Poor acceleration after carb rebuild

[Andretti05]

Hi all,
I have a 1984 Nighthawk cb650. The bike started to have some problems where it would hesitate and stall. I pulled the air filter out and it ran great for about 15 min ( had a ton of power, more so than usual). I assumed my airfilter was bad and ordered a new one. The next morning, I went out to start the bike to go to work and it could not stay running. The bike would stall constantly and barely could stay running for more than 5 seconds (with air filter removed). I then decided i would change spark plugs and order a carb rebuild kit. I changed everything, put new jets, diaphragms, etc in the carbs and put everything back together. The bike runs now, but there is a significantly noticeable lack of acceleration from before. Any thoughts what could be causing this?

[Bob H]

Did you change the spark plug wires when you did the plugs?
I ask because your symptoms seem intermittent, and the connection between the end of the wire and the part that clips over the spark plug can be screwed up with moved around (and you can't see the issue).

There is a video of an older nighthawk plug end falling off while the guy is pulling the wires.

A $5 spark tester from Harbor Freight would rule out bad spark.
https://www.harborfreight.com/in-line-spark-checker-63590.html

[Gene]

You should never pull on the spark plug wires, only the boot

[Andretti05]

No, I didn't change the wires. They looked in decent condition and I pushed them into the plug until I could feel the click of the metal passing over the threaded connector on the spark plug. I will definitely try using the spark plug tester though and post back when I do.

[Pete in PA]

You said replaced diaphragms.  Where did you source them?

I've seen the China ones, never tried them.  Don't know if they will act the same.

[mollusc]

Looking at the plug wires doesn't necessarily tell you anything.  They can easily be internally degraded and cause poor spark even if they look perfectly fine.
But since things changed so dramatically after you took the air filter off, I'm going to suggest that your carbs aren't properly cleaned or synched.  How did you clean them?  Did you bench sync before you reinstalled them?  What did you set the mixture screws to, and have you tuned it since then?

[Larry Fine]

with air filter removed

I'd say that's the problem. CV carbs depend on a known amount of intake restriction.

[draser]

The stock carbs are set up such from the factory to work with the bike intake/exhaust to match the power/torque curves of that engine. Changing carb components (or anything in this carb/intake/exhaust triad) affects this "factory tune" and power delivered by the engine.
Your problems started with hesitation and stalling, which are indicative of a carb problem, so the first step should be cleaning. Also, you'll need to give more detail on the issue, was it stalling at idle, hesitation at low rpm/high rpm, etc., because the carbs have several jets and each is responsible for engine operation at a certain rpm range.
If this were my bike I'd remove the carbs and have them cleaned (pilot, slow and main jets) and ensure the pilot and slow are really clean - your bike being same vintage as my 82 Magna I'm guessing you have similar jets. The pilot and slow jets will ensure operation at start-up, idle and about 1/4 throttle, main jet will take it from there.
If your problems were at higher rpms then it becomes a question of vacuum and slide diaphragms, you'll need the stock airbox and filter installed for this to work right.
I would install the original components back, after a good carb clean and bowl level adjust, making sure the diaphragms are correctly installed (not pinched) otherwise the high rpm (over 5-7K) will not work. I would try to have the bike running right in stock spec., then go from there. A bench sync should work just fine to get the bike running, then you can do a dynamic sync.
I'd make sure the tank is clean before using the freshly cleaned carbs trying to start the bike.
Any questions during this process, ask this forum of course.