Tuning a 4-stroke carb (XR200)

KDXrider1989 · Post by **KDXrider1989** » 08:49 am Jul 21 2013

Is it the same procedure as tuning a 2 stroke? The only 4 stroke carbs Ive encountered so far are for air cooled trail bikes and they're all similar to the XR 200 carb

cornishwrecker220 · Post by **cornishwrecker220** » 09:10 am Jul 21 2013

2 strokes have `air screws` ..4 strokes have `fuel screws` both for adjusting the mixture however the 2 stroke you screw in to richen & out to lean, the 4 stroke fuel screw its IN to LEAN & OUT to RICHEN...4 stroke fuel screws are located at the front of the carb...air screws are to the rear .

KDXrider1989 · Post by **KDXrider1989** » 06:20 pm Jul 21 2013

besides that is the tuning process pretty much the same?

http://kdxrider.net/forums/viewtopic.php?f=105&t=1156

Ive tuned several 2-stroke bikes spot on using that guide and I hope I could get the same results from a 4-stroke

cornishwrecker220 · Post by **cornishwrecker220** » 04:45 am Jul 22 2013

can you be a little more specific when you say `tuning the carb` ..I would say a 4 stroke carb seldom needs much setting up & tuning ( if running ok)...they tend to run well most of the time day in day out, its when you you start having problems with other parts of the motor which can screw up the fueling....valves, piston, & bore, spark plug etc etc...age doesn't help matters either, gummed up jets, bad fuel & so on.

KDXrider1989 · Post by **KDXrider1989** » 08:23 am Jul 22 2013

like how could I tell if I needed a larger or smaller pilot jet and how can I tell what setting to leave the fuel screw at? I havent opened up the carb yet, but it sputters at low to mid rpm and pops on decel

ICRage42 · Post by **ICRage42** » 03:51 pm Jul 22 2013

Perhaps valves or adjustments ?

cornishwrecker220 · Post by **cornishwrecker220** » 04:38 pm Jul 22 2013

I would say fuel screw 2 turns out from fully in..fuel screws have a very tiny O ring which over time can perish so its worth inspecting this..if it has gone then this will screw up the low end running ( lean ) pilot jet on an xr wouldn't need playing with from the factory, any adjustments needed can be done via the fuel screw...needle clip mid setting, main jet depends on how it runs mid/full throttle, exhaust & air filter...check needle for wear as the xr is an old bike now...check the spark plug..if black & sooty then its running rich....popping on de cel is a sign of lean mixture or a leaky header pipe...check plug first & air filter.

KDXrider1989 · Post by **KDXrider1989** » 02:39 am Jul 23 2013

I figured it out, the fuel screw was turned in all the way and was running lean. fuel screw is now at 1 1/8 turns out and runs excellent, carb is clean and needle jet is in good shape. that little o-ring on the fuel screw was worn so I replaced it. valves are properly adjusted, header pipe does have a small leak at the cylinder and the air filter is dirty still, both will be replaced soon. thanks for the advice guys!

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