When my Honda CBR900’s engine is cold, it works only on three cylinders. When the engine begins to warm, all goes fine and all the cylinders begin to work. What can cause this?
Answer in progress (see comment to the question for clarification questions).
Checking spark plugs and spark
First thing I would check is condition of the spark plugs and quality of the spark on each cylinder both before and after warm-up.
- Take all the ignition wires off the plugs.
- Pull the plugs out, and check their condition: look for soot contamination, any difference in glazing, damage to the ceramic insulator and/or evidence of flooding (it would be wet with petrol). Use this reference.
One by one, check each plug (make sure other plugs are out to avoid starting the motor needlessly) by putting ignition wire on, touching the ground electrode to the engine casing, and cranking it to see the spark. The spark should be nice, big and blue. If it is too weak, or different colour, we might have a culprit.
Safety Note: checking the spark that way is easy, but be careful not to get shocked (especially, if it could be spark plug wire boot shorting). Shock can be noticeable, but not too dangerous (unless you have heart pacemaker or somesuch) as voltage is high, but amperage is low. If hesitant, best use the special spark testing light (though it shall not rule out any particular bad plug).
- If one of the plugs has no or poor spark, check this plug on known good wire, and, conversely, check known good plug on that wire to determine whether it is a plug issue, or supply (then we shall be checking wires, distributor and so forth).
- After thoroughly checking everything out, put everything back on as it were, then warm up the engine (best by actually going somewhere on a short errand if at all drivable), and repeat the steps to see what has changed once it reaches proper operating temperature and starts to work fine.
Make sure to be thorough and cover all the steps so as not to miss any possibility. Check back after it is done.
The CBR900RR has the following attributes.
Carb and FI versions depending on year.
4 Carbs or 4 throttle bodies, depending on year
Two coil packs, 1 for cylinder 1 and 4, 1 for cylinder 2 and 3
If a coil were bad you would have an issue with two cylinders more than likely. Coils going bad on high energy lead connection to the coil is very rare.
A single bad fuel injector is possible
A single bad carb is possible
A single high energy lead failing to a sparkplug is possible
A single sparkplug bad is possible
A sticking float bowl on a single carb. Check needle and seat and ensure the needle is dropping down
A tear in the CV diaphragm at the top of a single carb is possible. This would create a very lean condition that would be more pronounced when your choke is engaged. When you go off choke the vacuum is reduced and the lean condition is less evident. While riding, downshift and go off throttle, if you get popping in your exhaust check the diaphragm. This could be a source.
As another post/comment indicated, you could have an oil fouled plug. Do you have oil smoke coming out of your exhaust? Take your finger and wipe it in the exhaust pipe exit. If it's really black and oily then you may have a bad valve guide or rings. If it's just black and sooty then your too rich. If the color is not black but a bit brown, that's better and indicates a more normal mixture and lack of oil in the exhaust. Rev the engine at night in front of car headlights and see if you see the smoke in the headlights, if it's very light you may not see it during the day. Doing the headlight trick will reveal oil burning without question. Be sitting on the motorcycle and look at the exhaust plume through the light. Not the view from the car drivers position.
Bad high energy lead. Check the resistance of the lead to ensure it has very low ohm reading using a multimeter. Validate spark by putting a sparkplug into the lead and turn the engine over while grounding it on your valve cover or other conductive and grounded component.
Bad spark plug. Make sure it isn't black and sooty. Carbon is a conductive material. If it's built up with black carbon it can ground the insulator and there will be no spark. You can clean it with carb cleaner and a toothbrush and test again for spark as above
You might have multiple issues, you might have one. Provide more information and I can edit this to reflect the data given.