One of my bikes – a 2000 Kawasaki KL250 Super Sherpa dual sport – is a hard-starting son of a gun. Reason? It’s jetted ultra-lean. Meaning, it’s starved for gas.
It’s the same issue that plagued cars back in the late ’70s/early ’80s – when cars still had carbs.
Fuel flow using a carburetor is mechanically limited by whatever jet size is installed in the carb. A “jet,” by the way, is a small orifice through which the fuel passes on its way to the engine. A “leaner” jet has a smaller-diameter orifice; a “richer” one a larger-diameter orifice. There are – usually – two types of jets. The pilot jet meters the fuel at idle – a big factor, cold-start (and starting, period). The main jet meters fuel once the engine’s running faster than idle, as when you’re trying to accelerate.
The only way to nose those late ’70s/early ’80s-era carbureted cars through increasingly stricter emissions testing was by leaning them out (less gas in the air-fuel mix) until they squealed.
Or rather, until they sputtered and coughed and refused to start.
You may remember.
That problem was fixed via fuel-injection, which allowed for more precise (and – key thing – electronically adjustable) air-fuel mixes, especially at cold start – when emissions are highest.
Many bikes built before about 2005 or so still came from the factory with carbs. And the bike manufacturers dealt with the conundrum of getting past “smog” – emissions standards – the same way that car manufacturers did 30-something years ago: They leaned the proverbial snot out of ‘em. The pilot and main jets are sized to make government happy - not you. They are typically at least a couple sizes too small for efficient/quick cold-starts and maximum performance. As in the case of my hard-starting, takes-forever-to-warm-up KL250.
The fix, luckily, is easy: Up-jet that son-of-a-gun!
First, though, you’ve got to get at the jets. That is best done with the carb off the bike – in part because you’ll be able to see what you’re doing better – very important as regards the small/fragile pilot jet especially – but also because the little screws you’ll need to remove to get the fuel bowl off (to access the jets, underside of the carb) are seemingly made of cheese and very easy to chew up unless you use exactly the right size Phillips head screwdriver and it’s exactly centered on the screw. This is hard to do with the carb still attached to the bike.
So, Step One: Carb removal -
Begin by removing the seat and then the fuel tank (two 10 mm bolts at the rear; plug the rubber fuel line hoses to keep gas from leaking all over). You’ll next need to remove the air box – a large hunk of plastic that – in addition to housing the air filter – also serves as a mounting point for the battery as well as the bike’s electric components. Unbolt the battery and set it aside; slip off the rubber thingies that secure the electrical stuff and gently place the electrical stuff off to the side. It is not necessary to disconnect these components – and lose track of what goes where.
Now, loosen – but do not remove – the rear mud guard. There are four large – obvious – Phillips head screws holding it to the frame. Take ‘em off, and you’ll have the necessary jiggle/wiggle room to work the air box out of the frame. It, incidentally, is secured to the frame by a couple of also-obvious 10 mm bolts – and a pair of not-so-obvious 10 mm bolts that secure the underside of it (facing the rear tire) to a rubber mud flap near the swing arm.
Next remove the rubber tube that connects the carburetor to the air box. It is clamped to the carb’s throat on one end and to the air box intake on the other. Loosen the clamps, then work the rubber tube loose and take it off. Remove the air box and set it aside.
Now, for the carb!
You’ll next need to slip the throttle cables (there are two, push and pull) off the carburetor’s body. Loosen the 10 mm adjusting nut, then by hand rotate the throttle arm on the carb so that you can pop out the cable ends and separate them from the throttle arm. The last cable you’ll need to deal with is the choke cable. On this bike, I find it is easier to loosen the nut at the choke pull (up by the handle bars) and slip the cable off the bike and remove it still attached to the carb rather than removing it from the carb. This will save you much hassle come re-install time.
Now you can remove the carb and bring it over to your work bench for the work that needs to be done.
We’ll get into that in detail in Installment Two – which should be up next week sometime!
Throw it in the Woods?