Quote:
Originally Posted by Megadan
The number one reason people brought their bikes in to the shop feeling frustrated because they couldn't get it to run right summed up in one sentence. Nobody takes the time to understand that there is more than 1 jet, and more than one circuit per jet.
The other big mistake is people will use the needle as a bandaid to other jetting issues.
Things the uninitiated should understand:
Pilot jet affects idle mixture AND low throttle. You might be able to get a good idle mixture setting, but the engine may still be too lean/rich under light throttle causing running issues. Just because the idle mixture works, doesn't mean
The main jet affects the needle jet and needle fueling just as much as it does the 3/4 to wide open range. Example: My PZ30b required the needle to be dropped down a notch when I went to the 125 main jet from the 120 because it was letting enough fuel through to become too rich.
It is important to find the main jet that works best and then tune the needle last. Not just in height, but diameter and taper as well. While this may be a little difficult to do with the cheap clone carbs, if you get something like my Nibbi that comes with a size stamp on the needle, this can be used to tune the mid range. Length of the straight section, diameter of the needle body, and taper can be used to tune the lower and upper halves of the fueling curve the needle provides. A larger diameter will lean out the bottom half in relation to the top half, where a more aggressive taper will richen the top half vs. the bottom half. A longer or straight section before the taper will alter how soon the needle starts to contribute fuel, which is great for dialing in jet transitions.
Getting jetting dialed in as precisely as most OEMs have to do is a very tedious process, because one change in one area may require changing another.
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This is something almost no one (in my limited experience and my self included) knows anything about.
This comes up over and over and over again when I sell my kits and also others who public;y show stuff.
I understand it in a basic form but I couldn't tell you or even be sure what I have is 100% correct.
Most Hawk folk and other prob make the bike 'run ok" and that is it - hence I have several jets in my kit as that seems to cover most peoples expectations.
Reality the day and temperature/weather conditions of the day will technically want a slight rejet and that is what road racers on old bikes do - they have a whole chart with known settings jets and worked out pretty much the scale when the air temp or conditions of a day change to jet it the best they can for THAT condition on THAT race at THAT specific temp/conditions.
Jets typically increase by 0.01mm on jets or there abouts
New Hawk/TBR7 or any Chinese bike I suggest something like stock pilot to 40/42 and main jet 105 and needle 1 lower then center as a starting point (screw out 1.5 to 2 turns) and THAT is a starting area only not the true final end.
Can take several hours to get it right and that's assuming you know what your'e doingish. if you don't then its a long learning curve.
My bike I have slightly wrong as main is 105, pilot drilled 45 clip, 1 lower ) then center, screw 1.75 turns (best idle), but I never ride that bike so I can't be bothered as I have other things I wanna do (it stumbles at 7500 RPM and suspect a little rich)