'94 M900 FCR running issues

[Howley]

Hello!

Some of you may remember me from many years ago. My '94 M900 has been quietly waiting for my kids to grow up and me to get more time, and that time has finally sorta come.
When last left the bike was running perfectly, probably 10 years ago (!).
First thing I did was pull the FCR carbs, take them apart and clean them. All the jets, floats and accelerator pump came apart but only the top and bottom covers, I didn't split the carbs or open the mid joint.
I also replaced all the fuel hoses and fuel filter.
The jets were gummed up and furry and were cleaned with carb cleaner. Everything was blown through with compressed air.
I DID NOT clean the carb in an ultrasonic cleaner.

On reassembly the bike was rideable but was popping on decel and a bit on acceleration. After returning from a 30 minute mild ride the bike was hot and apparent that it had been running lean.

I pulled the carb again and re-cleaned everything, put in new plugs and ran it again (this is about a year later now) and it seems worse, popping and missing more on acceleration. Throttle response on a blip is boggy. A full blip will kill it.
If I open the throttle slowly there are fewer issues and at speed with more open throttle everything seems normal.
I suspected the fuel but fresh fuel made no difference.

I did suspect the accelerator pump. The spring between the arm and the plastic actuating lever seemed weak so the arm was moving but the lever was not. I tightened that up and it seems fine now, I jet a good squirt from both jets when the throttle is opened.

I've got the carbs set where I had them which is NOT the settings recommended in the ca cycleworks documentation. With open exhaust and air box I've got 2-1/8 turns on the fuel screw and 2-1/4 on the slow air screw.

Can anyone point me in the right direction here? Do I need to get the carbs in an ultrasonic cleaner?

Thanks.

Luke

[Howley]

Should also note the bike starts and idles fine.

[Howie]

First thing you need to do is fresh fuel and a new fuel filter.

[greenmonster]

2,25 on air screw often too much vs recommended-running lean. Usually 1-1,5.
What jets and needles?
Settings, needles etc?
What airfilter?
Idle steady?
Plug colour?

[Howley]

First thing you need to do is fresh fuel and a new fuel filter.

Fuel is fresh and fuel filter is a year old, is that fresh enough?

Settings are:
155 main jet
200 main air jet
60 slow jet
EMT needle at 3rd from top

K&N filter in open air box.

Idle is steady, with mixture screw further in it seems to hang up above idle after revving.

I'm not sure I've run it enough to colour the plugs but the front cylinder insulator if white and the electrode dusty white/grey, and the read cylinder insulator is brown and a bit shiny/wet with a dark grey electrode.

Like I said these settings are unchanged from a point where it was running perfectly.

Howie and greenmonster, good to see you still around. Greenmonster I still have your map in my ignitech ignition!

[koko64]

I take it that they are FCR39 carbs?

Have you physically cleaned the pilot jets or just soaked them? Deposits can block or "sleeve down" the pilot jets. Soaking often isn't enough and jets need a physical "floss" due to the modern fuel additives waxing up. You can buy cleaning wire kits from K&L that look like welding tip cleaners. Clean, flush with carb cleaner then blow through with compressed air.  Sonic cleaners are great and I use one but manual cleaning is still required.

If the fuel tank is harbouring filth in its nooks and crannies you may find yourself cleaning the carbs a few times. Cleaning out the tank is important. Mind you,  it's possible to also disturb crap in there that may have stayed put. You can't win. If you clean it, clean it thoroughly.

You can get build up on the float valves causing richness and flooding and build up around the inner walls of jets leaning them off. You may have each issue on each cylinder as one appears lean and one wet. I have seen some float valves sticking shut as well as not fully seating from the goop that forms over time. Sounds like you have dealt with the blocked accelerator pump passages.

Some carb cleaners are less lethal nowadays but also less effective. Ultrasonic cleaning is only part of the solution and elbow grease is still required. Buy the K&L jet cleaning kit.

With an open airbox I would run 160 mj for 39s, but that setting is with our fuel down under.  The slow air screw is out a long way but if it works for you it works. Local conditions and fuel plays its part for sure.

[Howley]

Thanks koko. The carbs are 40s. What you say makes sense. I actually noticed I could see fuel. Pooling around the slide on the left hand carb so that would explain the wet plug on the rear.
Sounds like a need to clean better!