How to adjust the mixture - rich/lean?

[andy65]

When driving on idle the Johnson 70hp VRO from 1986 died repeatedly, and everytime I had to use the primer to make the engine restart, so I think the mixture is too lean. How do I make it richer, is there some screw on the carburators?

 

[fireman57]

Re: How to adjust the mixture - rich/lean?

Sounds more like a weak fuel pump. Next time it starts to die, give the primer bulb a good squeeze or two and see if it picks the engine up. All you are doing by this if "bypassing" the fuel pump.

 

[F_R]

Re: How to adjust the mixture - rich/lean?

The mistures on that carb are fixed, no adjustment possible except for changing the orfices. You probably don't want to get into that.

However, dirt or gum deposits in the orfices will effectivly reduce their size, making it leaner.

 

[Kevin W]

Re: How to adjust the mixture - rich/lean?

What RPM is it running at?
maybe its just too low and if a cyl misses it will stall.
as for a mixture adjustment...there isn't one for your year.
you can also check for a fuel restriction.

 

[andy65]

Re: How to adjust the mixture - rich/lean?

But if the fuel pump was the problem, wouldn't it be even more obvious at max speed and rpm?
However, I'm going to squeeze the primer bulb the next time, thanks for a good tip. One thing that strikes me, is that the primer bulb never gets as stiff as on my earlier boats, the fuel filter inside the engine cover is getting fuel though, and there's no problem with the engine at top revs.

 

[tashasdaddy]

Re: How to adjust the mixture - rich/lean?

the either you idle is set to low, or you low speed jets are clogged. idle rpms, in the water in gear, should be 650-700. also the fuel pump could be weak, as it pumps on the rotations of the engine. there also could be an air leak in the hose or coupling, that it can overcome at low rpms.

 

[andy65]

Re: How to adjust the mixture - rich/lean?

Where do I find the low speed jets? Are they called anything else?

 

[tashasdaddy]

Re: How to adjust the mixture - rich/lean?

http://www.evinrude.com/en-US/Accessories/Literature/
follow the prompts on this link, it will take you to the complete list of engine diagram parts and parts list. you will need a special tool to do the job. it can be made from a quality screwdriver, or bought$18.00. the jet are hidden under plugs, that have to be pried out, and then replace with new ones that come in the carb kit. you need a kit for each carb. may as well do all of the jets while your at it. here's a link to the tool you use this to unscrew and replace the jets after the plug is removed. http://i155.photobucket.com/albums/s311/frankr_photos/FixedJetScrewdriver2.jpg?t=1177353186