70hp Johnson will not idle under 2500 rpms

roger3645

Petty Officer 1st Class
Joined
Aug 30, 2005
Messages
271
I?m just stumped on this one. I?m running a 1991 70hp Johnson. It first started acting up when it would not get my top rpms, would not run over 4000 rpms. After going over the fuel system, taking apart and cleaning the carbs and fuel lines, still the same. Then it got worse and I noticed the fuel coming out the carbs was milky. To me that indicated water in the fuel. First I thought I may have pumped some water in the tank when I bought fuel. Which would not have been the first time. But that wasn?t it. I did a compression check and cylinders 1 and 2 were at 90PSI and #3 was at 120. Originally all 3 were at 120. I replaced the head gasket and now all 3 are back to 120. Now when I start her up she will not idle under 2500 rpms. It did this once before and it kind of fixed itself. Don?t know why it is doing this. I know it is not the linkage, the butterflies on the carbs are closed, the timing base is in the idle position, the link & sink is correct and the idle screws in each carb, are set correctly. I haven?t had it back on the lake since the repairs and I?m running on muffs in the driveway. Also, while running it in the driveway, I guess I let it run too long at these high rpms and it got hot as it fried the rectifier I saw smoke come from it. I replaced the rectifier and added a temp gauge, still high rpms. The coils and power pack were replaced 3 years ago.

I?m hoping once I put it in the water with some backpressure it will correct itself again or just running the motor on the lake will help. If not I?m just lost.
 

roger3645

Petty Officer 1st Class
Joined
Aug 30, 2005
Messages
271
Re: 70hp Johnson will not idle under 2500 rpms

The carbs were rebuilt 12 months ago. Also when I wrote still high idle I meant is was idling over 2500 rmps about 2800 rpms. Thanks
 

david_r

Lieutenant Junior Grade
Joined
Aug 11, 2008
Messages
1,118
Re: 70hp Johnson will not idle under 2500 rpms

Also, while running it in the driveway, I guess I let it run too long at these high rpms and it got hot as it fried the rectifier I saw smoke come from it. I replaced the rectifier and added a temp gauge, still high rpms.



i think you may have trouble some where else. idiling in the drive with muffs shouldnt knock out your rectifier.....the overheating could have had something to do with your head gasket though.does yours have the updatedone on the pee hole?



heres the update

http://forums.iboats.com/showthread.php?t=222677&highlight=pee+hole+tell+tale




as for the high idle have you checked to make sure your fuel pump diaphram isnt torn or worn out?.....do you have any air leaks around the carb gaskets?
 

roger3645

Petty Officer 1st Class
Joined
Aug 30, 2005
Messages
271
Re: 70hp Johnson will not idle under 2500 rpms

Yes it has the updates. The diapram was good the last time I checked it and I'll recheck for airleaks as well. Yes I was thinking the same thing about the rectifier. I did noticed that when I start it up the new rectifier gets pretty warm to the touch. Just what I need something electrical, I'm lost in that ballpark.
 

roger3645

Petty Officer 1st Class
Joined
Aug 30, 2005
Messages
271
Re: 70hp Johnson will not idle under 2500 rpms

Well I found the high idle problem. Turned out to be the 4 wires from the power pack, blue, green, white, and purple. If I wiggle these wires (pull away from the block) the idle will increase dramatically. If I push them toward the block the idle will go back down. I guess I could try and see if it's only one of the wires and try a repair. But better off with new power pack.
 
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