70hp running weak - suddenly

[richardbrown67@yahoo.com]

My 1980 J70ELCSA started running at about 30% across the power band today, after running strong all summer. All afternoon today I tried all the regular stuff - disassembled and reassembled fuel pump - no change. Swapped with another fuel pump - no change. Tried different gas tank - no change. Tried different fuel line from gas tank - no change. Checked all fuel lines for leaking, including small lines to carbs - no leaking was evident. Bulb pumped up fine. Fresh gas and oil mix. Strong blue spark on all 3 cyls. 120 lb compression on all 3 cyls. Motor has new timer base, stator, rectifier, power pack, coils, wires, plugs, thermostat, all OE parts. Water pump is strong / telltale has strong stream, motor is not overheating. Carbs have new seats and needle valves, OE. Choke works properly. Throttle box and cables work well. So - what am I overlooking? Thanks in advance... Richard

 

[Haffiman]

Re: 70hp running weak - suddenly

Might be a blocked main jet or a main jet not 'starting' due to a defective gasket (air-leak) or blocked jet.
Try running with front carb cover off and spray fuel/oil mix into the carb throats, one at the time.
Even try very shortly to block each carb throat and notice the difference. This should lead you into which carb/cylinder not working if a fuel issue.

 

[JB]

Re: 70hp running weak - suddenly

Oh my stars!!

You have wasted a lot of time and bux, Richard. Replacing parts is the most used, most expensive and least effective troubleshooting method known to man,

Do a Link' 'n' Synch', by the book, then a compression test, again, by the book.

Good luck. Let us know what you find.

 

[richardbrown67@yahoo.com]

Re: 70hp running weak - suddenly

Thanks - that sounds like a good way to assess the carbs. I'll let you know what I find out.

 

[richardbrown67@yahoo.com]

Re: 70hp running weak - suddenly

Agreed on the link and sync - I'll check out those things as well. What has me puzzled is the sudden loss of power - ran great for months - then suddenly no power.

The parts replacements were related to different problems and an overall need to upgrade the engine. It was quite neglected and I want to use it long-term, so while I replaced the necessities (cracked stator, fried rectifier, crumbling plug wires) - I replaced all the electrical parts.

 

[richardbrown67@yahoo.com]

Re: 70hp running weak - suddenly

Also - fortunately I owned the extra fuel pump, gas tank, and fuel lines from another boat. I guess it looked like I went crazy buying stuff - not the case.

 

[boobie]

Re: 70hp running weak - suddenly

Is your timer base advancing? Did any linkage fall off?

 

[richardbrown67@yahoo.com]

Re: 70hp running weak - suddenly

Haffiman - wherever you are, THANKS!

I sprayed gas mix into the carbs just as you said. #1 carb wasn't getting gas - easy to diagnose according to your directions. Took carb off, disassembled, shot some carb cleaner through all the jets, blew out fuel line, reassembled, and the motor ran like a champ. No trip to the mechanic, no repair bill. Thanks again, Haffiman!!

Richard