1978 9.9 Johnson must choke to run at WOT

tvanden

Recruit
Joined
Feb 19, 2008
Messages
5
Just bought this motor. Starts, idles, trolls great. Twist the throttle to go wide open and it'll take off fine until it hits 1/2 speed and then bogs down. Pull out the choke, it runs much better and will run almost reach top end - still sounds like it could go another 1000 rpm's though. Put it back down to trolling speed and I have to push the choke back in otherwise it'll quit. What would you guys try first? Thanks!
 

The-Machinist

Petty Officer 1st Class
Joined
May 4, 2007
Messages
299
Re: 1978 9.9 Johnson must choke to run at WOT

Run down to your local OMC/BRP dealer and pick up a service manual and a carb kit. The rest should be self explanatory
 

Relliott

Seaman Apprentice
Joined
May 6, 2008
Messages
34
Re: 1978 9.9 Johnson must choke to run at WOT

Check the Fuel Filter. It might have some trash in it keeping it from opening up. An inexpensive fix if that is the problem. If that doesn't work I would take apart the carbs.
 

The-Machinist

Petty Officer 1st Class
Joined
May 4, 2007
Messages
299
Re: 1978 9.9 Johnson must choke to run at WOT

Chances are that if the filter is plugged enough to keep it from opening up the choke still wont pull enough fuel to make a difference. But, go ahead and check the screen, you may luck out:)
 

iwombat

Captain
Joined
Jul 12, 2006
Messages
3,767
Re: 1978 9.9 Johnson must choke to run at WOT

"Run down to your local OMC/BRP dealer and pick up a service manual and a carb kit. The rest should be self explanatory"


Bing! bing! bing!

We have a winner!


Seriously, your high-speed jets are most likely clogged and need a good cleaning.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: 1978 9.9 Johnson must choke to run at WOT

High speed orfice plug (jet) is partially clogged. It must be absolutely positively clean without a trace of any deposits in the orfice. That will cause the trouble you describe--guaranteed.
 
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