82 GPZ1100 engine "chugging"

Hi guys- haven't been on in a while but curious if anyone can offer advice.
I aquired an 82 GPZ1100 some years back and have slowly brought it back to life. The issue I'm having now is at low rpm's(below 1500 aka while letting the clutch out ) the bike makes a "chugging" noise the same as when throttle bodies are out of sync. Once above 1300-1500 rpms - no such noise. I  purchased this as a non-runner so I have no idea whether this is normal or not- I can only compare it to an 1100F I used to have years ago that would make such a noise when the carbs were out of sync. Aside from this everything seems to be fine however , based on my memory my old 1100F would pull the front wheel upon acceleration were the GPZ does not.
So, I'll give a run-down of what has been done(engine-wise)so far :
Over-bore with Weisco higher compression pistons (old rings rusted to the cylinder wall with DEEP pitting).
New gaskets/o-rings from cases up.
New stock spec spark plugs(NGK)
Spark plug caps replaced(too much resistance) and spark plug wires replaced.
Running stock fuel injection/throttle bodies (synced to within 1hg).
Stock fuel pump and pressure regulator (33psi at idle/ 35-36psi at running speed).
Return valve to tank functioning correctly.
All valves gapped to spec.
Timing done per factory manual and proofed out with timing gun including advance.
Stock coils and ignition(produced nice spark once I grounded it to metal instead of paint!)
Plugs burning nice tan color across all cylinders.
Stock intake boots but are flexible and no cracks (check for leaks with ether/starting fluid).
Air temp. and engine temp. sensors both within spec's and giving consistant readings.
K&N filter using stock airbox.
Delvic 4 into 1 exhaust.

So everything SEEMS correct but always willing to listen to advice!  Just doesn't seem QUITE right yet. And yes-I'm aware the factory manual states that idle speed should be 1500rpm but that just seems high.
If you have any ideas I'd appreciate the advice ! Thanks guys !
 

Is it dropping cylinders or just making a weird sound? I had an issue last year with my coils or wires arcing to my frame if I let the idle get too low.

Try to adjust the TPS on the throttle body. Turn the TPS in small steps to get the highest rpm at idle and the best air/fuel ratio.
Then try to lower the idle back to 1000-1100 rpm.

I would change the intake boots.  40 years of heat-cycled rubber.  They are overdue and relatively cheap.

I would also remove the K&N air filter and install a Hiflofiltro brand, paper air filter. 

These bikes are not closed-loop DFI.  There is no 02 sensor and no fuel correction.

What did you use to synch the throttle bodies?  You didn't synch them at 1,500RPM, did you?
Is the bike idling at 1,500RPM now?  That figure is incorrect, it should idle around 1,050RPM.

I only use a mercury manometer but I recently bought a 4-channel Digi-Synch.  I will use it to
set-up my GPZ.  It has a built-in digital tach so it's real handy to adjust the TPS.

Here's mine running recently.  Untuned.  Good luck.


 

Hi ghostdive,
Doesn't appear to be dropping (losing spark) to the cylinders but I will check it out in the dark to check for any arcing.
Thank you for the advice!

Hi Scirocco,
I did adjust the TPS via an ohm meter to keep the low end and high end within range (neglected to mention that) but I will try your method out.
Thank you !

Hi Highway Magician,
You may be right on the boots-pretty inexpensive. They seemed pretty flexible with no cracks so I never gave it another thought.
Why would you switch to a paper filter-to richen the mixture slightly? Plugs seem the perfect tan color across all cylinders.
Yes- I did sync them at 1500 ! Hadn't considered that I need to re-sync at the lower RPM! I used a Carbtune unit for the sync - instead of mercury uses stainless rods. I have good success with it over the years since my old mercury filled was broken years ago.
Thanks for the video shot- I will put all these pieces together and see what I come up with !

This is a primitive DFI system and it cannot compensate for increased airflow, like a closed-loop system can.  So, it should have a factory-style air filter.
I use the Hiflofiltro brand, #HFA2906.  ~$12 shipped.

What condition is the fuel filter in?

I had a Carbtune a long time ago but the stainless rods were sticking.  So, I took it all apart, got them moving freely and then sold it on eBay.

Here's the Digital Synchronizer I bought recently.  Got it in 2-days via Amazon Prime.

www.amazon.com/gp/product/B086PC4Y2S/ref...00_s00?ie=UTF8&psc=1

Take a look at this DFI document.  There are many potential leak points and all of these have to be checked out.
There are holes in the airbox for a grommet (at the top), a rubber drain plug at the bottom, airbox to breather
cover hose, and vacuum hoses, etc.  Make sure the airbox is sealed (no open holes drawing extra air in).

It should definitely pull a wheelie if it's running right.







 

Wow- never seen a unit like that-looks sweet. I will doublecheck the airbox as well.
Again- thank you for the great tips !!

You can cover half of the airbox with tape to see if it runs better or differently.
Then remove the tape and open the airbox slightly to see if that causes a change.