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RV-6 engine pause

R

rledwards9

Member
Just started flying RV6 with wood Sensenich prop and Lyc 0320 engine.
Flys great but engine feels like it temporarily pauses after you reduce power.
It then resumes at the new power setting as if nothing was wrong. Is this normal with a lite weight prop? Any suggestions?
 
Same thing

I have a 0-320AD with wooden prop, at about 1200 ? 1400 there is a bump. I notice it when advancing the throttle slowly. I have been told it may be the idle mixture is too lean or too rich, there is a transition from idle jet to main jet and it seems to happen at that point, metal prop might make it less noticeable as there is more weight to carry it through . I have 110 hours on it and have never had a problem. I have tried to adjust. The local A&P said it was not uncommon with some carbs.
 
Not quite the same thing

His is acting up on reducing power and yours is acting up increasing power.

You may be right as to why, but I would keep looking.

I have an 0-360 that had a tiny intermintant miss, so small others couldn't feel it and A/P's wrote it off to normal. I finally replaced the carb after replacing everything else and it went away! So I'm sure it was something that wasn't right in the carb.

I'll be interested in how this turns out.
 
[email protected] said:
I have a 0-320AD with wooden prop, at about 1200 ? 1400 there is a bump. I notice it when advancing the throttle slowly. I have been told it may be the idle mixture is too lean or too rich, there is a transition from idle jet to main jet and it seems to happen at that point, metal prop might make it less noticeable as there is more weight to carry it through . I have 110 hours on it and have never had a problem. I have tried to adjust. The local A&P said it was not uncommon with some carbs.
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Ditto. Had the same exact hesitation around 1350-1400 rpm with my o320/wood prop combo. I was also told it was due to the tansition from main jet to idle jet and not to worry about it.
 
Me, too

I have a wood prop with O320 also and notice the tiny dead spot upon power reduction after takeoff. I have not noticed it while increasing power.
I figured it must be in the carb and was waiting until I flew with someone who was more knowledgeable about it. That hasn't happened yet.
It is a very brief hiccup and when I try to get back to that throttle setting to recreate it, it runs fine.
My carb is a new Precision Airmotive and the engine is a zero timed PennYan 160 hp.
It is interesting and reassuring to hear others have had the same experience. My engine and -9 have 118 hours and it has happened from day one and has not changed since so it is not a concern for me. However, I'd like to know a reason for it.
Glad you brought it up.
 
RV6 engine pause

I appeciate all the replys. The engine is an 0320E2D andI'm not sure about the carb since I'm out of town but I think it is a ma4 whatever is standard for this engine. Fresh overhaul and had a bent idle needle valve butreplacing it didn't change anything. am glad to hear that others have this problem and it doesn't get worse or affect safe operation. I suspect it is the carb and will probably not fix itself with further operation. I will replace it next and see if that fixes the problem. By the way, I can't seem to adjust the idle mixture to get the rpm increase before shutdown with slow mixture cutoff. This needle valve is normally adjusted slightly rich to achieve this slight rpm increase prior to shutdown. Maybe this is a clue to the carb problem?
 
I have Bob Martins old carb and had it overhauled before my first flight. It still has a hesitation after overhaul so I would bet my bottom dollar it is your carb.
 
Carb. model

rledwards9 said:
I appeciate all the replys. The engine is an 0320E2D andI'm not sure about the carb since I'm out of town but I think it is a ma4 whatever is standard for this engine. Fresh overhaul and had a bent idle needle valve butreplacing it didn't change anything. am glad to hear that others have this problem and it doesn't get worse or affect safe operation. I suspect it is the carb and will probably not fix itself with further operation. I will replace it next and see if that fixes the problem. By the way, I can't seem to adjust the idle mixture to get the rpm increase before shutdown with slow mixture cutoff. This needle valve is normally adjusted slightly rich to achieve this slight rpm increase prior to shutdown. Maybe this is a clue to the carb problem?
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RL (?)

The O-320-E2D can have two different carbs in it's certified version - both are MA-4SPA, with models 10-5009 and 10-5135.
Perhaps you should speak to a carb. shop and find out the differences between them.
Lycomings Service Instruction SI-1305C specifies a different nozzle for the 10-5009 mod, and if your carb has been modified, it should have a "N" stamped after the model number.
Apparently a modified carb. becomes part number 10-5135.

Do you have the latest model carb installed?

gil in Tucson - extracting data from the Grumman list, since -E2Gs with the same carb. also report a similar problem.
 
Good to hear

664781 said:
I have Bob Martins old carb and had it overhauled before my first flight. It still has a hesitation after overhaul so I would bet my bottom dollar it is your carb.
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Kurt,
Glad to hear you had it overhauled, and sorry that didn't fix it!

For others reading this, I disclosed the entire history of the carb to Kurt at time of sale. I had purchased a new carb that had been removed by another RV builder for a FI upgrade. The new carb fixed my problem.
More history: the guy I bought the plane from in Florida had flown the plane for about 100 hours and said he never noticed the miss/hesitation.

I'm amazed at how some people say the carbs are dirt simple like tractor carbs, but when I look at the info from Precision Airmotive, I bought the OH CD, it doesn't look so simple to me and now Kurt had a carb OH'ed and it didn't correct the little problem......I treat my carb with respect!
As I said before, keep looking for the problem. Maybe swap with a known good carb, just to see if it makes a difference. Just a suggestion.
Good Luck.
 
I once flew a 140 hp Cherokee (PA28-140) that had the same issue. Everyone said it was normal so I flew on. It did a great job to teaching me not to just shove the throttle in but do so slowly when I wanted to go around.

If it were my plane, I would try to resolve it before I took it for granted that it "was normal".

That Cherokee was so old the mixture was way over on the right side, exactly where a passenger might look for a cabin heat knob.
 
I have seen a similar issue when my plane had a slightly loose float bowl and (presumably) an induction leak.

Give your airbox the wiggle test and see if there is motion between the carb bowl and the carb body or between the carb body and the sump.
 
One peice venturi

A while back there was an AD that required switching from a two piece venturi in an MA-4 to a one peice as there was a percieved danger by the FAA that the two piece could come apart and give your engine some bits to ingest.

The drawback of the one peice venturi has the symtom of hesitation switching from idle to main jet (1200-1500RPM). This is well documented in spam can literature. If you have a new carb, or recent repair exchange, you will likely have the one piece venturi. I recently installed a rebuilt carb on my Cardinal and is has same symptom.

l heard during a recent hangar flying session that the AD was recalled because many state the two peice venturi's run better, but I do not know this for sure.

Dale Lambert
C177
RV-6 finishing kit.
 
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Two piece Venturi

Prior to the venturi AD my O-320 carb had always worked fine... installed the one piece unit and all of a sudden had the same described hesitation on throttle position changes. Got tired of it and just simply put the old parts back in the carburetor and it went away...

Fly safe
 
Just a thought

I too had the intermitant miss on my TMX O-360. I had and still have the lean carb jet but my fix was a little unconventional.

The miss on my engine was just like someone else described, it was very subtle with no change in engine sound. It was more like a pulse. Most flights went without a hitch. When it did miss, it would be in groupings of 3-4 pulses.

I was still able to lean the mixture and get a EGT rise when it did the miss thing during a local flight at fairly low altitude. The leaning did not aggrevate the missing and the missing actually stopped (this may have been coincidence since the missing event was so short in duration).

It was explained to me (and I am probably missing a lot) that this is a common problem in RVs with the lean carb. The issue is not that the mixture is too lean, which I proved to myself when I leaned without making the missing worse AND getting an EGT rise, it is a distribution issue with the mixture that seems to rear its head with this carb in some RVs at certain times. I am not pretending to really understand this but read on.

The engine builder was more than happy to swap out carbs and I started to pursue this. When I was unbolting the carb, I noticed that the throttle/mixture bracket was ever so slightly impinging the intake area between the carb and intake manifold. I am talking a .001-.002 in one quadrent of the circle. So I enlarged the entire bracket hole so that it was 1/16- 3/32 larger that the manifold hole.

I was not expecting much from doing this but it worked. I am still flying with the lean carb. YMMV but I hope this helps.
 
Engine pause

That may be my problem and I'll check it because I have that same brackett on my engine. Thanks alot for the possible fix. Rv6-n666R :cool:
 
McFly said:
The engine builder was more than happy to swap out carbs and I started to pursue this. When I was unbolting the carb, I noticed that the throttle/mixture bracket was ever so slightly impinging the intake area between the carb and intake manifold. I am talking a .001-.002 in one quadrent of the circle. So I enlarged the entire bracket hole so that it was 1/16- 3/32 larger that the manifold hole.
McFly said:
I don't understand this comment. I have a RV-6 with o-360 c/s all standard Vans setup. The throttle/mixture bracket mounts over the carb flange on the 2 rear threaded studs. nowhere near the intake manifold gasket.
Do you have a different set up?
FYI, I just installed the enrichment kit (part 666-660) in my my MA4-5 10-3878 that converts it to the richer carb 10-4164-1.
Just test flew it this evening and it lowered my TO CHT's by about 25-30 degrees. Good Luck with the stumble issue
Click to expand...
Click to expand...
 
RV6 Engine pause

OK guys. Some of you were right and it fixed my problem. The pause was caused by the lack of a mod which changes the carb to an 10-5009N. The N mod was installed (new nozzle which has small holes that spray and mist the fuel) and the plane flew without any problems. The engine would consistently stumble between 2500 and 2300 rpm while reducing the throttle.
The problem doesn't occur anymore after replacing the nozzle. Yea! This internet is great and you experts saved me many bucks. Thanks again for your valuable advice. ;) :)
 
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