Johnson bad idle

[5string]

I have a 1994 48HP Johnson that idles BAD, cuts off, spits and sputters unless I give it gas. Took the carbs off and it is clean as a whistle, jets are all clear, set the throttle linkage by the book and fiddled with the idle mixture screws some. Changed the plugs and they were in good shape, a little black but not bad in my opinion. Is there any way to get a SMOOTH idle out of this thing?

 

[clanton]

Re: Johnson bad idle

Check plastic cap with screen on fuel pump for split or bad o-ring. Replacement pn 433518. <br /> Check for 1 tan and 1 black wire on left side of engine by main harness connector. These 2 wires must remain unconnected and taped. <br />Check ignition coil with meter.<br />Locate 2 wires going to coil from power pack, pull these wires out and inspect for bare spots, you may have to remove the power pack to get to the wires.<br />Inspect power pack ground wire.<br />Check idle screw plastic linkage for stripped threads.<br />Overheat horn must be the correct one, and working.<br />Check rollers in timing linkage and throttle linkage for clear plastic sleeve, the sleeve<br />breaks and drops off, when this happens timing is off about 4 degrees.

 

[CFO94]

Re: Johnson bad idle

I'm not sure how similar a Johnson lower unit and overall mechanical theory is to a Yamaha, but if the lower unit has been removed lately, check this. The Yahama has a small, easily lost or overlooked, metal tab that fits into rubber gaskets, that seal the water pump chamber from the exhaust chamber. When changing my lower unit I overlooked this piece and the engine did all sorts of strange things. It wouldn't idle good, would stall, and the engine would overheat sporatically. When I finally got to checking out the lower end and found the omitted part and replaced it, all the problems ceased.

 

[Dhadley]

Re: Johnson bad idle

Make sure your fuel is FRESH 87 octane. And 30 day old fuel is not fresh. Use Champion (Q)L77JC4 plugs. <br /><br />What you describe (spitting) is caused by an air leak. Disconnect the throttle linkage and make sure the butterflys are completely closed. The plate on top of the carbs may suck in air too.<br /><br />Good luck!

 

[5string]

Re: Johnson bad idle

clanton wrote..."Check rollers in timing linkage and throttle linkage for clear plastic sleeve, the sleeve breaks and drops off, when this happens timing is off about 4 degrees" This is the one thing I don't see,the plastic linkage is there and connected but a clear sleeve? Is this in the Clymer book so I can see what it looks like? <br /><br />THANKS again

 

[clanton]

Re: Johnson bad idle

The roller has, what looks like a piece of clear fuel line over the roller.