Cant keep it running over 3000rpm!!!

[fishingman220]

I was out today on my boat, first good cruise this year. well it ran good all day and on the way back it died out, it would start up and run fine out of gear and could rev it up, then once in gear, if you slowly worked it up to 2500, it would die. i had to idle all the way home at 1200rpm. i was sun burnt and everyone was ired and red as lobsters. but once i went and got the truck it died all together and could not get back started. about 2 months ago i had a problem where it would run high but would not idle. i replaced the fuel filter, plugs, wires, cap, and rotor and had he carb re built. any thoughts would be appreciated, Thank you. 96 proline 5.7 merc thunderbolt IV 2 bbl mercarb, colsed cooling, alpha dive gen 2, need any other info???

 

[captmello]

Re: Cant keep it running over 3000rpm!!!

Hummm... Sounds like its not getting fuel. Might want to check the contents of the new fuel filter. Did you adjust the timing? Could the dist. be loose? Could something be working its way loose in the rebuilt carb.
Your situation is a good example of why sometimes you should do only one repair at a time.

Good luck!!

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

i am thinking i will replace the fuel filter, the rubber lines(which i wanted to do anyway) and pull the hard line off the carb and check the filter screen there and see if i can get it cranked up. if that doesnt work i will check the fuel pressure and then rebuild the carb again. any thoughts on doing something different???

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

any other thought??

 

[wca_tim]

Re: Cant keep it running over 3000rpm!!!

What about the tank vent?

 

[TBarCYa]

Re: Cant keep it running over 3000rpm!!!

Check the spark plugs. I had a cracked insulator on one of 4 and it caused similar symptoms. It always started, but wouldn't run high RPMs and got worse as the day went on.

 

[shayne]

Re: Cant keep it running over 3000rpm!!!

Try replacing your water seperator. The new gas made from corn only has a life of 30 days, then breaks down to h20.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

how do i check the fuel vent??, the plugs are about a month old and have maybe an hour and a hlf on them. the fuel that is in it is from last fall, but has stabil in it.

 

[captmello]

Re: Cant keep it running over 3000rpm!!!

If the fuel vent is clogged you can open the cap to the fuel tank to manually vent the tank.

You may want to run a temp hose from the fuel pump intake to a gas can with new fuel to see if your problem goes away. If it does you'll have isolated your problem to the tanks and its various parts.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

ok iwill try that, little busy but i will work on it this weekend and let you know how it goes

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

ok so i just fiddled around on the boat. i pulled the vent hose and blew threw it and suck on it, and no block. then pulled the line from tank at the f/w seperator and blew into the tank to see if there was any obstruction, and it went through fine. then pulled the flame arrestor, and worked the linkage, and there was a solid spray of fuel in to the carb. i guess i will check timming tomorrow night. anyother ideas??? i am going to recheck the wires, and the screen in the carb. i will replace the rubber lines and put in a in-line filter and replace the f/w. if any one has any ideas please let me know, thank you.

 

[TBarCYa]

Re: Cant keep it running over 3000rpm!!!

I know you've already dismissed it, but check the plugs. Even new plugs can get damaged and even if they're not damaged, the electrodes can tell you if the engine is running right.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

i really dont want to, but i will(they are a pain to get too), what do i need to look for?? white? what would be broken??

 

[captmello]

Re: Cant keep it running over 3000rpm!!!

Look for one of them to be different from the rest that would indicate something wrong with that cylinder. Do a compression test if you haven't while the plugs are out.

 

[hoot]

Re: Cant keep it running over 3000rpm!!!

don't neglect looking at the ignition system. could be heat building up in the electronics and limiting rpms and eventually shutting down.

 

[MikDee]

Re: Cant keep it running over 3000rpm!!!

At the fuel tank, there should be a mandatory spring loaded antisiphon (one way) valve, and screen, or filter, on the fuel pickup, make sure both are clean, & not clogged with debri. It is a common problem on older boats, restricting fuel flow as you speed up.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

at the spot where it comes out the tank, it has a 90deg fitting, then a shutoff valve, then i think the anti siphon, it is all really corroded, what is the best way to clean it before i pull it all loose??? it looks kind of like corrsion on a battery. also if the anti siphon was working, should i have been able to blow into the tank with my mouth into the hose where it comes into the f/w seperator???

 

[MikDee]

Re: Cant keep it running over 3000rpm!!!

at the spot where it comes out the tank, it has a 90deg fitting, then a shutoff valve, then i think the anti siphon, it is all really corroded, what is the best way to clean it before i pull it all loose??? it looks kind of like corrsion on a battery. also if the anti siphon was working, should i have been able to blow into the tank with my mouth into the hose where it comes into the f/w seperator???

WD-40 should clean it all up for you. The antisiphon valve is a one way valve, you should only be able to blow through it on the tank side. Be sure to check the in tank pickup for any clogged screen as well.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

there is no way to get to the tank pick up, it is under the floor and only have 3 check plates, one is the pick up, one is sender, and one is the fill, vent.

 

[fishingman220]

Re: Cant keep it running over 3000rpm!!!

i just went out and checked and there is no anti syphon valve, just the 90, the cutoff, and then the hose.