Evo 46 won't needle, runs too lean
08-21-2018, 02:06 PM
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Join Date: Nov 2003
Location: Weatherford,
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Evo 46 won't needle, runs too lean
After my TT 40Pro powered Skyraider Mach II got LAPPED by a guy (who was running an Evo this time) that I usually run head to head with, I picked up a used Evo 46 (not NX version). I had to replace the 2-piece muffler with the 1-piece version to be legal. The engine was thoroughly cleaned in an ultrasonic cleaner, so I don't suspect dirt being the problem. I installed it and tried to get it to run. It runs too lean even with the needle backed all the way out. In fact it fell out and I lost it in the grass for awhile. It had a dried out o-ring in the needle, so I replaced that, I installed a smaller tank and pushed it ALL THE WAY to the top of the tank compartment to try to get more head pressure. Still no luck, it runs much too lean even with the needle all the way out. I tried relocating the remote needle valve to the forward position on the throttle, but there was no difference. Unfortunately, crankcase pressure is not allowed, so I need to find some way to get more fuel pressure. There is no easy way to lower the engine either. The guys in Georgetown, TX have apparently had similar problems and are partially restricting the size of the muffler exit to increase muffler back pressure. Other than doing that, I can't think of any other tricks to try.
It runs OK and will needle with the old, 2-piece muffler.
It runs OK and will needle with the old, 2-piece muffler.
I just put the calipers to the mufflers. The original, 2-piece muffler has an exhaust opening of. 0.254". The newer 1-piece muffler measures 0.310. So that's part of the issue and the obvious reason that the Georgetown guys put a restrictor in the 1-piece muffler.
Any suggestions?
Any suggestions?
09-07-2018, 04:09 PM
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Join Date: Jan 2006
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Gary,
Not sure about your set up but both of mine needle good and don't go lean in the turns like a lot of them do. (and I don't use the exhaust restriction)
I have the newer engines so I guess they are the NX?
When I'm building, I make little platform for the tanks that more or less keeps them level and as near the top of the fuse as possible. I completely cut out the top of one plywood bulkhead. The one that's a little over an inch in front of the one at the wing saddle, and the platform runs from the firewall to the one just in front of the wing.
I also use a 4 oz. tank. It allows the bottom of the tank to be higher than the bigger tanks.
One is set up with a Jet remote needle and the other one still has the original.
It sounds to me like your sucking in air somehow. things I would look at:
1. tank connections (stopper and tubes)
2. fuel lines.
3. filter
4. engine backplate/needle/ venturi seat/ front bearing?
see ya next week,
Jim
Not sure about your set up but both of mine needle good and don't go lean in the turns like a lot of them do. (and I don't use the exhaust restriction)
I have the newer engines so I guess they are the NX?
When I'm building, I make little platform for the tanks that more or less keeps them level and as near the top of the fuse as possible. I completely cut out the top of one plywood bulkhead. The one that's a little over an inch in front of the one at the wing saddle, and the platform runs from the firewall to the one just in front of the wing.
I also use a 4 oz. tank. It allows the bottom of the tank to be higher than the bigger tanks.
One is set up with a Jet remote needle and the other one still has the original.
It sounds to me like your sucking in air somehow. things I would look at:
1. tank connections (stopper and tubes)
2. fuel lines.
3. filter
4. engine backplate/needle/ venturi seat/ front bearing?
see ya next week,
Jim
Last edited by scattermaster; 09-07-2018 at 04:15 PM.
