Topic: 1969 Mercury 9.8 lack of power in forward – Antique Outboard Motor Club,Inc

This topic has 14 replies, 6 voices, and was last updated 2 weeks ago by crosbyman.

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October 29, 2024 at 5:31 pm #291801
TerryTom
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US Member
Hello all,

New here and to outboards in general. I have an odd running problem with my 1969 Mercury 9.8 serial # 2704166. Sorry this is long…. Brief history, about 4 weeks ago I bought a 1960 Rich Line Challenger 15ft semi v with this motor on it. The older gentleman that I bought it from stated it had been serviced at a local marina and he had the receipts to prove it. It had carb rebuild, lower unit overhaul, tune up, etc.. We tested it in a tank prior to the purchase, and it ran well other than it was a little hard to start (several pulls). One of his other comments in the conversation was that the motor did not have reverse. I didn’t think much of that at that point again, this is my first boat/outboard I know nothing about this.

So, the next day my sons (7 and 12) and I take the boat for a test run and a little fishing. The motor started up fine and ran OK up the lake (we had nothing to compare it to). On the way back it dies out, I pump the bowl and it starts back up. Anyway the fuel pump went out, and the only way to get it back was pumping it. I found the fuel pump was cracked and could not find a suitable replacement so, I swapped a pump on it from a 9.9 Evinrude. I also rebuilt the carb at this point since I had it off, soaked it in the ultrasonic cleaner and got it all nice and clean. With these two things it now starts much better and does not die. So, we head out again, it is running fine, but just does not seem very fast, so I check it with gps and it is running 6-8mph.

So I start fiddling with it some and find that if I push the shift lever forward there is a reverse. And when it is in reverse, the engine will rev out. i do not currently have a tach, but if I were to guess it has twice the RPM in reverse as forward. This leads me to thinking that something is swapped or reversed. So, I check everything and can not find that anything is in the wrong place or reversed. The tiller handle does limit rpm’s in neutral, but I can’t see that there is anything that does that in reverse or forward. But there is a noticeable difference in the RPM with the lever in forward or reverse. Does anyone have any ideas as to what to try next? Or know of anything that would potentially “hold” this engine back? Thank you for reading this if you got this far.
October 29, 2024 at 6:50 pm #291803
Gary H.
Participant
US Member
When you put it in reverse, did the boat actually go backwards? You stated that the previous owner said there was no reverse. Is it possible that the lever goes in reverse but not engaging a reverse gear and putting a load on the engine? This could cause the engine to rev higher than when it is in forward gear.
October 29, 2024 at 9:14 pm #291811
TerryTom
Participant
US Member
Hello Gary, Yes, I should have said that as well, it does go into reverse and moves backwards (a pleasant surprise). That is what makes it strange. I will have a tachometer here tomorrow and am hoping to get real #’s. Let me know if you have any other thoughts or ideas. Thanks again!
October 30, 2024 at 11:01 am #291823
seakaye12
Participant
US Member
Does the physical movement of the tiller grip throttle change as you change from Forward to reverse? The motor has a mechanical linkage under the carburetor that should be physically restricting the amount of throttle travel when in Neutral and Reverse. Of course there should be no limitation when in Forward.

Those engines do have an odd shift linkage design. Unlike others…..moving the lever forward (down) gets Reverse and moving the lever back (up) gets Forward. That part is normal.

The other thing that I would look at; if there is no physical limitation of throttle opening in Forward is whether you could be running on one cylinder.
October 30, 2024 at 1:15 pm #291826
TerryTom
Participant
US Member
Hello Seakaye12, thank you for your response. To me it seems to be limited in Forward and Neutral, but not in reverse. So I was wondering if anyone knows how it is limited in Reverse normally (linkage or ignition). I only feel a physical limitation in neutral. By physically watching the movement, it appears to move the same in forward and reverse. I can also see that the ignition system is fully traveling as well as the carburetor butterfly is fully opening in Reverse and also appears to be in Forward.

I also got the tachometer today, so I am going to try to set this up in a test tank to see if I can get some actual rpm readings. I am going to start working on the linkage to see if I can find anything “holding” back. The more I get into this the more I feel that it has been running this way for a while. I remembered one other thing that the previous own said “The trolling motor has more power than the outboard”. Yes, it is a small engine but, it should not top out at 6 mph. I am guessing we have 550-650 LBS in people and gear I will update soon with my findings. Thanks again!
October 30, 2024 at 1:21 pm #291827
crosbyman
Participant
Canada Member - 2 Years
check prop slip if it has rubber sleeve inside. mark it with a felt marker aswell as the prop side … run the engine wot and if they don’t line up after the run the rubber hub is slipping

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October 30, 2024 at 1:26 pm #291829
TerryTom
Participant
US Member
Hello Crosbyman, thanks for the input, I would not have thought of that one. I have a question on this, would this work in a test tank or do you have to have the boat in the water with a “load”on it? Thanks for your help!
October 30, 2024 at 9:07 pm #291839
crosbyman
Participant
Canada Member - 2 Years
try max load on the water where you actually feel it acting poorly

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October 31, 2024 at 10:14 am #291845
TerryTom
Participant
US Member
That is exactly what I will do. I will install this tach and mark the prop, then go and test her out. Thanks for the help!
November 7, 2024 at 5:06 pm #291974
JAMES WILDGEN
Participant
US Member
Hello,
I have the same issue with a 1966 Merc110, so just slightly older than your ’69.

Mine clearly runs on one cylinder in forward but “seems” to run fine in reverse. The thing to remember is at high reverse speed there’s a lot of air entering the blades due to the exhaust gasses. In forward gear these gasses exit the propeller but in reverse they wind up caught in the blades. The motor revs well because there’s almost no load with all those air bubbles disrupting the water.

That said, your (and mine) motor is very likely running on just one cylinder when there’s a decent load on the propeller.

My 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.

Jim

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TerryTom
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