OMC 4.3 fuel probem. Need your opion.

[bigbasty427]

Ok car guy here so bare with me.
We picked up a 1988 Doral Tara a couple of months ago and we have had some fun for sure. Been on this site many times to read up on the boat and stuff and thank you all for sharing here and helping others. So here is my problem the best i can explain it.

Was out on the boat seeing what MPH i could get it up to before i change the points out with a new electronic ignition. Well I did hit my best MPH but on the way back the boat lost power. It was still running but had no balls. I pulled back on the throttle till it came back to life. I could cruz at 2500rpm but anytime i tried to give it more gas it would just fall on its face. It idled fine. ran fine till i gave it to much gas. First thing i thought of was filters needed to be changed. so ok, got it back to dock and changed the carb filter and the water separator filter. went out real quick and found it running just fine. Less MPH then the last time but not by much. maybe 2-3 mph. So figured i got it and the loss of MPH was because it was getting more fuel then before now the filters have been changed bla bla. Wont bore you with why i thought that. So next day i set out with the fam to go tubing. I get about 10 min out and it did it again. the motor sounds fine. If i stop and let it ideal then try again it rev's for a bit then falls on its face again. In my head its not getting enough fuel and i am draining the boat dry. Thats why after sitting its fine again for a lil. So pump is working but maybe its not able to keep up with the demand under WOT.

What do you guys think. am i on the right path or is this a boat thing that i am missing?

I will soon maybe today go get some stuff to install a pressure gauge after the pump to see if the PSi is low. IF that checks out not sure what to do. Its not like i can drain the boils testing it in the driveway.

The motor is said to have 350 hours on it and the boat itself has 1025 hours.

Thanks for your time and sorry for the long winded post.

Rich

 

[bruceb58]

Just to make sure you don't have a tank venting issue, run without the gas cap on.

 

[bigbasty427]

Can try that next time i am out. Maybe able to think of a test for that in the drive way too. Heading out to get some stuff to check the PSI pump. guessing it should be around 4-6 psi?

 

[bigbasty427]

Well it has 6psi so that shouldn't be it. checked the vent as well. Its flows free.
Well going to give it some more thought i guess,
May take it out next weekend one last time before i put it away to test the ignition system i just put on it. Maybe i will take an electric fuel pump and some other stuff to help figure it out. Just hate i have to go all the way to find out whats what. lol

Thanks for your help

Rich

 

[bruceb58]

You have to test it under load when you have full fuel flow.

 

[Maclin]

Did you dump the water separating filter to take a look and see if it had trapped any water?

 

[jerryjerry05]

In the tank: there should be an anti-siphon valve.
Remove it and see if the tube has any blockage or junk in the tank.
Being as it's an 88 be careful with the screws, clamps, anything that can strip.
My neighbor "only changed the fuel tank sending unit" and stripped out fittings and was down for 2 months until he gt the right parts to fix it.
The carb might have a filter in it.
The new electronics.They working correct?
The distributor tightened down?
The coil not getting too hot?Should be able to keep your fingers on it.

 

[bigbasty427]

Yes changed the filter in the carb as well as the water separator. Did not pay much attention tho to what i seen at the time as i was convinced it was a fuel filter plugged. I think i will hard line a fuel gauge to the boat so i can keep an eye on it. It did fill up quick and was steady at 6 psi but i understand load is needed to test it right. I have just now put the new coil and ignition in so that had nothing to do with the problem but so far seems to be running fine with the new stuff. I did check the vent to the out side of the boat and it seems to be working fine. will have to look for this anti siphon valve you talk about. Not sure what that looks like. Dont have any on the race cars lol


thanks for the feed back and ideas guys. Much appreciated!!!

 

[Lou C]

On my boat the anti siphon valve caused a similar problem. My mechanic replaced it 10 years ago and its been fine since.

 

[bruceb58]

Run the engine on an external fuel tank. If it still has the same issue, you have a tank/siphon valve problem

 

[bigbasty427]

great guys thanks. I am hoping to take it out one last time this sat. At lest i have some ideas to try.

Thanks again

Rich

 

[HT32BSX115]

Well I did hit my best MPH but on the way back the boat lost power. It was still running but had no balls. I pulled back on the throttle till it came back to life. I could cruz at 2500rpm but anytime i tried to give it more gas it would just fall on its face. It idled fine. ran fine till i gave it to much gas. First thing i thought of was filters needed to be changed. so ok, got it back to dock and changed the carb filter and the water separator filter. went out real quick and found it running just fine. Less MPH then the last time but not by much. maybe 2-3 mph.

Howdy,


There's a great collection of items in the "Sticky" that you could check. You might have a look at the following thread http://forums.iboats.com/forum/engi...69-must-have-technical-information-for-diyers

Focus particularly on item #14!

Regards,


Rick

 

[jbetzelb]

My 89 4.3 experienced this problem after I did the same thing. I decided to wind it up and see what it would do. Shortly after I had a problem where it fell on it's face between 2 and 3K rpm. In my case a new power valve on the carb fixed it. I don't know if I sucked something into the power valve or it got stuck or what. It cost $8 bucks for a new power valve so it would be a cheap item to try. Had to pull the carb to get to it.

 

[HOOKEDONSONICS]

the anti-siphon check valve is located on top of the fuel tank where the fuel line attaches. inside the valve is a spring loaded ball. The valve is designed where the spring pushes the ball closed when the motor is off and is a safety item in case of an accident. Under the suction pressure from the fuel pump, the ball is pulled away (toward the carb.) allowing fuel to flow. Over the years, the spring gets weak and under full / hard throttle, the suction from the fuel pump pulls the ball too far to the other side of the valve closing off fuel flow. Then you are at full throttle for the remainder of fuel in the cab. causing the motor to "starve" and stall out.... "fall on it's face".... These are easy to replace and you can get them at boating stores for about $15. They look like a hose barbed fitting. I replaced mine last year with a brass barbed fitting from lowes for about $2. I did this as a test and my boat ran great afterward. My intentions were only for cheap testing and replacement if that was the problem. Another test you can do. Take the valve off and punch the ball out with a thin screw driver and remove the spring. Then reinstall and go for a test run. Hope this helps.