'84 200X Carb Questions

[M.Pargiello]

I have a few questions that need to be answered before I run my engine. I want to get trouble free power, consistently through the RPM range, at all positions in the throttle. Here is what I have done, Hopefully this has been done time and time again so the answers won't be too hard. I searched but couldnt find anything concrete on it.

1. Ported head
2. New, Stock size valves
3. DG RCM Exhaust
4. No airbox, K&N on the end of the carb
5. Stock bore and compression
6. XR200 Camshaft

Now, Should I run the stock 24mm Keihin and fool with the jets and adjustments? OR run a larger carb, I think a 28mm would be the max.

What should I do to the carb to see the most consistent, useable power? Any information is appreciated

[yaegerb]

The starting point for stock engines with bolt-on modifications is to increase main jet size by at least 3 sizes and move needle clip down one position (richer). The starting point for modified engines with larger displacement is to increase main jet size by at least 4. Move needle clip down one position (richer). Pilot jet usually stays stock.

Since your mod's are mostly bolt on applications I would say start your jetting circuits 3 sizes bigger. Assuming you have a stock 24MM Keihin, your main should be a 110. So you need to go to a honda dealership and get a 112, 115 and 118 main jet. Start with the 118 (Fat) and work your way down (lean). I would also recommend getting at least two sizes larger for your pilot, but that's up to you.

How to properly jet is below.

1. Find a gentle slope that you can ride in 2nd or 3rd gear. Look for something that will put a reasonable load on the engine. This will be your “dyno”.
2. A basic outline of which jet is active at a particular throttle setting: Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main Jet = 3/4 to Full Throttle. (Changing the Main Jet size won’t affect how your engine idles or runs at 1/4 throttle. Engine RPM isn’t what determines which jet is active - throttle position does)
3. Make the recommended jetting changes. Always start rich and work leaner.
4. Start and warm up the engine, then ride your ‘dyno hill’. Any point where you feel the engine stumble or hesitate indicates a tuning problem. Note the throttle position and modify the corresponding jet (1/4 to 1/2 throttle = needle. 3/4 throttle or more = main jet).
5. Only change jetting by 1 step at a time, and 1 circuit at a time (don’t change needle and main at the same time). Re-check after every change.
6. Once the engine runs smoothly throughout, you’re jetted!

Other item to note. I am also running a 28MM Mikuni siphon mount. My Mikuni came stock with a 200 main and a 40 pilot. Currently I am running a 170 main and a 35 pilot. Long story short, when modifying a motor and getting your carburetor jetted correctly, a bolt and go method doesn't exist (at least to my knowledge).

Good Luck!

[M.Pargiello]

Thanks for the info brendon! Exactly the type of post I was looking for. Huge help!

[yaegerb]

No problem, anytime.