Johnson 48spl won’t idle

[MJernigan]

Motor help!

I recently got an ‘89 Johnson 48spl for my jon boat,it lived its life on a pontoon until it wouldn’t run correctly and the older couple removed it and put a newer motor on it, that’s all the history I know on it.

I’ve torn down the carbs and they was sludged up, cleaned them so they are spotless and replaced the float, float seat and needle, and all gaskets and o rings in the carbs. I ensured all jets are clean and all passageways through both carbs are clear. Low speed needles are set to 2.5 turns out for top and 3 turns out for bottom, that’s where they was set when removed.

The motor will start, idle, and run with the primer engaged but when you turn the primer off it will die so to me it seems as if fuel isn’t being drawn through the carbs. I removed the drain on the bowls and both were full of fuel.

Compression is 146 on top and 145. Spark jumps a 7/16” gap bright blue as it should according to the manual.

Removed the carbs this morning and inspected the reeds and they open and close properly when cranking the motor. There’s no visual chips or cracks in the reeds that can be seen through the intake manifold and all reeds have good tension when lightly pressing them open with a screwdriver.

Diaphragm fuel pump is confirmed good and both carb bowls are full after the motor dies. Fuel line primer ball remains firm.

Carb sync procedure has been completed as described by the manual but timing has not been confirmed yet, I don’t have a timing light yet.

I also replaced all fuel lines going to the carbs to rule those out and no change. The fuel tank is brand new so there should be no issues there either.

Any help would be greatly appreciated.

 

[GYPSY400]

Im sure Pappy will chime in with a good answer.. But how are the crank seals?

Seems to me you've ruled out the entire fuel system.

 

[MJernigan]

I’m not sure how to go about checking the crank seals but if you tell me I’ll be sure to inspect them.

 

[Pappy]

Do NOT jump off the deep end and "check" crank seals!
Folks.....we have said it before.....if you do not know specifically what you are talking about and how to troubleshoot an engine do not offer radical answers as these answers can cost people serious time and money!!! Others can read this and possibly believe what "you" are writing as fact!

Few things I noticed in your write up and by the way you have done a good job describing what you have done so far.
First off. The primer bulb does not and will not stay firm when the engine is running. It is on the suction side up the fuel pump.
A suspected fuel pump can be checked (for a fuel supply issue) by pumping the primer bulb which is apparently what you did. This will bypass the fuel pump and supply the carbs with fuel in place of the pump. However, a secondary check of the fuel pump may reveal they only way a fuel pump can run the engine while making it run poorly. That check is to remove the pump hose attached to the crankcase or to remove the fuel pump from the block if no hose and pump the bulb. If fuel come out of the air motor port you have a failing diaphragm in the pump and that extra fuel will flood the cylinder it is running off of so......check it.
Second. You set the carbs as they were set by someone in there before you. Why? Never assume they were correct to start with. Richen all the needles, start the engine, and set them where the engine wants them! Hint - those are very sensitive so when you get close only turn them around 1/8 turn at a time and let the engine respond for around 30 seconds or so before continuing. Second hint. Your water level while running on a hose and setting carb needles will need correction once the boat/engine is in the water due to a change in water level on the engine and resultant back pressure.
Third - You made no specific mention of disconnecting the link rod between the carbs while the engine is running. For starters just disconnect this and start the engine. These engines run at idle on zero carb opening and rely on initial timing and fuel/air mix to idle properly. The roller on the carb linkage should not be touching the pick up cam at idle. If it is then back that off by loosening the screw and moving the arm and roller back a bit.
Fuel lines to the carbs are at this point a waste of time to check. All they do is fill the carb.....same as the fuel pump does. If one sucks air you would have noticed it when you pulled the bowl drains and found an empty bowl plus the engine would idle then speed up and run out of fuel....easy to diagnose. We are working on an idle issue not a fuel tank to carb bowl delivery issue. If bowls are full the carburetor does the metering not a supply line.
This should give you a good base to work from.

 

[MJernigan]

Pappy, thank you for the reply and extra items to check.
The throttle roller isn’t touching the cam when it’s at idle position.
I’ll remove the carb linkage in the morning and see if anything changes.
I’ll also check the back of the fuel pump to see if any is getting through the diaphragm. When I checked it I removed the line from each carb and turned the motor over with the starter and it was pushing good amounts of fuel but I’ll do the check you recommend.
The reason I set the sleeping w speed needles where I did is I’m an extreme novice tuning a carb so I was hoping the previous settings would be correct.

 

[MJernigan]

Also when I say the fuel bulb is still firm I mean it’s not sucked flat like they do when there’s a fuel line collapsing. It’s not as hard as when I first prime it.

 

[MJernigan]

Also I’m running the motor in a barrel to give the back pressure similar to a lake.
The motor won’t idle long enough to adjust the low speed needles before it dies without the primer turned on.

 

[MJernigan]

Morning update:
Checked motor side of fuel pump, no fuel bypassing diaphragm.
Disconnected carb linkage and began adjusting low speed needles, no change, motor will idle 5-10 seconds and die without the primer on.
Added air box lid and adjusted low speed needles again, same result.
When I make the needle adjustments I started at 1 turn out on each carb and went all the way to 6 turns out in 1/4 turn increments. I did notice when I got to 5.5-6 it didn’t want to idle at all.

 

[nccatfisher]

Are you sure you got carbs as clean as you thought you did? Not idling except with the primer on is indicative that it is starving for fuel. Did you soak the carb or just use spray cleaner, use use a small wire and compressed air to clean all passages?

 

[GYPSY400]

Forgive me for offering such a "radical" answer, but yes, Pappy does bring up some good things to check that were not mentioned by the OP. Im a little out of practice in February as we have a foot of snow on the ground. But I'm here to learn just like everyone else.

The reason I mentioned crank seals is the motor is 30 years old and im sure they are original.. it would be something to consider, after ALL else is ruled out throughly.

Sent from my SM-G960W using Tapatalk

 

[MJernigan]

Are you sure you got carbs as clean as you thought you did? Not idling except with the primer on is indicative that it is starving for fuel. Did you soak the carb or just use spray cleaner, use use a small wire and compressed air to clean all passages?

I soaked the carbs for 24 hours then used small wires to clear the sludge out of the jets and the tiny tube for idle that runs through the emulsion tube and also made sure the 2 sets of holes through the side of the emulsion tube was clear. I then used carb cleaner to spray through everything to make sure everything flowed good. Only thing I didn’t do was remove the core plugs on top but the carb cleaner flowed through the tiny holes in the throat good.

 

[CedarRiverScooter]

It's not hard to remove & replace the core plugs. Maybe you could do that & clean out holes good with wire.

 

[nccatfisher]

Are you sure you got carbs as clean as you thought you did? Not idling except with the primer on is indicative that it is starving for fuel. Did you soak the carb or just use spray cleaner, use use a small wire and compressed air to clean all passages?

I soaked the carbs for 24 hours then used small wires to clear the sludge out of the jets and the tiny tube for idle that runs through the emulsion tube and also made sure the 2 sets of holes through the side of the emulsion tube was clear. I then used carb cleaner to spray through everything to make sure everything flowed good. Only thing I didn’t do was remove the core plugs on top but the carb cleaner flowed through the tiny holes in the throat good.

From what I can glean from your posts it sounds like it is still a carb cleanliness/adjustment issue. The best I gather it is basically non responsive on your low speed circuit until it is screwed almost all the way out then wants to flood out.

I hate to beat a dead horse but did you use a factory carb kit where you removed the welch plugs and cleaned the ensuing passageways behind them also?

 

[MJernigan]

I’m going to remove the core plugs and double check everything again this week. Maybe there’s something in the carbs I’ve just not gotten out yet.

 

[Pappy]

Double check to make sure the nozzle gasket is in place around the high speed nozzle tube. You may have missed that on re-assembly, It has to seal or the idle and off idle will not pick up the fuel through the brass lift tube inside the nozzle.

 

[MJernigan]

Ok quick update, I removed the carbs yet again and removed the core plugs. The three little holes in each throat were clean. When I removed the bowls one of them had a tiny amount of trash that wasn’t there when I cleaned them previously so it seems as if it’s coming from upstream somewhere. Good news though, it will now idle on its own without the primer. It’s a rough idle but a starting point none the less. I will work on the low speed needles and get the idle smoothed out now. Thank you everyone for the help.