Dual 44 Mikuni observations

[homemadejoe]

Hello, and sorry for bringing back an old thread. Question to the group: I just finished reading this entire thread. I've noticed that almost all of these jet setting are way leaner than stock with a total jet load of anywhere from 220 to 240 seems to be the normal. A stock 760 (from a gp760) runs a jet load of 245 (front) and (247.5 rear) The only theory I can come up with is that all the mods we are doing to these engines causes the better, or larger air flow through the carbs making the jets more efficient. Is this true? If not can someone explain to me how you can run a leaner setting than stock ? Especially with these mods. Thanks, and great thread.

 

[kevbo]

It may be because most riders like to lower the popoff pressure plus aftermarket manifolds have no crossover port. This makes everything, especially the pilot circuit much richer all by itself. I recommend you forget about most of what you have read and just tune the carbs. Pick a popoff pressure close to 25psi then tune the pilot so it fourcycles a little at 1/4 throttle. Tune the main jet and top screw so it accelerates hardest at full throttle, preferably a little rich of peak RPM. There is a little overlap between the pilot and main jet. This means an overly rich pilot will allow you to completely peak full throttle rpm. A cleaner pilot setting will require the main circuit to be richer than peak rpm in order to get the same response.

 

[fastgtfairlane]

Aftermarket mikunis look very similar to oem mikunis with a few changes. The oems are designed for stock performance and fuel economy. Aftermarket mikunis flow a lot more fuel, already have the chokes removed and have some differences in the circuitry to accomplish that. This allows lower jetting combinations than with oem carbs. One thing never mentioned in these tuning threads is the hull the engine is in. Having a hood that allows air in vs pole breathers only will make a big difference in the carb tuning. Also, the pump setup that is in the ski. I have 2 buddies with the same hull, one is running a 62t ported 735, the other a 61x/62t Jetmaniac 727, both with the same pipe, head, ignition,carbs and arrestors. The lpw engine is pushing a Solas 144mag with a 9/15 hooker and bored nozzle, the Jetmaniac engine is pushing a oem155 with a 6/12 skat setback and a bored nozzle. The 155 ski has 1 size larger jets on both the high and the lows than the 144 ski. That same engine ran great in his old fx1 with a 144 mag. Once he put the new ski together with the bigger pump, he had to retune.