1967 Johnson 9.5 drops speed in drive

My very dependable motor just started dropping speed while in drive. Starts fine, runs great, but after a few minutes at top speed the engine slows to about 1/2 speed. I cannot recreate the problem in a tub, it only happens on the boat (14' Sears) in a lake. No fouling of the prop or intake - it just bogs down. After numerous experiments, I tried stopping and then re-starting the motor while in drive. Seems to work. I know this is not the best fix - any ideas?

Re: 1967 Johnson 9.5 drops speed in drive

Welcome to Iboats!!


Couple of things things you can do.

1. First check to make sure your vent on your gas tank is open when your are running your motor or that the little hole is not plugged up with gunk or oil and prevent air from entering the tank and allowing the pump to easily pull fuel from the tank. Try running the motor and see if that is an easily fix.

2. If suggestion number one is not the case, then take off the hood of the motor. Run the motor around for a for a while and see if the symptoms return. If the symptoms do not return then chances are very good that you have a exhaust leak. The 9.5hp Johnson/Evinrude motor of that era 1964 to 1973 were known to have this issue. You can do a search on exhaust leaks with 9.5hp motors and you will find a bunch of post on this forum about this subject.

I have a 1967 Evinrude 9.5hp luckily without any current exhaust leaks and it runs smooth and very good.

Please let us know what find out.

If neither is the cause, then start the usual compression, spark, and fuel delivery checks.

Good luck sir and again welcome the forum!!

Re: 1967 Johnson 9.5 drops speed in drive

In addition to the excellent suggestions above, make sure it is not overheating, although you would likely notice that in the barrel.

Re: 1967 Johnson 9.5 drops speed in drive

Thank you both for the suggestions!

When I first had the problem, the first thing I checked was fuel flow. Tank is venting properly, hose and connection are both solid. Squeeze the bulb - no change, fuel filter - good. So then I thought there might some mechanical indication visible if I ran the motor with the hood off. So I stopped in the middle of the lake (risky, I know) and removed the hood. Again - started great, ran fine and then after a minute or two it droppped to about 1/2 or 3/4 speed.

What really has me stumped is the fact that if I start the motor while in Forward Gear, I don't lose power! It will run at top speed, the boat planes well, you'd never know it had a problem!

A friend asked me if I thought maybe it was the ethanol in the gas?

Re: 1967 Johnson 9.5 drops speed in drive

Have you had any recent work done on your lower unit?? Does it kick in and out of gear suddenly when you are planing out?? If none of these symptoms are happening then you may have some type of ignition issue.

Are the coils original? Coils, when starting to go bad or have become cracked will intermittently fail at running temps. The insulation cracks and become compromised. It would be a good thing to inspect your coils, points, condensers, and points. It may be intermittently running on one cylinder. Please check your wires to make sure that are not compromised, cracked or old. You could have a grounding effect. Some members have shown video of there motors in the the dark arcing on the motor.

Here is a link by JBJennings that does any excellent job of describing the tools needed and how to go about doing the inspection and possible replacement of ignition parts.

http://forums.iboats.com/showthread.php?t=294072

You can only adjust 1 point at a time then you must rotate shaft to do the other ,you can't adjust them both at once as one is in the closed position and the other is in the open mode. The rubbing block must be on the high lobe of the points cam (points open) this would be the gap setting position, turn the crank by hand and observe the rubbing block while also watching the points open, the rubbing block will remain on the high spot for a few degrees of turning the flywheel before it drops back off. (Place the flywheel nut on the crank shaft and use a wrench or ratchet set to turn it.) Please make sure the spark plugs are out so you don't accident start the motor.

Don't forget to make sure there is an oil wick in place. Don't want to prematurely wear down the point shoes.



Here is a link to a electronic parts diagram to your motor. (ignition parts can easily bought here at iboats

http://www.boats.net/parts/search/BRP/JOHNSON/1968/MQ-14D 1968/parts.html


Hopefully one of the 9.5hp Evinrude/Johnson experts will bite and give you a hand.


Oh, by the way tx1961whalerhad an excellent suggestion of checking your motor to make sure it is cooling properly. In addition of check to see if sufficient water is coming out of the exhaust relief hole, also check to see if your motor is not becoming blazing hot. Digital laser thermometer are decently priced. Your running temps should not be higher than 165 degree F.

Please keep us posted!