Motor goes WOT when disconnected from fuel tank?

[jonbellamy]

I had another thread going, but it became too cluttered and I think it will be best to start a new one. I've been having trouble with my fastwin not going WOT. The boat surges and sputters when I open the throttle, but doesn't have a trouble screaming when in neutral--although it does take a good amount of throttle to keep it in neutral (i have to have my hand on the throttle or it will die out). I replaced the Coils and Condensers and the spark looks good. I ran it in the bucket and pulled each spark plug and it ran fine on each cylinder alone (it actually would start on each cylinder by itself). The last time i did a water test i found out that when I pull the fuel line off the fuel tank the motor picks up and goes WOT until it runs out of fuel in the bulb and fuel line (the fuel tank wasn't suctioned). It actually ran pretty good when it was running WOT so i don't believe it's an electrical issue.

What are the possible causes for this? Fuel pump? Carburetor? I noticed that when I pumped the bulb on the fuel line before starting it the other day I tilted the motor up to get it in the barrel and gas started leaking from what i think was the carb.

I plan on doing surgery on the carburetor next weekend. The carburetor was redone by the "mechanic" about a month and a half ago so maybe he didn't do something right. Do I need a new carb kit if i just plan on opening it up and checking float, needle, etc?

You're help is really appreciated. I've learned a ton since being here on Iboats. I'm definitely a green horn when it comes to repairing boat motors. Sometimes I just wanna call it quits and scrap this motor, but it's something my grandpa passed down to me and the thought of cruising around with the wife and dog (or just the dog :lol have kept me going so far. Hopefully I have enough money left over for gas when all is said and done.

 

[colbyt]

Re: Motor goes WOT when disconnected from fuel tank?

Bad tank vent?????

 

[Watermann]

Re: Motor goes WOT when disconnected from fuel tank?

Year, HP and model of fast twin would be helpful. It's normal to have some fuel spill out of the carbs when the motor is tilted. If you could, borrow someones working fuel tank and the fuel line to test out the possibility that the tank is not venting properly. If the problem still persists look into replacing or rebuilding the fuel pump. Also did the mechanic replace the fuel lines from under the cowl as well?

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

Year, HP and model of fast twin would be helpful. It's normal to have some fuel spill out of the carbs when the motor is tilted. If you could, borrow someones working fuel tank and the fuel line to test out the possibility that the tank is not venting properly. If the problem still persists look into replacing or rebuilding the fuel pump. Also did the mechanic replace the fuel lines from under the cowl as well?

1968 Evinrude Fastwin, sorry just skipped my mind to include it. The fuel line from the motor to gas tank is new, I pulled the vent plug in the tank, and the fuel lines from the pump to carb and tank to pump are also new.

This is when i disconnect the fuel line (i did it several times and it did this every time):

 

[QC]

Re: Motor goes WOT when disconnected from fuel tank?

If I am reading the title right I am thinking you could probably sell that . . .

 

[AlTn]

Re: Motor goes WOT when disconnected from fuel tank?

sure seems like it's in the tank side of things...have you tried running with the fuel cap completely loose or off? I agree with Waterman, if you can borrow a known good tank and hose to try that would sure help.

 

[nwcove]

Re: Motor goes WOT when disconnected from fuel tank?

im still going with what i said in the other thread.....either the fuel pump is dumping fuel into the block, or the carb is flooding the motor. (every two stroke anything ive ever owned will rev up when they start to run out of fuel and go lean). you can easily bypass the fuel pump and connect directly to the carb with a gravity feed.

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

im still going with what i said in the other thread.....either the fuel pump is dumping fuel into the block, or the carb is flooding the motor. (every two stroke anything ive ever owned will rev up when they start to run out of fuel and go lean). you can easily bypass the fuel pump and connect directly to the carb with a gravity feed.

What would be the cause of the fuel pump dumping fuel into the block and how could i diagnose it? I did run the fuel cap completely loose and still same issue. I bought the fuel line from academy sports and it came with one of those quick connect that didn't fit the evinrude connector on the tank so i took it off and put the old fitting on like this: Academy - Attwood? Johnson/ Evinrude/ OMC Tank and Engine End Hose Fitting

A buddy at work suggested taking the fitting off and putting it in a carton or jug of gas. They also believe it's the tank and i sure hope it is.

Also, i have this style fuel pump (don't know if it's original) . It sure looks like sierra 18-7351. Do you guys think this repair kit would work for it: Fuel Pump Kit for Johnson/Evinrude 393103, GLM 40820 - Sierra - iboats

 

[nwcove]

Re: Motor goes WOT when disconnected from fuel tank?

the tiniest pinhole in the pump diapragm will flood whichever cyl the pump gets its pulse from, but dont go throwing parts at it to trouble shoot, trouble shoot properly and you will find the issue. as mentioned, its quite easy to bypass the pump by connecting your existing tank/hose/primer bulb directly to your carb. you will need to have the bottom of the tank higher than the carb tho. if you go that route, take all precautions necessary...ie dont stand up with the tank in one hand while you go to wot!!!

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

the tiniest pinhole in the pump diapragm will flood whichever cyl the pump gets its pulse from, but dont go throwing parts at it to trouble shoot, trouble shoot properly and you will find the issue. as mentioned, its quite easy to bypass the pump by connecting your existing tank/hose/primer bulb directly to your carb. you will need to have the bottom of the tank higher than the carb tho. if you go that route, take all precautions necessary...ie dont stand up with the tank in one hand while you go to wot!!!

I'll start by doing this. I'll let you guys know the results!

 

[Watermann]

Re: Motor goes WOT when disconnected from fuel tank?

Above is some good advice to follow for sure. One other thing, get rid of that gray garbage Attwood fuel hose and shell out for the real deal OMC fuel line with connectors. Trust me on that I had one that turned as stiff as a railroad track in a few months. 10 years later the OMC is soft and supple as new with no leaks at all at the connections. The Attwood tank should be ok, but you never know. It looks like you added an elbow to the tank too.

The fuel pump uses a hole in the block to create vacuum that pulses the diaphragm in the pump and that's how it COULD dump extra fuel into the crankcase. I've seen the problem being that the diaphragm becomes stiff like a piece of leather that doesn't pump the required amount of fuel.

I really like the look of that Fast twin, what's your tinny it's on?

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

Got a couple of questions if someone could help me out. The attached picture shows the fuel lines on my pump. I want to replace them with clear fuel lines and add an inline fuel filter. Do you put the fuel filter on the in-going (to the pump) line or the out-going (to the carb)? Also, I don't see many 5/32 fuel lines like the one on mine going to the carb. Is this a normal fuel line? Could i use something different? What is the normal size of fuel line to the fuel pump? I know the inline fuel filter i'm looking at comes in 5/16 and 3/8...

 

[hogg]

Re: Motor goes WOT when disconnected from fuel tank?

What if????
When you disconnect the Hose from the tank, the fuel pump was suddenly able to get fuel, and the engine loved it so much it went into WOT heaven?

 

[Watermann]

Re: Motor goes WOT when disconnected from fuel tank?

Get a 3/8" inline filter and put it in the fuel line to the tank, downstream of your primer bulb. My problem with clear lines is that you should only use fuel rated gas lines and aren't those clear lines vinyl?

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

Get a 3/8" inline filter and put it in the fuel line to the tank, downstream of your primer bulb. My problem with clear lines is that you should only use fuel rated gas lines and aren't those clear lines vinyl?

You're probably right. I saw somewhere that a guy used a clear line from his pump to carb so he could check and make sure he was getting fuel to the carb; maybe he was just doing it to test. I'd like to change that 5/32 fuel hose but they don't even sell it on iboats.com, wonder if i could use a larger one...

 

[F_R]

Re: Motor goes WOT when disconnected from fuel tank?

1. Forget the clear fuel lines. I hate them. Use the right stuff.

2. You don't need an in-line filter, you already have one. It is under the plastic cover on the fuel pump.

3. Remove the fuel pump from the bypass cover, hoses still attached, and give the primer bulb a squeeze. Does fuel come out the hole in the back of the pump? If it does, the diaphragm is ruptured and is the cause of your flooding.

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

3. Remove the fuel pump from the bypass cover, hoses still attached, and give the primer bulb a squeeze. Does fuel come out the hole in the back of the pump? If it does, the diaphragm is ruptured and is the cause of your flooding.

I'm glad you told me this. My pump looks like the sierra 18-7351, but i don't know if it is original. Will there be a number on the pump somewhere? Could i use this repair kit: Fuel Pump Kit for Johnson/Evinrude 393103, GLM 40820 - Sierra - iboats

 

[milliesdad]

Re: Motor goes WOT when disconnected from fuel tank?

That's a normal run-away lean condition.

Keep it up and you will need a motor rebuild or new motor.

When run lean, there's no oi l(lubrication) to the motor and if continued, you will melt a couple of pistons.

Make your "mechanic" rebuild the carb properly. Check compression and test spark with a spark tester, not by grounding out the plugs and pulling it over.

 

[jonbellamy]

Re: Motor goes WOT when disconnected from fuel tank?

Well guys, I think I found the problem!!!



Gonna get a fuel pump repair kit, but not sure which one to get. This is my fuel pump and it has M 304809 (or 804309) on the back...anyone know this number?

 

[pn]

Re: Motor goes WOT when disconnected from fuel tank?

I vote for all newbies to be required to check their fuel pump before posting it take 10mins and should be standard procedure, also i believe all fuel pump diaphrams are the same for 9-150hp, correct me if i'm wrong.