My1984 procraft/1984 merc 150 has some type of fuel restriction problem. The motor starts great, idles smooth, and has great pick up.

As soon as I get 1/8 mile or by the time I am trimming out to WOT the motor starts to stumble, then stall.

The items I have checked or replaced:

New tank pick up tube

Confirm tank ventilation

Eliminated anti-siphon tank valve

Replaced fuel lines from the tank fitting to the fuel pump

Replaced primer bulb (installed correct direction)

Replaced fuel pump (rebuild kit)

Replaced fuel lines from the fuel pump to the carbs

Replaced gas with fresh 89 octane / quicksilver lube

The water separator is currently bypassed - running from tank to fuel pump - removed gas hose coupling and recepticle

The gas tank gas was emptied and I visually looked into the holes into the empty tank and it looked clean. I also took a digital picture of the empty tank through the hole so I could really examine it on the computer by zooming in. I could not see anything that might be causing a problem. The tank is not able to be easily removed.

Although I cant see anything, I suspect the problem is there.

Any suggestions on a cleaning method or something I overlooked?

Kevin

Are you sure it is a fuel problem?  If these problems go away after it cools down it sounds like a thermal problem.

Other things to check:-

Ignition - could be getting weak as the temperature rises.

Friction - could be a bearing problem as temperature rises, when it stalls check that it still rotates free and is not bound up.

Thermal shutdown - Locate/replace the high temperature shut off thermostat, it may be faulty and have a marginal connection at operating temperature that interrupts the ignition for a while then opens up although this would normally also trigger an audio alarm.

Oil pressure - depending on your engine it may have an oil pressure monitor that shuts it down.

After the motor stalled, I checked the primer bulb and it was flattened.

The bulb returned to normal after a 20 seconds.  

For the bulb to go flat like that, it would mean that the fuel pump is working well, pulling a good vacuum, and that the problem is an obstruction in the fuel line.

I will ask my mechanic about the other points you brought up.

Thanks Ann Marie

Oh, I forgot to mention, the motor will start back up right away.

It usually runs rough for a second or two until the gas gets to all the carbs, then she runs smooth.

I dont think it is a thermal problem, it has a newer water pump and thermostat  (less than 1 year old).

The electrical collar (dont know the name) and wiring around the top of the powerhead was replaced two years ago. It has been running great until this recent problem.

here is what i think......i see ya confirmed gas tank ventilation........i had a lawn mower that would start and run fine for a few minutes and then shut down.....i would remove gas cap and reinstall.....the mower would run fine for a few minutes then shut of again....come to find out the vent hole in the gas filler cap was plugged up......fixed the vent hole and it is still running great.....perhaps the vent tube or hole in the cap....if it has one... is plugged and want let it draw fuel.....just my 02 cents

My1984 procraft/1984 merc 150 has some type of fuel restriction problem. The motor starts great, idles smooth, and has great pick up.

As soon as I get 1/8 mile or by the time I am trimming out to WOT the motor starts to stumble, then stall.

The items I have checked or replaced:

New tank pick up tube

Confirm tank ventilation

Eliminated anti-siphon tank valve

Replaced fuel lines from the tank fitting to the fuel pump

Replaced primer bulb (installed correct direction)

Replaced fuel pump (rebuild kit)

Replaced fuel lines from the fuel pump to the carbs

Replaced gas with fresh 89 octane / quicksilver lube

The water separator is currently bypassed - running from tank to fuel pump - removed gas hose coupling and recepticle

The gas tank gas was emptied and I visually looked into the holes into the empty tank and it looked clean. I also took a digital picture of the empty tank through the hole so I could really examine it on the computer by zooming in. I could not see anything that might be causing a problem. The tank is not able to be easily removed.

Although I cant see anything, I suspect the problem is there.

Any suggestions on a cleaning method or something I overlooked?

Kevin

I have some similar problems with my 1967 Evinrude Starflite 80 hp. I have done all the things you have done. Found a loose fuel connection there fuel line attaches to fuel pickup on tank, and my glass fuel filter cartridge wasn't screwed together tightly. Now I can't get it to idle. No matter how I adjust the low speed jet screws, once the rpm drops, the motor sputters, or backfires , and dies. It will run at higher rpm, but not at idle speed.??????????????

You listed that you replaced the tank pick-up tube. Are you sure that it has enough clearence off the bottom of the tank, that is if it is a ridgid tube?

I measured the old tube and cut the new one to the same size. I changed the tube because I though I was loosing vacuum where it attaches to the fitting. After changing it, I still had the same problem.

I am going to drain the gas again this weekend. I am looking for a liquid product that will neutralize the gasoline. My plan is to use a old shop vacuum with a PVC pipe on the end to suck out any debris and liquids that might be present on the bottom of the tank. While I am in there, I am going to cut the tube 1/2" shorter so it will not be on the bottom.

Any thoughts?

Anyone know of a product that will neutralize a little bit of gasoline?

A couple things.

My Yammie used to do something similar.  The culprit was the fuel line connector fitting right at the engine.  I took it off and ran the fuel line through the hole the fitting used to be in in the cowling and straight to the fuel filter inside.  No, I can no longer pull the fuel line and let the engine run the carbs out of gas but that's never been a problem.  One last thing, the fuel line attaches straight to the fitting on the gas tank and has a hose type clamp right?  It's not a snap on fuel connector that allows you to take the line on and off?  

I measured the old tube and cut the new one to the same size. I changed the tube because I though I was loosing vacuum where it attaches to the fitting. After changing it, I still had the same problem.

I am going to drain the gas again this weekend. I am looking for a liquid product that will neutralize the gasoline. My plan is to use a old shop vacuum with a PVC pipe on the end to suck out any debris and liquids that might be present on the bottom of the tank. While I am in there, I am going to cut the tube 1/2" shorter so it will not be on the bottom.

Any thoughts?

Anyone know of a product that will neutralize a little bit of gasoline?

Let that tank air well before you put a shop vac anywhere near it. Ka-Boom.

I will wear some extra sun block and have a few fire extinguishers handy.... LOL just kidding.

I decided against the vacuum idea because I could not find anything to make the gas inert and non explosive.

I did make some calls and there is a guy locally that can drain the tank and clean the bottom.

Better safe than sorry.

Thanks for the help and I will let you all know how it turns out.

A couple things.

My Yammie used to do something similar. The culprit was the fuel line connector fitting right at the engine. I took it off and ran the fuel line through the hole the fitting used to be in in the cowling and straight to the fuel filter inside. No, I can no longer pull the fuel line and let the engine run the carbs out of gas but that's never been a problem. One last thing, the fuel line attaches straight to the fitting on the gas tank and has a hose type clamp right? It's not a snap on fuel connector that allows you to take the line on and off?

I bypassed everything. The fuel line runs from the pick up tube straight to the fuel pump. When I hit the gas, then about a 1/8 mile later near WOT, the primer bulb is flattened and the motor is starved.

It could also be the check valve right on the primer inlet.

How did you confirm the vent on the tank. I had one that the hose between the tank and the vent topside had seperated. You could blow through it and smell gas. But apearently the lineing would colapse and not allow air movement. Loosening the fill cap and having the primer expand is what finaly made me check the vent closer.

Glad you didn't use the shop vac on the tank.

I had the tank cleaned by a professional and my boat is running great again. The money I spent was definately cheaper than a trip to the ER with 3rd degree burns LOL

There were clear silicone chunks and small cookie sized pieces of clear silicone as well as black gasket parts and sealers trapped in the cleaning filter.

Thanks to bruce at gunn marine in ft lauderdale

In the pre-ethanol era, lines , gaskets, sealsetc. were made of rubber materials that degrade rapidly when exposed to fuels containing ethanol. It seems you have dealt with all the external items but there is much internally that must be replaced. Just my personal experience.