Yamaha F100 Carburetor problem -- baffled
 

Hopefully someone has a thought on this.

The engine has four carbs. It is a four stroke 100HP. The engine will
not start. A few days before the problem occured I used the boat for
about 2 hours chasing stripers around the bay. The engines were turned
on and off at least a dozen times. They seemed to be running just fine
at the time.

The next time I went to start the engines they started right up.
However one of them would not idle. I tried to start it again and it
started, rev'ed up but quickly stalled and would not start again.

To find out while troubleshooting, I am getting plenty of gas pumped to
the carbs by the two fuel pumps. But, (and this is the odd part) the
float bowls are all empty. Not one or two or even three but all four!
If I remove the hose that feeds the carburetor and remove the float
bowl drain screw and blow into the hose as hard as I can it is apparent
that the path is blocked (on all four carbs). I perform this same
experiment on the good engine and I can blow air right pass the needle
valve and out the drain.

What could cause all four channels to clog simultaneously? If I have
to take the carburetors off, of course I will. But all four are an
assembly and not a trivial thing to do.

Any thoughts,
--Mike

Yamaha F100 Carburetor problem -- baffled
 

It's been a while, but I think that the fuel pumps on your engine are
vacuum operated diaphram pumps. Since you have two pumps, one may have
lost a diaphram (little rubber thing) and the other could still be
pumping enough fuel for you to see fuel, but maybe the diaphram from
the other pump has broken free and clogged the carbs. Can you separate
the output from the two pumps and check them individually? That's all
I can offer for now. Good luck.

Mijoy wrote:
Hopefully someone has a thought on this.

The engine has four carbs. It is a four stroke 100HP. The engine will
not start. A few days before the problem occured I used the boat for
about 2 hours chasing stripers around the bay. The engines were turned
on and off at least a dozen times. They seemed to be running just fine
at the time.

The next time I went to start the engines they started right up.
However one of them would not idle. I tried to start it again and it
started, rev'ed up but quickly stalled and would not start again.

To find out while troubleshooting, I am getting plenty of gas pumped to
the carbs by the two fuel pumps. But, (and this is the odd part) the
float bowls are all empty. Not one or two or even three but all four!
If I remove the hose that feeds the carburetor and remove the float
bowl drain screw and blow into the hose as hard as I can it is apparent
that the path is blocked (on all four carbs). I perform this same
experiment on the good engine and I can blow air right pass the needle
valve and out the drain.

What could cause all four channels to clog simultaneously? If I have
to take the carburetors off, of course I will. But all four are an
assembly and not a trivial thing to do.

Any thoughts,
--Mike

Yamaha F100 Carburetor problem -- baffled
 

Yes I can check that. Good point, the problem would appear to be
something of this nature. Possibly something internal (as oppose to
dirt) that has somehow clogged all four carbs.

They are two seperate pumps. I have disconnected one of the two and
checked for gas flow (which was strong). But I didn't check the other.
The two pumps are connected together for some reason, via a hose.
Possibly for balancing purposes. Which means if one semi disolved or
something of that nature, it could make its way to all four carbs.

Thanks, I'll look into this.

Disney Dad wrote:
It's been a while, but I think that the fuel pumps on your engine are
vacuum operated diaphram pumps. Since you have two pumps, one may have
lost a diaphram (little rubber thing) and the other could still be
pumping enough fuel for you to see fuel, but maybe the diaphram from
the other pump has broken free and clogged the carbs. Can you separate
the output from the two pumps and check them individually? That's all
I can offer for now. Good luck.

Mijoy wrote:
Hopefully someone has a thought on this.

The engine has four carbs. It is a four stroke 100HP. The engine will
not start. A few days before the problem occured I used the boat for
about 2 hours chasing stripers around the bay. The engines were turned
on and off at least a dozen times. They seemed to be running just fine
at the time.

The next time I went to start the engines they started right up.
However one of them would not idle. I tried to start it again and it
started, rev'ed up but quickly stalled and would not start again.

To find out while troubleshooting, I am getting plenty of gas pumped to
the carbs by the two fuel pumps. But, (and this is the odd part) the
float bowls are all empty. Not one or two or even three but all four!
If I remove the hose that feeds the carburetor and remove the float
bowl drain screw and blow into the hose as hard as I can it is apparent
that the path is blocked (on all four carbs). I perform this same
experiment on the good engine and I can blow air right pass the needle
valve and out the drain.

What could cause all four channels to clog simultaneously? If I have
to take the carburetors off, of course I will. But all four are an
assembly and not a trivial thing to do.

Any thoughts,
--Mike