On this 1978 Evinrude 85hp, runs great at high speed or so I think. About 33 mph @ 5500 rpm. Starts good idles somewhat rougher than other Rudes I've had. At no wake speeds it just doesn't feel right (I think most of you know the feeling when something just isn't right) with a sorta rough running and slight vibration in gear. Carbs are clean, new plugs.
Had it out in rough water for a good hour at 3300 rpm so it was warmed up and it ran decent but when coming back into port at no wake speed it ran rougher than before. Doesn't stall. I'm still leaning towards bad coil(s)
Since the motor is almost 40 years old with original coils I'm thinking of just replacing all four of them.
Have you checked the compression? Within 10% between the cylinders?
Take airbox off and idle engine - sound normal? Possible broken feed?
Adjust idle mixture screws - can only get good adjustment in water with lower unit at normal operating depth for exhaust back pressure.
I read your other post on this issue. My experience is bad coil causes misfire while accelerating and on a 4 stroke. On a 2 stroke it will show as a bad idle but typically shows as a plug that will foul after a brief idle, not immediately. Have you checked for hot blue spark when cranking? Really need a spark board, not just holding the plug to ground. Spark should just 3/16" easily.
Managed to squeeze in a compression test this evening. All are between 112 and 115 so I'm good with that but all the new plugs were somewhat fouled.
Pulled the carbs off, there is raw gas in the motor pan under them. Actually looking for a way to adjust the mix but I think they're fixed jets. Didn't see any screws to adjust anything.
What really bothered me was all the hose connections were put on with tie wraps, every one of the hoses were loose and turning on the connections. Probably where all the gas was dripping from. Going to be picking up 12 quality hose clamps and replace everything. The fuel lines themselves are good, not hard.
After engine is warm, adjust each screw one at a time to max RPM then open it back 1/4 turn. Turn each screw slowly and allow maybe 30 seconds for it to stabilize (need time for crankcase to get "saturated" mixture). After doing all 4, do it again.
Ops, looks like your is one of the years with no mixture screws. Instead you need to change the orifice to alter the air jet. That would be #6 I believe. Only did it once & that was on a mid 80s 50 HP.
Went to a local OMC dealer, he didn't have any jets in stock but could special order them. I placed an order for four of them from Marineengine.com. those usually arrive in a few days.
Looks like someone had rebuilt those carbs at one time before. Some scars from screwdrivers and wrenches. The jets were NOT seated tightly but were loose. Wondering if the PO did a rebuild and forgot to tighten everything up or even put in the wrong size since there are three or four sizes depending on horsepower for that particular year.
I did replace all the hose clamps today.
When I rebuild that fuel line mess, I use Corbin clamps. Small spring clamps. I like then because no matter how hot or cold the day, they keep the little fuel line section tight on the T's and other nipples w/o over tightening
Really cuts down on the amount of loose fuel flowing around the engine instead of in the engine
Yeah, sounds like the previous rebuild or carb clean was not a very good one ...