4.0 hp high rpm problem

stu_family

Cadet
Joined
Sep 21, 2008
Messages
10
I have a 1978 40(4hp) outboard and she starts right up but I am un-apply to get her to run a high RPM's. She bogs down as if she is flooding. I noticed that when I turned over the gas I was able to rev her up just before she ran out of gas and died. Can anyone tell me what is going on? I can understand not getting enough gas, but to much! Thanks all
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: 4.0 hp high rpm problem

You need to rebuild the carb or at lest install a new inlet and set the float height.
 

monk-monk

Chief Petty Officer
Joined
Aug 27, 2006
Messages
642
Re: 4.0 hp high rpm problem

theres really not much to learn from shutting off the gas supply and being able to rev it up just before it runs out of gas, this "high rev" when running out of gas is typical of a two-stroke engine...the pistons do not have to compress as much fuel vapor...it might let the motor rev high, but it will not make much power when "leaning" the fuel supply out. in my experience "Bogging out" is generally a fuel supply issue (lack of fuel). you might want to check your timing and carb synchronization...the distributor timing has to be right with the carb throttle plate opening position to burn this added fuel, if the spark timing and fuel delivery rate are not in sync, this could create loss of top end RPM's (no timing advance) and bogging from not igniting the fuel at the correct time. very few motors "bog" from excess fuel, especially trying to achieve high RPM's, low RPM flooding, quite possible...high RPM bogging or flooding from gas...doubtful. just wondering about the timing? LOSS of top-end power = poor compression, insufficient fuel supply or no timing advance.
 

stu_family

Cadet
Joined
Sep 21, 2008
Messages
10
Re: 4.0 hp high rpm problem

But Monk, it sure acts like it is getting to much gas when I rev it up. She starts smoking and then when I lower the throttle she sputters until it seems she burns the excess gas and then starts to idle perfect again.
 
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