johnson 40 hp question

[Jeff Walkowiak]

I recently inhereted an old 40 johnson super sea horse with a model number of RDS22, I am wondering what year this engine is my guess is late 60's it has electric and pull start with compression release, the cover is white with a round disk formed on top, it seems to run however I can't seem to get the low speed setting on the carb set correctly, the fuel system is quite odd in comparison to newer engines, I cleaned the carb and it will run at high speed but it won't idle. any info would be appreciated.

 

[Paul Moir]

Re: johnson 40 hp question

That would be a 1960 engine.<br /><br />The initial setting for the carb is to screw the low speed mix screw in all the way (take the knob off) until it just seats. Then back it off 1 and 1/2 turns. Start and run the engine and turn in the mixture control until you get the best idle, pausing a few seconds after each adjustment so the engine can react to the change.<br /><br />If the control doesn't seem to be doing anything, pick up a carb kit and rebuild the carb, removing the soft metal plug in the top centre of the carb. Directly beneath that plug is the idle jets which are tiny and tend to clog. The factory kit comes with a new metal plug, float, needle & seat, gaskets and packing for the mixture controls. Cost is about $20-$30.<br /><br /><br />Another helpful test is to pump the primer bulb while the engine is running and see how it reacts. If it burbles it could have a leaking needle & seat in the carb, or a torn fuel pump diaphram. The old style fuel pump is cheaply and easily rebuilt unlike modern ('64-) pumps.

 

[Jeff Walkowiak]

Re: johnson 40 hp question

thanks for the info, I will take a look and see is this a type c carb I believe the float is in pretty bad shape but it is seating the needle, I also noticed some air bubbles in the clear bowl while it was running, but then they went away, The compression is good and the carb isn't leaking when I pump the primer so I don't think the fuel pump is leaking

 

[Jeff Walkowiak]

Re: johnson 40 hp question

one more question what is the primary setting for the high speed needle, thanks

 

[Paul Moir]

Re: johnson 40 hp question

If the fuel pump leaks, it leaks into the crankcase. Easy enough to check it out though - just pop the pressure pulse line off the fuel pump, the one that runs to one of the intake covers, and pump up the primer bulb. If it's dry it's good. One guy here about a year ago filled up the entire bottom crankcase with gas before it started spilling out the exhaust!<br /><br />Initial setting for the high speed mix is 3/4 of a turn out. Usually you end up around 1/2 turn out. Once it's set for the highest rpms, richen it a bit. Better too rich at WOT than too lean afterall.

 

[Jeff Walkowiak]

Re: johnson 40 hp question

thanks again, I believe I will need to replace the old cork float it started leaking past the needle again, the float looks really bad, once I do that having the basic settings will be a great help

 

[Paul Moir]

Re: johnson 40 hp question

The Sierra carb rebuild kits (18-xxxx part numbers) do *NOT* come with floats. Get the dealer one (439074). We got a report here recently that one of these older carb kits came with a cork float; the modern one ought to be plastic. <br />The new float needs to be bent so it sits even with the bowl-gasket-mating-surface when you hold it upside-down. The level is not especially critical on the adjustable carbs though.<br />You should check the synch do once you're done with the rebuild:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=033290

 

[Jeff Walkowiak]

Re: johnson 40 hp question

thanks again