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Marvel Schebler poor mixture

R

rnoel

I'm New Here
I have installed an O360 from my Cherokee 180 . Sinve the engine/carb are on my rv8, I am able to lean mixture only on full trottel. I think that the air admission on a rv8 is greather then a Cherokee. If it is the case or the problem itself does any one knows how to adjust the card for a better gaz consumption ?
Or where should I look for this trouble ?
 
Welcome to VAF!

Welcome to VAF---------I have no idea what the problem is, but there are a lot of smart folks on here that may have the answer.

Hopefully someone will jump in soon.........
 
On some engines such as yours they can be jetted on the lean side ,I have had to drill main jet to the size of a #31 drill ,if you decide to enlarge jet be sure to polish inside of jet when done any burrs left could make things worse.
 
rvsxer said:
Try this thread: http://www.vansairforce.com/community/showthread.php?t=30115&highlight=ma4-5+lean

You can also search "MA4-5 too lean" or similar. This is a well-known problem and is usually solved by installing a Service Kit (originally intended for Mooney aircraft) or just installing a larger main jet. I had this problem and went the Service Kit route. You might look into doing the newest float Service Bulletin, too, if you haven't already.
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AFAIK you can also change the carb to a 10-4164 which essentially does the same thing as installing the service kit. This change will increase your fuel consumption slightly (increase of .5-1gph) but nothing to worry about.

:cool:
 
Installing the service kit changes the carb part number. It not only installs a larger main jet but also changes the size of the air bleed, further enriching the basic mixture. The accessories specialist at Bolduc Aviation here in Minneapolis advised against drilling the jet but I know many listers have had good results with that.
As far as fuel economy goes, you are probably flowing less than 15 gph (not enough per David Brown) at WOT full rich so you'll actually be normalizing your fuel flow.
 
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Just another note on drilling jets, this is from Holley automotive carburators,

3. Holley jets are broached, flowed, and stamped according to flow rate. NEVER drill jets, as this seriously alters flow characteristics. Stamped numbers are reference numbers and DO NOT indicate drill size.
4. Spark plugs provide the best indication of proper jetting.
 
Jets

Hundreds, perhaps thousands of people have enlarged the jets on marvel carbs on EAB aircraft. Not more than .003 at a time, use a reamer, not a drill. Reamers are available from MSCdirect.com. Lots of lubricant with a new reamer and you will get a satisfactory finish.
The N kit is a different style nozzle that will probably accomplish the same result as reaming the old style nozzle.
 
Thank you for all replies.
Instead of drilling the main jet, can I buy a larger jet to replace mine ?
 
Marvel Schebler?

Do you have a 4 cylinder engine monitor, specifically to monitor the EGT's of the cylinders at various throttle settings? Have you done a lean test and found what the peak EGT's are for each cylinder at various throttle settings?

I found my mixture distribution after the carb varied a lot based on different throttle positions. You cannot change the distribution after the carb, although moving the throttle butterfly and or carb heat can alter the distribution. Full throttle yielded more than 200 degree difference in EGT's between cylinders, partial throttle evens things out to within 30 degrees or so.

I found in colder weather (20 degrees F) that my leanest cylinders were only 80 degrees rich of peak EGT. My idle mixture screw was also 4 turns out. I spoke with and sent in my carb to the guys at Marvel Schebler, they did flow test (it was within specs for a 3858) and were able to properly richen it up for me. I found their service very exceptional, it didn't hurt that it was free of charge because my carb was under warranty.


Website: http://msacarbs.com/
Phone: 336-446-0002
 
Do you have a P/N 10-3878 carburetor? Years ago, I was having problems with my O-360 stumbling at high power settings, especially at power reduction to climb power. I installed the Service Kit to change my 10-3878 carb to a 103878M. All problems rectified.
If you search the forum threads, you will find my postings about the fix, inclusive of the SK P/N.
Here it is! http://www.vansairforce.com/community/showthread.php?t=30424
Marvel Schebler Service Bulleting A11-62 is contained in this file. You will have to scroll down (about half way) to find it (they are NOT in numerical order). http://hhh.gavilan.edu/hspenner/Main/Manuals/marvel-scheblerservicebulletinsyears69-59.pdf

Here is a quote from another member in one of my old posts.
mahlon_r said:
Mooney mod is a modification to a 10-3878 carb to change it to a 10-3878-M. It makes the carb slightly richer and also helps a little bit with fuel distribution. Other O-360 carbs 10-4164-1(exact same thing as a 10-3878M) and 10-5193 already incorporate the mod. So if you have a 10-3878 it is worth doing if you have an intermittent miss. You will have a slightly richer fuel burn at full rich after it is done but the intermittent miss should be eliminated. One of the classic symptoms of needing the mod on a 10-3878 carb is an intermittent miss in cruise that is worse when hot and is also sometimes but not always caused by starting to lean or enrichen the engine or by starting to activate or turn off the carb heat.
If you have one of the other part number crabs, the mod is already incorporated.
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...
 
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