91 70 hp johnson high idle

Steveng

Seaman Apprentice
Joined
Aug 15, 2010
Messages
30
The rebuild of my engine has caused a problem of high idle. A couple of ideas that have been suggested resulted in no change. Those were to check for air leaks around the engine, carbs, etc. Check the timing and check the linkages. I have checked for leaks by ear and i used WD-40 around all the carbs and the case joints. The timing was dead on and I found no signs of leaks anywhere on the engine. (the engine case was pressure tested prior and it held 8lbs for over 8 hours). The linkage on the carbs has been checked and there is no opening of the throttle plates(the cam just barely touches the roller as described in the manual). Even if I push the linkage down all the way it does not change the idle. Because the engine has been rebuilt, the fuel oil mixture has been adjusted to a 25 to 1 mixture by adding oil to the fuel and the use of the VRO system. What am I missing?

Thanks, Steve:confused:
 

mblill0825

Recruit
Joined
Mar 3, 2014
Messages
3
Re: 91 70 hp johnson high idle

The rebuild of my engine has caused a problem of high idle. A couple of ideas that have been suggested resulted in no change. Those were to check for air leaks around the engine, carbs, etc. Check the timing and check the linkages. I have checked for leaks by ear and i used WD-40 around all the carbs and the case joints. The timing was dead on and I found no signs of leaks anywhere on the engine. (the engine case was pressure tested prior and it held 8lbs for over 8 hours). The linkage on the carbs has been checked and there is no opening of the throttle plates(the cam just barely touches the roller as described in the manual). Even if I push the linkage down all the way it does not change the idle. Because the engine has been rebuilt, the fuel oil mixture has been adjusted to a 25 to 1 mixture by adding oil to the fuel and the use of the VRO system. What am I missing?

Thanks, Steve:confused:


Hey Steve, I am having the same problem with my 70 hp Johnson after a rebuild. Did you find out what the problem was?
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 91 70 hp johnson high idle

Couple of comments regarding setting the idle. 1. I set mine up so that the cam is not touching the roller at idle. I set mine up so that you can slip a slim pc of paper between them at idle. That way you know there is no possibility the carb butterflys are hanaging open. 2. The idle must be set when the boat is floating normally in the lake and is in forward gear. You can't set it on the trailer. The idle screw sets the timing-adjust so that the engine idles at around 700 when in gear. Don't worry about what the idle timing degrees are-set it by the tachometer rpm's. The idle timing is different for every boat-due to the depth of the lower unit in the water on each and every boat(backpressure) and the pitch of the prop. It's normal for the engine to idle at 1200-1300 when on the trailer, running on the garden hose-there is no backpressure from the water.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: 91 70 hp johnson high idle

mbl. this post is over 3 years old. Read the rules and start a new one.
 

mblill0825

Recruit
Joined
Mar 3, 2014
Messages
3
Re: 91 70 hp johnson high idle

Thanks emdsapmgr , I should've been more specific. The motor idles high right after I start it for about a minute and a half or two minutes then backs down to a normal idle. I don't have a tach on the boat so I cant give exact rpm's but it runs fine after the two minutes, I figured it just needed to warm up. But no matter if you run it all day, every time you start it up it still goes through the two minutes of high idling.

Someone has suggested that maybe the voltage regulator needs to be replaced, I haven't tried that yet I am just wondering if someone else has ran into this problem before.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 91 70 hp johnson high idle

That's an unusual problem. New one to me. Something you can check: It's possible that the airbox is accumulating a little excess fuel at the bottom of the housing after the engine shuts off. (Might be more likely if you tilt the engine up after using.) (sometimes the carbs will leak a little fuel out the mouth of the carb after running.) There is a suction line at the bottom of the airbox which recirculates/consumes any unused fuel back into the bottom cyl. During that initial start up time it takes to burn off any excess/leftover fuel, it's possible that the engine might run rich-as if it's on a slight high idle.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,043
Re: 91 70 hp johnson high idle

some motors have what is called " quickstart " on them.---------On a cold motor it automatically advances the timing untill the motor warms up.------Slows down once warmed up.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 91 70 hp johnson high idle

Racerone is probably correct. The 91 3 cyls (not on tiller models) show the quickstart feature in the sales brochures. I'm a little surprised, as I have a 92 70 hp on my pontoon and have never noticed the quickstart feature in the 5 years I've had it.
 
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mblill0825

Recruit
Joined
Mar 3, 2014
Messages
3
Re: 91 70 hp johnson high idle

Thanks a lot for the suggestions. My motor is a 93 70 hp Johnson. I'll check to see if it has the QuickStart and I'll try the tilt trick to see what happens
 
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