have a problem when, in the absence of any clear data, a malfunction is attributed to 'vapor lock'. I've put up with all the rhetoric for a lot of years running auto fuel ..... in FL, on hot days, with both injected and carb'd engines (yep, run auto fuel through the injected engine too ..... but not near as much as through a carb) with nary a hiccup. Not even any more hard starting problems than using 100LL. I guess the statement 'looked like vapor lock to me' just rubbed me the wrong way. Sorry. I really would rather have statements backed up by data or first-person-experience, not (to seal a line from a song) 'I heard it from a friend, who, heard it from a friend, who .... '.
The point I tried to make (and failed, I guess) is that all that engine running after startup should have purged any heat-soaked fuel. Once the heat soaked fuel is gone (from the firewall forward), the possibility of vapor lock goes way down ......
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[b]
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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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| Posted: Mon Feb 12, 2007 8:54 pm Post subject: I've sworn off purge valve installations |
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First you have to consider the brand of injection. Bendix does not need
a purge valve(unlike aftermarket brands). I operate my Mooney(200hp
IO360) with it in AZ in 110+ temps and rarely have any hot start
problems. Yours sounds like it is out of adjustment. Does your pull to
idle cutoff give a 50rpm rise, or less? Any more than that is too rich,
no rise is too lean. How long since the servo was overhauled or checked
on a flow bench? They do need service after several years. Are you
giving enough throttle for cranking? I use 1/2" for first try, 1" for
second. After about 6 blades I start easing the mixture in slowly, and
it usually catches at 1/2 way in on mixture. If that doesn't get it, go
full throttle, mixture idle cutoff, which after a dozen blades will have
any flooding/vapor cleared if it doesn't catch.
Panama wrote:
| Quote: | I am sorry to get into this dog fight a little late, but, I do not
understand. My engine definately is hard to start and hard to keep
running at idle during hot weather. I run an IO-360 (180 hp) Bendix
FI system.
On taxi to and back from the runway on a hot day I get some pretty
violent engine surges, settles down with boost pump on. It can take
30-40 revolutions to start the engine. Before I installed the purge
valve, one time during a hotstart I had to take the cowl off and wait
90 minutes for engine cool down! I have even been supervised by Don
Rivera himself during engine startup. My current solution; don't fly
in hot weather
If this is not vapor lock, then what is it? .
You guys really got me confused
Bob
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
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