Why does the motor rpm fluctuate while running?

Possibly could be a throttle position sensor, outside of that I would recommend replacing the choke cable, and maybe the choke itself.

most governor springs do have slack... they are designed to apply pressure during operation... the governor tries to run the engine wide open, the governor spring brings it back to a safe usable rpm... most small engines run well between 3200~3600 rpm's... I don't know what engine you have so I can't help more

Yes, spring may have broken or maybe it just needs adjustment. There is a high idle cam that makes the card idle higher when the choke is closed or partly closed.

Overhaul automatic choke or fit a manual conversion (if its available)

Just a hunch. Clearly there is a fuel issue on one of the cylinders. Although you cleaned the carb, please confirm that the intake valve is clean and/or reed valves are working properly. It is possible that the 2nd cylinder is only firing occasionally even at the higher RPM but it's less noticeable because of the engine's inertia at that speed makes it "seem" to be running smoother. The clue lies in the fact that the engine runs smoothly at idle when the choke is applied and starts to miss when choke is open ... this is indicative of fuel starvation. And yes, on a 2 cycle, a lack of fuel means a lack of lubrication.

Out of curiosity, take both spark plugs out and crank the engine. Do this outside away from an open flame. Compare the amount of misted fuel that comes out of each cylinder head with the choke closed and then again with the choke open. If it isn't even then the cylinder that is blowing less fuel is being starved. This should identify the problem cylinder and help to narrow down the elements left to troubleshoot and replace/repair/clean. Good luck and hope this helps

dirty jets in the carb will cause the rpm's to fluctuating

Here is how to do it. First disconnect the throttle cable to the carb and let it hang loose. Make sure the outdrive is in neutral and the boat is secured to the dock or on a trailer with a water ****.

Pull back on the throttle by hand directly on the carb throttle shaft. Observe the Choke cam on the opposite side of the Carb. Let go of the Carb throttle shaft and see where the Stepup Cam is set. The Choke plate should be closed most of the way. You will not have very much time to make an adjustment.

Start the engine and let the Choke work and observe the RPM. There are usually adjustments you can make to put the Stepup Cam on a lower step by bending the Link Rod if it is running too high in Choke. Sometimes the Cam is left alone and a screw similar to the Curb Idle screw on the Throttle side just needs reduction to ride lower on the Choke Cam.

After the Choke is warm, it disengages with a pull on the Throttle. Now you are using the Throttle side of the Carb to operate the engine RPM. You want a low RPM for sake of the outdrive gears and NO WAKE zone. The adjustment screw opens the Throttle shaft, You set it for the Manufacturers Spec. probably 550 RPM.

The Throttle cable is now adjusted so it pushes slightly against the Carb. This forces the throttle closed. The Throttle cable has threads and a sort of Knurled knob which runs on these threads. This device is used to lengthen or shorten the cable so that pressure is applied against the Throttle.

When the outdrive is in water you will has resistence on the Exhaust. This will slow the RPM. If the motor stalls you will need to adjust the motor to idle Specs while in the water.

For best economy, find a Vacuum port and attach a Vacuum guage to it and adjust the air mix to the highest Vacuum reading then turn in the Mixture screws slightly until the vacuum starts to drop.

Hi again Ed,
Starting at the carb throttle shaft, your linkage rod (with tiny spring wrapped around it) should be connected directly to the governor's arm. If there's more than one hole in the arm, connect the rod in the upper-most hole.
Now, at the base of the governor's arm is another hole (possibly on a tab jutting from the arm). The main governor spring should be hooked in this hole and then back to the sliding throttle control that moves when the lever on the dash is moved. (This one definitely has a tab and hole.)

The choke cable end hooks directly on the choke shaft and it has intuitive movement. Verify that the choke butterfly closes and opens relative to the cable control on the tractor's dash.

To insure that we only do this procedure ONCE, and we get it right the first time, let's set the internal governor to base-line at this time.

With everything bolted back up, move the throttle control lever on the tractor's dash to full throttle. Then get a 3/8 wrench and a slotted screwdriver and locate the round governor shaft coming out of the engine block. The governor arm attaches to this with a clamping-bolt. You will notice that the round shaft is slotted for a screwdriver as well.
Loosen the clamping bolt slightly with your 3/8 wrench, insert your screwdriver and rotate the round shaft clockwise until it stops. (It has VERY little travel, so turn it both ways to verify that your are at FULL clockwise position.)
Hold screwdriver there and move the governor's arm in the same (clockwise) direction until the carb's throttle is set to WIDE OPEN throttle. Still holding the screwdriver clockwise, retighten the clamping bolt with the wrench.
Next, move the throttle lever on the dash of the tractor to idle and back to full several times and observe the carb's throttle shaft, it should come down from full throttle to idle and back again freely.

Start the engine and be prepared to shut it off if it over-revs.
If it doesn't over-rev, your base-line settings are correct.

By bending the tab on the sliding throttle control (the one that has the main spring attached) you can now increase or decrease spring tension and change top speed of the engine. Do this in small increments and if you have a tachometer for single cylinder's set top speed to 3400-3600 RPM.

Sorry this is lengthy, but as mentioned above, we only want to do this once.

Hope this helps, and feel free to ask away if you need more info!
Dolf-

If the bike will run with the choke on then you have a lean fuel/air mixture condition. Most common cause is a vacuum leak or faulty pitcock. Spray some carb cleaner around the carb mounts with engine at idle, if the rpms change there is your leak.
Your petcock should have two hoses attached to it. One hose is the main flow to the carbs. The other hose is/should be a vacuum hose that allows the gas to flow (when vacuum is applied). When your petcock is in the PRI position, this will bypass the vacuum hose. Leaving it in PRI when motor off could possibly flood the engine. Check to see if that vacuum hose is attached properly with no splits or cracks near both joints. If all is attached properly your problem is the petcock itself. It has a diaphragm and 'return' spring. Weak return spring, clogged petcock, damaged diaphragm can all cause your problem. Also, after you recleaned and inspected the carbs, were they synched... if not, this needs to be done.
Good luck...i hope this helps..please rate me a fixya.

Hi, Did you notice the motor actually reving higher when the tachometer was reading a higher rpm.. If it was it could be your transmission slipping.. Set your cruise control and listen to your motor while the tachometer starts moving erratically.. Good Luck