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Author Topic:   1996 Johnson 70: Runaway RPM

gmoulder posted 09-13-2014 10:33 PM ET (US)
Hello. The 1996 Johnson 70-HP engine [the starboard engine of a twin engine installation] was missing when I last had it in the water. Just before that, it was running great. I suspected the fuel had gone bad, as it had in the port engine. I put together a mixture of Seafoam, oil, Stabil, and gasoline, and I fed it to the engine using a 2-gallon container. I had done this before with success.
The engine instantly started and went into maximum speed with the throttle in idle or neutral. The air inlet cover had been removed, so I could see that the throttle plates were closed. I shut down immediately. I tried two more times with same results. Changed back to permanent fuel system: same results. I have not done anything to this engine since it last ran. What could be going on with this? The engine was clearly headed towards break-up. Thanks, Glen
jimh posted 09-14-2014 09:17 AM ET (US)
Try starting and running without any fuel hose attached. It sounds like the engine is burning off excess combustible material in the combustion chambers.
gmoulder posted 09-14-2014 09:17 PM ET (US)
Jim,
Thanks. Will try to find a way to slow down rpms while the engine burns off the fuel. Ideas? Perhaps method would be to put it in the water and after starting, immediately put in gear. Glen
kwik_wurk posted 09-14-2014 11:06 PM ET (US)
How long did it take to rev up, immediately as in 1-2 seconds, or did it climb over 10 seconds. -- If it revs immediately, than yes extra fuel in the chambers.
A simple check on the throttle cables, as it could be that it is are stuck wide open...or the carb linkage is off. -- Granted you state the plates are closed.
I am not familiar with choke mechanism on this motor, but you should hear a click for the solenoid (assuming this vintage it has one).
The carbs could be stuck open, and dumping fuel, and may need a cleaning.
No don't put it gear whilst it revs, you grind the lower unit, and have other problems.
deepwater posted 09-15-2014 12:52 AM ET (US)
Something is stuck open ,,Tapping on the carb bowls might unstick them and never throw any thing in gear when its running at high rpms,,If it dosent break its going to leave ya
gmoulder posted 09-19-2014 06:29 PM ET (US)
All is well, I think. Took the boat to Acie's in Dickenson; they do great work. Turns out that both carburetors were slightly open, allowing the runaway. They looked closed to me, but what do I know. No ability to trim up on the port engine was do a broken limit switch, which is apparently not needed on my setup, so was bypassed. Acie's tested compression and ignition while they were at it: all good. And they did a "link and sync" in their pond. Now, if I can just keep it going. Thanks everyone, Glen

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Author	Topic: 1996 Johnson 70: Runaway RPM
gmoulder	posted 09-13-2014 10:33 PM ET (US) Hello. The 1996 Johnson 70-HP engine [the starboard engine of a twin engine installation] was missing when I last had it in the water. Just before that, it was running great. I suspected the fuel had gone bad, as it had in the port engine. I put together a mixture of Seafoam, oil, Stabil, and gasoline, and I fed it to the engine using a 2-gallon container. I had done this before with success. The engine instantly started and went into maximum speed with the throttle in idle or neutral. The air inlet cover had been removed, so I could see that the throttle plates were closed. I shut down immediately. I tried two more times with same results. Changed back to permanent fuel system: same results. I have not done anything to this engine since it last ran. What could be going on with this? The engine was clearly headed towards break-up. Thanks, Glen
jimh	posted 09-14-2014 09:17 AM ET (US) Try starting and running without any fuel hose attached. It sounds like the engine is burning off excess combustible material in the combustion chambers.
gmoulder	posted 09-14-2014 09:17 PM ET (US) Jim, Thanks. Will try to find a way to slow down rpms while the engine burns off the fuel. Ideas? Perhaps method would be to put it in the water and after starting, immediately put in gear. Glen
kwik_wurk	posted 09-14-2014 11:06 PM ET (US) How long did it take to rev up, immediately as in 1-2 seconds, or did it climb over 10 seconds. -- If it revs immediately, than yes extra fuel in the chambers. A simple check on the throttle cables, as it could be that it is are stuck wide open...or the carb linkage is off. -- Granted you state the plates are closed. I am not familiar with choke mechanism on this motor, but you should hear a click for the solenoid (assuming this vintage it has one). The carbs could be stuck open, and dumping fuel, and may need a cleaning. No don't put it gear whilst it revs, you grind the lower unit, and have other problems.
deepwater	posted 09-15-2014 12:52 AM ET (US) Something is stuck open ,,Tapping on the carb bowls might unstick them and never throw any thing in gear when its running at high rpms,,If it dosent break its going to leave ya
gmoulder	posted 09-19-2014 06:29 PM ET (US) All is well, I think. Took the boat to Acie's in Dickenson; they do great work. Turns out that both carburetors were slightly open, allowing the runaway. They looked closed to me, but what do I know. No ability to trim up on the port engine was do a broken limit switch, which is apparently not needed on my setup, so was bypassed. Acie's tested compression and ignition while they were at it: all good. And they did a "link and sync" in their pond. Now, if I can just keep it going. Thanks everyone, Glen