> Motorbike running on 3 cylinders untill it's been running for 5 mins or so?

Motorbike running on 3 cylinders untill it's been running for 5 mins or so?

Posted at: 2015-04-14 
Drain the carbs by the carb drain plug underneath and gather the gas that comes out the leak hose in a clean jar. When there was water inside you should be able to see it on the bottom. Some bikes have condensation problems but that said: it won't run great either when that is the problem.

Apply fuel line cleaner in the gas (seafoam or another proven product), hopefully this will solve problems with carburettors before you have to open them for cleaning. A float or vacuum valve can be stuck or perhaps a pinch hole in the vacuum rubber or a dirty needle. Pay special attention to the choke needles. It is easy to find out if they move up and down freely and you may unscrew the plastic ring so that you can see them but... sometimes the choke needles are badly stuck or the plastic ring can not be reached without taking the carbs off the bike.

From the outside you can diagnose vacuum leaks on the rubber boots from and to the carburettors. On YouTube you can see people spraying liquid gas or solvent like brake cleaner or deodorant around on the connections in order to see if the idle refs changes. This is hazardous so one should ventilate often and thoroughly, protecting the burnable fluid from the sparks. At own risk. Do not operate the engine inside the garage.

Brings me to leaking sparkplug cables and boots. Sparks must not be seen in the dark when you spray a little water vapor to the spark plugs and cables. Also judge by your own eyes that they look good.

The current on the battery should be 12,6 to 12, 8 Volts in rest and 14,2 with engine running no matter the revs. One could easily check all electrical connections and see if one coil perhaps has heat marks on it.

Cleaning carbs is a professionals job and synchronizing them afterwards can best be done with good instruments. That is when you turn to bringing the bike to a shop. The dealer can also measure the exhaust gas with the warm engine running. Greetings. Alfred - The Netherlands

Actual motorcycle make, model, year would be REEEEALLY helpful. My old Goldwing had a run on three until warmed a bit problem- seems on sparkplug cap wasn't sealing and water was getting to base of plug and 'shorting' against head until slow warmed head had dried spark plug base. rain mad this obvious and you note you had 2 fail in rain for a few minutes-SO, take a close look at spark plug caps and cabling, area of head around plugs- moist cruddy area with burn marks is obvious clue. If that doesn't seem problem- look at carb base for manifold bolts, rubber gaskets, balance tubes mounting. a cracked rubber O ring mount with a pinhole leak when cold may swell enough warm to allow full charge to get to cylinder. A 4 carb retainer block with a loose bolt toward center will have minor leak until whole block is heated and puts pressure on the loose intake manifold hole. Others have noted the possible water in carb float bowl problem.

it could also be in dire need of valve lash adjustment with a valve not sealing until it gets warmed up

Change out the spark plugs. Change the oil, basically, tune it up and see if that helps.