Carb troubles 1998 Johnson 50hp SPL

MikeB0307 · May 27, 2013

Our boat had sat for a little over a year before we purchased it. I drained/flushed the fuel system, installed new filters, cleaned/rebuilt the carbs, replaced the water pump, replaced the oil in the foot, and put in new plugs. It runs great above 2000rpm, but, it idles rough. I then realized that when I drained the tank, I didn't get all the fuel out, so I drained it again, flushed the tank, recleaned the carbs, verified that compression was good/even, and tried it again. Same result. When I built the carbs I counted the turns removing the jets and installed them back in the same place they came out. I think this may be the issue. Can someone tell me the proper way to adjust my carbs? Any help is appreciated. Thanks.

MikeB0307 · May 27, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Also noticed for the first time yesterday, after a 45min run from Disappearing Island, then another 45mins idling waiting our turn at the ramp, that, while idling, warm water was misting/spitting out of the exhaust port located on the back of the engine just below the cowling. Is that normal and I've just never noticed it?

multimech · May 27, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Yeah. Go through the synch and link procedure thouroughly. The turns out are 2 1/2 as BASE. You will need to adjust the carbs carefully to get the right adjustment. These engines are a pain in the ***.

MikeB0307 · May 27, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Thanks Multimech. I do the adjustment while idling in neutral in the water, right? (We have a 120gal test tank)

James R · May 27, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

What were the compression?

multimech · May 27, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Here is a tip on getting these engines to idle properly.

First and foremost, as James R says...what is the compression?

Get the normal engine checks done first.

Then, with the synch and link done correctly, the idle screws turned out 2 1/2 turns....get a set of plug wire pullers. In turn take of the plug wires. You will find a cylinder that is not hitting as the others are. You may get a die out when 1 or 2 is pulled. Adjust the idle screw, outward and inward until both hit at just about the same amount. You have balance. This must be done in a test tank, like yours, that will imitate a water test. At the end, test it in the water in a real life situation.

Remember the base turns out are just that, a base to start from.

MikeB0307 · May 28, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Thanks to all for replying. Compression was @125 on both. I'm getting ready to put her in the tank and get started!

MikeB0307 · May 28, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

OK, it runs best at 4 1/4 turns out but the bottom cyl. still sputtering. Re-checked compression and the sync, both are good. I assume my next step is to pull that carb and re-clean it, expecting to find more trash in it. Any comments are appreciated. Thanks.

MikeB0307 · May 29, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Anyone have any other suggestions? If not, I guess I'll pull the carbs again and re-clean them once again.

James R · Jun 5, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Still need to prove the carbs. Idle jets and drillings are tiny and block easily. Sounds like you have a lean idle due to blockages. It is possible to find which carb by shooting fuel mix into the throat of each carb in turn and see if the motor picks up. 2.5 turns out is the standard start point for the idle needles as said. Always use Stabil in your fuel to help prevent carb troubles.
Also of interest but not in your case. WSM has the incorrect part number in the catalog for 30 over pistons for this motor. They are shipping pistons for the 3 cylinder motors.For those who need to know.

MikeB0307 · Jun 6, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Thanks James, I pulled the plug wires while idling and found the culprit to be the bottom carb. I pulled it off and re-cleaned it, reinstalled it, adjusted them and all is right with the world. We don't add anything to our fuel because we generally take it out for the day at least once a week.

James R · Jun 15, 2013

Re: Carb troubles 1998 Johnson 50hp SPL

Todays fuel deteriorates very quickly. It can go bad in 30Days. In addition to that alcohol supplemented fuels will eat the fuel lines leaving the resulting residue to block the carbs. Use Stabil Marine religiously to avoid all the problems. No I don't have shares in Stabil but I do try to have all my friends and customers use it.

Carb troubles 1998 Johnson 50hp SPL

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