'78 Johnson 75HP will not return to idle.

[Whitetail55]

Remote checks out okay but had been in the weather for several years. Cables are free when disconnected from engine. I have removed throttle/shift lever assembly cleaned and lubed, still will not return to idle stop and I really have shove down on control to get WOT. Next step is to get out OEM manual and step by step start over with set up, again.

 

[flyingscott]

Broken cable or bad shift linkage

 

[Whitetail55]

I got it to work as it should but the carburetor cable is adjusted almost all the way in. I am thinking that cable may have broke at the remote and was shortened or replaced with longer and cut too short. This thing has been massaged! I replaced the pwr head with a '78 75hp Stinger. Looks like I need to do a seal kit, impeller assy., and inspection on the Stinger lower to get the 75hp out of it. I am still using the original '85 lower from 70hp as I resealed and replaced the impeller assy.

 

[racerone]

Does the 75 HP use the 15" gearcase or 20" ?

 

[flyingscott]

Doubt the 85 lower unit is a 15" lower. All the 3 cylinder 20" motors used the same gear case 78-87. Don't know how a gear case will make a 75 hp run better. The 15" mid section used a much less Robust lower unit. Not worth using for the average person.

 

[racerone]

Just asked the poster to clarify what he has.----Some folks may not be aware of the difference in lower units.----I agree the 2 cylinder lower units are not robust , not even strong enuff for the 50 HP motors.

 

[flyingscott]

He said is current lower is an 85. I am not aware of the shorty being produced in 85

 

[racerone]

edited

 

[Whitetail55]

Doubt the 85 lower unit is a 15" lower. All the 3 cylinder 20" motors used the same gear case 78-87. Don't know how a gear case will make a 75 hp run better. The 15" mid section used a much less Robust lower unit. Not worth using for the average person.

75HP has a different gear ratio according to my OEM repair manual, it also shows 65 and 75 both have under 3" bore. I will have to check the gear ratio on the lower that came off the 75. There is no telling what parts have been changed on these old engines. All are 20" mid section, don't know what dif. that would make in linkage adjustment. Like I said the throttle linkage may have been shortened at some point. Best thing is that it is smooth and quiet and we can go fishing. The original was worked over probably because of VRO failure and the guy who worked on it didn't own a good torque wrench. The 2nd power head had scores on top piston skirt but all cyl. had 120lb comp. If not I still have a complete 70HP hanging on the A-frame. Thanks

 

[flyingscott]

Highly doubt you have a factory manual. Difference between a 75 and 70 in the 49 cid block are porting and the head. Bore and stroke are identical. In 1986 the 70 hp went to the 56 cid block. The 75 stayed on the 49 cid block. Buy a good manual. The short shaft motors had different lower units. Probably not yours. Same gear ratio 78 through 2000s. Put up a pic of your motor from the side.

 

[Whitetail55]

Well you are very correct except about my book. Guess I should have the book in front of me before I rattle off incorrect specs. I had the 49cid and 56cid switched around, my book is OEM but a1987 not 1985 as I thought. So assume the 1978 75HP is 49cid and the 1975 70HP spare is also. The 87 book says the 60HP and 75HP were still 49cid. It also says the gear ratio in the 75HP is diff., looks to be a lower gear if compared to automotive. I have a good manual just the wrong year. lol Still wonder what you were referring to about the 15" compared to the 20". Would that effect the throttle? I am pretty sure the cable is a little short. I got lucky on this power head it has 120psi compression when warmed up and wet, all cylinders. Quietest one yet! Thanks again for your input.

 

[jimmbo]

Deleted

 

[racerone]

Some of the 75 HP models used a 2 cylinder gearcase.----That is why there is a different gear ratio.

 

[flyingscott]

One gear ratio is for a short shaft
One gear ratio is for the long shaft. The long shaft is MUCH more common. All the long shafts use the same ratio regardless of horsepower. The short shaft uses a completely different lower unit, with a different gear ratio. Good luck with your motor