1986 Johnson 50hp factory jet size?

[salmonplease]

Hi,
I have a 1986 j50belcde, VRO disconnected, it has a small miss at idle and a flat spot at 3/4 throttle (don't have a tach), full throttle is fine.

Carbs rebuilt, new fuel pump, new plugs, new head gasket (all professionally done) engine had been sitting for 3yrs

Does anyone know the factory size jet numbers? My top carb jet is 32, my bottom carb jet is 36.

Are the jets supposed to be the same size?

Does anyone know the factory size?

Could this be the problem?

Thanks in advance,
Brian

 

[Joe Reeves]

Re: 1986 Johnson 50hp factory jet size?

My book states that the idle slow speed jets are both #36 (.036), however that may be superseded and if so, I'm sure someone will jump in here with that upgrade.

The jets meter air, not fuel, so the smaller the jet, the more fuel will be inducted.

The usual cause of a slight miss, if what you are experiencing is more of a spitting back of the carburetor occasionally at idle, is normally caused by one carburetor running slightly lean, OR the throttle linkage between the carburetors being out of adjustment which is holding one throttle butterfly slightly open while the other is closed.

You can determine which carburetor is running lean (if this is the case) by inserting two fingers into the carburetor throat or blocking off the idle air jet somewhat to richen the mixture while the engine is idling. When the engine smooths out, you've found the offending carburetor.

The flat spot when advancing the throttle is normally due to a slightly clogged high speed jet, OR having the throttle butterflies opening too soon in relation to the timing. The scribe mark on the cam should be dead center with the throttle cam roller just as the butterflies start to open... not before or after.

 

[salmonplease]

Re: 1986 Johnson 50hp factory jet size?

Thanks Joe!
I grabbed a bottle of Johnson/rude engine tuner. Sprayed it into carb throats, just enough not to stall the engine. Used half of a can doing this. Then ran it out of gas and filled the carbs with the tuner spray and let it sit. Then I pulled the plugs and put a healthy spray in to each cylinder and manually advanced the pistons several times. Then I tilted the motor all the way up making the cylinders as vertical as possible. Another healthy dose of tuner was sprayed in to each cylinder, then the plugs were replaced ( finger tight and not hooked up). The motor was left in this condition over night. Next day, lowered engine, pulled plugs, used compressed air to blow out/ dry out tuner fluid in cylinders, replaced plugs and hooked them up. Next I drained the tuner fluid from the carbs, hooked up the gas, primed it and fired right up. It smoked heavily as expected and blew a lot of carbon out (way more than just running a can of sea foam through a gallon of gas). The motor is now running way way better. No flat spot anymore but still a very SLIGHT miss at idle. I'm assuming as Joe suggested it was an air flow issue. I don't believe the jets were completely clogged, just one of them was smaller than factory spec. It is a 32 and needs to be a 36 as Joe stated. I have a 36 ordered and am pretty confident the right jet will cure the miss. I'll keep you posted. Thanks again Joe!

 

[Joe Reeves]

Re: 1986 Johnson 50hp factory jet size?

Remember that the larger size Idle Air Bleed Jet will result in having that cylinder use "less fuel" and more "air" which may very well make the problem worse.

Did you try the fingers in the carburetor throat trick to see if the engine would smooth out?