1978 Johnson 140hp running rough. Need advice

[Bman2895]

Picked up a boat recently with this 78 Johnson 140. It had a poor idle. Pops out the exhaust and stumbles. Eventually dies. Also most of the time it hates transitioning from idle to WOT. Most of time just stalling when coming off idle under load. When it does make it through it does fine at WOT. Took carbs apart to clean and they looked okay. Sprayed through the jets. All looked okay. New plugs. Sparks good. 100-110 psi on all 4.

Read a post stating to put two fingers into the throat of the carbs individually to determine if it was a fuel issue at idle. And the top carb if you do this to both bores it'll smooth out and idle quite nicely. So I know it's fuel related.

On these 78s they're fixed idle circuit?. The post recommended stepping up the idle jet sizes to accommodate the needed fuel. Is there something I'm missing on these carbs idle circuit? Everything seemed clean. Seems pretty simple. I'm not sure theres much to the idle circuits unless I need to pop out the plugs on the carburetor as well?

Should I keep looking for something I missed or just jump up some jet?

 

[jimmbo]

Did you take the Carbs off, and clean out all the Passages, including any that are covered by little Disc Plugs? Those would need replacing so, Carb Kits are needed. Are the Floats correctly Set. Is the Fuel Pump providing enough Fuel. Once reinstalled the Sync between the Carbs and Spark Advance needs Verification and possible Adjustment.

Is the Spark on ALL Cylinders strong enough to jump a 3/8" Gap? Don't tell me it jumps the Plug Gap, that means Nothing.

 

[racerone]

Step #1 on those engines is a compression test.-----Post actual values here.

 

[Crosbyman]

100-110 all 4 see post #1

 

[racerone]

Well---100 psi is too low.----Remove cylinder head and inspect piston that has 100 PSI in that cylinder.-----Or remove bypass cover.

 

[Bman2895]

I've used two testers. When I bought the boat The sellers tester read 110 across the board every cylinder was spot on the same reading(nicer gauge. easily readable) . The tester i used just yesterday is one thats cheaper has 90psi then next number on the gauge is 120. The needle lands right center of the two. On all 4. Thats why I say 100-110. If compression were to be the issue why do the bottom two cylinders run and idle fine?

And I have not pulled those plugs out of the carb yet. Was hoping to leave them alone but I will.

 

[Bman2895]

I went off my clymer manual. Stated that minimum compression would be 100 psi, but that it was more important that 4 cylinders are even.

 

[racerone]

Here a crossflow V-4 would come apart for rebuild if it showed 100 PSI compression.-----These motors have a history of broken piston rings !

 

[Bman2895]

Here a crossflow V-4 would come apart for rebuild if it showed 100 PSI compression.-----These motors have a history of broken piston rings !

Oh I know. My Buddy went through 3 power heads before he got one good one.

 

[Bman2895]

Oh i know. My Buddy went through 3 power heads before he found one decent one.

I think i may already have it fixed however. And I THINK it was due to crappy carb bowl gaskets. I took it back apart (top carb). Popped those welch plugs out and those little holes for the idle circuit looked fine. But I sprayed them out anyways. Two new plugs back in. Verified the whole circuit from bowl to venturi was clean. What I did notice is the bowl gaskets from the kit slightly covers the holes the circuit pulls its fuel in through. I trimmed them out just slightly to make sure that they were 100% unobstructed. Put that carb back on and now it's idling smoother. Not doing the popping and rough idling.

 

[airshot]

I went off my clymer manual. Stated that minimum compression would be 100 psi, but that it was more important that 4 cylinders are even.

The only use for Clymer manuals, is a backup for when you run out of toilet paper.....you have some more testing to do before we can help you.

 

[Bman2895]

Well I took it to the lake and initially everything seemed pretty good. Idle was decent still hiccups a little till it was warm. Transition from idle to throttle just fine. Was pretty happy with it then it just did a complete 180. Didn't want to idle didn't want to go from idle to wide open. Got so bad by the time I was putting it on the trailer it was only really running on the bottom two cylinders. If you bump the choke you hear the talk to come in for a few seconds and then drop right back out. So by the time I put it on the trailer it wouldn't take any throttle just barely enough to move. Checked the compression still 110 across the board. That's now with three different compression testers.

Gona

 

[Bman2895]

Going to wait till it gets a little darker test spark gap. But it seems like it's isolated to the upper two cylinders

Update. Spark on all 4 coils jumps 1/2" pretty easily.

 

[Bman2895]

Kinda frustrating I know it's a fuel issue. the carbs are "clean". All circuits blow through fine with carb cleaner. On the lake when it was running on just the bottom two the choke for a second would cause the top two to pick up and when I got it home and ran it on the horns it did it again where the top cylinders kinda cut out and it was mostly idling on the bottom two. Shot a little carb clean in while running and it immediately picked up on the top two. Definitely in the top carburetor some how. Idle jets are 33s btw.

 

[cyclops222]

You may have crud coming loose randomly. Throughout the carbs. It is a 1978. have you tried a carb cleaner mixed into the gas tank. Like Seafoam. The are slow dissolvers of varnish. E 10 gasoline will dissolve the varnish covering of old CORK floats.
Chased that one on a old green Seahorse motor. Start great then about 5 minutes later the motor started to run rough and stop. Got lucky and saw the SHEEN of gasoline right at the motor prop area.

 

[Bman2895]

Well the problem was pretty simple. Welch plug didn't stay put. Was hanging out the hole. I used a kit supplied with the boat. Honestly didn't like it. What kits are everyone using? And could I fit this engine with another v4s carbs that are adjustable idle mixture?

 

[airshot]

Kinda frustrating I know it's a fuel issue. the carbs are "clean". All circuits blow through fine with carb cleaner. On the lake when it was running on just the bottom two the choke for a second would cause the top two to pick up and when I got it home and ran it on the horns it did it again where the top cylinders kinda cut out and it was mostly idling on the bottom two. Shot a little carb clean in while running and it immediately picked up on the top two. Definitely in the top carburetor some how. Idle jets are 33s btw.

If not a complete and thorough rebuild with a factory rebuild kit, then setting each carb to the specs given in the kit, your carbs are not good....spraying carb cleaner all over, usually makes things worse by loosening all the crud and shoving it into the areas you missed. Just cleaning a carb rarely fixes anything, but does make more problems. Pull the flywheel and check all the ignition components, age is not your friend on electrical components..

 

[cyclops222]

Most carburetors with some fixed jets run very well. However the odd case can be created when a motor goes to Alaska. Is rejetted for there. Then the motor is shipped to Florida. A rejetting may be required again. MAY is the key important word.
If the person is not a experienced carburetor mechanic ?

 

[Bman2895]

I have no reason to pull the flywheel. Spark is strong and all indicators point towards a fuel issue. Like I say it was running pretty good. Id say the issue on the water was that Welch plug getting loose then coming un-seated again. I wouldn't think they were still making OEM kits for the carbs this old.

I've dealt with many carburetors and I appreciate the simplicity of these fixed jet carbs. But I will say an adjustable will always be better. And I hate Welch plugs. Never have good luck messing with them.

 

[jimmbo]

I've dealt with many carburetors and I appreciate the simplicity of these fixed jet carbs. But I will say an adjustable will always be better. And I hate Welch plugs. Never have good luck messing with them.

They certainly not my Favorite Item either, but many times I have removed them on Carbs that the Owner insisted were spotless, and found a pile of Gum/Varnish/Dirt hiding behind them with no way to get out.
On the Carbs with fixed Idle Jets, Settings like the Float become Critical, as well as proper Gasket Fitment, as you mentioned above. Wear on the Throttle Shafts can become an issue over time, as that can allow excessive Air to enter, which is undesirable as the Throttle Plates are Fully Closed at Idle, actually quite higher than Idle Speed, and an Lean Condition can occur.