1976 Johnson 70-HP Workhorse Giving Me Fits

[Ocean31]

For all the older model OMC Wizards:

I have a 1976 Johnson 70-HP in-line three-cylinder outboard engine that will not maintain full throttle. You can back the throttle off to about two-thirds-full for a couple minutes, then go to wide-open throttle (WOT). When you first go to WOT, the engine takes off and gives full power, but after 15 to 30 seconds it bogs back down to about 80-percent power. One time she actually ran at full throttle for almost a full minute before she bogged down again, but that only happened one time.

Background and already completed trouble shooting:

--the carburetors were professionally cleaned and rebuilt,
--water pump [serviced],
--the thermostat replaced. and
--the fuel pump replaced.

Then the engine was put on a stand. Every year I would go out and start the engine, running stabilized non-ethanol fuel, and then I would run the engine out of fuel. After six years on the stand I installed it on my classic 17. Currently the engine starts right up and idles extremely well.

Since then engine feels like it is surging when it bogs down to 80 percent power, I put all new coils on the engine.

I have filled, drained, soaked the carburetors in Sea Foam three times with no major change or maybe a slight improvement. I have tapped on the side of all three carburetors numerous times, thinking I have a stuck fuel float with no improvement.

I have tried other portable fuel tanks, primer bulbs, and hoses with no change.

I pulled the three small hoses connecting the carburetor fuel system on the port side of carburetors, and could not find any restrictions.

Short of replacing the fuel pump again, I am out of ideas. Do you have any thoughts?

[Seahorse]

Have you monitored the fuel pressure througout the RPM range?

[Oldslowandugly]

[The engine has] a fuel starvation problem.

As suggested, if you can mount a pressure gauge on the carburetor side of the fuel pump, it will tell you if you are loosing pressure at WOT.

Aside from a weak pump that is just not delivering enough volume, [the cause of the problem] could be the wrong part for a three-cylinder engine. They all look and mount very similarly.

There could also be an air leak on the supply side letting the pump suck air instead of fuel or too small diameter fuel line. A good test for that would be to have someone pump the primer bulb while you are running the boat at WOT. That would put positive fuel pressure to the pump and temporarily mask the problem.

Another thing would be the vent on the fuel tank cap. It may be dirty and preventing venting thus restricting fuel flow.

If all this fails, maybe try a fuel pump designed for a V4 that has the same mounting pattern. Perhaps the extra volume will overcome whatever is starving the motor at WOT.

[Ocean31]

Thank you all for the quick replies.

I was starting to think I was off base in believing [the cause of the problem] to be a fuel starvation problem I re-checked the carburetor synchronization, and it looks good--right on the mark as per the manual.

The current fuel pump is a Sierra aftermarket pump. Maybe the supplier sent me the wrong one.

I put on this 70-HP on to replace a 1974 Johnson 115-HP V4. I loved the V4, [but] the fuel milage was awful. I was willing to give up some horsepower for much better fuel consumption. I could try pulling the V4's pump and installing it on the 70-HP.

Give me a couple days to try the change-out of fuel pump and or pumping the primer bulb (as soon as I find someone to drive while I pump) and I will let you know what happened.

Thanks again.

[Oldslowandugly]

I have had a LOT of [problems] with Sierra products. It may be a one-size-fits-all application. If an OMC part is available new, I pay happily. If not, then now I will either rebuild the part or find an OEM part on eBay (or somewhere). Let us know what happens.

[Ocean31]

The results of test run: the engine ran great, the best it has since I mounted it. I am not sure exactly which part made a difference. Here are the steps since my initial posting last night:

--the three-way fuel supply was pulled off and checked for obstructions; none were found;

--before putting back on the three-way fuel supply hoses, I gave each carburetor a shot of aerosol SeaFoam into the fuel intake fitting on the carburetor. Prior to this I had flooded with SeaFoam the entire system from engine fuel connector thru the fuel pump; I drained and refilled the carburetor three times with SeaFoam;

--a very minor, minute adjustment was made to the carburetor linkage; I am not sure I even moved anything, so minor was the adjustment; and,

--new cable ties were installed the three-way fuel line.

Here are the results:

--at the ramp the engine (of cours) smoked and kicked with the SeaFoam in the carburetors;

--when at WOT, the engine bogged way down, kicked, then went to WOT and ran great.

--tst run was about ten minutes;

--the primer bulb was pumped up when we first went to WOT, but that was the only time.

New steps to be taken next:

--fill all the fuel tanks (including portables) and go for marathon run--a good excuse for a day on the water--just to make sure the engine is running right.

Thanks for all the replies.

Ocean31

[jimh]

Of the several actions taken, the only one that seem to be plausible to have had an effect was the use of the aerosol SeaFoam on the fuel intake fittings of the carburetors.

[Oldslowandugly]

I'm glad you got it sorted out. Was the fuel pump changed? That would be the most likely improvement. Since the carbs had been rebuilt I doubt adding SeaFoam would have helped much except maybe to de-carbonize the combustion chamber.The fuel intake fittings on OMC carburetors are plenty big and it would take a lot to clog them. The needle and seats were probably clean as well or else the carbs would have flooded. The likelyhood of all three carbs having a problem are pretty slim, but the single fuel pump delivery system is highly suspect. If the same Sierra pump was used then something else was inadvertently corrected. If the V-4 pump was used then keep that one and toss that Sierra in the trash where it belongs.

[Ocean31]

The latest:


To oldslowandugly, I never changed out the fuel pump, maybe I should have since.........

Yesterday, (after the engine ran well for 10 mins) I went out for another run, The engine at first ran poorly, then ran good, then ran extremely poorly. At the end it was like one cylinder was not getting any fuel at all at WOT. Still idles well. During this run, I had was using a portable tank set up by the seat and I was able to pump up the bulb, no change.

I am afraid what I have is some foreign object in one of the carbs, more likely the bottom one, Unless someone has a better idea, I think I will remove and disassemble the carbs. Previous to this I wa trying to get her running without actually removing the carbs, but it doesn't seem like that is going to work.

Thanks

Ocean31

[Oldslowandugly]

First change that pump. If no difference then carry on. Have you ever rebuilt a carburetor? It is ridiculously easy and what you are really doing is cleaning it. The only parts that may require replacing are the needle and seat, float, and gaskets. You stated the carbs were rebuilt- by whom? How long ago? If they were done correctly, your starting and running dry should not have caused any problems. If you had left fuel in the bowls then I would expect a gunky carb needing cleaning. I would suggest getting an OMC manual and read up on carb overhaul. Then take one off and check it out. You will see how easy they are to service. Those carbs use fixed jets for idle and high speed, so cleaning is all that is needed, no adjustment. There is also the possibility that when they were serviced, a main jet was removed and damaged, and replaced by a smaller size because that was handy. When you have them apart, verify that the jets are the ones that belong there. Here is an exploded view of the carb- http://www.crowleymarine.com/johnson-evinrude/parts/43230.cfm

[Ocean31]

Thanks Oldslowandugly, your post is where I am. Thanks for the post. I will keep you informed on the continuing drama.

I do have a full OMC factory manual. I was just being lazy, and ending up making more work for myself. I should have pulled and cleaned the carbs first.

I found this afternoon that the bottom coil (all coils replaced by OMC shop as previously noted) had a crack in the mounting bracket. OEM coils were out of stock when the shop did the work, so they installed CDI coils. Back to the shop, and they (dealer) said they would install a new coil early next week.

As soon as she gets back from the shop (coil installation) I will pull and clean the carbs. As long as I am careful with the gaskets, probably will not even need a rebuild kit, just clean the carbs. As mentioned earlier, I figure I got some bit of junk, foreign object stuck in the bottom carb. Something that is going to take disassembly to remove this junk/object


Ocean31

[Oldslowandugly]

Sounds good. A guy with a factory manual and not afraid to open carbs? I love it! Check the float setting. They should be parallel with the gasket surface of the bowl. Too low a float level would definitely cause your problem. Tip- a thin smear of grease on the gasket will allow it to come off next time without sticking or tearing. Also, what kind of choke is on those carbs? Solenoid operated? Sometimes the butterfly is loose enough to close slightly at WOT.

[Ocean31]

Okay, latest and not so greatest:

Got the boat back from the shop, they fixed the mounting bracket for the coil on the bottom cylinder.

The shop mech said, "by the way you have a bad power pack."

II ordered a used power pack, put it on, and no change; major loss of power. See last test run. [Where?]

I had already ordered a carburetor rebuild kit. I tore-down and cleaned all three carburetors. The carburetorss were spotless inside, but I cleaned them anyway. Bolted-up everything and thought I would check for spark. Darn: bottom cylinder [number-three] has no spark.

I moved number-two orange wire from power pack to number three coil, No spark
Move number-three spark plug and wire to number two coil, have spark.
Move number-two spark plug and wire to number three coil, no spark.

This leads me to believe I have a bad new coil: am I correct? Or, did I miss something to check if it is a bad used power pack?

I have a shop manual but when the manual starts talking about ohms this, and test lead that, my head gets confused. If I move number-two orange wire down to number three coil, and still no spark, that should say bad coil, right?

Thanks

Ocean31

[jimh]

If you are not familiar with electrical characteristics like Ohms, you probably should not be attempting to perform electrical diagnosis.

A general rule for testing systems involving multiple components:

Assume a system "A" has these components:

A1 --> A2 --> A3 --> A4

If there is a parallel system, "B" that works and "A" does not, you can substitute components between the two systems. You start with the first component of the system under test, "A1". You test "A1" as follows:

A1 --> B2 --> B3 --> B4

If the test system does not work, the cause is A1. If the test system works, add the next component from the "A" system to the test system:

A1 --> A2 --> B3 --> B4

Repeat this process until you find the bad component.

HINTS:

A1 = Power pack individual cylinder circuit
A2 = Spark coil
A3 = High-tension spark lead
A4 = Spark plug

[Ocean31]

Thanks JIMH,

A much cleaner way of outlining the steps.

The only thing I have not checked is moving the A1 (number three power pack wire) to B (number two cylinder coil) and see if I have spark at number 2.
If so.....no way around it, bad coil. Or possibly bad ground on the coil, I will check the ground before ordering a replacment coil.

Looks like I had two seperate problems with this engine. In cleaning the carbs I have ruled out a fuel concern.

Thanks again for the reply

Ocean31

[Oldslowandugly]

Ocean31- I too am a simple fellow and your test seems valid to me, indicating #3 coil is bad, or perhaps maybe the high tension lead. When it comes to electrical items it is always possible to get bad components even brand new. The easiest path is to just replace them. I like to use an inductive timing light to test for spark. That would be the kind used on automobiles that just clips to the spark plug wire. Much less chance of being "bitten" by an errant spark.

[Ocean31]

Okay, I am missing something here. Now I have an engine that will only give me about half throttle, and wants to bog down and quit when I go to full throttle. Idles fine though, starts right up.

So the latest in the saga: Remember I had no spark on number three coil, so I took it back to the shop that had installed the new coils. They took a look at the engine, supposedly bringing back one of their retired mechanics that had experience on this kind of engine. The diagnosis, either bad stator or bad timing ring. SO.......off I purchase a used stator and timing ring off ebay, Remembering I had all ready purchased a used power pack off ebay. And before anyone pipes up to loud about used electrical parts off ebay, please remember this is a 1976 engine, All new electrical will run way more then engine will ever be worth. Went ahead and put on a new rectifier/regulator, it was cheap. Bottom line, now I have lots of spark at idle.

But take it to the lake for a test run........ no change. So....again I pull the carbs and check them for obstructions, Perfectly clean.

Well, maybe I blew a piston, so I check compression, 120lbs all three cylinders.

Darn, what I am missing?clean carbs, good spark, 120lbs compression, it should run. Could somehow the timing be way off? I am out of ideas.

[jimh]

I like your latest diagnosis. If the engine spark timing is not advanced as the engine speed increases you will soon run out of acceleration in engine speed. Whenever you change anything physical or mechanical in the timing system you better check the timing.

Do you have the OEM shop manual for the Johnson engine? It should have a very clear and well illustrated procedure for setting the ignition timing. Typically there is a mechanical linkage to the throttle lever; the link rotates the Timer Base slightly to change the timing. You need to set the idle throttle position timing, then the pick-up point when the timing will begin to advance, then the maximum amount of timing advance. It's all in the shop manual.

ASIDE: when I replaced the Power Pack in my 1990 Evinrude 3.0-liter V6 looper, it was recommended to check the timing, even though nothing mechanical or physical changed. But a different Power Pack could have slightly different timing behavior.

Since you have changed the Timer Base coil assembly and the Power Pack, you should check the timing. It could be way off.

[Oldslowandugly]

Check the gear shift safety lockout as it may need adjustment. It is on the starboard side of the motor. You can not go past part throttle unless the gear selector is in forward gear and the lockout allows the linkage to go to WOT. I am skeptical the timing might be off, but best to check. My reasons are: the flywheel is keyed to the crankshaft, and the magneto is located by screws. If the linkage was never fooled with, it should be as it was. That said, timing is checked two different ways. The factory wants the motor in a test tank, with a test wheel prop installed, and the timing checked with an inductive timing light at the specified rpm. The other way is on a boat, under way, with the engine cover off, one person operating the boat, and another person checking the timing. Not safe, but doable. A less dependable way is to drain the carbs of all fuel and disconnect any fuel lines, disable the starter neutral safety lockout so you can start in gear, remove all the spark plugs, ground them to the motor, have a helper spin the motor in forward gear with the starter, and manually advance the timing using the throttle while you check timing with the light. A PITA, but it works. Check that gear shift lockout first.

[jimh]

I am reminded of how I checked the timing on my 225-HP engine. I borrowed a test wheel propeller from my dealer. I checked the timing while the boat was moored in a boat slip at a marina. You don't realize how much noise a 225-HP engine makes at high-throttle settings and how much water is pushed around by the test wheel propeller, even though the boat is not propelled forward. People at the marina thought I was crazy.

[Ocean31]

Okay, Pointer missing on engine, Not a insurmountable concern, just take the pointer off the 115 Johnson and move it over. The pointer is just screwed in.

But in meantime.......once more, pulled all carbs, examined, all look good.

Took the boat to the lake, this time bringing someone to steer. Air intake removed from engine, Go WOT, only have about 2/3 power, exam all butterflys and spark advance, everything seems to opening just fine. Hold my hand over number 1 cylinder carb, engine immediately bogs out, Hold my hand over number 2 carb, engine immediate bogs out. Hold my hand over number 3 carb, minimum effect. SO......problem remains number 3 cylinder? The suction effect felt on my hand does seem slightly weaker on number 3 cylinder then on 1 or 2 cylinder However there is suction on number 3, you can feel it pulling on the back of my hand held up to the carburetor opening.

I have spark on number 3 cylinder at the house. Pull the plug, ground it to the block, observe spark even in bright sunlight. If the spark was intermentian, I would have misfire while at WOT, instead I have no power on number 3 at all. The engine idles a little rougher if I pull number 3 wire but not a lot rougher. I have torn down this carb 5 times now, I can find nothing different from any of the other carbs. SO whats left? Leave valve(s) sticking closed? Can I pull nuumber 3 carb, spray carb cleaner around the leave valve(s), PUll the number 3 plug rotate engine to clear out any carb cleaner, and try test run again?

Sorry to be a pain on this, but I am having a hard time figuring out why I do not seem to have power to number 3 cylinder.

Thanings

[Ocean31]

PS:

Just tried something, Went out started the engine at house in idle, on muffs for water. Shot aerosol sea foam into number three carb, no effect. Shot sea foam into number two carb, immediate bog out. So just a double check, it definetly seems number three cylinder is the problem.

So.....double check number three for spark, No spark....!!!. Darn it, this time I did wanted I wanted to do three messages ago. I exchanged number two coil for number three. Now no spark number two. Its the coil......garh!!! I told the shop when the boat went back to them, they said the coil is fine, it is new, the problem is the stator or timing base. No......the problem is interment failure of the number three coil. Never take these old engines to the shop, you can just trust the OMC book and your instincts, A lesson to myself, belive what I see, not what the shop tells me.

So...today is Sunday, no new coil is available, and I am tied up Monday thru Wed. I will see if I can get a coil localy on Thursday. Hook everything up and let you know what happened.

Thanks

[jimh]

Sounds like you finally found the culprit.

Re diagnosis of spark ignition problems: you can use the cheapest-first philosophy. When I was working through a troublesome intermittent spark problem, it was hard to pinpoint what component was at fault because the problem would come and go all the time; it was never constant. I just began substitution of all the elements of the circuit, starting with the cheapest and working toward the most expensive. The order was:

--spark plug ($5)

--spark wire ($10)

--spark coil ($25)

--Power Pack ($250)

I went through $40 of new plug, wire, and coil, and I still had the intermittent problem. That convinced me to take a chance on the expensive Power Pack replacement. For my problem, the Power Pack was the remedy to the intermittent problem. I ended up spending a few dollars more, but then I had some good parts left over that I could carry as spares.

[Ocean31]

Okay, Did not want to wait three days, so.......pulled one of the old coils out of the trash can, Installed the old coil in place of the new but bad CDI coil.

Down to the lake, It now runs on all three cylinders. Yeah.

Initially I had some light surging (please see my original message) but that stopped and she ran fine at different throttle settings including WOT. When I first hit the throttle the first time, she boged down then took off. After that initial time (which is also the time she lightly surged) the engine would go right up to WOT with no problems. Then while going back to the dock she quit, I had to lightly choke and restart.

SO.......I am still due to change out the new Sierra fuel pump and put on the fuel pump from the 115 Johnson. Same model OMC number between the two engines, so it should work. Then back out there on Thursday and see if that improves anything. In the meantime order a new OMC coil and install it in place of the older used OMC coil dug out of the trash.

Then do any fine tuning needed. But at least I got all three cylinders to run at WOT. SO we are making progress.

THanks for the replies, I just need to trust myself and the book more, and the shop less.

[Oldslowandugly]

"pulled one of the old coils out of the trash can". Some of my best parts were considered "trash". You are absolutely right relying on instinct rather than shops. They are in business to make money. Sometimes it seems if they solve your problem it's a coincidence. I am confident you will get this motor running like a champ.

[jhomeister]

I'm not familiar with this engine and I haven't followed this thread, but as I read it, it sure sounded like the coil was a problem, and that seems to be confirmed but it also sounds like there is still another problem. I haven't heard any mention of the fuel filter. Is there an inline filter, and was it bypassed when you ran the alternate fuel tank/line? Also is it upstream or downstream of the fuel pump. Consider changing the filter and installing it downstream of the pump. The pumps seem to be better at pushing fuel than sucking fuel through the filter.

[Oldslowandugly]

Just remember that these old motors were in use when the current mechanics were not even born yet. They are trained and have experience on the new motors which have very little in common with the old stuff. We old timers have no problem at all running these simplistic antiques because our skills are adequate for the task. That is why a factory manual and forums like this are invaluable to us. If you know of a dealer with a great working knowledge of these old motors it behooves you to patronize him- he is a rare bird.

[Ocean31]

Okay, Think I got it licked, the minor fuel starvation that resulted in only 90% power being available at WOT.

I moved the older OEM 1974 fuel pump over to the 1976 engine, Nah, things were actually a little worse. SO put the New Sierra pump back on.

Then I just went through the powerhead, Make sure all bolts and fasteners were tight, especially anything I had moved such as Coil and carb fasteners.
Recheck spark gap, increase plug gap to 0.045. Manual calls for 040, but one person on a old engine forum said his 70hp runs better at 050. So split the difference.

One of the problems has always been a concern about pinched/crimped fuel lines. The original design calls for two 1/4 inch fuel lines with 90 degree preformed elbows. However that part is discontinued and OMC says just use straight hose and make your own assembly. THe problem is the hoses has to be long enough not to crimp at the bend, and long hoses get pinched when the air silencer gets installed.

Back to lake, yet again for another test run. Engine ran good, but I still have not reinstalled the air silencer yet, so back to the dock. Reinstall air silencer, ever so gently as to not pinch any fuel lines. Back out on the lake, engine still runs good. I think I finally got it.

SO.....last thing to do is a marathon run, I filled up the main fuel tank in preparation for a long test run. But this is now Friday afternoon on a 4th of July weekend. Memorial day, 4th, and Labor day weekends you do not want to be on the water around here. To crazy. So maybe Tuesday I will get a chance for long run.
Thank you all for your inputs, it was helpful

Ocean31

[Oldslowandugly]

Sounds good. I hate OMC fuel lines. Especially the idiotic primer system they used in the '80s- '90's. Whatever size they used (1/16th ?) is unavailable anywhere. The tiny nipples break as soon as you look at them. And why can't the fuel pump and carb use the same size line like in the real old days? Yes, I 'll be sitting it out this crazy weekend too. As mad as I would be about going through all that work, as soon as I began to catch fish I would forget all about it.

[jimh]

I don't understand how some sort of hose used in the 1990's on OMC engines could be affecting this 1976 engine.

The fuel enrichment system on my 1992 Evinrude engine used 1/8-inch inside diameter hose to distribute extra fuel to each cylinder.

I did not find the design of the fuel enrichment system to be idiotic. It worked very well and greatly improved engine starting under cold start and cold weather conditions.

[Oldslowandugly]

Jim, I respectfully disagree. I have used both the manual and electric primer system and both are terrible. The solenoid for the electric type is prone to failing at the worst time and then testing OK later when it doesn't matter. The solenoid is over $100 if you can find one. At least the electric type has a manual over-ride that saves you if you know how to use it. Can you say "read the manual"? I do but most do not. As for the manual type, the plunger leaks, and must be rebuilt regularly. On both types there is a rat's nest of those tiny hoses that can get easily pinched or worse, the tiny plastic nipples break at will. Now you need to buy the plunger body for the manual, but at least the electric has a replacement top cap with the nipples. Both types are expensive. So what is my solution? I back fit a good old reliable choke. On a tiller model a manual choke is right there in front of you. On a remote model, the electric choke is key operated, but also has a manual lever built in just in case your battery is dead. Personally, I have never had a choke fail. Not trying to start anything, but sometimes older technology is superior.

[Ocean31]

Okay, Thought I had it the last time I worked on the engine. Took it out for a Marathon run, and it was still doing the same thing. Light surge, loss of power, laboring sound out of the engine.

I was out of ideas, so I ordered a heat stik, to check if the engine was overheating at top throttle. There is two valves in the head that are supposed to open when at top speed.

My son and I just got back from the lake, Nah,,,,,it is not overheating.

But here is the remarkable thing, Pull the hood, and the engine sounds better and the speed increases by 3.3 mph. Top speed with the hood off is 30.6 mph, put the hood back on, the engine sounds laboring, and speed drops to 27.3 at best. Mostly around 26 mph. Try running with the hood on at reduced throttle, Throttle up to 25 mph, engine is not laboring, but does not sound great. Leave the throttle alone, pull the hood, speed jumps to 27 mph.

If you remember my last post when I thought I got it, I was running the engine with the hood off, and I was installing the air silencer box to the front of the carbs. I was trying to not pinch the fuel lines. When I thought I got it, I had not run it with the hood on.

After Church tomorrow my son and I will try again. I am going to remove the front of the air silencer. See below drawing. Then run the engine with the hood on. See if that changes anything. I did not bring my tools to the lake today, since this was a check for overheating. I just brought the heat stik. I am going to remove part 41 cover. http://www.marineengine.com/parts/evinr ... /40754.gif
Engine section

A check of the hood shows no obstructions in the airflow. Air flows from the top of the hood into the engine compartment. I looked for something stuck in there. It all looks clear, so I do not know why the hood would make a difference except it sounds like the engine is not getting enough air.

Engine idles and starts right up though. Kind of bogging coming out of the hole with the hood on, but that makes sense. There is lots of new parts on this engine, compression is 120 lbs, Should not be having this kind of problem. Really weird.

So if anyone has any input, please feel free to chime in.

Ocean31

[GRAND NUSSIE]

I don't remember whether you checked your plug leads. My 35 hp Evinrude idled fine but could barely plane the boat with one person on board. When the throttle was advanced a plug lead was grounding out on the engine block.

[Ocean31]

Okay better run this morning.

Air silencer cover off, hood on. Back throttle slightly (maybe 90% throttle). Boat does 27.5 mph with minimum laboring or surging.

I think I will try changing out the high speed jets, easy and cheap check.

Thanks

Ocean31

[jhomeister]

What is the condition of the exhaust manifold and its seal where it enters the leg? If its leaking, the hood fills with exhaust and yields these symptoms.