Marvel Schebler poor mixture

[rnoel]

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 ?

[Mike S]

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.........

[RV Jerry]

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]

Try this thread: http://www.vansairforce.com/communit...ght=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.

[GalinHdz]

Originally Posted by rvsxer

Try this thread: http://www.vansairforce.com/communit...ght=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.

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.

[rvsxer]

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.

[bret]

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.

[jrs14855]

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.

[rnoel]

Thank you for all replies.
Instead of drilling the main jet, can I buy a larger jet to replace mine ?

[crabandy]

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