engine loses power dramatically, stalls (M750)

[sonofabike]

Carbed '99 M750, FRESH out of the garage for its 18K service.  The bike was running well before the service.  After the service, first 30 miles or so riding around the city, and on the freeway to home, the bike was running amazingly.  I mean just amazing.  Took the long way home and headed out to the twisties not far away.  First run of a 6-mile stretch of road, tame pace, all's good.

The reverse run was quicker, and I kicked up the revs quite a bit, then trouble began.  Started losing power, 3rd, 2nd and 1st, all revs -- didn't matter.  Giving it more gas seemed to worsen the problem, exhaust groaning louder/deeper.  Throttle unresponsive, what power was left was really rough, engine seemed like it was starving for fuel.  Then... STALL.  Almost as if I had ran out of gas.  But I had a full tank.

Somehow -- beats me how -- but SOMEhow, I managed to get the bike running again after some difficulty restarting.  At times after the restart, things seemed almost normal, but power was still irregular and lacking, throttle still less responsive than normal.  I basically limped back home, another 5 miles, but not without having the bike stall the same way TWICE more, with the same struggle to restart afterwards each time.

Bike has new plugs.  It also has a new breather hose (old one was cracking, but never once caused issues like this before the service).  Naturally, the bike's going back to the shop tomorrow, but WHAT -- pray tell -- are some things I should be mindful of that would cause this?  Jjust so I'm better educated when presenting the problem to the shop, and making sure the right things are addressed by them.

Thanks, thanks, and many thanks to any of you who can shed some light.

[hooligan machinist]

 Let's see..... 30 miles or roughly 1 gal of fuel into a fresh tank.
Just came from being serviced.

  Try opening the fuel cap. Look for any pinched fuel lines in and around the area of the tank hinge.
That's the first thing that comes to mind. Since you just had it serviced, if the tank was raised, it's a possibility.
Could also be a clogged or pinched vent tube.

  Of course it could very easily be any number of other things.
Hope this helps.

[Howie]

You are doing the right thing bringing it back to the dealer.  Describe the symptoms as you described them here.

[sonofabike]

Try opening the fuel cap. Look for any pinched fuel lines in and around the area of the tank hinge.
That's the first thing that comes to mind. Since you just had it serviced, if the tank was raised, it's a possibility.
Could also be a clogged or pinched vent tube.

Thanks for this.  I suspected the issue had to be something with fuel delivery too.  Lifted the tank this AM and discovered the mounting bracket for the fuel petcock broke, so the it was basically hanging loose and that could have been pinching the line.  I was able to limp back to the shop, and the bike's up on the stand.  Wrench also observed that the fuel line used from tank to petcock is non OEM and longer than usual, which could be in turn pinching the second line to the motor.  Thirdly, he also heard a bit of air release when he opened up the tank -- vacuum in the tank suggesting perhaps a pinched vent tube just like you said.

If the problem persists after fixing these issues.  I'll be sure to document here.