50 Johnson won't idle

[coafdm6]

Have resoved many issues, rebuilt carbs, fuel pump and water pump.

Just discovered the roller for the throttle was warn down missing ht eplastic jacket, replaced it and engine running well in gear low and hig rpm.

Will not idle, am attempting to adjust the mixture screws per the shop manual but still having issues.

How touchy are the mixture screws?

On cars, use to use a vacuum gage? any easier methods?

 

[gejandsons]

Re: 50 Johnson won't idle

If the only way you can get it to idle is by choking it a little, then the jet is probably plugged. If adjusting the idle adjustment screw seems to do nothing, then the jet is probably plugged. You'll have to remove the jet & possibly the seat which could mean removing & tearing down the carb.

 

[Silvertip]

Re: 50 Johnson won't idle

Are you attempting to adjust idle speed and mixture on muffs? Since there is no exhaust back pressure when running on muffs they will need to be reset when it's dropped into the lake. If you have not done the link & sync procedure, you must do that first. The adjustment procedures will not help if you have a dirty/clogged carb so if all you did was clean the float bowls, you need to make sure every passage is squeaky clean. The mixture screws affect two aspects of how the engine runs. 1) idle quality and 2) hole shot. First, set the idle "speed" to whatever speed is necessary to just keep the engine running. Then adjust the idle mixture screw inward in 1/8 turn increments (pause between changes) until the engine just begins to bog down. Note the position of the screw. Then turn the screw in the opposite direction until the engine just begins to bog. Again, note the mixture screw position. Set the screw in the middle of that range and then repeat the process for the other screw. At this point the engine will probably be idling quite fast. So -- turn the idle "speed" down to the point where the engine just stays running. Repeat the mixture adjustments. You may need to perform this process several times. When you launch the boat, if the engine does not accelerate quickly or seems to stumble a little when you try to get on plane, turn the mixture screws out a little.