1996 Johnson 70-HP: No Low-RPM Power - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  1996 Johnson 70-HP: No Low-RPM Power

search | FAQ | profile | register | author help

Author Topic:   1996 Johnson 70-HP: No Low-RPM Power

gmoulder posted 06-27-2014 11:08 AM ET (US)
Hello. My boat is 1988 Outrage 18. It's engines are twin 1996 Johnson 70-HP. I have run the boat regularly, and have included fuel inhibitor into each refueling. Am in Orange Beach on vacation--has to happen on vacation--and Port engine has these symptoms: starts well from cold or hot condition, idles well, runs well from 2000-RPM and higher. Problem: from idle to 2000-RPM generally does not take load in transition and cuts off, not back to idle, shuts completely off. It requires many attempts of "popping" the port engine through the 1000- to 2000-RPM phase before I can get into the higher useful RPM. I talked to boat repair people in Houston. They advise was to remove "air box", spray cleaner into carburator body, and remove "screw" in bowl. I would like to have additional opinions as to problem and remedy before I begin messing with engine. I might not attempt fix here, but would like to know emergency fix for future. Thanks, Glen
tedious posted 06-27-2014 03:24 PM ET (US)
The place you called is right. Chances are one of the carbs has a blockage of the high speed jet. I don't remember the exact setup on these carbs, but I think it is indeed at the bottom of the float bowl, and removing the screw that covers it and spraying in some cleaner may help. You'll need to try all 3 carbs until you find the one that cures it - it's unlikely more than one went bad. Unfortunately, it's also unlikely that a simple spray will cure it - you may need to take off the float bowl and blow it out from the back side, or get the special tool that allows you to remove the jet.
As to how I know - I had the exact same symptoms, and the root cause was a tiny piece of fuzz in one carb - and I mean tiny, like a carpet fiber, much thinner than a hair.
If you get the factory service manual and rebuild the carbs yourself over the winter, you'll know all about working on them.
Tmi
jimh posted 06-28-2014 03:22 AM ET (US)
Check for loose spark plug wire on one cylinder.
gmoulder posted 06-29-2014 06:03 PM ET (US)
Tedious and Jim,
Thanks. Back in Houston. Love that Outrage. Trolled outside the ORA pass, and boat and engines were great. Removed cowl for port engine; think that I can handle the rebuild, it is getting the carbs off the engine that looks most difficult. West Marine [across street] does not sell the factory O&M manual for the Johnsons'; how would I get one of those?
GRAND NUSSIE posted 06-29-2014 07:16 PM ET (US)
One simple thing you might try before you tear into it. IF it has low speed mixture screws that you can adjust with a screwdriver, open all three up an eighth of a turn and see if that helps. Do not confuse with idle speed screws. It's possible that one or more may be gummed up or have some dirt stuck in there. I had a similar problem with my 8 hp. It would backfire at certain medium speeds and finally quit and then be hard to start.
Dick
tedious posted 06-30-2014 08:26 AM ET (US)
Glen, I got my manual here: http://www.marineengine.com/parts/parts.php#manuals
You definitely want a factory service manual, not an aftermarket one.
With all respect to Dick, if the motor is idling well I would not mess with the idle air bleed.
If I remember these carbs right, the bottom of the float bowl has a drain screw. If you remove that, the fuel will drain out of the bowl. The high speed jet is behind that screw, down a tube. OMC has a special tool to remove it, or you can make your own - it's basically a fairly thick-bladed screwdriver ground to a narrower width, to fit in the tube. In your situation, I'd be tempted to try removing, cleaning, and reinstalling the jets before going with a full rebuild.
One thing to mention - all the linkage adjustments on these motors work together, and you do not want to just tweak one adjustment. It's unlikely to make anything better and very likely to make it worse. The process of getting things back into adjustment is called a "link and sync" - it's not hard, and is explained well in the manual.
Good luck!
Tim
gmoulder posted 07-01-2014 09:06 PM ET (US)
All: Once again thanks for all the good counsel. Have been reading manuals and looking at online videos regarding carburetors. Seems that the problem must be in the low speed transition from low to high speed jet. Can see how to get to high speed jet, but not sure how to get to low speed. Advice please. Also, just watched utube video of fellow with 6 cyl Johnson 2 stroke. Exactly my problem. This guy first sprays carb cleaner into the carb throat and an orifice, then runs the engine on a mixture of carb cleaner and fuel for 20 minutes or so. It certainly cured the problem, but I do wonder about the effect of the carb cleaner on the inside of the engine. I missed the ratio of cleaner to fuel. Has anyone knowledge of this method of cleaning the carbs. Thanks, Glen
mkelly posted 07-02-2014 12:15 AM ET (US)
I had a 1986 70 HP Johnson on my Whaler. It started and idled beautifully, and ran great at high RPM. We battled the acceleration and motor dying for quite some time before a mechanic identified it as the Reed Valves. I have no idea what that is but is carburetor related. I would ask your mechanic. After we took care of that it ran beautifully all thru RPM range.
tedious posted 07-02-2014 07:56 AM ET (US)
Glen, if memory serves, there are no low speed jets, per se, on these carbs - just a series of drilled holes. There is an adjustable idle air bleed to tune the idle mixture - but you're idling fine, so clearly your idle circuit is in good shape. And because of that, I think your problem is not just dirty carbs - those little drilled holes usually plug up first.
Here's what I would try, in order (having been in a situation with exactly the same symptoms before):
1) Try carb cleaner: remove the float drain screw. Stick the little red tube on the carb cleaner can into the hole and spray out the high speed jet. Reassemble and test.
2) Try removing the high speed jet and clean it, as described above - you'll need the special tool, or make one. Reassemble and test.
3) Redo the link and sync per the service manual.
4) Carb rebuild.
The snake oil won't do any harm, but it's also unlikely to do any good.
Tim
tedious posted 07-02-2014 08:01 AM ET (US)
Also, although it's unlikely, your problem certainly could be a reed valve that isn't seating or is damaged. In that case, you'd be getting a spray of fuel back out of the carb when operating. You can check this by running with the air intake off.
Tim
jfortson posted 07-03-2014 09:53 AM ET (US)
Just a little advice if you plan to remove the carbs, take plenty of pictures from all angles before taking off and also after laying carbs on the bench. It will be a great help when putting the linkage back together.
I think you have 3 carbs. I rebuilt 1 carb at the time. If I was not sure about something, I always had another to look at or take apart to see how it was put together.
Al-in all it was pretty simple and I would have no problem doing it again. I did have a service manual for the float settings, etc. and I think you can find sites on the internet with pictures.
gmoulder posted 07-06-2014 12:58 PM ET (US)
Thanks to everyone. I believe that I have solved (with lots of good help) part of the problem, and helped the engines in other ways. Here is what happened:
1. Removed "air boxes".
2. Removed float bowl drain screws and squirted carb cleaner into carb throats and into float bowls. Could not find main orifice access screw.
3. Replaced screws and ran engines while squirting carb cleaner into throats. Determined that bottom port float bowl drain screw was very loose (hummm), in fact no fuel came out of bowl. Fair amount of smoke from engines.
4. De-carbed engines in accordance with "Sal" method. Noticed that port engine much more difficult to turn by hand than starboard.
5. Started engines next day in water. Big smoke again. People stopping to see what I was doing. No two stroke people had ever heard of de-carbonizing.
6. Made jury rig fuel system for port engine of two gallon container, squeeze bulb, hose and fuel fitting. Ran two gallons of fuel (with oil) and two cans of Seafoam through port engine.
7. Results: noticable improvement in both engines. Much quicker start-up, smoother running. Port engine cut-off only once during low rpm (1100) load, as opposed to almost everytime while in OBA week before last.
8. Caught Clear Lake on a morning when the surface was not 'lumpy". WOT yields 6000 on starboard and 6200 on port. Bouncing between 39 and 40 mph with bimini up.
9. Am not taking the Whaler to the boat doctor just yet. Will do the Seafoam business again, and then consider rebuilding the port carbs if it bothers me. The operation of the engines are certainly acceptable and reliable.
10. Please add my name to list of de-carbonizing advocates.
tedious posted 07-07-2014 10:20 AM ET (US)
Nice work - sounds like you dislodged whatever was clogging the high speed jet, and a decarb is often a good thing. Smokes a bit, doesn't it?
For reference, there is no main orifice access screw - the main orifice is down the tunnel under the float bowl drain screw. The brass jet itself has slots milled into it to accept the special tool, or a modified screwdriver.
Tim

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 1996 Johnson 70-HP: No Low-RPM Power
gmoulder	posted 06-27-2014 11:08 AM ET (US) Hello. My boat is 1988 Outrage 18. It's engines are twin 1996 Johnson 70-HP. I have run the boat regularly, and have included fuel inhibitor into each refueling. Am in Orange Beach on vacation--has to happen on vacation--and Port engine has these symptoms: starts well from cold or hot condition, idles well, runs well from 2000-RPM and higher. Problem: from idle to 2000-RPM generally does not take load in transition and cuts off, not back to idle, shuts completely off. It requires many attempts of "popping" the port engine through the 1000- to 2000-RPM phase before I can get into the higher useful RPM. I talked to boat repair people in Houston. They advise was to remove "air box", spray cleaner into carburator body, and remove "screw" in bowl. I would like to have additional opinions as to problem and remedy before I begin messing with engine. I might not attempt fix here, but would like to know emergency fix for future. Thanks, Glen
tedious	posted 06-27-2014 03:24 PM ET (US) The place you called is right. Chances are one of the carbs has a blockage of the high speed jet. I don't remember the exact setup on these carbs, but I think it is indeed at the bottom of the float bowl, and removing the screw that covers it and spraying in some cleaner may help. You'll need to try all 3 carbs until you find the one that cures it - it's unlikely more than one went bad. Unfortunately, it's also unlikely that a simple spray will cure it - you may need to take off the float bowl and blow it out from the back side, or get the special tool that allows you to remove the jet. As to how I know - I had the exact same symptoms, and the root cause was a tiny piece of fuzz in one carb - and I mean tiny, like a carpet fiber, much thinner than a hair. If you get the factory service manual and rebuild the carbs yourself over the winter, you'll know all about working on them. Tmi
jimh	posted 06-28-2014 03:22 AM ET (US) Check for loose spark plug wire on one cylinder.
gmoulder	posted 06-29-2014 06:03 PM ET (US) Tedious and Jim, Thanks. Back in Houston. Love that Outrage. Trolled outside the ORA pass, and boat and engines were great. Removed cowl for port engine; think that I can handle the rebuild, it is getting the carbs off the engine that looks most difficult. West Marine [across street] does not sell the factory O&M manual for the Johnsons'; how would I get one of those?
GRAND NUSSIE	posted 06-29-2014 07:16 PM ET (US) One simple thing you might try before you tear into it. IF it has low speed mixture screws that you can adjust with a screwdriver, open all three up an eighth of a turn and see if that helps. Do not confuse with idle speed screws. It's possible that one or more may be gummed up or have some dirt stuck in there. I had a similar problem with my 8 hp. It would backfire at certain medium speeds and finally quit and then be hard to start. Dick
tedious	posted 06-30-2014 08:26 AM ET (US) Glen, I got my manual here: http://www.marineengine.com/parts/parts.php#manuals You definitely want a factory service manual, not an aftermarket one. With all respect to Dick, if the motor is idling well I would not mess with the idle air bleed. If I remember these carbs right, the bottom of the float bowl has a drain screw. If you remove that, the fuel will drain out of the bowl. The high speed jet is behind that screw, down a tube. OMC has a special tool to remove it, or you can make your own - it's basically a fairly thick-bladed screwdriver ground to a narrower width, to fit in the tube. In your situation, I'd be tempted to try removing, cleaning, and reinstalling the jets before going with a full rebuild. One thing to mention - all the linkage adjustments on these motors work together, and you do not want to just tweak one adjustment. It's unlikely to make anything better and very likely to make it worse. The process of getting things back into adjustment is called a "link and sync" - it's not hard, and is explained well in the manual. Good luck! Tim
gmoulder	posted 07-01-2014 09:06 PM ET (US) All: Once again thanks for all the good counsel. Have been reading manuals and looking at online videos regarding carburetors. Seems that the problem must be in the low speed transition from low to high speed jet. Can see how to get to high speed jet, but not sure how to get to low speed. Advice please. Also, just watched utube video of fellow with 6 cyl Johnson 2 stroke. Exactly my problem. This guy first sprays carb cleaner into the carb throat and an orifice, then runs the engine on a mixture of carb cleaner and fuel for 20 minutes or so. It certainly cured the problem, but I do wonder about the effect of the carb cleaner on the inside of the engine. I missed the ratio of cleaner to fuel. Has anyone knowledge of this method of cleaning the carbs. Thanks, Glen
mkelly	posted 07-02-2014 12:15 AM ET (US) I had a 1986 70 HP Johnson on my Whaler. It started and idled beautifully, and ran great at high RPM. We battled the acceleration and motor dying for quite some time before a mechanic identified it as the Reed Valves. I have no idea what that is but is carburetor related. I would ask your mechanic. After we took care of that it ran beautifully all thru RPM range.
tedious	posted 07-02-2014 07:56 AM ET (US) Glen, if memory serves, there are no low speed jets, per se, on these carbs - just a series of drilled holes. There is an adjustable idle air bleed to tune the idle mixture - but you're idling fine, so clearly your idle circuit is in good shape. And because of that, I think your problem is not just dirty carbs - those little drilled holes usually plug up first. Here's what I would try, in order (having been in a situation with exactly the same symptoms before): 1) Try carb cleaner: remove the float drain screw. Stick the little red tube on the carb cleaner can into the hole and spray out the high speed jet. Reassemble and test. 2) Try removing the high speed jet and clean it, as described above - you'll need the special tool, or make one. Reassemble and test. 3) Redo the link and sync per the service manual. 4) Carb rebuild. The snake oil won't do any harm, but it's also unlikely to do any good. Tim
tedious	posted 07-02-2014 08:01 AM ET (US) Also, although it's unlikely, your problem certainly could be a reed valve that isn't seating or is damaged. In that case, you'd be getting a spray of fuel back out of the carb when operating. You can check this by running with the air intake off. Tim
jfortson	posted 07-03-2014 09:53 AM ET (US) Just a little advice if you plan to remove the carbs, take plenty of pictures from all angles before taking off and also after laying carbs on the bench. It will be a great help when putting the linkage back together. I think you have 3 carbs. I rebuilt 1 carb at the time. If I was not sure about something, I always had another to look at or take apart to see how it was put together. Al-in all it was pretty simple and I would have no problem doing it again. I did have a service manual for the float settings, etc. and I think you can find sites on the internet with pictures.
gmoulder	posted 07-06-2014 12:58 PM ET (US) Thanks to everyone. I believe that I have solved (with lots of good help) part of the problem, and helped the engines in other ways. Here is what happened: 1. Removed "air boxes". 2. Removed float bowl drain screws and squirted carb cleaner into carb throats and into float bowls. Could not find main orifice access screw. 3. Replaced screws and ran engines while squirting carb cleaner into throats. Determined that bottom port float bowl drain screw was very loose (hummm), in fact no fuel came out of bowl. Fair amount of smoke from engines. 4. De-carbed engines in accordance with "Sal" method. Noticed that port engine much more difficult to turn by hand than starboard. 5. Started engines next day in water. Big smoke again. People stopping to see what I was doing. No two stroke people had ever heard of de-carbonizing. 6. Made jury rig fuel system for port engine of two gallon container, squeeze bulb, hose and fuel fitting. Ran two gallons of fuel (with oil) and two cans of Seafoam through port engine. 7. Results: noticable improvement in both engines. Much quicker start-up, smoother running. Port engine cut-off only once during low rpm (1100) load, as opposed to almost everytime while in OBA week before last. 8. Caught Clear Lake on a morning when the surface was not 'lumpy". WOT yields 6000 on starboard and 6200 on port. Bouncing between 39 and 40 mph with bimini up. 9. Am not taking the Whaler to the boat doctor just yet. Will do the Seafoam business again, and then consider rebuilding the port carbs if it bothers me. The operation of the engines are certainly acceptable and reliable. 10. Please add my name to list of de-carbonizing advocates.
tedious	posted 07-07-2014 10:20 AM ET (US) Nice work - sounds like you dislodged whatever was clogging the high speed jet, and a decarb is often a good thing. Smokes a bit, doesn't it? For reference, there is no main orifice access screw - the main orifice is down the tunnel under the float bowl drain screw. The brass jet itself has slots milled into it to accept the special tool, or a modified screwdriver. Tim