Home › Forum › Ask A Member › 1978 Johnson 75 hp Stinger stalls when throttled up
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fleetwin.
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August 19, 2015 at 11:20 pm #2312
The motor runs well at idle and will go into gear and run at slow speed but when you try to increase the throttle it will stall.
August 20, 2015 at 12:23 am #22370What boat is it on and what propeller do you have on it?
August 20, 2015 at 12:46 am #22373Watch the throttle arm on the side of the motor as you increase the throttle. Most of the initial movement will be the timer base (spark advance) with only a bit of carburetor levers movement. Once it reaches full spark advance, then the carburetors really open up. What I’m saying is if the carburetors are opening up before spark advance takes place, it will stall. The usual culprit is a sticky timer base.
August 21, 2015 at 7:32 pm #22447Looks like the carbs are opening after the spark advance. I’m cleaning the carbs today and will see if that helps.
August 21, 2015 at 8:18 pm #22450The carbs are probably just going to be dirty but make sure the nozzle gaskets are in place. I remember a DIYourselfer who didn’t put them in a 70 and it had the same symptom.
Long live American manufacturing!
August 21, 2015 at 8:37 pm #22453What are the nozzle gaskets?
August 21, 2015 at 8:45 pm #22455The reason Pappy asked you about the WOT RPMs the motor will turn is because the 75 hp motor has a very peak power curve. Low end power is poor. Depends on the type of boat, but if the boat needs a bit of power to put it on plane, then you have to get the RPMs up or it will just stall. Now all systems on the motor have to be correct, but we (Pappy and I)wanted you to be aware of the characteristics of this motor. It needs to turn a full 6000 at top end to have any bottom end power. The fact the it starts and idles well gives you some idea that the engine may be OK. I had a ’78 75hp on a skiff and ran a 15" prop. We used it for trawling. It would run 6200 empty, but loaded we needed that to get out of the hole. We never ran that boat WOT. It was a great engine as long as you knew its limitations.Super on fuel!
Dan in TN
PS: Sorry I could never figure out how to get that TNT to you for under $100!
August 21, 2015 at 10:39 pm #22468No problem on the TNT Dan, I got one and installed it. As for the motor I cleaned the carbs and still no change. But I did notice the jet in the bottom bowl of the bottom carb one of the sides of the jet is broken off. The part you turn to get it out. Could that be the problem.
August 21, 2015 at 11:43 pm #22473No, unless it was clogged and then the motor probably wouldn’t idle to well on that cylinder. If you can get that jet out I have replacements. I know I can mail you one of those! Just let me know the number on the jet and letter, should be a D jet?
Probably damaged because someone didn’t have the proper tool to remove/install it with. I believe someone has shown how to make a jet tool since the new site has been up. Maybe Mumbles. The official tool is expensive. I have made some out of Craftsman round Phillips screwdrivers. The smaller ones with the shaft that will fit in the carb jet bore. A small ease out should remove the broke jet, but you will have to drill it out some to get even a small ease out in. The worst that could happen is have to replace the carb bowl. Of course you can just leave it be if the jet looks clean and the proper size compared to the others.Dan in TN
August 22, 2015 at 2:07 am #22482It looks pretty good. For now if it’s not causing the problem I’ll leave it in. What else can I try? What about the screws in the top of the carbs? Is there an ajustment for those?
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