My KZ750 nearly got me killed today. Need Older Guru Help

Next time it happens, open up the filler cap and listen/feel for vacuum in the tank. Then see if it runs. If so, the vent is clogged.

My take away here is the PO saying he would shut off the petcock and the bike would run better for a short distance. My first thought was an over filled float bowl. But in theory it could also be the vent. Closing the petcock could allow time for the tank to equalize then turning it back could allow the fuel to fill the bowl. With the PO mentioning the spike in RPM might indicate the later vent issue and running lean… 

I did not mean to indicate the tank vent was the issue but rather it is easy to check.  Test it without a full tank of fuel as it could leak all over you when riding .  Open the tank lid push it down but not closed tight/locked. Go for a ride and see if the issue is resolved.  

Awesome. Thanks! 

what would be the best way to resolve this? and would dirt getting in the carb have caused it?

is there any way to LOOK at the vent in the tank cap and see if its blocked? this is all new to me.

Yes dirt caught in the carb can cause drivability issues. First I’d try gd4now’s procedure to test the tank vent. One test at a time and his is the lease intrusive. Report back and I’m sure the forum will have more things to test.

RIght but this is what im getting at.

Is there a away to VISUALLY inspect the vent to see if its blocked? Lets say I do what gd4now tells me and leaving the lid open solves the problem. THEN what to I do to SOLVE the problem?! No one has mentioned HOW to clear a blocked tank vent.

You’d have to post a picture of the inside of your cap. On my big4’s there are 3screws to remove a yellow chromate cap, under that is a paper gasket and it covers a winding grove in the upper half. At the end of the groove is a hole. If it’s plugged or an insect has built a nest in the groove you’ll see it.

OK so the fix or way to inspect other than riding with the cap open (which I will do anyway) is to remove the three screws and inspect it. Got it.

My cap looks like this:

 

Looks just like mine. You can take it apart. Take photos of each step so you get it together correctly 

Yes you can look at cap and clean if required without driving with the cap open.  Is the pic you posted your actual cap as it certainly looks brand new to me and if it is yours then the vent may not be the cause of the issue.  IMO it is still worth a test.

I did not word my response well, I just felt like it was an easy way to test if the vent was the issue, without pulling carbs or petcock to look for the problem. Which you will most likely have to if the vent is not the issue.

When I am attempting to find the cause of an issue I first try to see what could be the cause and then try testing the easy things to test with out pulling parts till I prove to myself that they are not the cause of the issue.