Home › Forum › Ask A Member › 1969 Mercury 9.8 lack of power in forward
- This topic has 14 replies, 6 voices, and was last updated 1 month ago by crosbyman.
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November 7, 2024 at 5:28 pm #291976
Take your spark plugs out and look at them. If it’s running on one cylinder, the plug not firing will be wet with the gas/oil mix. These motors will run pretty smooth on one cylinder.
Dave
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November 7, 2024 at 6:50 pm #291980just some interesting reading on Merc ignition
https://wrcoutboards.org/wp-content/uploads/2021/02/The-Phase-Maker-CDI.pdf
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November 9, 2024 at 10:08 pm #292026My advice is that you check your points and try to get a stronger spark, install new spark plugs, check compression on both cylinders, and otherwise pursue the notion that one of your cylinders isn’t firing well when your motor is under load.
Thanks Jim, this is exactly what the problem is, lack of spark or low spark in forward for the top spark plug. The funny thing is that it works perfectly in the test tank, but in the water back to low power. What I found was the RPM when in the test tank was like 5500rpm in forward or reverse. But in the lake, 3650 max forward and 4300rpm in reverse.
Take your spark plugs out and look at them. If it’s running on one cylinder, the plug not firing will be wet with the gas/oil mix. These motors will run pretty smooth on one cylinder.
Thanks Larry, the top plug is wet (especially after being in the lake), so I have (with all of this help) found that the top plug is not sparking enough or is arching out under a load.
just some interesting reading on Merc ignition
https://wrcoutboards.org/wp-content/uploads/2021/02/The-Phase-Maker-CDI.pdf
Thanks Crosbyman, I am in the process of reading this, it is very interesting to me. My Merc appears to have a standard magneto setup. So, I guess I will be cleaning the points, checking the plug wires and replacing the plugs. Thank you all for the help on this so far, I feel that I am getting close now and hope to update this and say that it is fixed soon. I will keep you all posted and thanks again!
Gerry
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November 10, 2024 at 8:59 am #292027https://wrcoutboards.org/magazine-articles/
see articles from mr. Mohat … all you need to know on ignition concepts
regular magneto ( not phase maker ) is even simpler. I refurbed 4 small Mercs and ignition wise they all worked fine.
check resistance from boots to engine frame ..compare results
capacitors can test ok with small meters but fail under real life … see article on testing caps.
you can always do the capacitor BASIC test by unbolting the capacitor and doing a basic resistance/short test ….
on a analog meter the needle swing test will ormally will swing towards 0 ohms then gradually work up to infinity as the cap. charges up .,
How to Test a Condensor on a Vintage Outboard Motor
Mercury 9.8hp 110 and Mercury 7.5hp 75 With Points Ignitions, Setting Points
btw 5500 rpm in a thank ?? …is agood way to destroy your investment !! better wear a face mask 🙁
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November 10, 2024 at 11:32 am #292030FYI …something to check …closely btw what is the exact model# and ser# on the plate
71′ Mercury 110 (9.8hp) spark problems | Aluminum Boat & Jon/V Boat Discussion Forum
336-3981 Mercury 3.9-20 HP Outboard Insulator Blocks | Green Bay Propeller & Marine LLC
Need help on rewiring points on a 7.5…. | Boat Repair Forum
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