Yamaha 30AE loses power at full throttle

[pintailed]

30hp model AE, loses power at 3/4 to full throttle. It seems to be a fuel issue. When it starts to lose power I can squeeze the bulb once to keep it running for another 30 seconds or so until it starts running weak again. Squeeze bulb and it improves. Could drive around all day just fine if someone wanted to sit in the back of the boat and squeeze the bulb every so often.

Originally took the motor into the shop because I was having periodic bogging/flooding issues and when you squeezed the bulb to prime it you could just pump fuel past/thru the carb. Guessing a float was stuck and carb needed to be cleaned up.

Shop put in a carb kit, new fuel pump, new spark plugs, all new fuel lines under the hood. Did a compression check which came out ok. Took out thermostat which had disintegrated.

Took it out and motor starts right up, idles, low power is just fine. full throttle it can't get enough fuel and has the 3/4 to full power issue. I then replaced gas tank, fitting at gas tank, fuel line and bulb, fuel line fitting on motor side. Still the same issue. Shop said the new fuel pump might have been faulty - they warranteed it and replaced. Still same problem. They are at a loss and don't seem to want to look at it anymore. Their next guess would be to put an electric fuel pump on. The motor had no issue with the original fuel pump aside from the original carb issue, am doubting I need a different type of fuel pump now.

What's next?

Also would like to know what year the motor is, the serial number look ups I find only go back to 1984. Was told this was a 1990 when I bought it. Serial #689 S 103993

[boscoe99]

Looks to be a 1984 model year motor.

[99yam40]

Could be sucking air from somewhere causing the fuel in bowl to drop too low.

Slip in a clear piece of tubing in right before the pump for testing to see if you can see air bubbles. You can also test fuel pump vacuum and pressure to make sure all is well.
I do not think they could have set the floats too low in carbs to cause them to run out, as the pump should keep up with the amount of fuel as long as there is not restrictions to the fuel going into the carbs

[pintailed]

I kept an eye on the fuel bowl and it stays full. Will try the clear tubing to look for air bubbles but with all of the changes/swaps in fuel lines, bulbs, fittings I am skeptical that I am sucking air - is entirely possible though. I should have eliminated air issues when swaping out all of the different parts (bulb, fittings, lines) right?

[pintailed]

Thanks for the year info!

[pintailed]

Previous mechanic stated that Yamaha's had tiny jets and it was hard to tell if they were clogged or not - and said they were easy to plug with tiny particles? Might the jets be plugged again even after the carb was cleaned/new carb kit? If plugged, I shouldn't be able to keep it running at full throttle by squeezing the bulb should I?

Another possibility, could they have put in the wrong fuel pump? maybe one that is too small or does not pump enough fuel? How universal are these?

[zenoahphobic]

Sounds a bit like the new pump was installed with a leak. Base this on doubting your mechanic not full bottle. Why would he say that Yamaha jets particularly small? It is a small engine so they are small but not really much different to any other similar same number of carbed HP motors.

[pintailed]

Zeno - this is the second "new" fuel pump. Symptoms have been the same with both of them. Thanks for the insight on the carb jets, that helps.

[99yam40]

test fuel pump pressure and vacuum
and put in a piece of clear line during testing at fuel pump to see if there are visible air bubbles in the system