1978 Johnson 70hp Bogging(?) Ideas Needed Tried the usual answers.

jbo_c

Seaman Apprentice
Joined
Aug 1, 2008
Messages
41
Woke up this new to me motor after 4 years of sitting. Started out by changing lower unit lube, water pump impeller, and rebuilding the carbs before I did anything. Put it on the muffs and it cranked right up. Woohoo! Off to the lake.

Put it on the water and it cranked right up. After it was good and warm, I hit the throttle and it died. Did it over and over again. Finally just made myself happy on the lake puttering around at idle speed. Held my head high and acted like that's what I wanted to do anyway.

Got home and spent a few days researching. Got some motor baselines:

Compression: 109(T), 112(M), 105(B)
Spark: 1/2" jump on all three
New Plugs
Fresh Fuel Mix(with a little Sea Foam)

Decided there was a problem with one or more of the high speed jets. Seems like the classic symptoms. Pulled all three carbs again last night and went back through them with wire and carb cleaner.

Out this morning. She cranks like she's already warmed up. Didn't even need the cold start lever. Warmed up. Hit the throttle. It died. Tried a few more times. Finally, she jumped up on plane. Ran like a champ for 20 minutes or so. Guess I blew something out and now we're ready to go. Slowed to idle speed to go under a bridge. Out from under the bridge and hit the throttle. It dies. Tried a handful more times with more dying. Then, finally, jumps up on plane and off for another half hour run at around 30mph with no problems. Slowed down to idle speed for another bridge. Hit the throttle. Dies. After a few tries back on plane with no problem.

After a swim, same thing - throttle die throttle die . . . up on plane and going again.

Tried hitting the choke as it died to see if it that might help it catch up, but didn't change the result. Couldn't really pattern what was going on when it finally decides to go ahead and throttle up.

Now home again wondering if you can help me with what to check now.


Thanks.

Jbo
 

jbo_c

Seaman Apprentice
Joined
Aug 1, 2008
Messages
41
Also new fuel bulb/line. No clog in the filter in the fuel tank.

Advance moves before throttle plates best I can tell.
 

SilverSS07

Petty Officer 1st Class
Joined
Jun 13, 2012
Messages
266
How are the fuel lines on the engine going to the carbs? Check/rebuild the fuel pump?
 

jbo_c

Seaman Apprentice
Joined
Aug 1, 2008
Messages
41
New lines on the engine. How do I check the pump? Obviously I know it pumps some. How/what do I check it against? Thanks. Jbo
 
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