TOPIC: 1967 80HP Evinrude Loss of thrust and shuddering

Motor is a 1967 80HP Evinrude Selectric Shift. Well today I came across a new issue. I road around for a good 5-10 minutes with my mom and brother, came back to the dock, got my dad and grandfather with my brother and we road the same route and right before we got to the dock the motor experience a loss of thrust and seemed like we were "jumping" forward in short bursts. I throttled down, put it in neutral and continued on at a slower speed. Got back to the dock and let everyone off. I thought it might be my selectric wire connectors at the motor. Checked them and they were fine, and then took apart the control box and cleaned all of the terminals in there. Then went for a ride, with just me. Seemed to do fine for about 45 seconds into the ride and then the same problem occurred and wouldn't stop "jumping" until I throttled down. I just put in a new impeller, and I was VERY careful with the wires, I'm sure I couldn't have messed them up. Could I have spun the propeller hub? I didn't have my spare or anything to mark it with to see. I'm hoping it's nothing wrong with the clutch and gears, because the oil is free and clear of any water and the like. What could it be?

If the boat is out of the water you will be able to tell if the prop spun by grabbing it and twisting it to see if there is any play in it. You might want to check to see if you fuel line is not breaking down from your fuel. I had the same problem a couple of weeks ago. There was a tiny piece of rubber in one of my carbs and it just made it run like crap. Best to really clean the carbs good and then go from there. Good luck and keep us posted.Skip. PS, You did use type C fluid right?

The fuel lines are less than 6 months old, and the carbs have recently been cleaned very well. Yeah I have used type C lower unit lube. It only seems to happen under a heavier load like getting on plane and beyond.

So, when you experience this loss-of-thrust, are you getting a corresponding rise in engine speed?

If so, the most likely cause is prop hub slippage. Easy to tell, make a match mark on the bronze center hub, and a corresponding mark on the aluminum prop body.

Take 'er out and run 'er until you get the problem, then check the prop. If the marks have moved in relation to each other, the rubber hub bush has separated from the bronze hub.

If it's not the prop, something may be going on with the electric shift. Is this the style with the "high speed", pointy-type lower unit? Normally on those the locating tang on the forward gear spring breaks, and you lose all forward propulsion. Not as common for them to slip under load, unless really worn out or a weak electrical system. Is the battery fully charged and is the alternator output OK??

HTH & let us know what you find........ed

i experienced this very same thing today! exact same deal. went out, tooled around, went WOT for 15 minutes of so with no problems, then bam, started doing what yours did. lowered throttle and it went away. had to limp back to the dock. no bueno.

only difference... mine's a '58 50 LU with a '65 60 powerhead. manual shift. shift dogs wearing out? took it out of gear, ran the motor up in RPMs and held. no stumbling or anything like that (that was noticable, anyway). back in gear, and ramped up the throttle... clunk clunk.

motor runs fine otherwise, both at idle and WOT.

-Chris

Chris, "clunk clunk" sounds like bad shift clutch/forward gear dogs. My recollection of my old Johnrude doing that was it sounded like someone was beating on the transom with a hammer!

You might check the shift adjustment to make sure there's no slop in the linkage, and that the "bias" on the shift adjustment is set to put a bit more pressure on the fwd gear. This will help hold it in gear and may prevent your in-n-out action.

Unfortunately, once the jumping-out-of-gear stuff starts, it does a lot of damage and usually just gets worse and worse.

If adjustments don't fix, I'm afraid you'll be splittin' that gearcase soon......ed

ed -

figured as much. dreaded as much. i looked at the dogs before reassembling and they looked in tip-top shape. i have the shift linkage adjusted so that it will bury itself in forward. there's no slop and no extra room (at the motor) for it to go any farther forward, even if i wanted it to. i did all that just to avoid this problem. so... does an electric shift have dogs and all just the same and they're only shifted eletronically, or are they completely different? my problem seems alot like La007's... and why only under load? it's as though it's not far enough into forward, but that's not the case. and this isn't the first time it's been wet since i last messed with the LU.

Thanks, and sorry to hijack the thread right off of the bat
-Chris

Chris,

If the popping out of gear can't be corrected by adjustment - they you have little choice but to pull the lower unit. Inside the exhaust tower is a "bell crank" where the upper and lower shift rods meet. I'm not talking about the shift rod connector that attaches to the lower unit. This is above that. There is a pin in there that is known to get slop in it. If the pin has slop, the lower unit will not stay in gear & will "clunk" when power is applied under load. It is a royal bitch to get to it. Lower unit and powerhead must be removed - it's a big job.

Remove the 2 access plates on the motor tower that access the shift coupler. Reach in and hold the shift rod coupler with pliars while you move the shift lever back & forth (cable removed) to check for slop. Also - it the lower unit shirt rod was not correctly seated into the shift coupler BEFORE the couple bolt was installed - that could also be the problem.

Good luck.

Before I left for College, I had the thought of checking my plugs because my Jet Ski's have done the same thing, loss of power and the their plugs were always fouled. The plugs looked pretty bad, except for one, so when I go home next I'm going to get some new plugs and run the old ones till I get the problem, then swap 'em out to see if it fixes it. Could this have been it? I might've been running too much oil in the gas for the plugs to handle.