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77 Stinger Running lean

M

maugli

Member
I have a 1977 75HP Johnson Stinger 75ELR77. Have been working on it for a while chasing things. In a previous thread i was chasing an electrical problem that was fixed with a help of O=scope. Now it is a LEAN condition. Carbs rebuilt. new Bulb and hose and fuel pump. still it runs lean. Last night i used a can of carb cleaner on it while it was running. It seems to be sucking on both sides of the split block. But more on the exhaust cover side. So i figure that pulling and resealing the power head is unavoidable. Now the decision to be made to replace the pistons and go with a rebuilding or not? The compression is 112 in each cylinder. Would ring replacement only boost compression? And which pistons to use if i were to replace them and bore the block? And outsource maybe it is more beneficial to find another used motor that is running?.
Any suggestions would be appreciated.
Thanks
 
Hi, it is very rare to get a leak at crankcase seam. Could be fumes are making their way to the intake/carbs. How do you know its lean? Compression is great, don't worry. If lean on top cyl it could be upper crank seal, any leakage of oil there? Carb jets need to be physically cleaned to proper orfice size by welding tip cleaner, wire, drill. I have a special drill index to clean jets to size. Deposits will line the orfices and make them smaller, air and cleaner will still pass but the jets are still part restricted. What did you find in the carbs when you opened them up?
 
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Thanks for answering timguy. After reading your post i will retest again. This time i will cut a large piece of cardboard to fit snug around the carbs. I used a can of carb cleaner to spray under the flywheel. there was no change in motor RPM. But when i sprayed on starboard side along the block seem the RPM went up and the engine smoothed out quite a bit. And when i sprayed on Exhaust cover on the port side the change in RPM was even more drastic. The carbs i went through a couple of times. there was no residue or junk in them. I will check the jets again. Are you saying you use a certain drill bit size for the jets? Very clever.!!! Is there a listing anywhere for the diameter needed for the jet orifice?
 
Normally orifice size is in thousandths, pretty close till you get up in the 70's. I have several old metering rods I've collected from years of automotive repair. I clean the jet as best possible with something softer like a welding tip cleaner and acetone, then mark the metering rod with a sharpie. Carefully push it in to the jet and give it a light twist, scrapping the ink off at the orifice size. Then with a 0 to 1 inch caliper micrometer, I gauge at the mark and use a corresponding bit from my massive drill index. The bit is used only with a hand holder and WD40 to wash. Sometimes I make very minor adjustments to the larger. Seems newer motors are often engineered on the lean side, but extreme discretion is needed.
So what are its symptoms that indicate it is lean and is it on certain cylinders?
 
Yah!... if the diameter of the jet opening is known... the drill bit used as a reamer would be a very desirable. The lean condition manifests it self as a "lean Sneeze" to the point that it will stop the engine. The engine will start like it should when it is cold. It will run for about 10 seconds fine wile decreasing RPM until it will sneeze and eventually stop. I can keep it running if i will put my index finger across the throat of a carb on cylinder number one. If i spray very little carb cleaner directly in to the carb it will smooth out for a few seconds. The Bulb stays hard like it should. Ignition has been ruled out. New Spark Plugs and firing. I sprayed under the flywheel and did not get any response. But spraying on the seem of a block on both sides made the RPM go up drastically. More on the exhaust cover side. :-(
 
Good. If the crankcase seam could be leaking then spray with soapy water to isolate the spot, then report back. There should be some bubbling when piston is going backdown. With cyl 1 lean we have to avoid operation as you well know, to avoid scoring the cylinder. Comp test shows okay yet.
 
That just gave me an idea. Let me run this by you. What is i make an aluminium 1/4 inch plate with an air nipple threaded in to it. Then bolt it down in place of a carb. I wonder how much pressure i can apply and spray soapy water on the block. Would that work?
 
A novel idea but no, the crankcase can withstand little pressure, much less the fuel pump diaphragm. It takes only 2 to 3 psi to operate the fuel pump. The compression side, above the pistons, of course, are a different story. If you could position the piston accordingly and regulate pressure to no more than 3 or 4 psi then it would have the effect you want. I'm not sure what pressure the crank seals will endure, but likely well above 4 psi.
 
Usually when the crankcase leaks it will whistle or bubbles will come out. When you spray on the exhaust side of that motor that is where the intake box inlets are. You were more than likely sucking the mix into the motor. Do this take the air box off and start the motor now cover each individual carb and see if you can isolate the cylinder. Your compression is not great but it should still run.
 
The air box is off. I will use the large cardboard "wall" to isolate carbs and will use soapy water. It just i have never seen an outboard leak on the seam. But i guess it happens.
 
Well. looks like back to square one. As little time as i had last night i tried to run it again. I did not get a reaction like did last time. Tried three times. So looks like you guys were correct. The Fumes must have made its way in to the carbs somehow.
The air box was off and it smoothed out now when i was covering the throat of a middle carb. Which is very interesting because last time it smoothed out while i was covering the top one. Did not have the time to use the soapy water. ( family time)
So i am back to your wisdom. It is running on muffs. Maybe i should put it in the barrel to recreate the real conditions to diagnose further.
A am back to square ONE :-(
 
Okay then, when did the lean problem start? After storage? What kind of fuel has it been used on over the years? Now the problem has shown up on cyl 2 also?
 
Is this all being done on muffs? If it is you will never chase a lean problem down for the simple fact they run lean on muffs, because of no exhaust backp ressure.
 
Timguy, I cannot tell you when the problem started. I got the boat 2 years ago. I don't know how long it sat. The owner had some sort of a lung issue and was not mobile. so i think for a while. So the first thing i did was clean and rebuild the carbs. Just before writing this i have removed and cleaned the low speed jets with a torch cleaning wire. Spark plugs are gaped, just checked that too. Pulled each plug wire and there was a normal change. It starts only with a choke on for a second or two. Without choke - pops but wont start. The fuel they used here contains up to 10% ethanol. At least near Milwaukee. Will be cutting the cardboard later today... after a trip to the market with wife. Will report then.

Flyingscott. Yes Muffs. I am looking in to some kind of water reservoir to submerge the motor in to. Will fins one.
 
Well.. I dipped the motor in to a plastic can with water hose running. One thing i can say for sure - i will never use MUFFs again.
I can actually hear the engine run. The back pressure does help. But it still will die after a while as it sneezes. One thing i do not know yet is what RPM it is running at. No gauge. Have to think of something. Another interesting thing is TIMING. I hooked up the timing light to the top cylinder ( assume that is cyl #1). the reading is around 4 degrees. The sticker says should be 16. Am i suppose to turn off advance somehow and test? Looking in to timing adjustment. If the timing is only 4 degrees then someone set it that way. Wonder why.
And still. I can start it only with choke. Need guidance.
 
Of course. The carbs not adjustable. Two jets, one on top Low speed behind the screw. leading to tree small holes in the body. Second High Speed feed in the bowl. The carbs are clean.
 
How did you clean the carbs? And what is your starting procedure? It is not uncommon to have a lean sneeze until the motor warms up.
 
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Each carb was taken apart. Cleaned with carb cleaner and torch cleaning rods. They are not leaking air. it should start with a turn of a key when it is hot. But this one needs a choke.
 
I have it idling for 20 min now. I do not know what RPM it is running at idle but i am trying to get as low of stable RPM as i can.
Ither i am missing something or someone retarded the ignition on purpose. All i had to do is shorten the link between the Carb cam and the throttle/timing arm on the left and. That allowed the timing to advance a bit and the carb butterflies close. Then by adjusting idle screw 3/4 turn made it run without sneezing and stopping the engine. The problem is i do not know the proper setup on the linkages. Flying blind here and using just common sense. Looks like someone was really playing with it at one point. But how do i check timing to throttle relationship?
 
The 16 deg timing is wide open throttle only the 4 deg is normal at idle. You need to do a proper link and sync get a manual, a good manual for your motor. The carbs being open was causing a lean condition. In a tub the idle needs to be about 1000 rpm the real idle speed needs to be set running in gear and warm. On muffs it will be about 1200 rpm. The timing should be left alone and a link and sync needs to be done. Idle timing does not matter it will be set with the idle speed.
 
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Just ordered this. [FONT=Tahoma, Geneva, sans-serif]506988 - Service Manual - 1977; 70, 75; 70EL77, 75ELR77, 75ER77; Johnson[/FONT]

[FONT=Tahoma, Geneva, sans-serif]They say will be here within 5 days. Will be interesting to see how much i was off :).[/FONT]
[FONT=Tahoma, Geneva, sans-serif]I really appreciate you guys for the input.
This makes it very interesting. [/FONT]
 
OK... I had time finally to perform link and sync. That is an easy procedure. I made the TDC tool to Set the proper position of timing mark indicator. Pulled the plugs and looked at the timing that was set on the engine. At idle it was at 4 degrees. But at WOT was around 25 degrees. I have loosened the adjustment nut and screwed in the timing advance stop bolt so at WOT it showed 16 degrees. So i assume the timing is set properly and the throttle cam also. I have the motor in a 55 Gallon barrel. I ran the tank empty yesterday till the engine died.
One thing i also checked was the engine temperature when it was idling for 20 minutes. I checked with laser thermometer. Th readings were 78-84 degrees. Is that normal?
Now i have to set the timing. I do not have a tachometer on hand . The boat does not have one. I would like to have one on the boat. Being a pilot i am a bit paranoid about engine performance and well being. What would you guys do in this case. I do have an O-scope that i will try to hook up to No1 plug wire to get a reading for the setup. From reading the forum i think the idle though be 1000 RPM in the barrel and in gear 800 RPM.
 
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