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Hot start issues

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birddog486

Well Known Member
I'm curious if all the RSA and Avstar fuel systems that dont have fuel returns have fuel vapor issues when doing hot starts on hot days.

I normally fly to another local airport for avgas and depart within 15min. and it never fails to boil if it's above 80 degrees.

It always starts but the rough idle and shaking below 1200 RPM is a bit annoying, It doesn't seem to make a difference full rich or leaned, fuel pump on or not and, I've waited 5+ minutes a few times to see if it clears up with no luck so I try to get to the runway fairly quick, once full power is in it clears up immediately.

I've reduced the injector size and increased the spring pressure in the manifold Per Airflow Performance, both with only slight improvement.

All lines FWF are fire sleeved and I'm considering adding a shroud to the fuel pump next.

Any thoughts on the issue
 
Exact same thing on my Avstar setup. I too get the runway quickly. Interested to see what others have found.

Edit: mine runs smooth starting at about 1200-1300 RPM.
 
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birddog486 said:
It always starts but the rough idle and shaking below 1200 RPM is a bit annoying, It doesn't seem to make a difference full rich or leaned, fuel pump on or not an, I've waited 5+ minutes a few times to see if it clears up with no luck so I try to get to the runway fairly quick, once full power is in it clears up
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This scares the bee jives out of me. The engine is running rough, so you say to yourself, “oh I know what it is” and go ahead and takeoff. One day, the engine may be rough and it WON’T be what you think it is and all heck will break loose and you will be in a difficult situation.

I think if the engine is rough, it should clear up during run up, or there must be some way to know if it will clear up before committing to a takeoff. I am not flying mine yet, so I cant give you any advice from experience, but reading the accident reports, it seems many are cuased by pilots thinking they know what the problem is, but this time it is different and they are surprised. This exact thinking caused a friend to stuff his Cardinal in 1998. I dont have a solution and I dont know what you know.
Maybe the solution is to just do a high speed taxi down the runway half way, taxi back and do a real takeoff. I dont know, I am just spit balling here.
 
Are you seeing any fluctuations in the red cube fuel flow? Also, does it clear after the run with full power? For example, what would happen after a few seconds of full power and you then pulled off the runway - would it idle ok?
 
jcarne said:
Exact same thing on my Avstar setup. I too get the runway quickly. Interested to see what others have found.

Edit: mine runs smooth starting at about 1200-1300 RPM.
Click to expand...

Jereme, I'm wondering if the fuels boiling inside my injector. Maybe with the outlet at the bottom the vapor cant get out until the fuel flow is high enough to flush the bubbles out the bottom causing the prolonged roughness. here's a pic

Is your hose routing the same or is your feedline to the spider come off the top of the injector?
 

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rv8ch said:
Are you seeing any fluctuations in the red cube fuel flow? Also, does it clear after the run with full power? For example, what would happen after a few seconds of full power and you then pulled off the runway - would it idle ok?
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Nope, at such a low fuel flow i dont notice anything strange. As I said, once full powers in, it clears instantly, not sure how it would idle again after that though.
 
birddog486 said:
Jereme, I'm wondering if the fuels boiling inside my injector. Maybe with the outlet at the bottom the vapor cant get out until the fuel flow is high enough to flush the bubbles out the bottom causing the prolonged roughness. here's a pic

Is your hose routing the same or is your feedline to the spider come off the top of the injector?
Click to expand...

That's different :)

You might want to use the "top" outlet and reposition the fuel line from the servo-to-the-spider -- the line will see a lot less heat, shorter run, not downhill & uphill, etc.

See pics from OP-22, and RV-14 49-06.
 

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birddog486 said:
Jereme, I'm wondering if the fuels boiling inside my injector. Maybe with the outlet at the bottom the vapor cant get out until the fuel flow is high enough to flush the bubbles out the bottom causing the prolonged roughness. here's a pic

Is your hose routing the same or is your feedline to the spider come off the top of the injector?
Click to expand...

Mine comes out of the bottom but it doesn't loop around the servo. It turns directly up to the spider headed the other direction from yours. If you do change this I would be interested to hear what you find if you change to the top port. This will certainly have less fuel in the hot side of the firewall and may help.
 
Nearly the same issue, but with a Airlow Performance FM-150 (without return lines). Not so rough as the other mentioned and fine at 1000 RPM. I have made a few heat shields that keep away the thermal radiation from the exhaust to the throttle body. Also, a spring loaded oil-door, that is ALWAYS open when on ground, no fuel pump shroud ...
 
birddog486 said:
Jereme, I'm wondering if the fuels boiling inside my injector. Maybe with the outlet at the bottom the vapor cant get out until the fuel flow is high enough to flush the bubbles out the bottom causing the prolonged roughness. here's a pic

Is your hose routing the same or is your feedline to the spider come off the top of the injector?
Click to expand...

fuel line comes much closer to the exh than I would like. Can't say if that is your core issue, but would find a way to get it further from the pipe.

Larry
 
What technique/procedure are you using for hot starts?

I have avstar FI as well. Absolutely no hot start issues. Here’s my technique...

1. Mixture- FULL RICH
2. Throttle- FULL OPEN. (Watch your residual fuel pressure decrease)
3. Mixture- ICO
4. Throttle- 1/2-3/4 OPEN
5. Starter- ENGAGE

It will take 4-6 blades and then she starts. Immediately bring throttle to IDLE, and slowly bring mixture in to keep it running. Works every single time
 
lr172 said:
fuel line comes much closer to the exh than I would like. Can't say if that is your core issue, but would find a way to get it further from the pipe.

Larry
Click to expand...

The pics deceiving, the exhaust pipe is about 6" from the fuel line pictured but any things possible I suppose
 
RV74ME said:
What technique/procedure are you using for hot starts?

I have avstar FI as well. Absolutely no hot start issues. Here’s my technique...

1. Mixture- FULL RICH
2. Throttle- FULL OPEN. (Watch your residual fuel pressure decrease)
3. Mixture- ICO
4. Throttle- 1/2-3/4 OPEN
5. Starter- ENGAGE

It will take 4-6 blades and then she starts. Immediately bring throttle to IDLE, and slowly bring mixture in to keep it running. Works every single time
Click to expand...

It's not the actual starting thats the problem. It starts right up but the vapor in the system causes a rough idle below 1200rpm for a prolonged period of time
 
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