Fuel starvation below 1/2 tank

1983 Kz750 L3 w/ Kerker 4-1, stock airbox and KN filter- I did a carb rebuild (rejetted mains one size up from stock)and synchronized recently (from the valuable info gained on this site) now it runs better than anytime since new or same service done at a "professional" shop or dealership.

One new issue has surfaced. Once the tank gets below 1/2 to 1/4 the fuel flow tappers off and bike stalls out. Refill it back up and it runs perfect.

Any suggestions?

During rebuild I replaced all vaccum lines and fuel lines as well as the vaccum plug. All connections look good. Also added a simple small see thru automotive fuel filter that fit the 1/4" line. Is this a petcock or some other type vaccum issue?

Either you are forgetting to turn the petcock to reserve or your reserve filter in the petcock is plugged. I have forgot to put the reserve on many times. I sit there and think I am out of gas for a few seconds. If it is the filter you have to remove the petcock and clean the filter that is the lowest. If it is that dirty there is most likely some rust in the tank.

suggestion...
if fuel flows freely when tamk is at problem level check float bowl ventilation.

How did you run your new fuel line? Same path as before?

Same path with no kinks.

Switching to reserve didn't solve the issue. Anyway the need to go to reserve this way is to soon compared with pre-rebuild.

make sure the tank vent in the cap isnt clogged

btchalice wrote:

make sure the tank vent in the cap isnt clogged

on that note..ride the bike till 1/2 full or when the problem arises. Open the tank and replace the lid if the problem goes away its your tank vent.....to cure it place the tank top in mild PHOSPHORIC ACID (clr)(overnight and rinse completely) it will remedy your clogged vent.

ALL Thanks....looks like I figured it out.

Pulled the "new" inline fuel filter which was a small Fram that fit under the tank and had 1/4" fittings.

Appear it required more vaccum than was available to draw fuel as the tank gets below 1/2.

I put the previous filter in that has a replaceable element and bike runs well all the way down to reserve as pre-rebuild.

Guess the lesson here is no car fuel filters.

Guess the lesson here is no car fuel filters.

I THINK Wired George uses them..just a plain old black one as I recall...he might chime in. I'll see if I can find the pic.

I do NOT use Fram fuel filters. I had bought several and had nothing but problems... they seemed to be all defective and didn't pull gas. Never figured out why but tossed them. They were clear and about 1.5" long and had long 1/4" barbs. Might have been the same problem as happening here... I did post a warning on this topic but it was awhile ago.

I remember the post about the fram filters, I had problems with fram oil filters years ago, I will not use any fram filters