Mikuni carb question - 00 M750

[citizin]

I got water into the fuel system. The bike stopped running.

I drained the tank and carbs. Pulled the carbs off and gave them a good cleaning.
New spark plugs were installed and I have spark.
The carbs are back on and I'm getting fuel to the float bowls.
I've got compression and vacuum pulling air past the carbs into the engine.
A spray of starter fluid let's the engine turn right over. (which made me quite happy to hear since it hasn't ran in a month)

A peek inside the carbs with the throttle open shows me that there is no fuel being pumped past the needle and onto the cylinders.

I've got the carbs back apart and can find no obvious clogs, so what else could prevent fuel from getting out of the float bowls, past the needle, and into the engine?

[ducatiz]

is the fuel pump definitely working?  did you change the filter?  water in the filter can make crud move around and clog.

make sure you have good flow off the tank

if you do, then remove the carbs and get them sonically cleaned.  or r&r with a new pair.

i bet it's the pump or the filter tho

[citizin]

Yes I definitely changed the fuel filter.

If the pump was bad, would the carbs receive any fuel. They are getting fuel to the float bowls.

[ducpainter]

Yes I definitely changed the fuel filter.

If the pump was bad, would the carbs receive any fuel. They are getting fuel to the float bowls.

If you're getting fuel at crank over the pump is working, or there is enough fuel in the tank to gravity feed.

Either way it should start if you have fuel in the carbs.

[koko64]

Hi there.

This applies if you're getting fuel but only a dribble. Like enough fuel to fire but not enough to rev. It's hard to know how much fuel is getting to the carbs. It's hard to believe it's not another problem if the carbs are being fed properly. If you disconnect the hose to the carbs, turn over the motor, and the fuel pulses strongly out of the hose into a can, then disregard what I'm about to post. If the fuel supply is ok, do the slides lift when you try and rev it? If they don't you will have to recheck how you put the carbs back together, ie the little O rings are there, the carb top seals ok, the floats were put back correctly, etc.

What kind of fuel tap? Vacuum or manual? If its a vacuum tap, sometimes the rubber diaphragm type seals bugger up over time and may be affected by certain fuel additives. Same for the pump.
Also check your vacuum hoses to the pump and tap, and the fuel hose from the tank to the tap for kinks (it happens more than you'd think).

You could fill the tank right up and bypass the pump with a hose to check if the carbs get more fuel and it runs. If fuel flows ok and it runs it's the pump, if it doesn't its the tap or a tank blockage.

There are good, cheap aftermarket taps and pumps you can get thru the forum sponsors.

People get around a bad pump by bypassing it but you can't use the whole tanks worth of gas with gravity feed only. It gets you by until you source a new pump but you need to refill after using only half to two thirds of a tank.

[citizin]

dp - there is definitely fuel in the float bowls

koko - I have no idea which one of those I have. It's a 00 Monster 750 dark.

So let me get this straight ------
Even if the pump or tap is bad, I can still get fuel to the carbs via gravity feed?

[ducpainter]

<snip>
So let me get this straight ------
Even if the pump or tap is bad, I can still get fuel to the carbs via gravity feed?

Fuel will feed until the fuel level is below the level of the carbs.

I think you still have a water problem.

It can hide in the system even though you have drained the tank and added fresh fuel.

[citizin]

koko - you edited your post while I was replying!

Yes the throttle plates open up properly. That was my first thought - that I had put something on the carbs incorrectly. But I've checked and rechecked and they are on properly.

But the trickle you talked about - I will try this tomorrow. I believe that you have pointed me in a better direction. The carbs are getting gas, but not enough to fire or run. I've cleaned them and checked everything. But if there is no pressure then the fuel wouldn't go anywhere, just sit in the carbs.

I've got no fuel tap except just a threaded fixture coming out of the tank and a hose attached to running to the fuel filter.

dp - if there is water hiding, then it's not anywhere between the gas tank and the carbs. I just pulled fresh gas out of the float bowls and no water was to be seen.

[citizin]

Let me ask what is a simple question that I just don't know the answer to....

What exactly causes the fuel in the float bowl to come up through the jets and into the main passageway of the carbs>engine?

[ducpainter]

koko - you edited your post while I was replying!

Yes the throttle plates open up properly. That was my first thought - that I had put something on the carbs incorrectly. But I've checked and rechecked and they are on properly.

But the trickle you talked about - I will try this tomorrow. I believe that you have pointed me in a better direction. The carbs are getting gas, but not enough to fire or run. I've cleaned them and checked everything. But if there is no pressure then the fuel wouldn't go anywhere, just sit in the carbs.

I've got no fuel tap except just a threaded fixture coming out of the tank and a hose attached to running to the fuel filter.

dp - if there is water hiding, then it's not anywhere between the gas tank and the carbs. I just pulled fresh gas out of the float bowls and no water was to be seen.

Carbs don't work on fuel pressure.

They work by vacuum

If there is fuel in the bowls it should at least fire and idle.

Have you looked at the plugs since you replaced them?

[citizin]

Just put a new set in this morning when I sprayed with starter fluid.

They've been fired once. Let me be clear, the carbs are not spraying fuel from where the needle sits in the emulsion tube.

[ducpainter]

Just put a new set in this morning when I sprayed with starter fluid.

They've been fired once. Let me be clear, the carbs are not spraying fuel from where the needle sits in the emulsion tube.

When you disassembled the carbs did you get the diaphragms for the slides and the little o-ring for the cover back in correctly?

The fuel the engine gets from starting enters through the pilot jet...not the emulsion tube.

[citizin]

Yes when I pulled the carbs off this afternoon, the diaphragm and o-ring were sitting properly. Where does the pilot jet input the fuel so that it can enter the engine?

And not to make things even more muddy - although the factory jets are installed, the needle was set at 2nd notch from the top (top meaning closest to the upper cover) and the idle mixture screws were five turns out. Neither of which is what my Haynes says is factory setting.

I feel (and probably sound ) like I'm running in circles and grasping at straws....

[ducpainter]

Yes when I pulled the carbs off this afternoon, the diaphragm and o-ring were sitting properly. Where does the pilot jet input the fuel so that it can enter the engine?

And not to make things even more muddy - although the factory jets are installed, the needle was set at 2nd notch from the top (top meaning closest to the upper cover) and the idle mixture screws were five turns out. Neither of which is what my Haynes says is factory setting.

I feel (and probably sound ) like I'm running in circles and grasping at straws....

Try turning the screws in a little...about one turn.

...and humor a humorless guy and check the plugs.

[citizin]

I will screw them in one turn....
and I'll humor you right now....I'm gonna go check 'em.