Idles fine but as I throttle up, she slows down?

csinger05

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Apr 30, 2007
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3
Ok, I read through a ton of threads similar to mine until my head started spinning. So I decided to start my own...

Here's the deal, I have a 1969 Johnson 85hp, I had it running great for the first few months of summer but the last time I had it out I had an issue getting up to WOT. Initially it started, idled, and got up to speed just fine. I throttled down to idle and putted around the lake slowly a couple times. When I went to get back into the throttle it vibrated horribly, started to sputter and chug, and would not gain power. I brought power back down and it smoothed out and again idled fine. I took it out of gear and started raising power, it revved up fine and sounded normal. So, I tried again in gear, same problem with the no power. It sputtered, made a weird phhst phhst phhst sound while it shot out some smoke, then died. I sat for sec deciding what to do, so I started it and it started and idled fine. I putted back to the launch.

I thought it might be the tranny since it only did this in gear so I took it out of the water, started it on land and put it in gear and revved up...it seemed fine. What's the deal? Why does this only happen in gear in the water? How do I get my baby running smooth again? I have a lot of anxious skiers and fisherman!
 

tashasdaddy

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Nov 11, 2005
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51,019
Re: Idles fine but as I throttle up, she slows down?

start with the basics, check compression on all cylinders, and spark. could be dropping a cylinder, it will sound normal without a load. was it running hot,
 

Boatnik70

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Jun 22, 2007
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Re: Idles fine but as I throttle up, she slows down?

I had the exact same symptoms a few weeks ago with my 1970 Johnson 85 hp, and it turned out that the carburetor high-speed jets were clogged. I bet you'll find you have some sediment in the bottom of your bowls, which is where your high-speed jets sit. Good luck!
 

tashasdaddy

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Re: Idles fine but as I throttle up, she slows down?

Boatnik you may be right, but testing compression and spark are free, before throwing parts at it.
 

Boatnik70

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Jun 22, 2007
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Re: Idles fine but as I throttle up, she slows down?

Boatnik you may be right, but testing compression and spark are free, before throwing parts at it.

Yep, I agree, and removing the plugs and blowing through the high speed jets with carb cleaner and compressed air is also free, requiring not even a gasket. It's always a good idea to baseline your compression and maximum spark gap, in any case.
 

licketdsplit756

Petty Officer 1st Class
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Jun 15, 2007
Messages
318
Re: Idles fine but as I throttle up, she slows down?

just wondering high speed jets are the large screws on the outside of the float cover ot the 2 small ones inside the carbs?
 

Boatnik70

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Jun 22, 2007
Messages
21
Re: Idles fine but as I throttle up, she slows down?

The large ones one each side of the bowls (4 total) are the plugs; remove those and you'll see the high speed jets.
 

csinger05

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Apr 30, 2007
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Re: Idles fine but as I throttle up, she slows down?

WOW, thanks for all the recommendations! I will try them all. You guys have just made my family very happy.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Idles fine but as I throttle up, she slows down?

the high speed jets are deep in the hole and you need this special tool to remove them. can be made from a screwdriver.
 

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