Monster 800 misses when hot

[ccasazza]

So against my better judgement, i picked up a 2004 Monster 800 with 1800 original miles.  The bike has been off the road since 2012 but was reportedly "serviced" about a year ago.  The timing belts look like new. 
The bike will start up immediately and idle.  It runs well for about a mile or so until it warms up. Then it starts to misfire and loses power and sometimes stalls. I thought it felt like a fuel problem but that is just a guess.  I replaced the in tank rubber fuel likes since i had them left over from my old ST2.  That didnt help.  I really dont want to start guessing and randomly replacing parts so i am looking for any assistance that the more knowledgeable ones here can share.  If anyone can point me in the right direction or 2 to start, it would be greatly appreciated. My next guess would be either the fuel pump or tps.  Am i on the right track?
Its a tough problem to diagnose because it has to be a hot motor and by the time i get it home and onto my lift, it cools down and runs normal.
I am really a Ducati beginner but have been working on bikes for years. Is a diagnostic tool for the FI system a must have?  I previously had a first gen M900 and an ST2 and a 750S but they were pretty trouble free.
Any help would be greatly appreciated.

[Howie]

A scan tool would make life a lot easier.  Is it a random misfire or a cylinder dropping out? 

[ccasazza]

A scan tool would make life a lot easier.  Is it a random misfire or a cylinder dropping out? 

It almost feels like the bike is running out of gas. The bike bucks and wants to stall.   It goes away most of the time if i get off the throttle and gets worse with more throttle.
Is there a scan tool that works ok and wont break the bank.
Thanks

[Howie]

Assuming you changed the fuel filter when you changed the fuel lines and the gasoline is fresh, first thing I would look at is fuel venting.  Easy check; when the bike starts running poorly, pull to the side of the road, open cap and see if the problem goes away.

As far as aftermarket scan tools go, I don't know what is presently available.  TechnoResearch only does Harley now.  One thing I learned is sometimes it is worth it to go to a good shop. 

[Orange16]

You can download the IAWDiag software from the GuzziDiag site, and buy the required cable from Lonelec.  That will give you diagnostics.

Crankshaft Position Sensors can often play up when hot, and return to working when they cool down.  Resistance should be in the 600 - 800 ohm range.  Check between the wires to find the active pair - the third is an earth shield.  If you see 2000 ohms or more, it's a good sign it's bad.

Another way to check for the CPS issue is to turn the key on while it's playing up and check that the fuel pump runs for a short time.  Then check if the fuel pump runs again while the engine is cranking.  If there is no signal from the CPS, the fuel pump won't run.

You could fit up a fuel pressure gauge you can see while riding.  That will tell you if there is a fuel supply issue.

[ccasazza]

You can download the IAWDiag software from the GuzziDiag site, and buy the required cable from Lonelec.  That will give you diagnostics.

Crankshaft Position Sensors can often play up when hot, and return to working when they cool down.  Resistance should be in the 600 - 800 ohm range.  Check between the wires to find the active pair - the third is an earth shield.  If you see 2000 ohms or more, it's a good sign it's bad.

Another way to check for the CPS issue is to turn the key on while it's playing up and check that the fuel pump runs for a short time.  Then check if the fuel pump runs again while the engine is cranking.  If there is no signal from the CPS, the fuel pump won't run.

You could fit up a fuel pressure gauge you can see while riding.  That will tell you if there is a fuel supply issue.

Thanks for the great info.  Upon further attempting to diagnose, it seemed to run ok under partial throttle and then once i give it full throttle, run poorly, miss and stall.  It felt like it was running out of gas.  So i changed the fuel pump and filter last night. I havent had a chance to test drive it yet.
I will definitely download the IAWdiad software and get a cable. 
Thanks

[ccasazza]

If anyone is following this, the new fuel pump and filter fixed the issue.  Thanks everyone for the help

[koko64]

If the bike was sitting for a long time then this makes sense. I have found fuel pumps clogged solid in bikes that have sat for years with old congealed fuel.