Do these jets make me look fat?
Ok I got this thing installed and running 68s pilot, 165 main, b53e(hop up needle) 4th position, stock internals on the engine, uni filter and a supper-trap isd2 8 discs.
I am getting poping at 3/4+ throttle, rough idle +/-150 rpm, smooths out around 2000 rpm. Fired right up and warmed up fast, no choke needed, when I open the choke RPM picks right up and it smooths out, fuel screw didn't seem to doing anything. What do you think?
I would have to agree with Kenzo on this one..........the 68s is a richer pilot and you've described a too rich condition @ idle. Make sure you are not set too high on the idle speed and picking up fuel from the needle along with the pilot. I doub't if you could get the idle mixture screw to compensate for that.
Lower that idle speed way down and allow the engine to draw only from the pilot and adjust it ( 1 1/2 - 2 turns +/-). Then...... if you feel you need to raise the idle speed do so by raising the slide up slightly (thumb screw) from the fully closed position.
All this above is going to amount to a hill of beans if you have an air leak between the carb and the manifold. Be absolutely sure it is sealed air tight and the choke is fully open ( I hope you didn't have the choke full on and the idle way up).
Since it's been determined that the 165 main is close to optimum for this engine, putting in an even richer needle and then raising it up on the clip position to make it even richer yet is going to play havoc on the 1/4 to 3/4 operation. Lower the needle by moving the clip toward the top of the needle in the #1 or #2 position..........start off leaner then progress in small increments richer.
The way I understand this (assuming the ignition timing is correct).......... that if you are back firing through the exhaust you are igniting unburned fuel in the header pipe from the flame front from the combustion stroke when the exhaust vale opens. Definitely too rich. Makes you wonder about the wall strength of a sheet metal pipe or muffler vs. a cylinder sleeve.
Too bad we can't get a convincing video sound bite from one of these fire breathing beasts revving up..........Anyone want to volunteer ???