Idles up in reverse

K

kucobra

Cadet
Joined
Jul 1, 2007
Messages
18
I have a 1978 70 hp Merc w/ pwr TNT. It goes into forward no problem, It will go into reverse but as soon as it engages the motor will suddenly rev quite a bit causing the the boat to lurch backwards. It will continue until you go back into neutral. It really revs quite a bit to the point of raising the motor. I've never seen this before, any suggestions appreciated.
 
L

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Idles up in reverse

Either the shift cable needs adjustment of the reverse shift lock cam is bad maybe both
 
fishdog4449

fishdog4449

Chief Petty Officer
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Jul 16, 2007
Messages
462
Re: Idles up in reverse

kucobra said:
I have a 1978 70 hp Merc w/ pwr TNT. It goes into forward no problem, It will go into reverse but as soon as it engages the motor will suddenly rev quite a bit causing the the boat to lurch backwards. It will continue until you go back into neutral. It really revs quite a bit to the point of raising the motor. I've never seen this before, any suggestions appreciated.
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Adjust shift cables; It is adjusted wrong so that when you pull the lever back to engage reverse, it engages the throttle prematurely. The motor shouldn't raise just by goign into reverse, that seems to be a whole other problem. You should have the reverse lock (if there is one) engaged.
 
K

kucobra

Cadet
Joined
Jul 1, 2007
Messages
18
Re: Idles up in reverse

OK Ill have the cables adjusted. The raising part is because motor is unlocked. (lake I fish is full of stumps)
thanks
 
L

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Idles up in reverse

When everything is working right on your engine it should be locked down in forward and neutral and release as it is shifted in to forward, if you have removed the tilt pin or wedged the reverse lock that will cause shifting problems all by it's self
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,148
Re: Idles up in reverse

There should not be a mechanical reverse lock on that motor. When the PTT is installed, the reverse lock is no longer necessary. You should use the tilt pin to protect the transom from being gouged by the motor.
 
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