i have a 1981 honda cb900 and it takes forever to get "warm"?

Question

i have to very slowly rev up to 9000 rpm before i can even start moving, and it takes at least 10 minutes to get it up that high. if i dont, it wont go over 5500 rpm and sputters really bad whil i ride. what can i do to fix this?

Answer 1

your carbs could need cleaned ;check plugs ; maby worn valves or worn rings on your piston low compression

Answer 2

Your fuel and / or air supply systems likely are contaminated by dirt or water or rust or old gas gumming / deposits. Your fuel system and air intake breathing systems are where you need to start. Or 1 of your individual carbs rubber diaphram may be torn. (Behind large round covers)
If you can, try removing the tank to inspect, turn it over and pop open the valve to find an internal gas line filter. Its has a screen to catch gunk before it travels out to your engine. Clean whatever you can. Check out the choke system and see if cables are free to move, oil the cable lines or change them if needed.

To clean the carbs you may want to do this before anything else. Try the most simple experiment first by filling your gas tank with premium gas. Run the bike out with 3-5 tank fulls. This alone may make the difference given your 80's carbs tolerances are not as tight and lean as today. Cleaning your 4 carbs can be as simple as that or more complicated like dipping and allowing to soak the bank of carbs in a petroleum solvent (remove any external rubber parts before soaking ) Do this outdoors using mask and rubber gloves and care.
Are you dealing with a CB 900F?

Answer 3

Check the valve clearances.
Tight or leaking valves will give those symptoms. The bike's 25 years old. Depending on the mileage, it might need a "valve job".
To check for valve leakage, bring a piston to TDC of the compression stroke (both valves closed). Blow in the spark plug hole with an air blow gun. Listen at the muffler and air box. If you hear any hissing, the valves are leaking.