Topic: recent rebuilt cb750k dies when it gets hot ???

[Shoeboxjoe]

I have this posted in my build thread (http://forums.sohc4.net/index.php?topic=52576.msg851531#new) but figured i'd throw something out here also.

The bike runs mint for about 15 minutes when it starts to stumble like its out of gas (has plenty of gas), twisting the throttle makes it sputter worse when in gear, and it eventually dies. If i leave it sit 5-10 minutes it starts right up and runs fine until it gets hot again.

It's a recently completed total engine rebuild, new gas tank (had some crap in it after drilling the petcock holes but i think i got most of it out) new fuel lines with in-line filters, running no air filters at the moment (they're on order), totally open exhaust, rebuilt carbs with stock rebuild kit, jets are new from the kit so probably stock jets. New plugs but old wires and caps, stock points.

Would improper jetting cause it to run like crap and die only when the engine gets hot? Or is it something far more sinister? Any advice would be appreciated! Thanks!

[Gordon]

Sitting for 5-10 min isn't nearly long enough for the engine to cool off at all.  Sounds to me more like a fuel delivery issue.  When it dies, shut off the petcock and open the carb bowl drains to see how much fuel is in them. 

[mick750F]

  A clogged tank vent would give you that type of symptom. Possibly clogged carb vents too.

Mike

[Shoeboxjoe]

Carb vents are just hanging for the moment near the battery box since there's no air box. Tank vent? as in gas tank vent?

[mick750F]

   Actually gas cap vent...not tank vent. If the vent is clogged gas flow will stop because of vacuum. Let it sit for a bit, pressure equalizes and it runs again...for 15 minutes. Leave the cap loose and see if it still dies.

Mike

[Shoeboxjoe]

That sounds likely the problem since the tank is an aftermarket fiberglass tank with this polished cap

[wookie]

I have the same cap.  Drill a couple of 1/8 holes in the spring loaded sealing plate.  It's enough to prevent vacuum lock.

[Shoeboxjoe]

Drilled two 1/8" holes in the plate/gasket under the cap. We'll see if that does it. I also noticed a leak in the seam of the tank which seems to be getting progressively worse. I contacted the manufacturer to see what he suggests but he hasn't been too cooperative in the past when ive run into issues with his products. If he doesn't come back with anything I was just going to try Caswell's epoxy tank sealer.