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  #11  
Old 07-11-2021, 04:24 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 290
Default Photos?

Some photos of your fuel line routing under the cowling might help us spot issues.
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  #12  
Old 07-11-2021, 04:30 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 571
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Quote:
Originally Posted by DanH View Post
Do the symptoms improve when you turn on the electric boost pump?
I didnít notice any improvement.
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  #13  
Old 07-11-2021, 04:32 PM
iamtheari iamtheari is offline
 
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Location: ND
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Quote:
Originally Posted by blaplante View Post
Some photos of your fuel line routing under the cowling might help us spot issues.
I plumbed it according to the RV-14 kit plans. Itís such a luxury to have that planned out for me. I donít have pictures handy but, from memory, the routing is from the lower center firewall up to the engine-driven pump, then through a fuel flow servo clamped to the left intake tubes with heat shielding wrapped around it, then from there to the fuel servo on the front of the sump, and from there up around to the spider on top of the engine.
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  #14  
Old 07-11-2021, 09:53 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
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Quote:
Originally Posted by iamtheari View Post
I plumbed it according to the RV-14 kit plans. Itís such a luxury to have that planned out for me. I donít have pictures handy but, from memory, the routing is from the lower center firewall up to the engine-driven pump, then through a fuel flow servo clamped to the left intake tubes with heat shielding wrapped around it, then from there to the fuel servo on the front of the sump, and from there up around to the spider on top of the engine.
So how is the fuel line insulated as it passes the exhaust pipes on the way to the servo?
And, maybe just as important, how is it insulated from the servo to the spider as it runs near exhausts and between hot cylinders?
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  #15  
Old 07-12-2021, 06:45 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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Quote:
Originally Posted by iamtheari View Post
I didn’t notice any improvement.
The symptoms suggest fuel heating and vapor generation. Although we tend to use 140F as a threshold value for vapor, the truth is that avgas is a mix of many volatile constituents, some of which have much lower vapor points.

No improvement with boost pump on says vapor formation is probably not happening prior to the engine driven pump.

Which brings us to Bryan's note above. The standard RV-14 firewall forward runs the servo feed line and fuel flow sender very close to the left side exhaust head pipes, in particular #2 (see attached). Personally I think that line should be shortened by an inch or more. Even if not a fuel heater, it would add some lifetime to the hose. For sure the pipes need heat shields.

In addition, there is an exhaust crossover under the rear of the servo. Do you have a heat shield on the pipe there?

BTW, the heat shields can be improved without much effort. A bare shield reflects some radiant energy. It absorbs the rest, and in effect divides it up. Some is carried away by convection, while some is carried to the other side by conduction, where it is re-radiated. Some of the re-radiated energy is reaching the servo. To reduce it, simply add an insulator to the servo side. Cut a patch of fiberfrax felt to match, and cover it with a wrap of aluminum tape. Done.
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Last edited by DanH : 07-12-2021 at 06:48 AM.
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  #16  
Old 07-12-2021, 08:47 AM
iamtheari iamtheari is offline
 
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Thanks for those tips. I did install the heat shields per the RV-14 plans, including the one on the cross-over. I'll consider trying to improve them the next time I am working with the cowl off, or at my first condition inspection this winter.

Is my #4 cylinder running much lower EGT at idle a red herring? I've watched it carefully and it is right in the middle of the pack in flight whether I am running ROP or LOP.
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  #17  
Old 07-12-2021, 09:34 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by iamtheari View Post
Is my #4 cylinder running much lower EGT at idle a red herring? I've watched it carefully and it is right in the middle of the pack in flight whether I am running ROP or LOP.
When you lean at idle, does it go up or down?

Remember, the numerical value isn't relevant. The points of interest are up-or-down with leaning, and does it peak at about the same mixture as the others.
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  #18  
Old 07-12-2021, 09:42 AM
iamtheari iamtheari is offline
 
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Quote:
Originally Posted by DanH View Post
When you lean at idle, does it go up or down?

Remember, the numerical value isn't relevant. The points of interest are up-or-down with leaning, and does it peak at about the same mixture as the others.
When leaning at idle, it tracks the others, it's just markedly cooler at idle. When I get the mixture lean enough, the engine does run smoothly. It's really lean, pulled back about 2/3 of the way between full rich and idle cutoff. I probably just need to re-do my idle mixture adjustment, with a hot engine on a cold day. I did it with a not-so-hot engine on a moderate day this spring. I don't want to get it too lean by adjusting it in the summer and then not be able to start the engine in the winter.
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  #19  
Old 07-12-2021, 10:06 AM
hoeser hoeser is offline
 
Join Date: Jun 2021
Location: Windsor, Ontario
Posts: 3
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Quote:
Originally Posted by DanH View Post
Do the symptoms improve when you turn on the electric boost pump?
Negative. Pressure is solid at 25-27 without the boost and about 29 to 30 with the boost and it has no effect on the idling condition of the engine when hot.
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  #20  
Old 07-14-2021, 09:43 AM
Tim Lewis Tim Lewis is offline
 
Join Date: Aug 2006
Location: Bristow, VA
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Quote:
Originally Posted by iamtheari View Post
Iíve been noticing that my IO-390 doesnít like to idle smoothly when itís hot. ...
Is there anything specific I should be looking at?
I used to have same problem. Fuel pump cooling shroud was no help. What fixed the problem (very significant improvement) was installing the new spider spring (4psi) called out in Lycoming SI 1539 and Lycoming SI 1489C. Part number 2577011. It makes a huge difference.

As I recall, I bought the new spring from Airflow Performance. I think the shipping was more than the spring.
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