78 Johnson, wont rev out. Starts and idles fine

[shawn_nj]

New member, did a quick search and didnt seen anyone with my year/specific issue. So I thought I would post a question.

Took my new (to me) boat out today. Boat ran awesome for first 25mins. Slowed down to go through a no wake, and then went to speed back up. Applied more throttle and the motor stalled. After this it would not rev out past 1/4 throttle. If you applied any additional throttle it would stall. Motor starts and revs fine. I have extremely limited knowlege of outboatds but I know 2smoke jetskis very well.

Did a compression test. 125-115ish on all holes, so the motor is physically ok. It really seems like a carb or electric problem. I quickly went over all the visible wires on the motor and the looked fine. I left the gas tank vent open for 2 weeks and its possible it got rained on...so water in the gas is a remote possibility. Anyone have links to multimeter tests I can run on the motor? Do there have overheat sensors that could be bad and stopping it from revving out?

ANY AN ALL HELP IS GREATLY APPRECIATED!!

 

[jtexas]

Re: 78 Johnson, wont rev out. Starts and idles fine

what horsepower?
If you suspect water in the fuel, I'd drain the tank to be sure.

What you're describing is a classic symptom of dirty carbs. But first, see if you're getting a good spark on all cylinders. Use an inline tester, set the gap at 7/16" and look for a sharp blue spark.

Good compression and good spark, then a carb rebuild is indicated. Here's a good how-to:
http://forums.iboats.com/showthread.php?t=244013

If you don't know the age of the water pump impeller, or if it's more than 2 or 3 years, this would be a good time to change it.

No reason you can't to all the repairs & maintenance on your motor -- the original factory manual is available on iboats.

welcome to iboats.

 

[shawn_nj]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

what horsepower?
If you suspect water in the fuel, I'd drain the tank to be sure.

What you're describing is a classic symptom of dirty carbs. But first, see if you're getting a good spark on all cylinders. Use an inline tester, set the gap at 7/16" and look for a sharp blue spark.

Good compression and good spark, then a carb rebuild is indicated. Here's a good how-to:
http://forums.iboats.com/showthread.php?t=244013

If you don't know the age of the water pump impeller, or if it's more than 2 or 3 years, this would be a good time to change it.

No reason you can't to all the repairs & maintenance on your motor -- the original factory manual is available on iboats.

welcome to iboats.

Its a 140HP. Thanks for the link. I am going to start at the carb and do the water pump impeller too. Only thing though, you said check the gap.... The plugs that were intealled have a dot in the center and are flat. They dont have the typical electrode that you would be able to gap. Any chance the guy I bought it from put the wrong plugs in it?

THANKS AGAIN!

 

[shawn_nj]

Re: 78 Johnson, wont rev out. Starts and idles fine

Another quick question, how many carbs are on the 140 model?

 

[bowtieboy77]

Re: 78 Johnson, wont rev out. Starts and idles fine

I have a 68 9.5 johnson outboard and mine did the same thing in nuetral it will rev up but in gear it would barly rev out more then a fast troll. It turned out to be 1 bad plug wire. I start with simple things before rebuilding the carb check for spark at plugs, check wires and finally check your coils.

 

[shawn_nj]

Re: 78 Johnson, wont rev out. Starts and idles fine

Cool, I had the plugs grounded when I was checking compression. I tried to check for good spark but did not look to closely. I am going to use new 94oct gas tomorrow in a tank I know is clean and water free. I will also buy a spark tester and try to verify I have good spark on the plugs. I would love to avoid having to take the carbs(s) off until the winter downtime.

 

[jtexas]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Its a 140HP. Thanks for the link. I am going to start at the carb and do the water pump impeller too. Only thing though, you said check the gap.... The plugs that were intealled have a dot in the center and are flat. They dont have the typical electrode that you would be able to gap. Any chance the guy I bought it from put the wrong plugs in it?

THANKS AGAIN!

you have surface gap plugs, if they're champions, they're probably good.

I said set the gap on your inline spark-tester to 7/16". You can get a spark tester for a couple bucks at any car parts store -- clip it to the engine block & connect the plug leads, one at a time. If your ignition system is delivering a weak spark to a cylinder, it can drop out under load and cause the kind of problem you're having. If it jumps a 1/2" gap outside the cylinder, that's a good indication that it's performing when you try to accelerate.

Carbs is more likely, but spark is easier to rule out so I usually do that first.

 

[Randybeall]

Re: 78 Johnson, wont rev out. Starts and idles fine

If you did get water in the carbs you should take off the air box and pull the bowl drain screws to let any out of the carbs before you run it again. Water generally will not pull through the jets and causes the engine to lean out. Much of that while running and you will need a piston or two. Better cautious than angry.
Randy

 

[shawn_nj]

Re: 78 Johnson, wont rev out. Starts and idles fine

If you did get water in the carbs you should take off the air box and pull the bowl drain screws to let any out of the carbs before you run it again. Water generally will not pull through the jets and causes the engine to lean out. Much of that while running and you will need a piston or two. Better cautious than angry.
Randy

Got a picture of the drain screws or a general descrpition of where they are located? I can take the air box off no problem, but I an not really sure where any specific parts are after that.

THANKS!

 

[shawn_nj]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

you have surface gap plugs, if they're champions, they're probably good.

I said set the gap on your inline spark-tester to 7/16". You can get a spark tester for a couple bucks at any car parts store -- clip it to the engine block & connect the plug leads, one at a time. If your ignition system is delivering a weak spark to a cylinder, it can drop out under load and cause the kind of problem you're having. If it jumps a 1/2" gap outside the cylinder, that's a good indication that it's performing when you try to accelerate.

Carbs is more likely, but spark is easier to rule out so I usually do that first.

They are champions, understand now what you were talking about with the gap. I will try that tomorrow!

 

[shawn_nj]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

UPDATE TODAY:
Swapped the plugs out and drained/installed fresh premix super gas. Motor would run up to 50% power instead of 30%...but still seems like its not getting fuel. I really believe the carb is blocked up with water.

Here is the weird part. If you put it in reverse, it revs out fine?!? But just cavitates and doesnt really go anywhere. Next troubleshoot will be removing the airbox and attempting to drain the carbs of any water.


I tried to locate a spark tester locally but was unable to. Will try an automotive store tomorrow. Its funny though, cuz it starts effortless and idles like a champ....just falls flat on its face when you open it up.

 

[jtexas]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

probably carbs -- spark test is just part of methodical troubleshooting approach. I just got tired of guessing and randomly throwing parts & money & time at 'em.

to view your engine schematics, go to www.shop.evinrude.com click on 'online parts catalogue' select "johnson" in the dropdown box and drill down to your year/model.

look for the hi-speed orfice plugs on the carburetor chart.

 

[shawn_nj]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

UPDATE 7/28:

Today we wanted to rule out the fuel pump, so we pumped the primer bulb while running the motor WOT. It made NO difference. Frusterated we went back to shore. I removed the intake cover to check the carb butterflys and they were perfect. So next move onto the fuel pumps fuel filter. The top of the filter looked fine and I almost reinstalled it. Right before I did, I looked in the tube on the bottom of the filter and held it up to a light. I COULD NOT SEE ANY LIGHT getting through the mesh?!?!? So I figured as a precaution I would replace the filter anyway...so I peeled the filter mesh back. TO MY SHOCK IT WAS COMPETELY GUMMED UP WITH SOLID DISGUSTING CRAP!! I dont know how this motor ran as much as it does. Guess the pervious owner(s) were not too careful with there gas. So tomorrow will be replacing the filter and tring another run. Also will be installing and inline filter and fuel/water seperator. I am REALLY hoping that is all the problem was, and I can wait until winter to service the carbs. I just want to be riding right now. Will post another update tomorrow, but very excited for this find!

QUESTIONS:
1) What RPM should I be seeing @ WOT?
2) What APPROX top speed should I be seeing on a 19' fiberglass boat.

 

[jtexas]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

The filter being bad as it was, I'd do the carbs before taking it out; some particles are bound to have got through, and partially blocked jets means a lean mixture & higher than normal combustion temps -- don't blame ya if you don't want to wait though. When you do get around to the carb rebuild, you'll see what I mean -- it's surprisingly simple. There's way worse ways to spend an afternoon.

If it bogs down when you try to accelerate, don't mess around with it, bring it on back & do the carbs. Any cylinder starving for fuel is also not getting any lubrication.

WOT RPMs depends on hull design, motor height and prop pitch. If the prior owner set it up right, he was running at 5500 to 6000. Speed obviously depends on hull design and weight/balance. Shouldn't be less than 37mph, could be upwards of 55. (an estimate based on messing around with similar motors -- somebody with more directly related actual experience might chime in with better info).

sure sounds like fun, though.

 

[iwombat]

Re: 78 Johnson, wont rev out. Starts and idles fine

You should also be able to save yourself some $$ and just run 87 octane gas. The 140 has high-compression heads though, so it's worth a double-check to see if that's the case.

Anyone want to chime in on that?

 

[79johnson]

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

Re: 78 140 HP Johnson, wont rev out. Starts and idles fine

The filter being bad as it was, I'd do the carbs before taking it out; some particles are bound to have got through, and partially blocked jets means a lean mixture & higher than normal combustion temps -- don't blame ya if you don't want to wait though. When you do get around to the carb rebuild, you'll see what I mean -- it's surprisingly simple. There's way worse ways to spend an afternoon.

If it bogs down when you try to accelerate, don't mess around with it, bring it on back & do the carbs. Any cylinder starving for fuel is also not getting any lubrication.

WOT RPMs depends on hull design, motor height and prop pitch. If the prior owner set it up right, he was running at 5500 to 6000. Speed obviously depends on hull design and weight/balance. Shouldn't be less than 37mph, could be upwards of 55. (an estimate based on messing around with similar motors -- somebody with more directly related actual experience might chime in with better info).

sure sounds like fun, though.

(SHAWNS FRIEND/BOAT COOWNER POSTING)

UPDATE 7/29:

JTEXAS, I think you maybe on to something. New fuel filter didnt make a difference at all....nothing. Took the boat for a 2min circle around to see if it would clear up and start to rev out...but nothing. Man, this is getting frusterating!! Looks like the carbs have to come out & be cleaned up to be 100% sure they are not the issue. Removing them looks easy enough, just have to figure out how to get the linkage off. Regardless I will be pulling the carbs tomorrow, and a buddy who has done a few outboard motor rebuilds will be assisting me to make sure I dont do something completely wrong.

I am starting to suspect the possibility that its spark related though. Motor just smells like gas, like its blowing fuel out and not firing completely. No visual fuel leaks whatsoever though. Spark tester should be being delivered tomorrow, and I will verify spark.

Tach said 1700RPMS was the max.... same as prior to fuel filter cleaning.

 

[79johnson]

Re: 78 Johnson, wont rev out. Starts and idles fine

You should also be able to save yourself some $$ and just run 87 octane gas. The 140 has high-compression heads though, so it's worth a double-check to see if that's the case.

Anyone want to chime in on that?

Thanks for the reply!! I know its not a direct comparison, but all our jetskis run high compression and aggressive timing advances.... so as a precaution I ONLY have super gas around, so I do not deto any of my toys. If I didnt have all the skis, I would probably just run 91 or 87.

 

[shawn_nj]

Re: 78 Johnson, wont rev out. Starts and idles fine

UPDATE 7/30:

IT NEVER ENDS! BUT PROGRESS MADE. Got my spark tester with adjustable gap. Turns out the cylinders on the starter motor side, were NOT FIRING!!! I immediatley suspected powerpack, so I started tracing out all the wires for it. One of the sealed wire couplers had come apart enough for the powerpack to not get any juice! So plugged that back together and ziptied it to try to stop a reoccurance. Checked spark, AND IT HAD GREAT SPARK ON THE NONSPARKING SIDE!!

Immediatly lifted anchor (boat is moored) and started it up. Let it idle up for a min and gave it some gas.......

MOTOR WAS STILL NOT REVVING BEYOND 2,000RPM. $#&#&@!

So did a 50second circle and went back to shore. Now I was pissed becuase I thought I had it figure out for sure. Now I pull the spark plugs to check them. Both top plugs have a good looking carbon build, the bottom 2 are still shiny brandnew looking!! WTF! So I checked spark on both bottom cylinders, and both have nice spark that passes the 7/16" test no prob. So immediatly I suspect the lower carb as being problematic.

I then remove the intake cover, and metal intake top. Start to remove the carbs when I relize I didnt have the 11mm wrench needed on the boat to remove them. So before I called it a day (night) I reached under the lower carb. The fuel line felt like S#$T, had NO ziptie/clamp, and it was leaking pretty bad. I FOUND MY FUEL LEAK!!! The bottom carb could not be getting much fuel if any!! YIKES!

PLAN OF ATTACK TOMORROW:
Remove carbs tomorrow after work and rebuild/clean them on Friday. I have 2 carb kits. Also replace EVERY fuel line in the motor as a precaution, while I have it aprat anyway.

Anyone have any other suggestions or input, anything I might be forgetting???

EDIT:

Also to get the 11mm carb nuts off, doI have to remove the flat head looking screws that are blocking the nuts from coming off?

Thanks for all the help so far, I really feel like I am making progress and learning a TON!! Fixed a bunch of small things that would have probably come up later.