The bike is new to me with 4600 miles on it. It starts easy and runs smooth except at steady speed or even light acceleration when it has a frequent miss. Under heavy acceleration it runs without missing a beat. When at home I can hold the throttle steady at 3500-4000 rpm and have no miss.

Have added Seafoam and fresh fuel, but have only logged about 20 miles. Adjusted the carb screws yesterday.
Plugs look good I think just changed by the PO, but thy're DPR8EA-9 instead of stock DP7EA-9.
Do I need to change the plugs to stock?.
Should I give the Seafoam more time to work?
The bike had sat garaged awhile before I got it.

could be this, very very cheap fix if not free if all your parts are there and you just have to cut the hose to the right ear in a 45 degree angle.

https://www.vn750.com/forum/showthread.php?t=18147

looking for another link on it now

heres another link, hope your problem is as easy as this. look between your carbs and see if you have a tube from each one joined by a t fitting, from the t it should run under your tank over to the right ear and inserted in to a slot on the ear, you might be getting to much air in it if not. good luck.

https://www.vn750.com/forum/showthread.php?t=17300

The plugs you have are an approved alternate.
If you decide to change them out, get NGK Iridiums, DPR7EIX-9.

Here`s a diagram for the carb vent hose that wib mentioned:
https://www.vn750.com/photopost/showp...o=1757&cat=503

Well... I got the vent hose trimmed and for the heck of it I drained the carb bowls. Didn't see any problems from the bowls. Went for a test run and it started out fine for the first couple of miles then started with the hiccup missing again. So now I've pulled and drained the tank, pulled and checked the petcock screens and sprayed some carb cleaner into the carbs and drained them again. It's all still apart, thinking about adding inline filters even though the petcock screens look perfect.
Could this be a firing problem?
Would a failing coil cause my symptoms?

Yes can be a bad coil, or just a bad connection. It can so be not a dirty carb but a bad diaphragm. Check all your electrics, from your ground to your ignition switch ...(make sue you just insert the bike key by itself... Keyrings with heavy fobs or other keys can amplify a bad switch.)

See if the bike holds a steady throttle at rest...at different rpms.

How difficult is it to replace the diapham?
I failed to mention that when I pulled the fuel lines from the petcock, gas continued to flow even though the petcock was turned to off. How does that happen?
When cruising steady at 3500-4000 rpm I have the irregular miss. Sitting in the driveway and holding the throttle to the same rpm have no miss.
I'll check electrical next. Then reinstall the tank.

if fuel flows with the lines pulled then your petcock is bad.
Fuel is only supposed to flow when the engine provides back pressure to the tank.