1984 gpz will only start when carb is covered with hand.

hi all. i have a 1984 gpz 750 that ive recently replaced the base gasket and the starter clutch rollers pins and springs. ive gotten it all put together and i believe im experiencing  a vacuum issue. the spark plugs stay dry but i can start it on starting fluid. my main question is could the butter flys on the carb being craked open to much when you are at dile create a vacuum leak? also if anyone happens to know how much vacuum each carb is supposed to read on a gauge? the plastic fuel pipe that connects the carb together also seems to be leaking a bit could that give me a vacuum leak? maybe im missing something

Are you running any type of air filter (stock air box or pods)?  To place your hand over the carb opening it sounds like you are not.  This would make for a rather lean fuel/air ratio.  

Is any fuel getting into the float bowls?

Take your time and took off the float bowls and clean all parts, like pilot and main jets. The bleeder pipe air openings,(where the pilot/main jets are screwed in), can also be clogged.
You will find a lot of info and manuals here how to clean, maintance and adjust a carb set right to your bike. As always: "Read the f**king manual!"

To answer your question about the vaccum value on a good runnig engine.

 
 

The throttle plates should be nearly closed at idle. With the engine cold, the enrichers should provide a rich enough mixture for starting.
Has anything inside the carbs been messed with since the last time it ran properly?
Are the carb holders soft and pliable, or are they hard and cracked?
A leaking transfer tube will not create a vacuum leak,  but it it could start a fire.

Have you carefully read pages 15 & 16, plus 150 - 157 in the service manual?

www.kzrider.com/modules/ServiceManuals/GPz750.pdf

See page 366 for updated float height measurements.

Clean carbs properly by fully taking them apart.  Replace all O-rings and gaskets after soaking the parts in carb dip.  Hold jets up to a light and make sure they are open.  Replace carb boots attached to the head.  Install airbox.  If the airbox boots don't install airtight replace those too.  Before attaching the carbs perform a mechanical sync, and after starting, do a vacuum sync.  

Short cuts are long cuts so save time and do all this before attempting to run your bike if it's been sitting.

thank you for the info and the manual! i have a clymers manual specific to kz750. turns out the valves were extremly loose. cylinder #2 and #3 on the exhaust side couldnt even fit a .002 feeler gauge. going to have to put this on pause to order the right size shims. as well as probably a new valve cover gasket. will see if this gets rid of my potential valve slap noise inside the motor (praying its just pre detonation from the lean condition). compression seemed low but it may have been leaking through the valve seats when extremely loose. going to do a poor mans leak down test and double check its not my rings. she has a extremely lean condtion right now. the jets are plenty clean but over over jetted in my opinion. need to go back to stock jetting. anyone had any experince with the rs-34 carbs on a stock gpz 750?

Ahhh, ok. So there are aftermarket carburetors. Mikuni RS34 carbs are completely different from the stock carbs. Has this bike ever run well with theses carbs? Do they have individual air filters? Are there any other modifications?
Yes, you will need to get the valves adjusted before trying to adjust the carburetors.

From what I have seen, the base jetting for a set of Mikuni RS34 carbs set up for an otherwise stock KZ750 should be — Pilot Jet: VM28/486-17.5, Needle: 9DZH1, Needle Jet: P-4 (568 Series), Main Jet: N100.604-115.

i have the stock cv34 carbs for it but it has bigger jets. im really interested in using the rs34 carbs but not sure if it is worth the money to put on a stock gpz 750 motor. still waiting on shims to arrive. once the shims show up i can adjust valves and retest compression if compression checks out ill try to start it and she what she does. ive never had the bike run real well with the current setup. i always just dealt with it. shes always ran rich. what are the chances with the right setting on a set of rs34 carbs that i would be able to slap them in and start up and go?