Johnson 48 SPL Idling Problem when Trolling

[timsheehan]

I have an aluminum 1988 Starcraft SFM160 in really great shape with a Johnson 48 SPL motor, same year I think. Appearance of motor is excellent. I've had problems lately with the idling after trolling a while. Plugs look like they're getting oily. I've changed the gas line recently, cleaned the filter screen, hooked it to a portable tank instead of inboard tank, rebuilt the carbs (even though after using it for 10 years they looked clean as a whistle when I took them apart), put gas dryer in the built-in tank (even though gas was treated before wintering), put in new plugs, and read the heck out of these forums. One last thing is to go through the carb adjustment procedure in the top secret file but the advice is for a v-4 engine or a single carb engine and as clean as the carbs were I'm not sure mine needed adjusting, so I haven't gone there yet.

So my question is two fold, should I keep this engine because you know it can be fixed to troll trouble free and your advise to fix it is...... or if trolling is important then consider buying a new motor of which you can advise me which make and model was designed to run trouble free for trolling. I think I'll stick to the 50 HP range if new is what is recommended.

Also went out this evening and tried pumping the bulb when the engine sputtered at idle (got the idea from another forum thread) but that didn't work.

Thanks for any advice given....TIM

 

[tashasdaddy]

Re: Johnson 48 SPL Idling Problem when Trolling

are you using Champion QL77JC4 spark plugs, and gap them at .035 first try, then .040 if .035 does not improve idle. opening the gap cuts down on fouling, when idleing. your carbs do not have any adjustments, it has fixed jets only. i have several of this motors siblings.

 

[rolmops]

Re: Johnson 48 SPL Idling Problem when Trolling

are you using Champion QL77JC4 spark plugs, and gap them at .035 first try, then .040 if .035 does not improve idle. opening the gap cuts down on fouling, when idleing. your carbs do not have any adjustments, it has fixed jets only. i have several of this motors siblings.

You would need the Q series only if you have sensitive electronics hooked to your power system.Otherwise the L77jc4 will do fine.

 

[ob]

Re: Johnson 48 SPL Idling Problem when Trolling

When you performed the carb job did you actually remove the idle orifice at the top right hand area of the carb face? A little gummy deposit goes a long way on a #36 orifice.Carb cleaner and a set of indexed torch tip cleaners work well to clear them back to spec.

Also, carb link/synch adjustment being on the mark is a must as well for efficient continual low speed operation.Insure that the carburetors linkage roller is exactly on center and "just touching" the fiber cam scribe mark when the throttle lever is in the neutral position.Too much gap between the roller and cam will cause the carbs to open late and too hard against cam will have the carb flaps cracked open in neutral.

 

[Okee Jimmy]

Re: Johnson 48 SPL Idling Problem when Trolling

Oily plugs would indicate low compression, weak spark, or a rich mixture. Could be worn pistons, stuck, or worn rings, ruptured fuel pump diaphram, or an enlarged jet (orifice). The first test you should perform is compression, I usually like to see all cylinders within 10%, your motor should have about 150# cranking pressure. The ignition system of your motor should be able to jump a 7/16 gap at cranking speed. To check the fuel pump diaphram, remove the 2 screws securing the fuel pump to the crankcase, and gently squeeze the primer bulb, no fuel should come out of the pulse hole in the pump that aligns with the hole in the block. To check the jets, a set of plug gauges is needed, a no. 35 jet=.035" ect. Also, I've seen the gaskets between the carbs, and reed plates/crankcase deteriorate allowing both carbs to feed whichever cylinder is providing vacuum. All previous posts are on the money, another possible solution (if all else fails) is to install a set of carbs that have a low speed mixture adjustment that can be tailored to meet your needs. Or you could buy a new 50 etec, low idle speed, less fuel/oil consumption, very low maintenance... Hope this helps, Jimmy.

 

[timsheehan]

Re: Johnson 48 SPL Idling Problem when Trolling

The advice you have given is excellent and much appreciated. Mothers day weekend may take all my time but if possible I may be able to check into some of the advice given. Mom raised 8 kids and we owe her big time. The spark plugs I installed are Champion 828-1 and the extra set are in the boat; can't remember what number was on the package that they replaced but I'll look. I either gapped them a .03 or .035 but I will try a wider gap. I ordered a owners manual and it recommends the QL77JC4 or L77JC4 plugs and .040 gap for Sustained Low Speed and Normal Operation (does that have my name on it or what). When cleaning the orifices I used a ribbed set of tools and carb cleaner. I was afraid of reaming them out so i went gentle and didn't know to gauge them. I'll try other things before I have to take all that stuff apart again. I replaced the rubber roller, the other one wasn't touching, the new one had a black layer covered by a clear layer and it touches but I'll check the pressure it applies. Thanks for all your help and for those who follow I'll report back on what worked. Take care of your Moms!......TIM

 

[timsheehan]

Re: Johnson 48 SPL Idling Problem when Trolling

On the carb link sinc comment I think there were two marks very close together on the cam. Which should it line up with or does it represent a narrow acceptable range? The marks are 1/8 to 1/4 inches apart from memory.

Also, the torch cleaner tips I used might be indexed but I didn't look. I just used one that was smaller to loosen any possible grime. I'll look for a gauge and check those.

Again....Thanks

 

[timsheehan]

Re: Johnson 48 SPL Idling Problem when Trolling

Here's what I got done today. Checked compression 130# on upper 120# on lower. Checked fuel pump by taking out two screws and seeing if any fuel squirting out the back, none so I assume its OK. Gapped plugs to .040. Butterflies are shut and linkage was against cam firm (remained that way through all adjustments mentioned below). Sent a small wire through each idle jet just in case. Put carb cleaner additive in portable tank; what the heck, I already had it.

Nothing really worked and an older gentleman strolled by and said why don't you just bump up the idle speed a hair. I told him looking at the linkage there are several way you can do this and I'm not sure which screws or dials to turn.

Here's what I did. Pretty much left the black plastic dial alone (pair of them side by side). Large adjustment screw (looking at motor broadside upper left on linkage assembly) that looks like the idle screw didn't affect things much. There is play in the linkage between the cam where the large screw is and the cam with the silver dial screw and the 7/16 nut. I loosened the 7/16 nut and messed with the dial and its better but not fixed.

If I run the boat for a mile or so and then idle down and take it out of gear it continues to idle high, racing slightly above idle for a couple minutes (seems too fast to be putting it back in gear), like it has to burn of some fuel and then it finally settles into a purr and idles fine. Speed it up a little and it slips back into the fast idle then dies down. Sometimes it sticks that way too long.

I ordered an OMC manual but if anyone has a clue to how close I am to fixing it or not I'm open to advice. Couple questions I have are the idle jets adjustable or just replaceable? Another gentleman at the dock strolled by and offered that those motors weren't really meant for trolling and that I should go get a small kicker motor. Is he right or with patience or eventually a good mechanic will this motor serve my needs.

Thanks....TIM

 

[tashasdaddy]

Re: Johnson 48 SPL Idling Problem when Trolling

the motor will idle all day, whether it is slow enough to please you for trooling is another question. if it idles too fast in forward, turn around and back troll.