Can't maintain power

[rockyrr]

We have a 21' walkaround with a Yamaha 150 4-stroke. After 3 or 4 minutes running it on the water it loses power and we can't get it back up to full speed when at full throttle. We had it looked at twice by a mechanic and he could find no problem. He did clean some filters, but that didn't solve the problem. The mechanic thinks we have a tank with "bad" gas. Recommended that we just run it to use up the gas or have the gas pumped out and replaced. Engine starts fine and runs fine for about 3 or 4 minutes, then loses power (can't get boat up to full speed). Any thoughts or feedback will be appreciated.

Thanks

 

[Bamaman1]

Re: Can't maintain power

You don't say what the age of the motor is, but can they run a scan on the engine? There could be many things wrong.

With 90/10 gasoline, the obvious thing to do on any motor is to change the gasoline and check out the filters for stoppages.

It could also be that the engine is binding up from overheating. Or there could be bearing and gear problems in the lower unit.

If that mechanic cannot diagnose it properly, go to another good marine mechanic.

 

[rockyrr]

Re: Can't maintain power

You don't say what the age of the motor is, but can they run a scan on the engine? There could be many things wrong.

With 90/10 gasoline, the obvious thing to do on any motor is to change the gasoline and check out the filters for stoppages.

It could also be that the engine is binding up from overheating. Or there could be bearing and gear problems in the lower unit.

If that mechanic cannot diagnose it properly, go to another good marine mechanic.

Thanks for the feedback......Boat/engine is 8 years old.

 

[phallgtown]

Re: Can't maintain power

Thanks for the feedback......Boat/engine is 8 years old.

I have a 7 year old F150 with 700 hrs on it, last week end out of the blue i had the same issue. No answers yet to fix it but i have had comments to check the tank vent as it is plugged it can create suction in the tank and the engine will be starved for fuel. I did bring it in to the shop and have not had any feed back yet, but idid aske them to check the vent. I noticed on my motor when the boat is in gear under load it the fuel level quickly drops in the fuel filter to the botom of the fuel filter element then the bulb goes soft. When the motor is idling or in fast idle this doesn't happen only when in gear and under a load.
I have seen positing on some other forums with silmilar problems.
This to me doesnt sound normal. You may want to look at this as well. If i get anywhere with my motor Ill let you know.

 

[rockyrr]

Re: Can't maintain power

I have a 7 year old F150 with 700 hrs on it, last week end out of the blue i had the same issue. No answers yet to fix it but i have had comments to check the tank vent as it is plugged it can create suction in the tank and the engine will be starved for fuel. I did bring it in to the shop and have not had any feed back yet, but idid aske them to check the vent. I noticed on my motor when the boat is in gear under load it the fuel level quickly drops in the fuel filter to the botom of the fuel filter element then the bulb goes soft. When the motor is idling or in fast idle this doesn't happen only when in gear and under a load.
I have seen positing on some other forums with silmilar problems.
This to me doesnt sound normal. You may want to look at this as well. If i get anywhere with my motor Ill let you know.

Do you also have trouble putting in gas?

 

[phallgtown]

Re: Can't maintain power

I have a 7 year old F150 with 700 hrs on it, last week end out of the blue i had the same issue. No answers yet to fix it but i have had comments to check the tank vent as it is plugged it can create suction in the tank and the engine will be starved for fuel. I did bring it in to the shop and have not had any feed back yet, but idid aske them to check the vent. I noticed on my motor when the boat is in gear under load it the fuel level quickly drops in the fuel filter to the botom of the fuel filter element then the bulb goes soft. When the motor is idling or in fast idle this doesn't happen only when in gear and under a load.
I have seen positing on some other forums with silmilar problems.
This to me doesnt sound normal. You may want to look at this as well. If i get anywhere with my motor Ill let you know.

The gas does seem to go in ok, however it just happened and i only topped up the tak the one time. that said the there may have been a little more back pressure at the end than normal as the fuel pump hadd clicked off a few times that i don't recall happening before. If i overfill in the past the fuel pump safety might click off one time and fuel would ususall come out both the fuel intake and the vent. This time it only came out the fuel intake. I do have the motor in to a mechanic and told them this as i was thinking the vent has a block and it could be creating a suction in the tank when the motor is running. Un fortunately they are busy and try to look at my motor between existing repairs they have on the books so I am skeptical how much attention it is getting. the Mechanic did say to check for this he did try a portable tank connected directly to my motor and it still behaves the same as well as he said he did a vacuum or suction test? to check the fuel system and he says it checked out ok. I wanted hem to pull the vent apart as well as the fuel pick up to confirm they are not blocked but he hasn't had a chance. i believe he doesn't feel this is the problem so he is looking elswhere more at the motor as the cause???
I am at a loss, and was hoping to use the boat this week end but i don't think thats going to happen.
does your have a problem with being fueled? have you checked your vent?

 

[rockyrr]

Re: Can't maintain power

The gas does seem to go in ok, however it just happened and i only topped up the tak the one time. that said the there may have been a little more back pressure at the end than normal as the fuel pump hadd clicked off a few times that i don't recall happening before. If i overfill in the past the fuel pump safety might click off one time and fuel would ususall come out both the fuel intake and the vent. This time it only came out the fuel intake. I do have the motor in to a mechanic and told them this as i was thinking the vent has a block and it could be creating a suction in the tank when the motor is running. Un fortunately they are busy and try to look at my motor between existing repairs they have on the books so I am skeptical how much attention it is getting. the Mechanic did say to check for this he did try a portable tank connected directly to my motor and it still behaves the same as well as he said he did a vacuum or suction test? to check the fuel system and he says it checked out ok. I wanted hem to pull the vent apart as well as the fuel pick up to confirm they are not blocked but he hasn't had a chance. i believe he doesn't feel this is the problem so he is looking elswhere more at the motor as the cause???
I am at a loss, and was hoping to use the boat this week end but i don't think thats going to happen.
does your have a problem with being fueled? have you checked your vent?

Yes, we have a problem when we add gas....have to be real careful or gas overflows. I know very little about the vent (don't know where it begins or ends; and, not a clue as to how to check/clean it).

 

[phallgtown]

Re: Can't maintain power

Yes, we have a problem when we add gas....have to be real careful or gas overflows. I know very little about the vent (don't know where it begins or ends; and, not a clue as to how to check/clean it).

I am no mechanic, but your does sound like a vent problem. If your vent is clogged or pinched there is no where for the air to go as the tanks fills other than out the fuel intake and all over your!. My vent is only a few inches away from the fuel intake, i would think most boats are the same. When I pump has in you can here the air coming out of it. it should jsut be a little fittling outside of your boat with the hole on the bottom so rain doesnt fall inside, and should have a hse clamped on the inside. take the hose off and should be a ring you can un thread then pull the vent out, check for blockages, maybe a bug got in and made a nest, or look for kinks in your vent.
Hope this helps.

 

[schematic]

Re: Can't maintain power

Engine starts fine and runs fine for about 3 or 4 minutes, then loses power (can't get boat up to full speed). Any thoughts or feedback will be appreciated.

Thanks

Try running with filler cap loose to answer tank vent suggestion. If no improvement, its not the vent.....

Is it possible that its overheating and going into limp mode?

 

[phallgtown]

Re: Can't maintain power

it was my fuel injectros, # 4 was stinck real bad. As soon as it was cleaned worked great. Not sure why the injectors don't let the fuel bowl fill as to me that was miss leading, always figured one to the cylinders were not firing correctly.
To any one else with this issue, once you try a portable tank and by pass your entire fuel delivery system to eliminate that part of the equation go straight to your injectors,
thanks everyone for all the help!