Random misfire when hot

[kirkswim]

Okay so here is a good one. Random misfires only when hot, both coils have been replaced with Yamaha coils, has new Yamaha stator, all plugs have been dielectric coated, drained fresh gas, tors has been bypassed, coolant is full fan cycles nornmally, tps values are good in diagnostic mode when cold.

Any thoughts to try next?

 

[Mooseman]

Although you didn't mention it, I assume you also replaced the spark plugs with the correct ones? Injectors? Fuel pump not supplying enough pressure? Vacuum sensor hoses leaking? Compression good? What kind of KM does it have? Valves due for clearance check?

 

[yamahas]

I had this happen to me a while back and I found one of the wires at the coil connector damaged at the crimp. It was barely holding on.

 

[kirkswim]

Plugs were changed with the coils(bought at dealer), there was a problem with a wire feeding the coil that broke next to the crimp fixed as it showed as a coil misfire, has 17000kms on it so valves should be good. i will try to check hoses next after I change the stater(spinning slow and have to turn clutch sometimes to get it to go)

 

[Mooseman]

I know that mine runs like crap when I forget to reconnect the hoses to those sensors. Maybe a slight leak after it comes off the warmup stage might cause it. Or one of the sensors is defective. If it's possible to read the sensors in diagnostic mode while it's running, check if they are close to being the same.

 

[74Nitro]

If it only misfires at higher RPM's you should try the cam sensor. I had a customer with a 2003 R-1 bike this past summer with a misfire, but only at higher RPM's.
The problem was in fact this sensor. Also, the ECU never had the error code for this stored, or showing, surprisingly.
You will notice when this part number is looked up that it supercedes to a new number.
Just something to try.

 

[2stroken]

Does it misfire at idle, or under heavy load or??

 

[maim]

from what my brother, kirkswim, has told me, it does it at all rpms. we have been bouncing this back and forth for 2 years chasing this.

 

[kirkswim]

okay so, just changed the starter (1 hour 10 minutes start to finish thankyou to whoever cut the little aluminum tab before I got it), and I changed the starter relay. Has never started better warm now 2nd cylinder fires and running. Idle has evened out small test burn seemed good. Hoping to get a longer run this weekend to see if it is till doing it.

 

[MrSled]

How many miles on it?

 

[kirkswim]

17000kms so about 10500miles. I also have video of the starter install from under the sled.

 

[MrSled]

Sounds like it needs a valve adjustment.

 

[74Nitro]

What would a starter have to do with a misfire when hot.

 

[kirkswim]

The starter probably nothing the starter let go last year I put a cheap aftermarket in it it didn't last a year now I put a Yamaha starter in it starts better . But while I was in doing starter stuff I change the starter relay which also feeds back power and stuff to the CDI I believe and any other plug that I could reach that I hadn't cleaned and dielectric yet I did . So my hope when I tested this weekend is it was just a bad connection in one of those connecters and now that it's clean and dielectrics it'll clear up.

 

[Mooseman]

What would a starter have to do with a misfire when hot.

That's what I was thinking. I too cut that tab. everybody should cut off this useless appendage.

But while I was in doing starter stuff I change the starter relay which also feeds back power and stuff to the CDI I believe and any other plug that I could reach that I hadn't cleaned and dielectric yet I did

I doubt that very much as that relay only supplies power to the starter, unless you also count the fuse for the fuel pump that comes with it.

My MP (same engine) has almost 17k km and purrs like a kitten. Unless it's been run on vegetable oil, the valves should be OK. I'd be looking for something that's supplied to the engine (spark or fuel). that's amiss. We'll see after you get a good ride in.