VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > RV Firewall Forward Section > Traditional Aircraft Engines
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-31-2020, 12:44 PM
Emery Emery is offline
 
Join Date: Jan 2018
Location: Whitehorse
Posts: 74
Default o-320 rpms climb by 250rpm when leaned @WOT/check float next/Have I overlooked anythi

So, I am running on the ground an O-320 that has been pickled for about 10 years. I have installed it on my RV-9. It has a decent idle smoothness. It has decent mag drops at all rpm ranges. I have unhooked the fuel primer line to eliminate that fuel source.

So far I have not spent any money on it.

When experimenting with different throttle RPM settings above 900rpm, the engine is rough until given major leaning (I'd say about an inch and a half of mixture knob movement) at which point the engine smooths out and I gain about 200rpm. At wide open it is closer to 250rpm.

I have not had the carburetor apart yet (Marvel schebler MA-4SPA) so that will be my next step. For the experienced out there, is this a classic Marvel case? I am also aware of marvels float problems and updates. I am comfortable with working on carburetors.

My best leaned WOT so far is 2150 rpm. Hopefully that will improve with work.

Any comments or similar stories will be appreciated. Thanks
Reply With Quote
  #2  
Old 08-31-2020, 01:37 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,173
Default

When you say you ‘unhooked’ the primer line, did you cap it off? You can’t leave a large air leak into the intake manifold.
Reply With Quote
  #3  
Old 08-31-2020, 02:07 PM
Emery Emery is offline
 
Join Date: Jan 2018
Location: Whitehorse
Posts: 74
Default

Yes. No vacuum leak.
__________________
E.S.
Reply With Quote
  #4  
Old 08-31-2020, 02:43 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,173
Default

With engine at idle, move mixture to cut off. You should see a small, 50 rpm rise just before it dies. Adjust idle mixture screw if necessary.
Reply With Quote
  #5  
Old 08-31-2020, 03:01 PM
Emery Emery is offline
 
Join Date: Jan 2018
Location: Whitehorse
Posts: 74
Default fuel leaking

I'm about to pull the carb off and realized that there is a bunch of fuel leaking out the airhorn. So yes, I'm going for the float and needle and seat. Thanks
__________________
E.S.
Reply With Quote
  #6  
Old 08-31-2020, 08:43 PM
Emery Emery is offline
 
Join Date: Jan 2018
Location: Whitehorse
Posts: 74
Default Not resolved.

Well, I took the carb apart today. The brass float was dry inside. I submersed it in 212 degree water to check for bubbles....nothing. Float level is 7/32 and float moves freely. Carb is very clean. Problem Could be the needle and seat. The main jet does not appear to have been drilled out as a #40 drill will not pass through and a .092-.093 bit will.

I'm going to sleep on it, but I might just put the carb back together and try it again.

A leaking needle and seat is bit abstract. Difficult to see and be definitive about. Usually you just change them. Too bad they cost $75-$100.
__________________
E.S.
Reply With Quote
  #7  
Old 08-31-2020, 11:11 PM
DavidAhrens DavidAhrens is offline
 
Join Date: Feb 2007
Location: Bakersfield, CA
Posts: 82
Default Carb problem

You can and should check the needle seal with air pressure while on the bench before reinstall. Common practice after carburetor work. Goggle it , if needed, I can give you more of an explanation.
Reply With Quote
  #8  
Old 09-01-2020, 06:37 AM
MiserBird's Avatar
MiserBird MiserBird is offline
 
Join Date: Mar 2018
Location: Cornelia, GA
Posts: 64
Default

Is your engine a 150HP with a part #10-3678-32 carb?
__________________
Dave McKinnon
KAJR - Cornelia, GA

1975 Cardinal RG N1593H since Mar 1993
1980 RV-3 N3VR Bought flying Sept 2017

Dues current 2021
Reply With Quote
  #9  
Old 09-01-2020, 07:53 AM
mahlon_r mahlon_r is offline
 
Join Date: Jan 2005
Posts: 1,043
Default

Some things to check if the carb is OK. But raw fuel collecting in the airbox would indicate that it isn't or there is a rag or something in the intake manifold.
Assuming you have a 10-5135 or similar carb, on the bottom of the carb there is a vent hole cast into the lower bowl. it is located just inside the airbox flange. Make sure this hole is not obstructed in anyway by a home made air box gasket or any part of the airbox. If that vent hole is blocked, the engine will not make power. Also make sure you have no heat leak into the airbox and that the air is free to move from ambient to the carb through it. Also, I would make sure your fuel pressure is in limits and that your engine breather is free and unobstructed.
Good Luck,
Mahlon
__________________
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
Reply With Quote
  #10  
Old 09-01-2020, 07:59 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,763
Default

Quote:
Originally Posted by DavidAhrens View Post
You can and should check the needle seal with air pressure while on the bench before reinstall. Common practice after carburetor work. Goggle it , if needed, I can give you more of an explanation.
+1

I would not put the carb back on without confirming the integrity of the needle/seat interface, given the symptoms you describe. Also give a look at the check ball in the accel pump chamber.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:20 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.