Bog, 1982 70 hp Johnson

[Bradg]

I have a 82 70 hp johnson that runs great most of the time. Lately once engine is hot the
engine has developed a bog when accelerating hard to get a tube out of the water. This
only happens with a hot soak(after taking a 15 min break then going again). I must feather
the throttle or the engine stalls if I hit it hard, once running it has no more problems. What
maybe the problem, one of my buddies said maybe fuel pump?

 

[Big Bubba]

Re: Bog, 1982 70 hp Johnson

Bradg,
when was the last time your carbs were cleaned out really good. I mean removing the carbs and removing everything and cleaning out all of the jets and orifices. I own a 1983, 70 horse Johnson and had a bogging issue once it was hot and had to tear down the carbs and clean them out really good and install brand new carb parts. I had to adjust the idle at 1000 rpm's out of gear in idle and that is in the lake and seems to be working great for me. Your bogg could be in your carbs because a float might not be shutting your needle and seat off or your needle and seat have trash in it keeping it from closing the fuel flow off when the carb bowl gets full of fuel. Let us know what you find out. Take care, Bob

 

[Bradg]

Re: Bog, 1982 70 hp Johnson

Carbs were compelely redone 2006, have had this problem before
and after carb work. The problem may only happen 1 to 3 times in
a weekend of hard tube pulling.

 

[jtexas]

Re: Bog, 1982 70 hp Johnson

Is the fuel line holding pressure?
Fresh gas? Water/debris in the tank?
Champion QL77JC4 plugs at .030 in good condition?

When was your last water pump service? Impeller should be changed every 2 years.

First, compression test.

Second, spark test (not a "spark plug" test): get an inline spark tester (couple bucks at autozone), set the gap for 7/16", clip it to the engine block, attach the plug leads (one at a time) and look for a strong blue spark while cranking. If it can't jump a half-inch gap in the open air without a spark plug, it's not firing in the hole under heat & compression.

Report your results.

 

[Bradg]

Re: Bog, 1982 70 hp Johnson

Has had Impeller replace recently, compression test last fall 135 in all cyl, plugs do not have alot of time on them but will replace them.
Fuel tanks are plastic and are cleaned regular, gas is always fresh
as I do not prurchase more than will last a week or two.

What do you mean by "is fuel line holding pressure"? Is there a special test for this. I have notice that the ball does not get super
hard when pumping up.

I will test to see if spark is strong, will be at the lake for next 2 weeks starting friday.

 

[jtexas]

Re: Bog, 1982 70 hp Johnson

new plugs won't help, if it currently has the right ones and they're in good condition.

If you pump up the primer bulb until firm (not tennis ball firm...more like a raquetball), and don't have to squeeze the bulb again all day, then the fuel line holds pressure. If you have to pump it up again during the day, then it's not holding pressure.

If the fuel line is holding pressure then the pump is ok. Unless RPM's increase when you pump the primer bulb while the motor's bogging down -- in that case, the pump needs rebuilding. Or, if gas leaks out that hole on the back of the housing.

If the line isn't holding pressure, look for a leak before thinking about the fuel pump.

Last fall's compression readings don't matter today...need to know what the compression is now. In fact, I would hold off on spending any money or time on the motor until you have compression results.

When you can nurse it up to WOT by feathering the throttle, but it dies if you put the hammer down, that's a symptom of a link & sync issue...throttle butterflies open too soon before the spark is advanced enough, it's like the pistons are running away from the flame. That or idle speed set too low. But that usually is independent of engine temp, or load. Still, it won't hurt to inspect all those throttle linkages, anywhere you have a plastic grommet holding the linkage rods in place, see if any are missing or cracked.