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SUBJECT: # 27774: 70 HP Johnson won't idle for long durations w/o dying

Submitted by Polecat (69.250.159.98) from MARYLAND on 5/29/2007 6:41:00 PM

Am having a continuous problem with my 1985 70 HP Johnson not wanting to continue idling for long periods while running a trot line. Some days it never stops, but lately it's been quitting after idling at about 700 RPM in gear for less than 5 minutes. It restarts immediately every time. Tried adjusting trim to no avail. Decarboned recently, less than 20 hours ago. Runs great at all other speeds, but slow. Any suggestions other than replacing the fuel pump which is next on the list? Exactly what is involved in sync & link. At times it seems like it is running lean since I have to bump the electric choke when I advance the throttle to get it to giddyup. Help appreciated on this one. Thanks!


  1. 6/2/2007 4:18:00 PM Submitted by Dunk79 (69.249.201.219) from NJ says Fuel Pump
    Thats either a pin hole in pump diaphram or you've got a slight air leak in the fuel line somewhere. A small air leak can be pulled closed when you advance the throttle by the suction of the pump. I'd check all the hose connections from the tank to the carbs.

    Could also be a bad primer ball. If you are burning E10 fuel thru an 1985 engine the fuel hoses and carb gaskets may not be alcohol resistant. It wasn't until 91-93 when outboard manuf's went to alcohol resistant materials. E10 could be eating away the rubber parts of the pump.

    Does the engine have a VRO or do you mix the oil in the tank.


  2. 6/3/2007 10:37:00 AM Submitted by Polecat (69.250.159.98) from MD says Thanks Dunk for the reply.......
    New fuel line and primer bulb have been replaced. Will replace fuel pump soon. VRO was removed and 50:1 gas:oil ratio has been mixed for the past 10+ years. All hoses to the carbs look good, but may also replace them after the fuel pump is changed and if no positive results follow. Motor is also decarboned with SeaFoam at regular intervals. Just began adding Seafoam to each 6 gal tank of gas every fillup. Will report on progress after fuel pump replacement. Still would like to know all that is involved in Sync & Link adjustments. Suspect all is not kosher in that department.


  3. 6/4/2007 11:06:00 AM Submitted by Dunk79 (69.249.201.219) from NJ says Sync & Link
    When the engine stalls try squeezing the ball. If it takes more than 1-2 squeezes to fill(top off)the carbs and get hard that means the carbs are going empty....and it's a fuel supply problem..

    Sync & link is the timing adjustment between when the carbs open and the ignition timing advances. It wouldn't have anything to do with it stalling after it's been idling. If the S&L was off the engine would just fall on it face when you opened the throttle. Getting just the right amount of timing spark and fuel is super critical for a 2 stroke engine when it's getting up to RPM, but unless it was changed manually or one of the cam rollers wore out and/or fell off it won't change by itself.


  4. 6/4/2007 5:03:00 PM Submitted by Polecat (69.250.159.98) from MD says Worn cam roller & plastic connectors??
    I recall once, many years ago that a roller that the throttle cam rides against was replaced. I'm not certain it was with the proper replacement part and ever since it has not always jumped to attention when the throttle was advanced off idle to full throttle. Usually the choke solenoid has to be activated and a shot of gas sent into the carbs to get it to giddyup. I think I'll order a new roller along with the fuel pump. Perhaps the little plastic adaptors that hold the rod that ties all 3 carbs together could stand replacement as well. Any other recommendations? Thanks!! I really appreciate your input and the time you take to help me and others on this forum, Dunk.


  5. 6/4/2007 11:58:00 PM Submitted by Dunk79 (69.249.201.219) from NJ says These Guy's...
    http://ishopmarine.com/ishop/jsp/AsplIsmHomeCcat.jsp?reqFor=29

    Have the parts you need and they are OMC/Bomb parts. Their 10-20% cheaper than local and their shipping is cheap.

    Yes that cam roller has to be right. The ingition timing has to be within 2 degrees or the engine won't get up to rpm the way it should. Any of those plastic parts could be worm and creating slack. They are too cheap not to replace when you are in there doing it.

    You stated the VRO was "removed"?? Was it replaced with a standard fuel pump or did you mean to say it disconnected from the alarms?? and oil just mixed in the tank?

    If you have to replace the VRO there is a gas only version. Ask those guys in the link above, they have the gas only version and it's 2/3rd's the price of a VRO oil/gas version.

    Those engines are not tough to convert to the old style fuel pump that only costs 50 bucks. You just have to replumb the fuel lines to the carbs. I've done a bunch of V4's, but they only have two carbs. Your's has three. I used 5/16" copper tubing.


  6. 6/13/2007 8:57:00 PM Submitted by Polecat (69.250.159.98) from MD says Rebuilt fuel pump made it like new again!!!!!!!!!
    I obtained a fuel pump rebuild kit locally for less than $25.00 and in less than an hour I had the pump rebuilt and the motor humming. The next day I went crabbing and let the motor idle for over 6 hours while runing the trot line. I revved it up only a few times between runs of the line and it ran flawlessly. Not once did it quit on me as it did so many times before the rebuild. When the throttle was advanced to full, it jumped to speed without hesitation. It was the best investment I ever made in that motor. I guess asking 15 years from a fuel pump is a bit much. WHAT a DIFFERENCE!!!! Thanks Dunk for taking the time to offer assistance. Greatly appreciated!!!


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