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Johnson 70hp Engine stops running on acceleration

D

davenaus

Member
I have a 1980 70hp Johnson; J70TLCSA. Have taken it out a couple times to water ski. Both times the motor stops running upon adding power to pull the skier. If I add power slowly then I can get the power to full and it runs fine there. It is the acceleration that seems to be a problem. I have checked the compresson. Top cylinder 130psi, middle 125psi, bottom 140psi. The engine runs smoothly at top speed. It seems to run pretty smoothly at idle. The fuel is 50:1 fresh unleaded, 93 octane. A friend thinks it is a mixture problem. The air filter looks clean. Have had a shop look at timing and they said it was fine a about 10 motor hours ago. Plugs seem ok and gapped properly. I have not adjusted mixture and need to find out how. Any other thoughts? Thanks, Dave
 
I do not believe there is a mixture adjustment ---------------No air filter on these when it left the factory!---------------Remove the high speed jet ( orifice ) found in the bottom of the carburetor bowls and clean it.----------No need to remove carburetors , except maybe the bottom one.
 
You are right Racerone... No air filter. Removed screw at bottom front of carb. See a small gold item inside with very small flat screw head. Tried turning it to get it out. Seems to turn ok but doesn't want to back out. How do you get the jets out? Seems like a special tool might be needed. Or a toothpick as there is a hole in the center. Are the upper screws and jets for idle? Cheers, Dave
 
The jet screws right out.-------------------I do not believe the motor came from the factory with low speed mixture adjustment, it is also fixed.
 
The jet screws right out.-------------------I do not believe the motor came from the factory with low speed mixture adjustment, it is also fixed.--------------On ------shop.evinrude.com----------you will see that the idle orifice #27 was larger for late production motors.---------------No adjustment on mixture other than drilling / changing the orifice !!
 
Hi Racerone, I was mistaken in jet we are talking about. Now I am on #27. It won't turn with small glasses screwdriver. I need to get another screwdriver with larger handle. Wonder if it won't turn with smaller screwdriver is due to corrosion. Don't want to strip slot in screw. Is a special tool required? Cheers, Dave
 
A 3/16" ( 5 MM ) shank screwdriver will take them out ---------------------There is a special factory screwdriver for the high speed jet in the bottom of the bowl but that is not usually needed.-------#27 is for the low speed mixture.
 
Dismantle the carbs. Clean and CHANGE gaskets, at least #20, a rebuild kit is the best.
http://www.marineengine.com/parts/j...LCSA&manufacturer=Evinrude&section=Carburetor
Use a spray can with carb cleaner and check that all channels are open, particularly those behind #5, #26 and #35
Note the different jetting in the different carbs, do not mix!
When reassembling, be sure all gaskets are good, even in the air-box. Vacuum created in the air box helps starting the main jets.
Check your link and synch, particularly the pick-up timing!! (when carbs starts to open, roller aligned with mark on cam).
 
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