What size main jet should I use?
A larger jet number means a bigger hole and more fuel. A smaller jet number has smaller holes and should be used if your engine needs to run more lean. Whether your machine is running too lean or too rich is a good starting point for choosing your jets, but using a jet calculator minimizes trial and error later.
Are all Keihin Jets the same?
No they aren’t all the same they have a few different ones. My ktm dealer had all different kinds for keihin carbs. I’d say they should have what you need.
How do I know if my pilot jet is too rich?
If the pilot circuit is rich, the engine will have a rough idle or may not return to idle without “blipping” the throttle. You may also notice a distinct smell of raw fuel and some eye irritation from the exhaust.
How are Keihin Jets measured?
Keihin jets are measured by the orfice size. A 180 jet is 1.80mm in diameter. The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.
What happens if main jet is too big?
For example, using too large of a main jet will cause more fuel to enter the combustion chamber than it can efficiently burn. This will result in a “sputter” at full throttle. It could best be described as a rapid misfire.
How many jet sizes go down?
The suggested change in jet size is to go down one jet size for every 1,500 feet in density altitude you go up. Conversely, for every 1,500 feet you go down in density altitude, go up one jet size.
Are Mikuni and Keihin jets interchangeable?
You can use Mikuni jets, but you will have to cross-reference to a Keihin chart. They thread right up and are nearly the same size.
Are carb jets marked?
Jets are threaded and have a small orifice through their center that varies based on the size of the jet. For example, a jet may be stamped (on its head) with the number 30.
Is it better to run rich or lean?
TLDR – running just a little lean could improve fuel economy and give extra power. However, run too lean and you risk engine failure because the engine runs too hot. Whereas running rich can waste fuel and increase pollution but will not damage the engine. You ideally want to run at the perfect ratio of 14.7:1.
What happens if main jet size is smaller?
Installing a smaller size jet will reduce fuel flow, which is ideal for high-altitude conditions where air is limited, where a larger jet size increases fuel flow for oxygen-rich, low altitudes.
What happens if main jet is too small?
Be careful: most engine jams occur when the main jet is too small. A lean fuel/air mixture will cause the engine to overheat fast.
