[NickHonda400Four]

It's been de-decompressored! Unfortunately, upon checking the compression after removing the auto decomp, the quick connector that links the hose onto the spark plug fitting fell apart. I believe some pieces are currently in orbit. Pretty lucky some parts didn't go through the kitchen window!

So I won't be able to check compression readings for a little while.

As for the bike. It no longer does that hideous clank but it's still not running right. I decided to take it for a spin near cold and it mostly hesitated when setting off. Not much misfiring and noticeable improvements in power. I could actually accelerate!

So I popped back home and disconnected the O2 sensor. Then it ran as terribly as usual. So maybe I do have a faulty O2 sensor?

I was going to reconnect the O2 sensor and do a longer drive. I hoped to try and pin-point a moment when the sensor warmed up and kicked in - therefore observing if the bike was behaving worse from that moment. As I set off, the lock on the filter side panel fell apart and the door swung open. It was already going dark so I took it as a sign to head back before anything else went wrong!

New lock ordered.

Do we think a faulty O2 sensor could cause these symptoms?

[gashousegorilla]

It's been de-decompressored! Unfortunately, upon checking the compression after removing the auto decomp, the quick connector that links the hose onto the spark plug fitting fell apart. I believe some pieces are currently in orbit. Pretty lucky some parts didn't go through the kitchen window!

So I won't be able to check compression readings for a little while.

As for the bike. It no longer does that hideous clank but it's still not running right. I decided to take it for a spin near cold and it mostly hesitated when setting off. Not much misfiring and noticeable improvements in power. I could actually accelerate!

So I popped back home and disconnected the O2 sensor. Then it ran as terribly as usual. So maybe I do have a faulty O2 sensor?

I was going to reconnect the O2 sensor and do a longer drive. I hoped to try and pin-point a moment when the sensor warmed up and kicked in - therefore observing if the bike was behaving worse from that moment. As I set off, the lock on the filter side panel fell apart and the door swung open. It was already going dark so I took it as a sign to head back before anything else went wrong!

New lock ordered.

Do we think a faulty O2 sensor could cause these symptoms?

  Whelp ... It WOULD be nice to know what your compression is now with the de-comp removed.    But blowing up your compression tester hose is likely an indication that your compression is OK now ?     Maybe you SHOULD have gotten the top of the line model ? 

     Testing and riding the bike when the motor is cold , is not the best indicator of things.   You should let it warm up ... and take that thing for a good ride and get at operating temp.    That will help blow out some of that carbon built up in the combustion chamber that probably has accumulated in there from the bike running poorly.     AND ... if you still have the TPS voltage bumped up a bit, it's likely running richer, causing the motor to take a bit longer to warm up if it too rich.     That fuel may be taking longer to vaporize and burn, and keeping your engine cooler a little longer.    Unplugging the O2 sensor would probably exacerbate the situation, because it is not there to trim the fuel.     So by disconnecting the 02 sensor.... you kinda of proved that it does work.     I would take that thing for a good long ride and see if it improves.   

 And if that bike has been sitting for a while .... and with all your testing and trying to start the bike and etc.   Your battery may be weak.  I would charge it and test it's condition.....  Compression tests will  also draw down the battery quite a bit.


  And BTW, if you are going to leave that TPS voltage bumped up a bit. You will most likely need to increase your idle speed a bit  as well... If it is running richer , your idle speed will drop a bit, especially when the motor is cold.  The idle speed WILL come up a bit when the motor is  hot.    So adjust it when the motor is hot.   Counter clockwise on that brass idle adjustment screw ... just a  bit at a time... will raise your idle .  Clockwise will lower it.     I think your going to need a little more air into that motor at lower rpm's now, with the TPS voltage bumped up and it running richer.   That air will help vaporize your fuel on a cold start as well.   Counter clock wise on that brass screw is letting more air IN.

 

[gashousegorilla]

   I am going to re-post  Nicks Video here .... with his permission and if that is OK.   And describe  when I exactly hear the auto decomp activating when the motor is running.     And it DOES sound different when the bike is a low RPM , like when one is starting the bike .    At low RPM , or at cranking rpms the noise IS more pronounced .  Clack ...clack .. clack  !!  Because the at those low rpms , the Hydraulic lifts wheel is making a more  dead contact with that decomp pin sticking up in it's path.     But when the motor is running , it's a more glancing blow as the counterweight is flapping about on that exhaust cam , as the throttle is opened and closed and rpm's change....  So the Hydraulic lifter is erratically hopping over that decomp pin.   NOT good !!


https://www.youtube.com/watch?v=OT5cgnZrJHQ&app=desktop   


  I hear it at the 3 second mark.....  at 7 seconds.... 14....15....  and again at about 22 seconds.  ALL while the motor is running.     

[Freddy1]

Primary chain autotensioner failure?

[JVS]

Do we think a faulty O2 sensor could cause these symptoms?

Have you load tested the battery?

Another easy check to rule out the battery would be to bond jumper leads to your bike's pos/neg cables and connect the other ends to your/a car's battery temporarily. Then rev the bike and see..

[NickHonda400Four]

Hi all,

Hope you're all well!

I've been trying to reply to this thread for ages but keep getting that database error.

Unfortunately the bike is back to square one. It started with a promising ride around town so in the evening i took it for a longer ride out into the countryside. After a mile it became unrideable. Serious lurching, backfiring, misfiring. I kept the appointment with the RE dealership from weeks ago so it's actually due to visit the workshop tomorrow. Hopefully they will be able to diagnose this problem.

[Dalmatian man]

Sorry to hear you are still having problems with the bike, let us know what the dealership finds, life is a constant learning curve.

[Bmadd34]

Unfortunately the bike is back to square one. It started with a promising ride around town so in the evening i took it for a longer ride out into the countryside. After a mile it became unrideable. Serious lurching, backfiring, misfiring. I kept the appointment with the RE dealership from weeks ago so it's actually due to visit the workshop tomorrow. Hopefully they will be able to diagnose this problem.

    I'm gonna go ahead and chime in here. Once your engine gets hot, that seems to be the problematic area. I would remove the head and take a look at the exhaust valve. I'll almost guarantee if you remove the exhaust valve and lay it down with the head hanging over the edge of a table/counter or what have you and the stem able to roll back and forth, you will see that the valve is warped. As your engine temps increase, the warp in the valve increases slightly depending on the temperature achieved and at the same time, the valve guide clearance decreases as the guides expand under temperature, further compounding the situation. I can almost promise you that is what is happening.

[NickHonda400Four]

So taking it to the dealership was a little bit of a waste of time. After an hour they came to the conclusion that it 'might' be the TPS. They've asked head office to ship them the diagnostics tool so they can plug it in and see what that says.

So, no answers as of yet.

[Dalmatian man]

A poor dealership  that doesn't have the tools, or the ability to test a simple component without the diagnostic  tool.

[Bmadd34]

So taking it to the dealership was a little bit of a waste of time. After an hour they came to the conclusion that it 'might' be the TPS. They've asked head office to ship them the diagnostics tool so they can plug it in and see what that says.

So, no answers as of yet.

    So, they couldn't take Ohm and Voltage readings to determine if it is out of spec.? I would have laughed in their faces. I am still pretty certain it is the exhaust valve.

[Dalmatian man]

Any joy with the bike yet?

[NickHonda400Four]

Hi all,

I kept trying to post this response at the time but I kept flagging up a database error. After several weeks I Have up. ~Time to try again and see if I can eventually let you know why the issue with my 500 was.

The bike is finally fixed!

Their diagnostic machine basically showed every fault code possible. They then cleared them and nothing reappeared.

After that they began to swap parts and sensors in the efi system from another used UCE 500 they had. After 4 hours of this it eventually turned out to be a faulty injector. It worked fine at idle but wouldn’t close properly at higher revs - constantly filling the manifold up fuel.

Swapped in for a new one a few days later and i’m now on the road. Total bill was about £280 for parts and labour...about the cost of a Mukini carb kit 😉 but unfortunately I couldn’t have been certain that would’ve fixed it.

Main thing is i’m on the road!

Thankyou all for your help and suggestions.

[olhogrider]

Hi all,

I kept trying to post this response at the time but I kept flagging up a database error. After several weeks I Have up. ~Time to try again and see if I can eventually let you know why the issue with my 500 was.

The bike is finally fixed!

Their diagnostic machine basically showed every fault code possible. They then cleared them and nothing reappeared.

After that they began to swap parts and sensors in the efi system from another used UCE 500 they had. After 4 hours of this it eventually turned out to be a faulty injector. It worked fine at idle but wouldn’t close properly at higher revs - constantly filling the manifold up fuel.

Swapped in for a new one a few days later and i’m now on the road. Total bill was about £280 for parts and labour...about the cost of a Mukini carb kit 😉 but unfortunately I couldn’t have been certain that would’ve fixed it.

Main thing is i’m on the road!

Thankyou all for your help and suggestions.

Great news and thanks for sharing the solution. Not one I would have thought of.

[Narada]

I think that's the first failed injector I've read of...   . I wonder what caused it?