1999 M900 Carb Fuel? Issues

[Dellikose]

The bike is a 1999 carbed M900 with 33,000 miles. A few days ago I was riding on a 92^oF day, and the bike bogged way down while climbing a small hill after about an hour of riding. It would restart and idle fine, and sometimes would take full throttle under load, but would ultimately bog down and die within a minute or so.

I check the following on the side of the road:
   - Kinked/collapsing fuel lines: all had slight resistance when pinched, and also verified all lines under tank were not kinked
   - Gas tank vent: Opened filler cap when running, but no "whoosh" sound
   - Vacuum petcock: Removed two years ago
   - Battery: Connections loose! I tightened them up and the problem still existed. I checked the battery voltage later on, which was 13.3v which is 90% charge for Shorai lithium
   - Electrical connections: All seemed fully engaged, no frayed wires or anything loose. All fuses intact

What is weird is what happened the next day. I replaced the fuel filter since they are cheap, and I have a fuel pump rebuild kit on hand, but not installed yet. With only the new fuel filter installed, the bike started fine but was bogging as before with throttle in neutral. I let the bike idle for about 3 minutes, and tried throttle again....and the bike did not bog! It accepted all throttle after that, but I did not have a chance to ride it. Maybe the fuel line had debris that was dislodged with the revving? I did cut open the old fuel filter and the paper media looked pretty clean.

A ride will confirm that it is better, but if not I am thinking the fuel pump may need rebuilt. Or maybe this was related to the battery being loose, but the issue was not resolved when the terminal connections were tightened up on the side of the road. Let me know what you guys think - thanks!

[koko64]

What do your spark plugs say?

[Dellikose]

Top of the plug is brown/black with no oil residue. The ground strap is more gray, and the insulator is clean white.

Was thinking about it more last night, and I shouldn't rule out a sticking carb float either.

[Howie]

Since you have the kit, rebuild the pump (unless it is a Winderosa kit, if so, throw it in the garbage.)  Go for a nice ride, then report back.

[Dellikose]

Howie - the fuel pump rebuild kit is a Mikuni MK-DF-62. I did not rebuild the fuel pump yet, just because I have not had any time.

Went for my ride last night, and he bike seemed to run just fine. I may have detected some exhaust popping on heavy acceleration, but it was very, very faint. I will continue to ride and see what happens since my confidence is pretty low right now.

I am still perplexed on what happened...I will continue to keep an eye on the fuel lines, but the best idea I have is still a clog in the line or a stuck float. If it happens again, I will give the float bowls a good tap just to verify. I am also going to inspect my manual shutoff to make sure no debris has collected in it.

[koko64]

If the carb float needle sticks open you will get a fouled plug on that cylinder and overflow out the carb drain hose if its flooding bad. White porcelain is lean so maybe fuel not getting through. Check both plugs to determine a blockage on one carb or fuel not geing pumped at all.
Does it run better with a full tank? If so suspect fuel delivery.
With your e fuels I would rebuild the pump like howie suggested. Some fuel tap rubbers swell and strangle supply and I have also seen stale fuel goop glue float needles shut.

[Dellikose]

I was thinking that the floats may be sticking on the low side, so the bowls wouldn't have enough fuel to take full throttle. Is that even possible?

Like both of you have suggested, I will rebuild the fuel pump and report back.

[koko64]

Internal filter on the carb inlet T can get clogged. I pull them out and trust a good in line filter.

[Dellikose]

Update!

I rebuilt the fuel filter. The old diaphragms were a little worn, but I did not notice any tears. The diaphragms in the rebuild kit are slightly different than the existing ones, but the concept is the same. I went for a nice ride and did not have any problems.

Just for shits and giggles, I checked the plugs after my ride. Like I said - the ground strap is gray, is this normal or indicating lean? Porcelain is not as clean as I originally thought. The top of the plug is more black than brown...maybe I am running a touch rich? Don't mind the silver area opposite the ground strap on the vertical cylinder plug, I accidentally got some anti seize on it.

Horizonal:



Veritcal:

[koko64]

Are those pics with a flash? If not the plugs look lean on my little phone screen. Does the light coloured porcelain go all the way to the base? Look down there with a flash light.
Are you running stock jetting with an open airbox? Are there any black dots on the porcelain?
Hopefully someone on a pc/lap top will pitch in. This phone screen is tiny.

[ducpainter]

On my laptop it looks like just the very end of the insulator is colored.

Maybe a little lean, or not much throttle. hard to say.

[Dellikose]

Those pictures are in direct sunlight, no flash.

I'm running an open air box with a Factory Pro jet kit (CRB-D12-3.1-TI) and new emulsion tubes (CRZ-EMU-100120k). I also partially cored the stock exhaust. When I installed the jet kit I tried the 150 main, which fouled plugs within a ride, 142.5 was too lean, so I have the 145 installed. What is stock main jet size...140?

Looking at the insulator, only the tip is colored very light tan. The horizontal insulator is white down to the base, and the vertical is white for 2/3 and the base is darker. I do not see any black dots.

I might be installing those 150s again over the winter and giving them another shot.

[ducpainter]

Factory numbers must be different from Dyno-Jet numbers.

I ran 165's in my Monster with a drilled lid and DP cans.

[koko64]

FP jets line up with oem while DJ run at roughly ten numbers higher for same size oem. So for example, 175 DJ main jets are roughly 165 oem Mikuni jets (or therabouts).

[Dellikose]

Do the mixture screws only control the mix before the mains pick up? I am thinking of fattening the mix for the time being, since I am only at 3 turns out.