Kz750 twin backfiring

Okay Im alittle low on cash and I'm about to run a cafe seat pan so I dont know how hight the lid will sit. I have some sheet metal and Im a great tig welder so maybe i should fabricate a metal lid to sit lower inside the bike. Can anyone provide a picture of lid on the bike and off? ( the original)

air filter

the top

No eBay APP ID and/or Cert ID defined in Kunena configurationNo eBay APP ID and/or Cert ID defined in Kunena configurationNo eBay APP ID and/or Cert ID defined in Kunena configurationAccording to Kawasaki.com the following models use the same part number:

KZ750-B1 (1976)
KZ750-B2 (1977)
KZ750-B3 (1978)
KZ750-B4 (1979)
KZ750-G1 (LTD II) (1980)

Here are some on eBay:

Okay I ordered a lid for the box, so that will probably fix some issues the bike is having while its running. As for the backfiring I am thinking its not getting fuel. I just cleaned the gas tank and added alittle seafoam to the new gas this morning . I'll see if maybe that helped and go from there . Thanks for ur help bountyhounter and Ed

I do have one last question ( please excuse me I do not know enough) . How would I go about the fuel lines from the petcock to the carburetors . It only drops about an inch and its hard for the fuel to flow down since there isnt much drop. I have a single outlet petcock going to a 3 way connector. Im really considering buying a dual outlet petcock but 100$ is alot for the ones I have found .

That petcock can drain your three gallon gas tank in about 3 minutes. If you are getting 20 miles to the gallon, you'd have to be going 1200 miles an hour to get ahead of it.

It's not the drop that feeds the fuel; it's pressure above the drop that feeds the fuel. The petcock is an inch tall and the gas is anywhere from zero to six inches taller.

In other words, my advice is to save your money and put it to something that will help you more later.

Schmeck wrote: I do have one last question ( please excuse me I do not know enough) . How would I go about the fuel lines from the petcock to the carburetors . It only drops about an inch and its hard for the fuel to flow down since there isnt much drop. I have a single outlet petcock going to a 3 way connector. Im really considering buying a dual outlet petcock but 100$ is alot for the ones I have found .

It doesn't matter if the fuel drops 1 inch or 10 - fuel flows downhill and it will flow fast enough to fill the carb bowls regardless of the amount of drop. The fuel flows through the petcock down the fuel line into the carb bowls and fills them to a specific level at which the float valves stop the flow. As fuel is drawn through the carbs it is pulled from the bowls, not the fuel lines (remember, these are carbs, not fuel injection). As the fuel is drawn from the carb bowls and the fuel level in the bowls drops the float valves open and allow more fuel to flow from the petcock into the bowls - this keeps the fuel in the bowls at the proper level as you ride.

What makes you believe you need a petcock with 2 outlets? The number of outlets on the petcock is not determined by the number of carbs. The petcock for a 4 carb KZ750 4 cylinder bike only has 1 outlet. A 2 outlet petcock is only needed if the carbs have 2 separate inlets and are not fed through a common "T." I'm not familiar enough with KZ750 Twin carbs to know how they are normally set up, but if the stock petcock had 1 outlet that's all you need. If it had 2 outlets you should have one with 2 outlets. Ed

Hey guys thanks for all the info it really helps seriously. I went out into my garage after cleaning the tank and tinkered some more on the ignition timing. Made sure every little detail was correct so I could rule that out . Then I little by little turned the idle screw or the one on the side in a full turn and put choke on . Kicked the bike over once and it fires right up. I stuck paper towels around the air filter so that maybe it would help until my lid gets here. No more back firing:) Im guessing I did something different than I did before? Hip hip , another kz750 on the road

It is most likely exhaust popping, not backfiring. "forward firing"
You can feel that popping, if you hold your hand behind muffler.
You can find out which cylinder is popping.

It was actually backfiring before , like a gunshot . Now the exhaust is very steady with the idling. Also Im running a 2 into 1 muffler which is rusted to pieces . Probably going to put a shorty on instead. Not sure how that will effect the bike, but I will figure it out . The riders on this site are incredibly helpful. Thank god for kzrider!