1985 70HP Johnson bogs around 2700 rpms

[nopromechanic]

I have a 1985 70 HP Johnson that runs fine around 2500 rpms. It will bog down if you try to go any faster.
I have checked the stator and it puts out 285 volts and the resistance is around 569 with no continuity to
ground.
The timer base puts out A=.5 volts B=.4 Volts and C=.7 volts. The resistance is around 12 on all three
connections and there is no continuity to ground.

The power pack puts out 250 volts while cranking and 300 volts at 2500 rpms to the coils primary terminals.

I have replaced the spark plug wires, plugs, three new coils and the rectifier just to make sure.

It still will only run well at 2500 rpms.

Any ideas other than maybe the carburetors are not supplying the correct amount of fuel.

Any thoughts and ideas are appreciated.

 

[LongLine]

Re: 1985 70HP Johnson bogs around 2700 rpms

Look at your gas supply. Look for Leaky fittings, hoses. Next time out, pump the primer bulb or hit the choke & see if it does anything.

Tom B.
(LongLine)

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

I have actually squeezed the bulb and it stays firm. I have not tried pushing in on the key switch but
I have tried turning the little red handle on the automatic choke. It did not seem to make any difference.
Even though the timer base seems to check out could it possibly be the culprit?

 

[Big Bubba]

Re: 1985 70HP Johnson bogs around 2700 rpms

When was the last time your carbs were cleaned out very thoroughly? If you cannot remember or know when then it might be time to clean them up. Your intermediate and high speed jets might be clogged up so I would start there.

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

I ordered three carb kits and redid them. The carbs were real clean inside and out but I went ahead
and went thru them. There didn't seem to be very much to them. The float and needle seat valve
and a couple of gaskets. I also replaced all the fuel lines while I had the carbs off. Bottom line it did
not make any difference in the problem. Where do I go from here except maybe the bottom of the
canyon. Any recommendations or ideas will be greatly appreciated.

 

[retiredfornow]

Re: 1985 70HP Johnson bogs around 2700 rpms

You may have a bad cylinder. Check the compression and let us know what it is.
Mine acted the same, and it was a bad cyl. Good luck.

 

[LongLine]

Re: 1985 70HP Johnson bogs around 2700 rpms

When you choke it at intermediate to high speed, it should lose some RPM.

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

The compression is 130 on a couple of cylinders and 135 on the other.

When I choke it with the throttle wide open it does seem to lose some RPM's.
Could the timing be off or maybe the timer base flaky?

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

If the temperature switch is defective will it cause the engine to only run at about half throttle? I have a
25 HP Mercury that will not run at full throttle if it gets hot. I was just wondering if in 1985 the 70HP Johnson
would do that.

 

[Bikeluver43]

Re: 1985 70HP Johnson bogs around 2700 rpms

I'd check the fuel pump and/or rebuild it.

 

[BonairII]

Re: 1985 70HP Johnson bogs around 2700 rpms

Make sure that your timing is advancing when you throttle up.

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

I appreciate everyones suggestions. I have also did a rebuild on the fuel pump. Apparently this engine originally
came out with a VRO fuel pump but someone changed it over to a regular fuel pump. The rebuild did not seem to
help either. I also checked the wiring harness to the key switch and everything seems tight there. About the only
thing left is the stator, timer base and flywheel. Any other bright ideas would be greatly appreciated.
This engine did not drop all at once. We noticed at times it would kind of sputter but would pick back up.
The last time it did that it stayed at the 2500 rpm range. My gut feeling is going to be the timer base.

 

[WernerF]

Re: 1985 70HP Johnson bogs around 2700 rpms

Could it be that someone updated stator and power pack to a SLOW mode type (1989 up)? The hard limit of 2500 rpm and running well below makes me think about that. For slow mode types the connector between stator and power pack is 5 pole (2x brown, 2x orange, 1x black/yellow).

 

[nopromechanic]

Re: 1985 70HP Johnson bogs around 2700 rpms

Thanks for the suggestion but it appears to be the stator for that engine. It has a three wire connection as described
in my service manual for a 1985 thru 1988 model. The stator seems to check OK with volts and OHMS. We took this
engine to a boat mechanic and all he did was change a spark plug wire (with a used one at that) and he called it fixed.
Not SO - I have since then changed out all the parts I listed above.

 

[yooper vern]

Re: 1985 70HP Johnson bogs around 2700 rpms

I have an 1985 70hp Johnson that runs fine for a half mile to a mile at 4800 rpms then drops to 3500 rpms. Had complete tuneup and a new fuel pump. No fuel flow problems, good spark all three cylinders, tanks are clean, new hose, and can't figure it out. Any suggestions?

 

[Kylebellis]

Re: 1985 70HP Johnson bogs around 2700 rpms

I have an 1985 70hp Johnson that runs fine for a half mile to a mile at 4800 rpms then drops to 3500 rpms. Had complete tuneup and a new fuel pump. No fuel flow problems, good spark all three cylinders, tanks are clean, new hose, and can't figure it out. Any suggestions?

You should start your own thread, hijacking is frowned upon
In this forum and you'll get better answers if you start your own thread!

 

[pn]

Re: 1985 70HP Johnson bogs around 2700 rpms

put a timing gun on it and watch it swing/advance. if it does then it's gotta be junk in your main jet or your throttle not opening up all the way. unscrew the float bowl to make sure your getting gas, fuel tank vented.