My bike needs to hold full throttle upon cold start

[muzzammil]

For info, I am riding a 2004 Yamaha XJR400R. This is my first carburetor bike so not much knowledge and experience. From what I know, carb bikes only need about 1 min max to warm up upon cold start and any longer can be harmful to the engine. But my bike need me to open full throttle on cold start and hold it there until revs build up. It takes about 2 mins of holding at full throttle for this to happen and the the feeling while holding throttle is like no power, until it revs up 2 mins later. If I press ignition without any throttle or turn throttle off too early the bike will die.

After 2 mins, I can let go of the throttle and idle will float around 1100 rpm. At that, I can move off but if I wait longer to see what happens, idle will eventually drop below 1000 rpm. This is my main problem as it means it will take quite long to move off from cold start.

Other problems include rpm taking few seconds to climb at low rpm such as when moving off from stationary and engine braking can be quite harsh or sudden as soon as I close throttle.

Not sure what the problem is, suspect that is something wrong with the carb. But the cause could lie elsewhere like rectifier or ignition coils or any vacuum leaks.

Any advice from old birds here?

[adesmond2]

On 9/9/2022 at 6:33 PM, muzzammil said:

For info, I am riding a 2004 Yamaha XJR400R. This is my first carburetor bike so not much knowledge and experience. From what I know, carb bikes only need about 1 min max to warm up upon cold start and any longer can be harmful to the engine. But my bike need me to open full throttle on cold start and hold it there until revs build up. It takes about 2 mins of holding at full throttle for this to happen and the the feeling while holding throttle is like no power, until it revs up 2 mins later. If I press ignition without any throttle or turn throttle off too early the bike will die.

After 2 mins, I can let go of the throttle and idle will float around 1100 rpm. At that, I can move off but if I wait longer to see what happens, idle will eventually drop below 1000 rpm. This is my main problem as it means it will take quite long to move off from cold start.

Other problems include rpm taking few seconds to climb at low rpm such as when moving off from stationary and engine braking can be quite harsh or sudden as soon as I close throttle.

Not sure what the problem is, suspect that is something wrong with the carb. But the cause could lie elsewhere like rectifier or ignition coils or any vacuum leaks.

Any advice from old birds here?

sorry, late response as I didn't see your post until I check the post one by one..

meanwhile, it sound like your carb is overflowing on a daily basis and thus you need to full throttle to pull up the rpm after 2 min.. I would suggest to service your carb if your bike is still the same as of today.

[quiksilver]

On 9/9/2022 at 6:33 PM, muzzammil said:

For info, I am riding a 2004 Yamaha XJR400R. This is my first carburetor bike so not much knowledge and experience. From what I know, carb bikes only need about 1 min max to warm up upon cold start and any longer can be harmful to the engine. But my bike need me to open full throttle on cold start and hold it there until revs build up. It takes about 2 mins of holding at full throttle for this to happen and the the feeling while holding throttle is like no power, until it revs up 2 mins later. If I press ignition without any throttle or turn throttle off too early the bike will die.

After 2 mins, I can let go of the throttle and idle will float around 1100 rpm. At that, I can move off but if I wait longer to see what happens, idle will eventually drop below 1000 rpm. This is my main problem as it means it will take quite long to move off from cold start.

Other problems include rpm taking few seconds to climb at low rpm such as when moving off from stationary and engine braking can be quite harsh or sudden as soon as I close throttle.

Not sure what the problem is, suspect that is something wrong with the carb. But the cause could lie elsewhere like rectifier or ignition coils or any vacuum leaks.

Any advice from old birds here?

Try to turn on a bit of choke on startup and then close it after warm up see if this works.

[apogeeXX]

did you use the choke ?
older carb bikes have this lever that you need to press or activate as you crank and start the engine.
then leave the choke on for a while as the engine warms up and stabilises.