1976 Evinrude 9.9 hp motor will only go to half speed

[playboy 7]

[FONT=&quot]Hello,

I have a 1976 9.9 hp Evinrude motor that has worked perfectly for many yrs.-model # 10624H. Last weekend, at the start of the weekend it was fine, however the following day, I took the boat out and it lost RPMs and now only runs at approximately 1/2 speed, although throttle position can still be moved to full speed. Interestingly, unlike a few other posts I have read here, the engine still runs perfectly at lower (and 1/2) speed, starts in the same manner as always (1-2 pulls). I had extra new spark plugs and put them in but the same issue occurs. Bulb on gas tank is always firm, and there are no other issues I can think of. It is not a critical problem (yet?) but it sure would be nice to have full power again. I am back in the city now, but I'll be heading back this weekend and any input anyone might have would be much appreciated. I am by no means a mechanic, but I will get my hands dirty if needed!

Regards,
Tony[/FONT]

 

[F_R]

Don't fool yourself, they will run just fine on one cylinder, just no power. If it isn't the plugs (usually is), then first check the compression, then spark. But I gotta remind you, those motors were death on spark plugs. Even brand new plugs.

 

[OptsyEagle]

Double post due a very bad technology on the site.

See below for reply.

 

[OptsyEagle]

Yeah, do a cylinder drop test. Start it up and let her warm up. Bring it to a fast idle and with a pair of insulated pliers pull one spark plug boot at a time. These motors will run remarkably well on one cylinder but with about 1/2 the power. So if the motor dies when you pull a spark plug you now know the other cylinder was never working or is very weak.

If it does die when a spark plug boot is pulled you might as well switch the spark plug boots to the opposite cylinders AND switch the clips coming out from under the flywheel to the coils. Do the drop test again and if the problem moves to the other cylinder you have isolated it to be the coil. Most likely it will stay with the same cylinder and that can be a few things. Switch everything back and report back.

An external spark test and a compression test is always useful at these times as well.

 

[playboy 7]

Thank you both for taking the time to respond. I will take another set of plugs out and try what you suggested. I promise to post here to let you know what happens.

Regards,
T

 

[OptsyEagle]

By the way, what spark plugs are you using. These motors go through Champions like candy. Use NGK B6HS or B7HS

 

[playboy 7]

Thanks for confirming. I am indeed using NGK B7HS (I did read on other threads about this recurring problem with Champion plugs). Will respond in a few days with results.
T

 

[playboy 7]

Update:
Sorry for the late reply, I only got back out to my boat yesterday. Firstly, I tested the engine again and it ran only at half speed. I changed out the plugs (new NGK B7HS) and it immediately ran at full speed and worked perfectly. I don't really understand why my new plugs (still in the packaging) didn't make a difference last week when I swapped them in, but the bottom line is that all is good again. I will keep another set of new plugs handy in the future. Thank you so much for your assistance OptsyEagle and F_R. It is nice to know that there is a forum online to assist us who may not be overly mechanical .

Regards,
Tony & my boat---The playboy 7
(if you saw it, you know it was a joke)

 

[OptsyEagle]

I always keep a spare set of spark plugs in my boats that are being pushed by that series of motors. The NGKs work a lot better but if anyone did any serious trolling (a couple hours or so) with that motor, even the NGKs will foul out. Those series of motors are for riding hard. If you were going to do a lot of trolling, try switching to the NGK B6HS.

Other then that it is a great motor. Very dependable and even the few times my NGKs have fouled the other cylinder has always got me home. They never seem to both foul at the same time. I am very thankful for small miracles.

 

[bwkre]

Spent half a season trying to figure out what was going on with mine. Changed a coil, points, condensers and wires. Then my brother said to change the plugs. I told him they were only a couple months old. Change the plugs he said. I did and now I'm a believer. I always carry a spare set ready to go. After a couple miss fires, usually at wot, I change the plugs and all is normal till next time. Other than that it's a great little motor.