1999 M900 Carb Fuel? Issues

[ducpainter]

I don't think vacuum tap sizes make one iota of difference because the measurement has nothing to do with flow.

The only other comment I'd make is you can't really tune a bike statically. Ride the thing.

[Dellikose]

Heading out tonight

[Dellikose]

Well, I didn't even make it out of the driveway. Same symptoms...the horizontal cylinder would drop and any attempt to add throttle would make it fall flat. It only idled for the amount of time it took to put my jacket, helmet, and gloves on.

I drained the gas and noticed that it was orange/yellow...I let it sit overnight, and no rust settled out. It could be that the ethanol absorbed some water and separated out. The gas didn't smell rancid, and wasn't very old.

I drained the tank by disconnecting the line from the fuel pump to the carb. It drained the entire tank...koko mentioned earlier in the thread that it should only drain from a full tank to about ~ 1/2 tank, so I guess the rebuild kit isn't installed correctly.

[koko64]

If the outlet is lower than the tank you are ok. It's just the carb inlet is high.

[Dellikose]

Thanks. The outlet was indeed lower than the tank when I was draining it.

[koko64]

If that cylinder is getting fuel you could have an ignition issue. Plug black? Or not black but wet? Or dry? You can ground the plug to the motor and see if you lose spark.

[Dellikose]

The plug smells a little like gas, but it is dry - not black at all.

I've sprayed every passage with cleaner and blew it out with compressed air. Also verified that the diaphragm has no holes, and all of the gaskets are intact.

I grounded the plug to the engine and have great spark.

[koko64]

Must be a fuel blockage or one slide is not rising. The diaphragm can unseat when you put the top on and then not raise the slide. It's a common and annoying problem.

Some soak the rubber in WD40 or spray it with carb cleaner to expand it so the rubber lip fits the recessesed ring of the carbs.

Caution, some carb cleaners may be too strong and dissolve some rubber. The stuff here has been softened to not kill you by the EPA so it only swells the rubber. Doesn't clean as well.

[Dellikose]

I'll try soaking the diaphragm in WD40 and check for fuel blockages.

The only other thing in the carb that would limit the fuel would be a sticking float, right? I think a cracked float would flood it.

[Speeddog]

Before you tear into it, pull the airbox lid and filter, and start it.

Visually check that both slides move in the same way, bouncing the same way at idle, and sliding up the same when you rev it up.

Watch your eyebrows, as it was backfiring out the carbs before....

[koko64]

Yep. Sticking float valve starves and sinking float floods.

Visually check it as Speeddog suggested. Can save a lot of work for nothing. Easy with pods. I run pods until I'm satisfied the diaphragms and slides are working correctly before I fit an airbox. I have had to pull the top off a carb 3 or 4 times until the rubber seated correctly. I recently found a local supplier of diaphragms and slides that are about $100 a pair for the complete parts.

I'm starting to lean towards an unseated diaphragm lip. Pita and not uncommon.

[Dellikose]

I checked the diaphragms, and both move in sync at idle and with throttle.

Do you guys think it is worth it to take off the side cover and check the pick-up clearance?

[ducpainter]

Pick up clearance doesn't change. If the bike ran well before I don't think that's your issue.

I'd start swapping electrical components between cylinders. Be careful if you swap the ignitors. They're fragile and expensive.

You could also check the pickups for resistance. howie knows the spec, or you could dig it up here on the forum. Another thing to check is the insulation on the pickup wires where they pass through the case.

[Dellikose]

I've already swapped the igniters and there was no change.

Here is what I found in the workshop manual as far as pickups...

[ducpainter]

I'd test the pickups and coils cold, and hot.