VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV Ongoing Maintenance Issues
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-27-2020, 08:30 AM
FitzRX7 FitzRX7 is offline
 
Join Date: Jan 2013
Location: FL
Posts: 80
Default MA-4SPA Intermittent Idle Flooding

First, thanks for any help.

I've got a O-320 w/ MA-4SPA carb that is giving me fits. Runs perfect, except for a nasty habit of flooding intermittently at idle. It's been thru 3 carb repair shops, some multiple times, and it still floods occasionally. Mechanical fuel pump was replaced about a year ago, 6 psi at idle, 2 psi at full throttle (.5-8 psi is the allowable range IIRC).

The main symptom of this is a slowly decaying idle while taxiiing. If I turn the fuel selector off the idle almost immediately recovers, back on and it starts decaying again. Hit a bump or taxi a bit and it stops misbehaving. Or starts doing it again. Pretty sure not getting needle seating well enough intermittently but nobody has been able to fix it.

The carb was upgraded to the new blue float (which is pretty much when all this $hit started), and alignment is perfect, needle/seat have been replaced 3 times I believe, still no relief. I can go complete flights without this behavior and then other flights it does it on taxi out and after landing.

Thoughts? Thanks again.

Jon
Reply With Quote
  #2  
Old 03-27-2020, 09:00 AM
DennisRhodes DennisRhodes is offline
 
Join Date: Jul 2007
Location: Taylorsville, Ga
Posts: 759
Default

It does sound like the float needle and seat are suspect. Are you a tricycle or tailwheel? Do you see the same thing in flight? Maybe time to swap that core out with a new factory or rebuilt one . Yes, I know they are not cheap but I do like to see that propeller keep on turning during final.
__________________
DRRhodes
2020 VAF Supporter
RV9 N908DR
Reply With Quote
  #3  
Old 03-28-2020, 11:12 AM
FitzRX7 FitzRX7 is offline
 
Join Date: Jan 2013
Location: FL
Posts: 80
Default

RV-4/Tailwheel. Occasionally have noticed it in level or descending flight, not nearly as noticeable as on the ground. Float/needle have been replaced 2-3 times in the last 4 years. I understand refurb should solve the problem, but it's maddening to not be able to figure out what's wrong with this one.

Jon
Reply With Quote
  #4  
Old 03-28-2020, 11:27 AM
DennisRhodes DennisRhodes is offline
 
Join Date: Jul 2007
Location: Taylorsville, Ga
Posts: 759
Default

Usually in the rebuild kits there is a guage template setting that float to valve setting. That might be a place to revisit. Without that guage its pretty much a guess. If carb is off on bench you might fill with some 100LL and even apply a little pressure to see if its running thru the seat and out the vent. Should have shut off even at couple pounds pressure. Look at it also at the tailwheel down position . Good luck
__________________
DRRhodes
2020 VAF Supporter
RV9 N908DR
Reply With Quote
  #5  
Old 03-28-2020, 11:34 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,893
Default

I would be looking for a crack in the main body of the carb housing, as well as a problem with seals or ball in the accel pump.

Have you properly adjusted the idle mixture with the engine hot? A fat idle mixture can cause your symptoms as the engine "loads up." Doesn't explain the resolution with bumps, however. That clearly points to a float or needle seat issue. Don't see how that happens with three new sets of parts. Also possilbe that the blue float is defective. You indicated that this all started when you installed it. A manufacturing defect could be creating a different level of bouyancy than normal and this would throw everything off.

Seems the float is the smoking gun, based upon your narrative. May be worth replacing it. This assumes it has never been replaced since it's initial installation.

It would be wise to verify the fuel pressure with a mechanical gauge, especially at idle. High pressure produces the same symptoms as a leaking needle/seat. It is not that uncommon for a pump to fail with high pressure. I would also be sure that you are not injesting debris into the carb from a failing hose.

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

Last edited by lr172 : 03-28-2020 at 11:39 AM.
Reply With Quote
  #6  
Old 03-28-2020, 01:35 PM
Finley Atherton Finley Atherton is offline
 
Join Date: Nov 2005
Location: AUSTRALIA
Posts: 743
Default

Quote:
Originally Posted by FitzRX7 View Post

needle/seat have been replaced 3 times I BELIEVE

Jon
Confirm the seat was replaced. I had flooding issues. The seat looked perfect, tried two new needles on the bench and both flooded. Problem fixed with a new seat.

Fin
9A
Reply With Quote
  #7  
Old 03-29-2020, 01:22 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,365
Default flooding

That this happened after float replacement indicates that the float is occasionally hanging up on the wall of the float cavity. I think there is a service bulletin on this and possibly a gage to measure side clearance on the float.
the fit of the float pivot is very sloppy and is also a factor as this allows a lot of sideward travel for the float. Put a little side pressure on the float and move it thru its full travel. Repeat in the opposite direction. If necessary bend the float bracket very carefully to obtain clearance.
Reply With Quote
  #8  
Old 03-30-2020, 01:17 PM
FitzRX7 FitzRX7 is offline
 
Join Date: Jan 2013
Location: FL
Posts: 80
Default

THANKS!! Lots of questions/answers:

-Mechanical fuel pump replaced 100hrs ago, no change in intermittent behavior.

-Accel pump parts all rebuilt by most recent shop.

-Carb shop bench tested carb with 6' of head pressure, no flood. I resinstalled carb and with facet boost pump fuel poured out of vent. Turn pump off, made a phone call, turned it back on and zero leaking.

-Carb shop has cutaway fit guide, zero clearance problems indicated by guide, minor witness marks around float hinge pin clearanced at most recent tear down, zero change in behavior.

-cold/hot makes no difference, today misbehaved slightly on taxi out, slowdown on base to land, and once on ground idled perfectly 5 minutes to hanger. Completely random.

-all engine fuel hoses new in last 100hrs, no debris ever found.

Last edited by FitzRX7 : 03-30-2020 at 01:20 PM.
Reply With Quote
  #9  
Old 03-30-2020, 03:05 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,893
Default

Quote:
Originally Posted by FitzRX7 View Post
.
I resinstalled carb and with facet boost pump fuel poured out of vent. Turn pump off, made a phone call, turned it back on and zero leaking.
That's concerning. Clearly your facet pump is not properly regulating, at least not consistently. Can you link all of your issues to the boost pump running? If so, I would replace it.

Do you have a fuel pressure gauge? I believe you may need one to sort this out.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Reply With Quote
  #10  
Old 04-04-2020, 07:04 PM
FitzRX7 FitzRX7 is offline
 
Join Date: Jan 2013
Location: FL
Posts: 80
Default

Thank Larry. No issues follow the boost pump, have a great Garmin G3X pressure gauge, never over 6psi even with the pump on. The fuel pouring out was just to indicated how random the seat not completely sealing is, put pressure on the carb and it flooded, 5 minutes later put pressure on it and it didn't. Just so strange that it can ever-so-slightly hang up and then work fine.
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 07:41 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.