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1978 johnson 70 hp

D

dofunny

Member
Hi Joe
I have a 70 hp Johnson

Hi Joe
I have a 70 hp Johnson
Model no is 70EL78C
Serial no is J4934075

The motor run great in the yard with the water ear attach to it. But when I carry it to the river the motor want make but 1800 rpm. I did some checking on the motor and found out that the motor suppose to make 5500 rpm. To make a long story short. I check the compression and everything check over a hundred and the spark jump 7/16 on my spark checker. I check the carbs and found out that one of the carbs high speed jet was clogg really bad and I cleaned all the carbs. But it still want make but 1800 rpm in the river. Some time the rpm will rev up to 2100 rpm but drop back to 1800 in a sec. It will rev up like that until I shut off the motor. It is about to beat my brain out. What else will not make this motor runn up to 5500 rpm like it suppose to do.
 
"Make sure that the linkages b

"Make sure that the linkages between the carburetors are set so that the carburetor butterflies are wide open at full throttle and closed at idle. They must all start to open at the same time. If one butterfly is out of synchronization, weird things will happen.

If you have proper compression and spark, you have either overlooked something within the carburetors, the timer base under the flywheel is sticking, or the throttle cable is not adjusted properly (butterflies not opening fully).

Spark plugs should be Champion QL77JC4 plugs, gapped at .040 ."
 
Hey Joe
I checked the linkage

Hey Joe
I checked the linkage and the butterflies are opening and closing like they should. I did have the wrong plug in the motor but I went out and got some QL77Jc4 and made sure the gap was set. You said something about the timer base under the fly wheel. I can see the rods and arm move when I push on the trottle. Can I just the timer base without taking the flywheel off? Can the different plug make that much different in the engine performance?
 
"The only other spark plug I&#

"The only other spark plug I'd recommend is the Champion L77JC4 which is the same plug but it does not have the suppressor feature. The "Q" in front of the designation indicates a suppressor plug that is designed to help eliminate interference in any electronic equipment.

Engine not running, spin prop while shifting to forward gear. Now have someone slowly move the throttle lever from the idle position to full throttle while you observe the timer base. The timer base under the flywheel should move smoothly from the idle position all the way to the full spark advance position which is having the timer base up against the black rubber tip of the full spark advance stop screw.

This can be observed without removing the flywheel."
 
Joe
Everything you are telli

Joe
Everything you are telling me is working like it is suppose to work. I can spin the prop and push it into grear and the prop stop. I can push the trottle slowly forward and I can see the timer base move to the stopper. There must be something else wrong with the carbs. Do you know of a site that has my carbs and a break down of the carbs. I cleaned everything except popping the little silver caps out. Did I tell you in the last post that the engine will rev. up to 2200 rpm and drop by down.
 
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