Checking the Jetting Calculator Against A Husqvarna Database of Keihin PWK Data


The idea here is to see how close the jetting calculators graph compares to examples in real life. Below you can see how close to reality the jetting calculator is and what % from the ideal is considered by riders to be near ideal jetting.
For instance in this first example the rider said that the previous jetting was too rich but the graph showed it wasn't unless gas without 10% ethanol was used. And only if he switched to 10% ethanol gas for his current setup would his jetting be spot on like the graph shows. (People tend to discount little things that in reality are very important and it was an error for the person who made this database to not ask the % of ethanol in the gas.)



The engine "laziness" this guy mentions at low throttle settings is shown on the graph to be very lean at 1/4 slide opening and a bit more. He mistakenly thought he could clean that up with a smaller pilot jet but the only way is to put spacers under the needle clip so the taper would kick in earlier to fatten up that area. Trying different values of slide open I saw that he needed to raise the needle 2mm.



Here is the same engine/carb with a 35 idle jet, a BGJ needle, a 175 main jet, and raising the needle 2mm. This is just one example of trying changes out on your computer before buying anything. It eliminates the hit and miss method


This guy only praises the top end power with his current setup which led me to think maybe his low end power was lacking due to being lean and that is exactly what the graphs show below 3/8 slide opening. He did call the low end power "nice", but that is expected from a well maintained Husky 250 even if it is a tad lean.



This rider praises the low end power (obviously past 3/8 slide) and hints that the top end is slightly lacking which the graph verifies by showing it to be just a tad lean on top.



The graphs verify the correct jetting for it to run "crazy strong". He obviously likes the idle mixture to be a bit too rich to compensate for some leanness at 1/4 slide.



Take note that often on older bikes with engines 250cc or bigger that their carbs needle jet will be a bit wallowed out which increases the beginning jettings richness that needs to be corrected with a smaller idle jet and a higher slide cutaway. So when the jetting calculator shows a lean condition at the left half of the graph but the rider swears that the jetting is right on then either he is full of crap or the needle jet needs to be replaced.

[database source]

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