1971, 9.8hp runs at half power

[gmarshall43]

I am working on a 1971 Merc 110, 9.8hp motor. It will start after a couple of pulls and idles nice. Sometimes when I throttle up it will run at full speed. Other times it will run at what I think is half speed at full throttle. This is happening more frequent. I have taken the flywheel (magneato??) off to check the points which are new and set at .020. what confuses me are the two sets of coils. One set underneath the flywheel and one set outside that go to the plugs. Also there is an electronic device under the flywheel, the rectifier I believe. can anyone tell me exactly what these all do and can anyone of them be my problem?

Thanks,
Gary

 

[JAG59]

Re: 1971, 9.8hp runs at half power

I believe the coils under the flywheel creat AC voltage that is stored in a capacitor on the stator. The capacitor discharges the stored voltage when the points close. The rectifier rectifys the AC to direct current and then sends it to the ignition coils to fire the spark plugs. The ignition coils beef the current up to make it hot enough to ignite your gas/oil/fuel mixture when the plugs fire.

 

[gmarshall43]

Re: 1971, 9.8hp runs at half power

Thanks for the info. Can anyone of these be my problem? If so how can I check them? I do check to see if I have spark when the problem happens which I do have.

 

[JAG59]

Re: 1971, 9.8hp runs at half power

I can't give you specific test procedureds for each item as I don't posses that knowledge. I am going through a similar problem on my Merc 40 4 hp.
It just so happened that I had a Mercury Outboard shop manual at hand when I replied to you. I would suggest that you obtain a manual, as well. I have found that it is a lot better than shooting holes in the dark to try and find a solution. I got this one at my local public library which reminds me: It's due back today. There are several good sources for shop manuals that you can purchase on-line. Just make sure that the one you get has a section that is specific to your brand, year, model, and hp. Good Luck.

 

[as-is]

Re: 1971, 9.8hp runs at half power

ok g i am haveing a sem promblem on a 74 9.8 it will run great in barrel but but on boat and with 2 men in 14ft v hull it well run 15 mph then drop to 2/3mpr then back to 15mph rebuilt carb/fuel pump and it stell dose thise i think it is elect. but as of now do not know if you find out before me then post as will i

 

[Chinewalker]

Re: 1971, 9.8hp runs at half power

When the motor drops off on power, try pulling one plug wire off and noting any change in the motor's running. If it stops entirely, then you were running on that cylinder only. If nothing happens, then that cylinder wasn't firing. Chances are your coil is breaking down. Could be cracked (not uncommon) or a bad ground (also not uncommon). You can swap coils (switch wiring top for bottom) and see if the problem follows the coil...
- Scott

 

[gmarshall43]

Re: 1971, 9.8hp runs at half power

When the motor drops off on power, try pulling one plug wire off and noting any change in the motor's running. If it stops entirely, then you were running on that cylinder only. If nothing happens, then that cylinder wasn't firing. Chances are your coil is breaking down. Could be cracked (not uncommon) or a bad ground (also not uncommon). You can swap coils (switch wiring top for bottom) and see if the problem follows the coil...
- Scott

 

[gmarshall43]

Re: 1971, 9.8hp runs at half power

As I stated in my first thread, I see a pair of coils under the flywheel and a pair on the side of the motor that go to the plugs. Did you want me to swap those or the pair under the flywheel or both?

Thanks,
Gary

 

[Chinewalker]

Re: 1971, 9.8hp runs at half power

Just the ones on the motor block - not the ones under the flwheel...

 

[gmarshall43]

Re: 1971, 9.8hp runs at half power

I was checking the coils and I found one of the coil wires coming from the rectifier had a bare spot and some of the wire is exposed. Would this cause my problem? I figure if it was rubing against the block, the motor would stop running.