BrianMatice
Member
Good morning all. In order to avoid the risk of receiving many conflicting opinions and not knowing who to follow, I'd like to ask the group for suggestions on a book or other reference for jetting a carb for my RV-7A O-320-D3G.
I'll include my story as well for those that are interested, however I'm only looking for the reference material.
The Story:
Initially (first 10 hours) I installed the carb I had which was an MSA MA-4SPA 10-5009. After fighting relentlessly with super high CHTs I turned to fuel for my cooling needs. This led me to do many many (many) hours of research into all possible carb models / jetting combinations available for the O-320. I have learned that the 10-5009 carb configured as stock, comes with the smallest jet possible. Stands to reason as it was designed for the 150 HP variant O-320. Research also led me to the 10-3678-32 which comes with the largest bore main jet in the MA-4SPA line. I also contacted Mark at MSA who informed me that most RV guys go with the 10-3678-32 when running an O-320. So I ordered a new MA-SPA 10-3678-32 from Spruce. I do understand I could have drilled the jet on the old carb to achieve the same result. I made the decision to purchase new as the old carb was last overhauled ~ 15+ years ago (I think) and I have no paperwork.
With the new 10-3678-32 carb installed, I will say that on takeoff and WOT the engine cooling effect is amazing compared to my experience previously. As with every change however, it introduces new concern. I'd like a way to gage if it is actually running with too much fuel. I know it is, but I'd like a method to take measurements to prove it.
I always taxi with a lean mixture completely strangled so it will not run above 1200RPM. This will prevent me from accidently taking off while leaned. WOT I am observing about 14.7 Gal per hour flow max at full rich. When reducing manifold pressure below 20 inches, the engine begins to pop lightly, and gets worse as I reduce throttle. I can clean up the backfire instantly by leaning the mixture. I was fouling plugs like crazy until the other day. Working with my mechanic friend, we opened the plug gaps a bit which has eliminated the fouling problem. Backfire remains unless leaned. When landing I must maintain the leaned setting all the way to engine shutdown. When setting full rich (traditional training sets this on down wind) the engine loads up by the time a go around is executed. After the full rich setting is used from down wind to final, when applying full power again the engine stumbles as it works through clearing out all that excess fuel in the cylinders.
My options are:
1 - Learn to manage this engine/carb combination by immediately leaning any time below WOT. This includes during landing. If executing a go around, I must remember to hit the red knob as well or the engine will overheat instantly.
2 - attempt to find/make a smaller bore jet which will not backfire/load up the engine at full rich but still afford me the cooling effects I am seeking on takeoff.
3 - sell the plane and go fishing instead.
Again, I'm looking for any reference material I can read to learn about re-jetting a misbehaving O-320 if it is out there.
Thanks
I'll include my story as well for those that are interested, however I'm only looking for the reference material.
The Story:
Initially (first 10 hours) I installed the carb I had which was an MSA MA-4SPA 10-5009. After fighting relentlessly with super high CHTs I turned to fuel for my cooling needs. This led me to do many many (many) hours of research into all possible carb models / jetting combinations available for the O-320. I have learned that the 10-5009 carb configured as stock, comes with the smallest jet possible. Stands to reason as it was designed for the 150 HP variant O-320. Research also led me to the 10-3678-32 which comes with the largest bore main jet in the MA-4SPA line. I also contacted Mark at MSA who informed me that most RV guys go with the 10-3678-32 when running an O-320. So I ordered a new MA-SPA 10-3678-32 from Spruce. I do understand I could have drilled the jet on the old carb to achieve the same result. I made the decision to purchase new as the old carb was last overhauled ~ 15+ years ago (I think) and I have no paperwork.
With the new 10-3678-32 carb installed, I will say that on takeoff and WOT the engine cooling effect is amazing compared to my experience previously. As with every change however, it introduces new concern. I'd like a way to gage if it is actually running with too much fuel. I know it is, but I'd like a method to take measurements to prove it.
I always taxi with a lean mixture completely strangled so it will not run above 1200RPM. This will prevent me from accidently taking off while leaned. WOT I am observing about 14.7 Gal per hour flow max at full rich. When reducing manifold pressure below 20 inches, the engine begins to pop lightly, and gets worse as I reduce throttle. I can clean up the backfire instantly by leaning the mixture. I was fouling plugs like crazy until the other day. Working with my mechanic friend, we opened the plug gaps a bit which has eliminated the fouling problem. Backfire remains unless leaned. When landing I must maintain the leaned setting all the way to engine shutdown. When setting full rich (traditional training sets this on down wind) the engine loads up by the time a go around is executed. After the full rich setting is used from down wind to final, when applying full power again the engine stumbles as it works through clearing out all that excess fuel in the cylinders.
My options are:
1 - Learn to manage this engine/carb combination by immediately leaning any time below WOT. This includes during landing. If executing a go around, I must remember to hit the red knob as well or the engine will overheat instantly.
2 - attempt to find/make a smaller bore jet which will not backfire/load up the engine at full rich but still afford me the cooling effects I am seeking on takeoff.
3 - sell the plane and go fishing instead.
Again, I'm looking for any reference material I can read to learn about re-jetting a misbehaving O-320 if it is out there.
Thanks