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MA4-5 10-4164-1 carburetor

Scott Hersha

Scott Hersha

Well Known Member
My O-360-A1A powered RV6 has a 10-3878 carburetor. Last month I read an article by Vic Syracuse (don’t remember which publication) about two RV6’s he was working with at His Base Leg business. Both of them had issues with high CHT’s. There were a couple problems that could cause this. One was ignition timing, but both of them had the 10-3878 carburetor. Vic said that the correct carb for our airplanes should be the -4164 - larger main jet, among other things. I believe he upgraded those two RV6’s to the -4164 carb, and they saw a marked improvement (I think). I have a fixed pitch Sensenich GA prop on mine. At full takeoff power, once airborne I’ll see 2250 RPM, ~28-29” MAP until I pick up some speed, but my fuel flow at that full power setting is 13-13.2 gph. On warm days I’ll have to reduce my MAP to 25-26” after I’ve climbed a couple thousand feet to keep my hottest cylinder(s) below 400*. In cruise my CHT’s slowly balance out in the neighborhood of 330-350* depending on OAT. So - question is - for those of you that have gone this route, did it help with high CHT’s, and what other indications have you experienced in other phases of flight? For the engine experts, what would you recommend. Vic - am I right about what I think you said about the -3878?

Thanks
 
I always use the 4164 on RV's for the higher FF. You can use the 3878 as the return core.
 
Carb‘d lycoming equals poor fuel distribution. Our RV air intake is really really high, which makes for a lean mix which we cannot control. I suffer the same on my O320 GA prop 6A. Your fuel flow is correct based on, baro, temp and RPM right? I understand the issue, in the Deep South in summer my initial climb is a little flatter for me too. I called MS and discussed, yep different carb was their recommended path if I wanted higher fuel flow at this phase of flight. Easier for me to pull back on the black knob for a minute or two, get past this worrisome issue, then enjoy the remainder of my flight….which is 99% of the flight 😀
 
When I bought my -6 rapid acceleration on take-off or during a GA caused the engine to kind of hesitate, and the FF was the same as yours Scott. The Mooney mod with a bigger main jet cured that a few years ago.
My new engine should be on the build next month (🤞) and will be fitted with a new 10-4164-1 to replace the current 10-3878...
 
Research MA4-5 Mooney Mod kit
It basically converts your carb to a 4164.
Made a big improvement on my RV-6A.
 
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D & G Supply also recommended by my A&P friend at my airport, and Jimmy at JBA. I called Russ at D&G and he will basically turn my 3878 into a 4164 - for about $150! What a good deal. Our airport closes on June 3 for about 6 weeks and that’s when the carb will come off. Also planning on putting a taper pin in my tail stinger during that time.
 
Scott Hersha said:
On warm days I’ll have to reduce my MAP to 25-26” after I’ve climbed a couple thousand feet to keep my hottest cylinder(s) below 400*. In cruise my CHT’s slowly balance out in the neighborhood of 330-350* depending on OAT.
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These temps seem perfectly fine to me (and to Mike Busch, and to Lycoming). If it went over 420 in climb maybe I’d consider a little baffling tweak. What am I missing?
 
Dugaru said:
These temps seem perfectly fine to me (and to Mike Busch, and to Lycoming). If it went over 420 in climb maybe I’d consider a little baffling tweak. What am I missing?
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I’m sure it would go over 420 in a full power climb on a warm day (in fact or has) if I didn’t pull the power back a little. That’s not OK with me, and the carb mod should fix it, because it has worked with so many others. The 3878 becomes a 4164 with the mods. That’s the carburetor that should be on this airplane.
 
rvbuilder2002 said:
Research MA4-5 Mooney Mod kit
It basically conveys your carb to a 4164.
Made a big improvement on my RV-6A.
Click to expand...
+1.

I had lean WOT issues with my 3878 on an O-360. The Mooney mod kit has a larger main jet and also a restrictor for the economizer cct which makes the carb run richer at WOT. May not completely solve your high cyl head temps on climb but you won't be lean at WOT any more.
 
Walt said:
I always use the 4164 on RV's for the higher FF. You can use the 3878 as the return core.
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Since the OP has an O-360, I am assuming that the 4164 is applicable to that motor. Or would that swap work for an O-320? I may be looking at an similar issue on my O-320 E2A equipped 9A.
 
Phyrcooler said:
Since the OP has an O-360, I am assuming that the 4164 is applicable to that motor. Or would that swap work for an O-320? I may be looking at an similar issue on my O-320 E2A equipped 9A.
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O-320 uses the MA4-SPA carb (smaller than the MA4-5) so your solution would be different.
A good carb overhaul shop should be able to help you determine if there is a different ten dash # carb that would be desirable for your engine.
 
Phyrcooler said:
Since the OP has an O-360, I am assuming that the 4164 is applicable to that motor. Or would that swap work for an O-320? I may be looking at an similar issue on my O-320 E2A equipped 9A.
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On a O-320, I had luck with the 10-3678 carb. Makes 14+GPH on takeoff
 
Interesting discussion, but, it brings up a question on my engine/carb setup. I have an O-360-A1D from a salvaged Piper Geronimo Apache; the carb that came with this engine was a 10-3878. Prior to installation on my RV-8 I had the engine field overhauled, plus sent the carb out for overhaul as well. The engine and carb were installed together and have been running well for over 17 years and 2100+ hours, no real issues other than occasional high CHTs on a hot day climb.

So now my question is, why was the 3878 carb adequate to run on a Geronimo Apache, but when the exact same engine is installed on an RV, it needs the 4164 carb? Is it a speed/airflow/baffle/cooling thing?
 
jbDC9 said:
Interesting discussion, but, it brings up a question on my engine/carb setup. I have an O-360-A1D from a salvaged Piper Geronimo Apache; the carb that came with this engine was a 10-3878. Prior to installation on my RV-8 I had the engine field overhauled, plus sent the carb out for overhaul as well. The engine and carb were installed together and have been running well for over 17 years and 2100+ hours, no real issues other than occasional high CHTs on a hot day climb.

So now my question is, why was the 3878 carb adequate to run on a Geronimo Apache, but when the exact same engine is installed on an RV, it needs the 4164 carb? Is it a speed/airflow/baffle/cooling thing?
Click to expand...
Different induction air boxes can have an influence on what the actual fuel air mixture ratio ends up being when it leaves the carb
 
jbDC9 said:
Interesting discussion, but, it brings up a question on my engine/carb setup. I have an O-360-A1D from a salvaged Piper Geronimo Apache; the carb that came with this engine was a 10-3878. Prior to installation on my RV-8 I had the engine field overhauled, plus sent the carb out for overhaul as well. The engine and carb were installed together and have been running well for over 17 years and 2100+ hours, no real issues other than occasional high CHTs on a hot day climb.

So now my question is, why was the 3878 carb adequate to run on a Geronimo Apache, but when the exact same engine is installed on an RV, it needs the 4164 carb? Is it a speed/airflow/baffle/cooling thing?
Click to expand...
Yes, I believe the higher speed plus more efficient air box makes some carbs run leaner than optimal. What’s your takeoff fuel flow?
 
Taltruda said:
On a O-320, I had luck with the 10-3678 carb. Makes 14+GPH on takeoff
Click to expand...
The carb on my O-320 is a 10-3678-32 that was fitted on the Piper Cherokee donor. There is also another 10-3678-12 carb that is leaner I think (I am not 100% certain). I hope that yours is a -32 because then mine should be OK too!
 
Taltruda said:
Yes, I believe the higher speed plus more efficient air box makes some carbs run leaner than optimal. What’s your takeoff fuel flow?
Click to expand...
Exact fuel flow I don't recall off the top of my head... but dang, now I feel like I need to send my carb in for an upgrade.
 
PaulvS said:
The carb on my O-320 is a 10-3678-32 that was fitted on the Piper Cherokee donor. There is also another 10-3678-12 carb that is leaner I think (I am not 100% certain). I hope that yours is a -32 because then mine should be OK too!
Click to expand...
Yes, I believe it’s the -32
 
rvbuilder2002 said:
Different induction air boxes can have an influence on what the actual fuel air mixture ratio ends up being when it leaves the carb
Click to expand...
I think that was the situation with the Mooney’s in the 90’s, and they modified the main jet, and maybe a couple other things to allow more ff at full throttle (Mooney mod). That basically morphed the 3878 into the 4164. Our RV’s have a similar situation because of speed/airflow into the carb.
 
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