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Old 09-07-2017, 07:43 PM   #1
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Mercury 9.8 thunderbolt outboard only half throttle

Its a late 70's early 80's merc thunderbolt 110 9.8hp. I can look up sn if needed.

Anyhow it starts and I can get half throttle then it cuts out every time in the water. Carbs I have pulled and cleaned.

Points looked a little cooked. (Points and condensors just a little before me) think its worth it to throw points and a condenser at it?
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Old 09-07-2017, 08:40 PM   #2
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certaintly worth the effort. but to be a Debbie Downer, I remember about 10 15 years ago stopping at Praire Du Chien Wisconsin on a trip home to get a merc 110 looked at (about 1969) vintage at a place known as fishing motor experts tell me that points were no longer available they filed what I had and reset the gap. ran good afterward so I never researched parts. sold the motor a couple years later. hard to believe there parts not available but its been nearly 60 years.
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Old 09-07-2017, 09:02 PM   #3
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Ill try it between now and spring. Its worth it.


Already filed the points slight improvement. Had to replace the 10 ga wiring between the points and coil packs to. They were all dry rotted to. She fired up when she was given to me all dead. Good project motor.
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Old 09-07-2017, 09:26 PM   #4
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Sorry to say so but but while cleaning the carb ... wait you say "carbs" as in more than one. This can only be a two stroke two cylinder engine. Almost certian it's a single carb engine.
Anyway It's real easy to reassemble carbs making mistakes. Been there done that. Check gaskets, float, pin and adjustments looking for other assembly ways to go astray.
Just my guess but it sounds like the secondary jet passageway isn't passing fuel. Low speed jet and passageways seem to pass fuel and permit normal running but not the high speed system.
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Old 09-08-2017, 03:47 AM   #5
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To carb, how was it cleaned? Sprays and many so called cleaners totally useless on dried out deposits. Only a soak overnight in a real cleaner like Gunk will get those deposits.
Not just the primary wire but high tension wire can be bad. Just off idle will run ok but as speed and power rises cylinder pressure rises leading to need for higher high tension voltage which is when the spark leads will start to fail. Old high tension leads may not stand up.
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Old 09-08-2017, 05:56 AM   #6
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One carb yes 2 cyl single carb. Never soaked it but pulled all of the jets.

C lectric I have replaced the wires between the points and coil packs if those are the high tension wires. First thing I did to it. Had to befor starting. All the insulation was dried up and cracking off.
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Old 09-08-2017, 07:36 AM   #7
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Mercury 9.8 thunderbolt outboard only half throttle

I've got a late-'60s 110 with only 25 hours on the clock: bought it from an old boy in Vancouver - was still in the box, never started, 'cos when he took it home from the store in '67, intending to take his grandchildren boating, his wife said "no you don't"! So it sat there for 46 years. I love it, and after replacing the old float with a plastic one, it runs perfectly. Point is, I had no problem getting new gaskets, needles, and so on, and I'm sure all the ignition-related parts will be available. Find a good local dealer. Failing that, Park Presidio Marine in SF will have everything in stock, and will ship. That's where I made up my spares kit. (415) 821-2628
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Old 09-08-2017, 10:18 AM   #8
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Late 70's merc has electronic ign with "maker" points, not classic ign with "breaker" points. But basically they do similar stuff. Check that you get spark from both coils. If so, points are doing their thing. These points can wear badly, get filed and go right back to work. Even if contact surfaces look horrible they will still work fine if making contact. Common after cleaning to get just a little debris in the contacts that will initially cause poor connection. Set gap around 0.020".

I had a 7.5hp from 1972 and ran that thing up until 2015 in saltwater. Bought it when I was 14 in 1978. Would have run longer but got stolen right off my jonboat. Rat bastard. Never bought points for it ever. 37 years of use, pretty good in saltwater!
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Old 09-24-2018, 09:23 PM   #9
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Not to dig up an old thread buuuut I've now begun again to tinker with this 9.8 again. Sn# 3487095. So I want to check the condenser. It never sounded like one of the coils were bad when I had it going. Carb I'll pull again and soak it this winter.

Just a small update to this motor.

"Bassey" got a little love to. Dropped lower end for impeller this winter and lower oil has been drained and refilled.Click image for larger version

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Old 09-24-2018, 11:40 PM   #10
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The high tension leads are the heavy wires running to the plugs themselves.
They may have to cary upwards of 20000 volts, maybe more. If the insulation is poor or the wires are too dirty the voltage can leak off at some point meaning the spark plug does not get the full charge so at some point power drops off.
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Old 09-26-2018, 12:45 PM   #11
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Quote:
Originally Posted by C lectric View Post
The high tension leads are the heavy wires running to the plugs themselves.
They may have to cary upwards of 20000 volts, maybe more. If the insulation is poor or the wires are too dirty the voltage can leak off at some point meaning the spark plug does not get the full charge so at some point power drops off.
Ok the spark plug wires from the coil to plug. (That's what I always call them) May not be a bad idea for a fresh pair. One night I'll clean the carb again it's off then I'll look for a barrel I can stick this in so I have the back pressure from the water.

First boat purchase will be impellar for my 70hp Johnson on bassey. The merc is what I can tinker with as I picked it up pretty cheap and it was not running. It's kinda a project motor to tinker with and learn outboards more. More to come as I put more time into it.
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