H

hughfi

Well Known Member
Hi there,

I have an RV6 with an 0-320 E3D on it. This engine has been rebuilt very well, and it has zero leaks etc. with 400+ hours on it.

Anyway, I have a scenario where the engine stutters. Its a momentary thing, but enough to give anyone in the aircraft the spooks. It normally happens when I touch the throttle to reduce power after levelling out after a climb. Its like the power drops for a 1/4 of a second and springs back on again.

I have a brand new carb from precision airmotive that I put on last year after my old carb started to leak. Its got a factory new fuel pump as of a few weeks back and it was happening before this change and continues to do so.

It should be pointed out that this happens only once during any flight and then everything works perfectly. Its almost like the float in the carb gets stuck or something and then falls back into place.

Any thoughts or ideas would be appreciated.

Thanks,

Hugh.
 
Hugh:

You said that you replaced the carb last year. Check that the carburetor is securely attached and the gaskets are in good shape.

I'm thinking that you have a loose carb, and pulling back on the throttle moves the carb enough to create a momentary air leak, just as you are reducing MAP.

Just a guess, but it fits.

Vern
 
Replaced the gaskets on the carb today and tightened up the carb.

I still don't seem to be solving the problem though. Any other thoughts? Thanks for your help so far. Any other thoughts would be appreciated.

Thanks,

Hugh.
 
intake leak?

Just a thought.
Check your intake system carefully, you can pressurize it with a shop vac in blowing mode with a filter over it, like a panty hose or some fabric.
Blow air in the intake system and spray soapy water on the intake tubes and rubber connectors and look for leaks.
When you are running the engine at wot and then close or reduce the throttle, you are restricting the pistons from getting air and it puts a suction
on the intake system. If it gets more air from somewhere and the carb is only putting out fuel for a given throttle setting, you could be getting a lean mixture for a second until things stabilize.
Just a thought, Good Luck.
 
If you have a p/n 10-5009 carb get it modified to 10-5009N and the intermittent shudder should go away.
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."
 
mahlon_r said:
If you have a p/n 10-5009 carb get it modified to 10-5009N and the intermittent shudder should go away.
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."
Click to expand...

Mahlon, what does the "N" mod involve? Just wondering what is causing the stumble.

Thanks.
 
Basically, a different discharge nozzle. The pepper box style nozzle that comes with the ?N?, allows better fuel discharge and distribution.
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."
 
hughfi said:
Hi there,

I have a brand new carb from precision airmotive that I put on last year after my old carb started to leak.

Hugh.
Click to expand...

mahlon_r said:
If you have a p/n 10-5009 carb get it modified to 10-5009N and the intermittent shudder should go away.
Good Luck,
Mahlon
."
Click to expand...

I didn't know that!
Wouldn't you think that a brand new carb would be an updated one without
a problem?
Assuming he has a 10-5009 carb that is!
 
Last edited:
This has nothing to do with the problem, but with the perception. Anytime I am making a throttle change, and especially a mixture change where I may have a stumble, I tell the passenger. I do the "big pull" and usually get a momentary loss of power. If they know it is coming, no big deal. Otherwise I have seen some pretty scary looks.

Bob Kelly
 
Carb Problem

Hugh..

You may want to cap off your primer and then try it again. If the problem goes away you have an air leak in your primer which is overly leaning the mixture. If nothing changes you know your primer circuit is okay. I also had a similar problem and I did the vacuum cleaner trick mentioned earlier as well. After replacing my old carb. with a Precision Factory rebuilt, my problem was backfiring at about 1500 RPM when the carb was switching from the low idle circuit to the high speed circuit.

I got Precision involved and they replaced the nozzle with the pepper box nozzle (very rich) but nothing changed. The actual problem was wrong sump on the engine. The old carb was flow matched to the sump which was for an 0-360 180 hp rather than a 160 hp 0-320 and I replaced the modified carb with a like model but Precision built theirs according to specs. Lycoming traced the numbers on my sump after I contacted them on a guess since the sump was the only component I hadn't researched at that point. I then ordered the correct sump from ECI for $575 and it worked. BTW, I have a 0-360 sump for sale very reasonable.

My engine was purchased as a zero time rebuilt from another RV builder who had the work done but ran into financial problems. My old carb ran too rich at idle and I had to lean just to taxi or the engine would stumble or miss and the carb was worn so I decided to replace it.

I don't know if my experience will help you any but the simple carb system can be very complex to troubleshoot. Good luck.

Dick DeCramer
RV6 N500DD 300 hrs.
RV8 Wings
Northfield, MN
 
Bob Martin said:
I didn't know that!
Wouldn't you think that a brand new carb would be an updated one without
a problem?
Assuming he has a 10-5009 carb that is!
Click to expand...
It isn't really a update but just a modification that makes the fuel distribution a bit better and the carb a bit richer. Most of the later crabs have the pepperbox nozzle but you can still buy a 10-5009 carb brand new without it. Some engines like the 5009N and some don't. The ones that don't, run crappy with the 5009N and great with the 5009 and then you get the exact opposite on other engines.
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."
 
I had the exact same problem with my 0-360 and i took the advice of malon and did the mod. Smoothed out everything! Increased fuel economy and was able to lean farther. It sounds like your running lean at that power setting.
Simple easy fix to try.
 
Thanks Mahlon

mahlon_r said:
It isn't really a update but just a modification that makes the fuel distribution a bit better and the carb a bit richer. Most of the later crabs have the pepperbox nozzle but you can still buy a 10-5009 carb brand new without it. Some engines like the 5009N and some don't. The ones that don't, run crappy with the 5009N and great with the 5009 and then you get the exact opposite on other engines.
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."
Click to expand...

Thanks for explaining the details! I'm still learning....:)
 
Wow, thanks for all the feedback. Here is what I have done.

1.) Replaced carb gaskets and yes, it is a -5009 model and not an -5009N yet...

2.) Ordered and recieved the carb nozzle from Aviall in Portland. After discussion with Precision who are on the same field as my airplane (Paine Field), they gave me the name of a company in Burbank CA that will put it when I take the plane down for annual in November. That company is 'Airmotive Carburetor' (http://www.yellowbot.com/airmotive-carburetor-co-burbank-ca.html) for anyone who is interested.

3.) Double checked all my intakes and primer lines. Could not find any leaks.

Test flew the aircraft after new gaskets. Result: Still a murmor but not as often now and much lighter in terms of the drop in RPM. This makes me think it could be a number of items. A.) The gaskets on the carb were leaking which I am almost certain was true. That is now fixed. B.) The nozzle upgrade is worth doing (after discussion with Precision and Lycoming) and will account for some roughness which would be entensified with a leaking carb gasket.

Thanks so much much for all your advice. This is really useful.
 
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