Logo
FULL SITE MENU

79 evinrude 100hp weak spark

J

jlove018

New member
"hi, im a newbie to boating, s

"hi, im a newbie to boating, so forgive my ignorance
lol...ill start my story from the beginning...bought the boat about 2 years ago, was told the motor would run but was shot...took it out a couple times and would run and idle but not go very fast at all...did my own tinkering and found there was a weak spark on the right bank...changed powerpack and took it out...boat picked up speed and ran pretty good for about a month...decided to put new battery in and inadvertantly connected battery up backwards (long story)...boat would eventually crank up that way, but ran rough and wouldnt idle...found out what i did and corrected the battery cables, no change in idle and still ran rough...checked the spark and had weak spark on both powerpacks, so i replaced them...no change...weak spark on both new powerpacks...what all could i have messed up when i hooked the cables up backwards? any help would be greatly appreciated...i forgot to mention that i also replaced the rectifier as well..thanks, josh"
 
"Note: Engine must crank over

"Note: Engine must crank over at least 300 rpms in order to energize the ignitiion system properly. A slower cranking rpm will result in weak or no ignition. If cranking rpm is okay, see the following.

Remove spark plugs. Disconnect the large RED connector at the engine. Test spark by jumping the starter solenoid (should jump a 7/16" gap).

If spark is now as it should be, the usual cause is a failied or failing ignition switch.

If spark is still weak or non existent, check the stator under the flywheel."
 
so i unplugged the red recepta

so i unplugged the red receptacle and charged my battery overnight and still weak spark....so im guessing its going to be the stator?
 
"Have a ohm meter set to high

"Have a ohm meter set to high ohms.

There are two sets of wires leading to the powerpacks. One set being Brown and Black/White, the other being Brown and Brown/Yellow.

The ohm resistance between either of those wires should be 560 ohms +/- 75 ohms. Any other reading indicates a faulty stator.

There must not be any reading between any of those wires and ground. A reading here would indicate a short.

However..... Inspect the stator visually. Should there be cracks in it and/or a substance oozing from it, dripping down on the powerhead area.... replace it regardless of what reading you receive.

Note that the flywheel nut must be torqued to 105 foot pounds. Anything less will result in a sheared flywheel key."
 
"so i checked the ohms on the

"so i checked the ohms on the stator yesterday and the left side barely check within spec and the right side was below spec...there were no readings between the wires and a ground, im going to take the flywheel off today and visually inspect the stator and sand it..."
 
"When replacing the flywheel,

"When replacing the flywheel, be sure to torque the flywheel nut to 105 foot pounds. Anything less will result in a sheared flywheel key and damage to the flywheel and crankshaft tapers."
 
"i replaced my stator and now

"i replaced my stator and now have a good spark, but the boat will not crank on its own, it will start with ether, but when i pull the idle lever down a little it bogs down then catches up, i have to do this to get it to idle, its a slow process and sometimes it won't idle..."
 
"Note: Crank does not mean Run

"Note: Crank does not mean Run. The electric starter cranks the engine over in an attempt to start it.

If the engine has compression and spark, I would assume that the carburetors require cleaning.

DO NOT use ether as it has absolutely no lubricating qualities. If you're going to spray anything in that engine, use a spray container that has premix fuel in it."
 
"i was putting the carbs back

"i was putting the carbs back on and noticed the butterfly hardly ever opened at wide open throttle, is that how its supposed to be? or should i adjust it so the butterflies are wide open at full throttle and half open in neutral? thanks"
 
Carburetor butterflies should

Carburetor butterflies should be FULLY CLOSED in nuetral at idle. You need to get a good manual. What is the compression on this motor???
 
"if the butterflies are closed

"if the butterflies are closed at neutral in idle, at wide open the butterflies barely move open at all, just wondering if this was normal, and im not sure of the compression, i'll check that tho"
 
You need to check linkages.but

You need to check linkages.butterflies are fully open at full throttle and MUST be closed at idle.They simply must be closed at idle.
 
"The throttle roller should be

"The throttle roller should be approximately 3/8" or 5/16" in diameter, somewhere in that area. If it is much smaller, it may have been a two piece roller which has had the outer shell break off, in which case, replace it.

The cam that glides against that roller has a scrine mark on it. The cam should contact the roller when that scribe mark is dead center with the roller, not before or after. Adjust the roller simply by loosening the set screw.

When time permits, visit my store at: http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store"
 
"so i finally got it cranked b

"so i finally got it cranked but it ran rough, wont idle and is hesitant to throttle up, has compression on the bottom two cylinders, but not on the top two...i blew air into them and it came out of the intake, no hesitation at all, like a straight through shot...air there any reed valves or somthing in there that might not be closing?"
 
"Shooting air into the spark p

"Shooting air into the spark plug holes..... If the piston is down somewhat and is exposing the intake port, the asir will flow directly thry the crankcase exactly as you state.

What exactly were the compression readings of the numbered cylinders?"
 
Back
Top