Runs with muffs but not in water

[ktryan]

Hi guys, i need a little help. im pretty new at dealing with boat motors, so im hoping this is an easy fix (like there is such a thing) anyway i have a 1977 70hp evinrude that runs great hooked to muffs never dies or bogs down no matter how much throttle i give it. but when its in the lake i can go about 2mph and if i give it anymore throttle it dies. it always starts right back up with no problems. i have tried different gas tanks and lines. any help would be appreciated.

 

[the machinist]

Re: Runs with muffs but not in water

Probably only running on 2 cylinders. Check you spark plugs or spark jump on each plug wire with a spark tester

 

[metriccrescentwrench]

Re: Runs with muffs but not in water

It's a whole different world between running on muffs and running in the water. When running on muffs there's zero backpressure on the exhaust, when in the water that's not the case and the engine has to overcome all that backpressure just to keep running.

Did this engine just start acting up, or is this something that you just recently bought?

First check the basics. As mentioned purchase a variable spark tester, they're around $15 or so at most any auto parts store. Set the gap to around 7/16" (that's what most manuals say to check it at) and make sure there's a healthy spark on each cylinder when you crank the engine.

Next check the compression on each cylinder. They should all be within about 10% of each other. If you don't already have a compression gauge they're also available at most any auto parts store.

Check these basics then report back on what you find.

 

[ktryan]

Re: Runs with muffs but not in water

i did just buy the boat. i will get the testers this week and do the tests. ty for all the info .i will let you know what i find out

 

[kevinlabrie]

Re: Runs with muffs but not in water

im having similer problems also

So here's the scoop. Bought a motor from buddy with a blown timing belt. 1971-2? 50hp 500 2 stroke thunderbolt ignition red stripe. Ad said new belt and water ready......but upon tearing the motor down, realized the distributor bearings were siezed. Replaced bearings and rebuilt distributor. Distributor button is keyed to the timing pulley and both that pulley and the flywheel have factory timing marks so im sure im okay there. tore the carbs down and cleaned but not sure if i set the jets back exactly right, (i counted rotations out, tried to set back in the same) having a hard time finding content on the net to find proper specs. checked fuel pump and water pump, working fine. so i rebuilt the motor and she turns over beauty with full throttle and no choke. i can throttle her back a bit, but cant get the low RPMs to engage the gears. (actualy i did at high RPM, and seem to have acceleration control but i know this is not good). took it in the lake to try it out and still starts out water but when it under load i cant turn it over. I started it trimmed up, full throttle, and sunk it and it continued to run but when i touched the throttle it died.i think my problem is in the carb tuning and the spark advance timing. Im trying to re-do the carbs properly, just tore them out 30mins ago (any free manuals for specs??), and found a good link for setting spark advance and idle/throttle/carb stops. new spark plugs, new gas tank, new battery. got my blood and sweet in this one, need help. Oh just got back in from the driveway and found a blown out hole in the block, i think on the bottom cyl, and and arm on the shift selector has been sheared off. anything will help

 

[boobie]

Re: Runs with muffs but not in water

I Think you're in the wrong part of this forum as this is for Evin and John mtrs. Read the forum rules at the top of it. It's not polite to hi-jack a post by another person.

 

[ktryan]

Re: Runs with muffs but not in water

Got it figured out. friend of mine has a brother who is a boat mechanic and he stopped by and looked at it for me. he saw right away that the exhaust manifold gasket is bad. dont know how i missed water coming out of a bolt head lol. got them on order so ill see in a week if thats all thats wrong.