2002 Vibration when warmed up

[Jim12345]

Looking for some ideas on what might be causing my bike to vibrate after 45 mins. of riding. The bike starts and idles ok, runs good for the first 45 mins., but then the exhaust note changes and a vibration comes from the engine, through the foot pegs and the grips. The vtec works, the vibration is not there under 4500 RPMs and when I pull the clutch it is gone. I changed the oil, no difference. I cleaned and adjusted the chain, no difference. It is worse under load, when going up hills... Any ideas? Thanks

[Knight]

Because it was under load and the engine would have long since warmed up, I was wondering about the clutch having a problem after a certain amount of use. But I know nothing about clutches so I will leave that for someone smarter.

 

To me the changing exhaust note makes me think of a vacuum issue on intake or exhaust. Along this path my uneducated best guess: A leaky exhaust, a failing header seal that happens after the pipes are hot. Some cylinders losing exhaust pulse reflections while others don't = imbalance, vibration, changed exhaust note. 

 

On the input side check that the air box is clean (no mouse nest.) Although the engine would probably always be weak if there was an issue here.

 

What temperature is your weather? Is the thermostat working, aka does it get to 180 in a couple minutes? The reason I ask, on a cool day, a stuck open thermostat will take 40 minutes to maintain 180°. (Ask me how I know!) In such case the time is not the root cause but the hot engine temperature is.

 

Along the hot engine path: Do you get surging? Or just the vibration? Surging = lean condition and not enough fuel for a load but but enough fuel otherwise. After a long ride open the gas cap and check for a "whoosh" from a vacuum buildup. Such problem would restrict fuel flow only after some time for the vacuum to buildup. Cause: Blocked vent tube?

Not sure if a fuel pump could be troublesome after warming up?

How old is the battery? Something that causes weird problems when aged and ready to be replaced. Have it load tested?

 

Check the resistance from negative terminal to frame. A bad ground can cause anything electronically controlled to act strange. Although it would build a charge much sooner than 40 minutes methinks.

[Jim12345]

Wow, thank you, I wasn't expecting this amount of a response. I have been wondering about the battery, not sure how old it is. My friend said it wouldn't be the battery, because it tests 12.8 volts and the bike seems to start up ok, sometimes it takes a second push (starts and stalls), but once started it will start right up the rest of the day. I think I will just replace it and then can rule that out. What do you think of the O2 sensors, or the VLC solenoid? I haven't ohm'ed them out yet... Thanks again... I am off for a ride in the morning to do more testing.

[Knight]

I would think a sensor problem would trigger a warning light. But I don't know.

 

Batteries - their voltage is not the entire story. When older they can show that good voltage but not be working correctly. I agree with you.

 

Two starts may mean you should tune the starter valves. 

I don't know what VLC is. Is that the VTEC solenoid? Interesting - is VTEC not engaging?

 

I don't know about that however, any solenoids, relays, or switches can be inspected and cleaned as part of the troubleshooting. When heated up they can fail due to too much resistance, then start working again when cool.

[Jim12345]

I have never had the Mil light come on or flash, so I think you're correct, if the sensor was bad a code would  come up. The no start issue comes and goes... Maybe starter valves need work? Vtec seems to work ok, I just read that the VLC opens to allow oil to divert to the vtec valves and thought if that wasn't happening maybe it would create a vibration? But I can open the vtec early when the engines still a bit cold and no vibration, so I guess this is out. I'm going to give the battery a try and hope it is that simple.

[Jim12345]

I just got back from I ride and it was 13 Celsius, the bike temp moved up very slowly, started at 41, stayed at 62 for some time and after riding a bit went to 72 and that was about it.  The highest it got to was 82. Do you think the thermostat is stuck open?!The bike is hesitating bad in lower gears under a slow steady acceleration? Vtec is working awesome and today was the first time I hit 10,000 Rpm, this thing really goes. Maybe, I'm just babying the thing too much? Today I road 6 K and above and it seemed to run better than at 4K? So, to my guestions, what should this bike put out for charge at idle and at 5K with hi beam on? Also, what should the battery drop to on start up? Thanks again

[Knight]

You are confirming two of my suspicions: One, the thermostat is stuck open and it takes  long time to heat up. Two the starter valves need tuning. 

 

A member gave a definitive test for the thermostat: Start the bike cold and feel the radiator or use a laser thermometer. If the radiator warms up slowly from the start, then water is flowing in it, when it should not be, and that confirms the stuck thermostat. Instead, the radiator should stay cold then jump to 180 when the thermostat opens. I am pretty sure yours will fail this test.

 

A light throttle engine shake/surge can be caused by the starter valves being out of synchronization. In my case I noticed that holding steady at 35 mph at 3700 RPM, the motor would not stay there. It shook and bucked until I gave it more gas and accelerated. That is a starter valve problem. Your stall on first start is another indicator that they are out of synch. 

 

The starter valves synch you can do on your own. You need 4 vacuum gauges or a 4-column manometer. There are lessons on this site and also cool YouTube videos of it.

 

The thermostat is a bit of work. When it is done consider several refresh items: 1) Replace vacuum tubes on the intake. 2) Replace the coolant hoses. 3) Wipe the intake off. Note: Get good recommendations on this as solvents can be harmful particularly to any rubber parts.

 

You do not have to do these items, but you may need to remove the intake to get the thermostat out, so it would be an efficient time to do them. When done, the bike will be good for 14 more years. Do not do these items and there is a risk of an old, dried up coolant hose leaking just after putting it all back together, or a dried vacuum hose cracking, etc. 

 

If you do not have it then get a copy of the factory service manual. I am not sure the voltage at idle with brights, however logically, since a good battery should be at 12.8, then voltage should be at least there at idle, so around 13.0. I forget but the peak voltage at 5,000 RPM should be something like 14-14.5. Check the service manual for the specifications as I am unsure of exact numbers. Too high is a problem as well and indicates the regulator has a problem.