1975 70hp evinrude not reaching WOT

edrandolph · Aug 27, 2010

I recently purchased pontoon with 1975 70 hp.starts and runs great,throttle it all the way up seems to be running about 1/2 throttle,does'nt spit or sputter runs smooth.have checked throttle travel and its going to wot.any help would be great.thanks in advance

Daviet · Aug 27, 2010

Re: 1975 70hp evinrude not reaching WOT

Start with the simple stuff first, compression and spark. If all is good move on to the fuel delivery system.

boobie · Aug 27, 2010

Re: 1975 70hp evinrude not reaching WOT

Agree with Daviet, could be running on only 2 cyls.

jtexas · Aug 27, 2010

Re: 1975 70hp evinrude not reaching WOT

yup, we've all seen that before, classic symptom of dirty carbs, but for sure rule out compression and spark first.

Spark test (not a "spark plug" test). get an inline spark tester (couple bucks at autozone), set the gap for 7/16", clip it to the engine block, attach the plug leads (one at a time) and look for a strong blue spark while cranking. If it can't jump a half-inch gap in the open air without a spark plug, it's not firing in the hole under heat & compression.

edrandolph · Aug 28, 2010

Re: 1975 70hp evinrude not reaching WOT

Thanks will check spark and compression,will let you know results thanks again

joey nathan · Aug 28, 2010

Re: 1975 70hp evinrude not reaching WOT

I also have this engine and discovered after troubleshooting for quite some time that the fuel line coming from the fuel pump and going to the middle carb can become pinched between the air silencer housing and the engine block.

Only takes a second to check it - there's actually a section cutout on the silencer to allow the hose to lie in there without being constricted.

Good luck with it, this engine is awesome when set up properly...

edrandolph · Aug 28, 2010

Re: 1975 70hp evinrude not reaching WOT

did the compression check this A.M.120p.s.i. all 3 cylinders also have good spark,will inspect hose routing also.I am thinking its probably gunked up carbs,think boat has been sitting for a couple of years,fuel was probably left in motor when put away.going to run it some more tomorrow with a little more stabil fuel treatment in it and see if it helps,i realize this is probably futile but want to wait to pull and rebuild carbs as suggested above.thanks to all again for the input

Fed · Aug 28, 2010

Re: 1975 70hp evinrude not reaching WOT

Could be over propped too, you never know what the PO did before you got it.

edrandolph · Sep 4, 2010

Re: 1975 70hp evinrude not reaching WOT

had it out last sunday,ran it down the river probably 8-10 miles still lacking power.got it home pulled plugs out they were replaced the day before,bottom plug nearly clean,rechecked compression good,checked spark good,pulled bottom carb and well it was very gooey inside.cleaned carb,put new needle/seat in it,reinstalled on motor.fired it up sounds like a new motor.thanks for the help,will be back in the water as soon as the gail force wind dies down.

jtexas · Sep 4, 2010

Re: 1975 70hp evinrude not reaching WOT

highly recommend do all 3 carbs...if #3 looked bad the others are not far behind regardless of what they look like to the naked eye -- you just can't see into all the tiny places where fuel has to flow.

The downside to running the motor with dirty carbs is a lean burn, which means elevated combustion temps, which will eventually lead to catastrophic piston failure.

skinners1 · Sep 6, 2010

Re: 1975 70hp evinrude not reaching WOT

Have the same motor (purchased 1 month ago) with the same problem, only when I pulled the carbs they were spotless with what appears to be "new" parts. Appears that these carbs have fixed or no high speed jets in the bottom of the bowl? Compression is 120 across the board, but the bottom plug was clean after 1 hr on the water and the other 2 were slightly discolored. Pulled the bottom carb again and the needle was sticking. Cleaned it thoroughly this weekend and when I blew the fuel intake with compressed air, blew out some carbon, seems to be fine now. Hope to take it out on the water this week and will advise...

jtexas · Sep 6, 2010

Re: 1975 70hp evinrude not reaching WOT

said it before I'll say it again, a visual inspection doesn't tell you whether a carb is dirty. If you got carbon in your fuel, you may have worse problems than you think. Start a new thread...it's too confusing to deal with more than one motor at a time.

skinners1 · Sep 6, 2010

Re: 1975 70hp evinrude not reaching WOT

jtexas said:
said it before I'll say it again, a visual inspection doesn't tell you whether a carb is dirty. If you got carbon in your fuel, you may have worse problems than you think. Start a new thread...it's too confusing to deal with more than one motor at a time.

Yes, jtexas, you have said it before, and it helped me tremendously, which is why I posted the reply that I did. Was not trying to "hi-jack" the thread, simply letting everyone interested in "this" thread know that I also had the exact same problem, and that your advise prompted me to do a thorough cleaning, and helped solve my exact same problem, which is what I thought that the threads were all about. Sorry to all if I "muddied the water".

jtexas · Sep 6, 2010

Re: 1975 70hp evinrude not reaching WOT

misunderstood...thought it was a nuther question, sorry I was short, thanks for sharing your experience

1975 70hp evinrude not reaching WOT

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