Need help fast

[DareDog]

at camp for the weekend notice the boat (a 1993 Bayliner Capri 20.5' with v6 mercruiser) dose not run right . it takes off fine but it will suddenly loose power, acts like it starving for fuel it losses power at full throttle, after in reaches about 3,500 rpm and ready reach top speed. got full tank of gas, once backed off at 3,000 rpm then runs fine. has electric fuel pump. choke is fully open, carb arrestor is clean.

any ideas what to look at? what type of diagnostics to perform? already checked the fuel filter and its clean. carb has been rebuilt in the spring. thanks in advance

 

[latin monkey]

Re: Need help fast

probably bad fuel pump

 

[Chris1956]

Re: Need help fast

Check or clean the antisiphon valve in the fuel pickup line at the fuel tank. If that doesn't fix it, repost problem in I/O forum.

 

[superbenk]

Re: Need help fast

Check or clean the antisiphon valve in the fuel pickup line at the fuel tank. If that doesn't fix it, repost problem in I/O forum.

A quick cheat is to get a NPT fitting for an air compressor hose (1/4" NPT with 3/8" barb works with 5/16" fuel line). It's the same fitting as an anti-siphon valve except without the valve & it's brass instead of aluminum. If that fixes your problem, you know you need to buy a new anti-siphon valve (it's a safety thing!).

Also check fuel filter(s) & if there is a water separator, drain it into a clear jar, check for water separation in the jar & replace the water separator (I think it's bad to put the old one back on after you've dumped it upside down).

It's possible the carb is gunked up too which means it'd need a rebuild. Last thing I can think of is tune-up related stuff, points, condensor, rotor, cap, plugs, wires, coil, etc.

 

[DareDog]

Re: Need help fast

now where is the anti-siphon valve? is there anything else to use instead of npt fitting? don't have one here at camp.

 

[Don S]

Re: Need help fast

http://forums.iboats.com/showthread.php?t=283269

The antisiphon valve is the fitting in the top of the gas tank that looks like a hose barb that the fuel line attaches to. There is a check valve and spring inside.

 

[DareDog]

Re: Need help fast

checked the valve and its broke but if blew air threw it it comes out the other end still dose same thing with the boat.

 

[Don S]

Re: Need help fast

checked the valve and its broke

Would probably be a good idea to fix it and see if you still have a problem.

 

[DareDog]

Re: Need help fast

yes going to try that get new one then see what happens

 

[chaparall villain 2]

Re: Need help fast

is the electric fuel pump factory or aftermarket marine ... i had an aftermarket marine on mine and it would do the exact same thing ... turned out the pump is designed to push fuel ... not pull it and when under full throttle it couldnt do it with the anti siphon valve ... i went back to a manual fuel pump and havent had a problem since ..... didnt want to remove the anti siphon valve

 

[MNMARK]

Re: Need help fast

Check the fuel filter first, and then the fuel pump. You can test the pump yourself by running 2 wires from your battery. Make sure your pump is dry, take a day to dry it out

 

[DareDog]

Re: Need help fast

how can you tell if its factory or aftermarket marine?

 

[DareDog]

Re: Need help fast

changed the valve and coils still same problem and its getting worse everytime

 

[Don S]

Re: Need help fast

Have you done the tests listed in the link I posted above? Here is the link again.
http://forums.iboats.com/showthread.php?t=283269

If you can't get fuel to the fuel pump, there is no way the pump can pump it.

 

[DareDog]

Re: Need help fast

well today took it to a local mechanic and did few things found out its the fuel pump, slow ride back from town would only go at idle speed no faster. went to 2 boat places and called around for one and no one has one in stock looks like got to get it online any one know good site for fuel pump for 4.3l mercrusier ?

 

[superbenk]

Re: Need help fast

well today took it to a local mechanic and did few things found out its the fuel pump, slow ride back from town would only go at idle speed no faster. went to 2 boat places and called around for one and no one has one in stock looks like got to get it online any one know good site for fuel pump for 4.3l mercrusier ?

http://www.iboats.com

 

[DareDog]

Re: Need help fast

took fuel pump off and replace it with new one Yep still didn't run took card apart and saw needle seat was stuck. fix that and it ran great.