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VegasEx'r
03-19-2002, 11:54 PM
I am currently running a 50/50 mix of 91 octane pump & VP c12 fuel. I am of course trying to find the best main jet to use. I started big & am working my way down (to a 170 now, I use a DynoJet needle on the 3rd slot). Race fuel makes the plug look lean, so other than listening for a lean pop when I back off the throttle, is there any other way to tell when I am jetted correctly? With the 42/170 setup I have, throttle response is excellent, it doesn't bog at WOT (although I haven't been anywhere to get it into 5th yet), no lean pop, but the plug is quite white. Of course my fear is running too lean for too long & doing some serious damage to the engine. So does anyone have any suggestions?
03-20-2002, 05:24 AM
I don't know alot about jetting the 400ex, But I do know quite alot about jetting racing engines. First, on racing fuel, if the plug looks lean, it is lean. Racing fuel when jetted right will look like egg shell brown. also the ex will run good even in a lean condition because a motor will make slightly more horsepower running lean rather than runing rich. I run pure racing fuel in my ex and mine is jetted slightly rich, you can see a little black on the plug. The motor will run cooler and I dont have to worry about a hole in the piston. I'm probably giving up a little horsepower running a little rich but peace of mind is worth something. Hope I helped a little..
ChadEXer
03-20-2002, 08:36 AM
Vegas with the c12 50\50 mix you will be running like jerry,,, a little on the cool side. thats a little too much octane. you will prolly lose a little power from that much octane but It will help your motor last longer. With my old 416. I ran half 91 and half VP RED 105 and that was still a little too much!
VegasEx'r
03-20-2002, 12:10 PM
Thanks for the info guys, when I ran straight pump gas it would ping at the top of 3rd, 4th & 5th (I guess due to the CR & advance timing), so I put in the 50/50 mix. I figured I could go down a bit (maybe to a 75/25 mix), but I won't play with that until I know it's jetted right. I was thinking of trying VP Red, too.