1990 150 HP staling issue

[tuccimf1]

We have a 1990 150 HP Yamaha. Every time we get on a plain for about 5 minutes then the motor sounds like it is choking and cuts off. I don't think it is getting enough gas. What could the problem be? Thank you!

[99yam40]

which 150 on this like is your motor
https://www.boats.net/catalog/yamaha...d-by-year/1990

[tuccimf1]

150 hp etld

[99yam40]

bad fuel pump, restriction in fuel line/filter,or maybe sucking some air instead of all fuel

[tuccimf1]

We by-passed the fuel tank and fuel filter and tested with a 5 gallon gas tank. With the oil and gas ratio mixture. It still does it. The motor has two fuel pump...... how do I know which one is bad?

[TownsendsFJR1300]

What RPM's (minimum) do you have to be when it acts up?

Or does it act up even at lower (less than say 4200) RPMs?

[99yam40]

when was the last time they were replaced?

I would inspect or just replace both it has been a few years

[tuccimf1]

The bottom fuel pump was changed but not the top. We have ordered one from ebay. Thank you for your help.

[tuccimf1]

Changed the fuel pump but the motor running worse still starving for gas. I took the new pump put it on the top and the one that was on there at the bottom replaced it with the top one. The bottom one did not have a tiny whole in it like the new one.

- This video is from today.

- This video is before I changed the fuel pump.

could it be from the gas can not being sealed...vacuum leak?

[99yam40]

not sure what pump had a hole in it or where the hole was, from what you wrote

a sealed tank would not let much gas to be pumped out.

Measure the pressure and look for a leak in the suction side sucking air

[DennisG01]

You just have the fuel line stuck into that jerry can, right? That's fine. If you sealed it, the engine would starve for gas as a vacuum would be created in the tank/can preventing fuel from being sucked out.

Run with the hood off - monitor the on-engine filter... does it go empty or stay full? "Full" is relative - I assume yours is similar to mine where it is never really "full"... maybe 1/2 to 2/3 full, which is normal.

Does the primer bulb stay mostly full of fuel and firm? If not, describe what it.

You can test the engine-mount LP fuel pumps/lines for pressure/vacuum - there's info in my service manual about doing it, anyways. I assume your service manual would have the same thing.

[tuccimf1]

The top fuel pump came with a little pin hole our bottom one did not have one that is why I put the new one on the top and move the top one we had on there down to the bottom.

The bulb was hard but I still had to have my wife continuously squeeze the bulb for us to make it in today during the test run. This was not happening before I changed the fuel pump.

We ran it with the hood off.

We are by-passing the fuel filter to the boat. There is not a filter on the engine.

[tuccimf1]

The gas is not being sucked in properly from the gas tank.

[tuccimf1]

We do not have a manual.....how would we access one?

[DennisG01]

No engine mounted filter? Did someone remove it from the engine - the reason I ask is because I see it listed in the parts diagram for your model.

You should be able to buy a service manual online - certainly from your local dealer.

If pumping the bulb kept it running, the most common thing is one or more bad lift pumps or the fuel bulb, itself, might be bad.

EDIT: Oh, it could also be a fuel line that is failing internally, creating a "check valve" - and it may only present at certain flow rates.

Of course... make sure you have the LP's installed correctly.