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O-540 carb on O-360?

jibby212

Well Known Member
I bought an overhauled O-360 A2F that came from an Aerocomander that was destroyed by wind on the ramp. The engine was sitting a while and I later discovered that it was full of corrosion. I replaced lots of parts including the cylinders and crankshaft. I am getting ready for my first flight and was wondering if i might need a richer main jet due to the speed difference of the donor aircraft and my RV7. The Carb is an MA-4-5 PN 10-4404 which appears to be for an O-540. I have ground run the engine, idles great, proper rpm rise with idle cut off and I am getting expected static RPM. I really don't have much faith in the person I bought this engine from and am guessing he gave me the wrong carb. Will the combo work?
 
Lot of hot rodders use large carbs to deal with issues like turbos and other enhancements that increase the intake CFM. From my experience, a carb that flows a lot more then the typical displacement requires will not do as well in the transitions or middle RPM ranges with higher vacuum. This is why most HP carbs are 4 barrel jobs with the large barrels not opening until 60% of mechanicl throttle travel. Even the stock muscle cars of the day used a quadrajet with the same arrangement for drive ability reasons; Too big of a barrel will lead to poor fuel metering when not standing on the throttle.

Larry
 
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I would NOT expect that carb to perform nearly as well on your engine as the MA-4SPA, except at idle and WOT where it will be fine. The accelerator pump charge will also likely be too large and lead to rich stumbles on acceleration, though you could tinker with the arm to tame it some.

Larry

The MA-4SPA is for the 320.
The MA-4-5 is the standard for the 360, the 10-3878 is spec'd for your engine but the 10-4164
is generally recommended for the RV because it flows a little more than the 3878.
The one you have may flow too much fuel, either have it flow checked or install the correct one.
 
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The MA-4SPA is for the 320.
The MA-4-5 is the standard for the 360, the 10-3878 is spec'd for your engine.
There are a few models that flow enough for the RV, don't recall the #'s off hand.

Thanks. I only have a 320 and a 540 and assumed the 320/360 were the same.
 
In my RV4 I have an 0-360 with a FP prop. When I 1st bought the plane almost 10 yrs ago it had a horrible, bog or sputter when coming off idle to full power like on an over shoot. Not really what you want or need at time point in time.

I've been able to tune that out so it pretty much behaves normal. Now that I've moved back to central Alberta with a field elevation of 3000 asl its taken on a new behavior on some of those hot summer days when we have temps in the high 20's + c. On final at reduced power settings or idle there is a light surge from the engine. if I lean the engine back on final then the surge is gone. Cooler temps its not an issue. When the cowl comes off next week I will lean out the idle mixture some more.

A few years ago I found out that the carb was off an O-435 or something so explains the headache.

Like most of us I've done the hot rodding thing lots on cars and sleds. When deviating from stock one of the first things we do is play with the carb. Then we lose drivability especially off idle. Maybe some gains on the high RPM power and more noise (think big block Mopar:D) but looking back it really wasn't worth it.

The carb will probably work but be prepared especially for your 1st over shoot and trying to tune will eat up a bunch of time and you probably wont be happy.
Tim
 
Bad assumption!

certainly. But I struggle to see how the same carb is used on both a 360 and a 540. That's a pretty big spread in displacement and suspect the variability across sub-models must be significant.

Larry
 
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