losing RPM after 10 minutes of running on 260 merc

[fisher person]

first off I just found this site and cant believe I didnt know about it previously. Lots of good info and folk on the board here.<br /><br />My problem is on my 1979 26ft Sea Ray. I have a 260 merc I/O and the boat loses RPM and sounds like it wants to stall out if I run hard for more than 10 minutes, say 3300 rpm. I have to knock down the trottle to 2400 rpm to keep the engine from losing power, and if I run at this speed for another 30-45 minutes, it starts to falter unless i keep lowering the trottle to under 2000 rpm.<br /><br />I've had new spark plugs and wires, timing, fuel filter,coil, and distributor replaced, added new gas. None of this has corrected the problem. <br /><br />Think it might be a carb problem? Someone on another thread mentioned an antispiphon valve or a screen on fuel pickup tube? <br /><br />Anyone will any ideas?<br />thanks in advance

 

[tommays]

Re: losing RPM after 10 minutes of running on 260 merc

the first easy thing to try is to open your fuel filler cap a bit and see if this helps the problem<br /><br />its common for the tank vent to become cloged and this will rule that out<br /> <br />tommays

 

[Bondo]

Re: losing RPM after 10 minutes of running on 260 merc

It's Definitely a Fuel Delivery Issue...........<br /><br />And,...<br />It could be Anywhere between the Vent,+ the Carb.,... But I Doubt it's the Carb.......<br /><br />Possibilities include,.. as you know,.. the Tank,+ it's related hardware,.....<br />The Hoses,+ Lines,...<br />Filters,+ their Housings,...<br />The Fuelpump,..<br />Or Possibly the Carb.....<br /><br /><br />A Fuel Pressure Gauge plumbed in at the Carb. inlet is a Great Tool for finding Your Issues.....<br />4 to 6psi is the Magic # that you're looking for.........<br /><br />Good Luck,........ And Welcome Aboard........

 

[pine island fred]

Re: losing RPM after 10 minutes of running on 260 merc

BY all means, check the finger filter screen in the pick up tube. Its the first thing in line. Amasing how bugs,leaves,etc can clog up that tube. fred

 

[fisher person]

Re: losing RPM after 10 minutes of running on 260 merc

thanks for the advice people, I'll look into fuel tank issue and try removing fill cap to see if that helps.<br /><br />I'm not the most mechanically inclinded, <br />i tried to remove the filter in carb, about the size of my thumb, but couldnet remove the housing without almost severly stripping the bass nut and almost cracking the metal fuel line.Think it might be this filter going to carb??

 

[Don S]

Re: losing RPM after 10 minutes of running on 260 merc

It takes 2 wrenches to remove that filter. A 1" wrench for the filter, and a 5/8" wrench for the line. Disconnect the line (hold the filter with 1" wrench) then remove the filter.<br />Hopefully you didn't crack the line or carb or ?????

 

[ry3100]

Re: losing RPM after 10 minutes of running on 260 merc

hello i am having the same problem on my boat, if you find the solution could you post it. thanks

 

[fisher person]

Re: losing RPM after 10 minutes of running on 260 merc

someone at a boat parts store recommended running the boat until the problem occurs, usually 15 minutes for me. then switch the fuel line to an outboard tank and try that a little and see if the problem goes away.<br /><br />If it does, he says that it's fuel line or gas tank related.<br />That that sound feasible? its worth a try i guess

 

[dubs283]

Re: losing RPM after 10 minutes of running on 260 merc

I am 99% sure your problem is a bad fuel filter in the carb. My boat had the same sympotoms you are describing to a "T". Tried everything you had done prior to checking the carb filter. Replaced the filter for $1.49 and the boat runs like a champ. It sounds as though you had some trouble with the fitting surrounding the housing. My suggestion is to remove anything that is in your way of properly removing the line from the housing to allow the best access to the two in-line nuts. This may require removing cooling hoses and some other componentry but it will ensure you do not damage your fuel line. If you are not comfortable doing this yourself, have a friend who is mechanically inclined help or take it to a shop.<br />Hope this is the fix you need, like I said it sounds exactly what I was gong through and I am now enjoying my boat!

 

[fisher person]

Re: losing RPM after 10 minutes of running on 260 merc

thanks for the info dubs283. I removed several hoses to give me good access to the damn nuts on that housing between fuel line and carb but couldnt budge it w/ 2 wrenches. <br />I have the filter, I'll be calling a professional soon .

 

[ziggy]

Re: losing RPM after 10 minutes of running on 260 merc

fisher person, are you useing a flare nut wrench? the one that has 4 sides and slips over your fuel line instead an open end wrench (contact on only 2 sides). ya can get a better grip on the smaller nut on the fuel line. it'll help ya not destroy the nut on the fuel line too and you should be able to get a bit more torque from that kinda wrench.

 

[fisher person]

Re: losing RPM after 10 minutes of running on 260 merc

ziggy, yes i tried one of those wrenches that have a slit cut in it to go over the fuel line. and i coulnt budge it. Maybe it hast ever been changed out , i was stripping the brass , so i stopped

 

[dubs283]

Re: losing RPM after 10 minutes of running on 260 merc

Try spraying a little JB-80 on the line nut. It is the best penetrating oil I have yet to find. It's called "80" cuz its "twice as good" as the other stuff. (Its actually about 10 times better) Should be able to find it at most auto parts stores, I know Champion carries it.

 

[hearly]

Re: losing RPM after 10 minutes of running on 260 merc

could it not just be water in the tank! or filter being kicked up after the short run!