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93 Johnson 70 dies at idle runs good at 3000+ rpm

M

MinerMike

New member
This is my first ever boat this old Johnson was on the Dauntless when I bought it a couple months ago. Original motor on the Boston Whaler Dauntless 15 (probably).

Starts up great - sounds a bit rough to my untrained ear. When going slow thru no wake zone or maneuvering to dock or load on trailer, it dies but starts right up. A lot of times before dieing it gives a gasp then stops. Other times, it seems to quiet down, run real smooth for a few seconds then dies.

It accelerates OK runs fine - even though it still doesn't purr - at 3000 or higher rpm. I've gone thru only about 30 gallons non ethanol 90 with a bottle of Lucas per 5 gallons. Seems to be doing a bit better.

Suggestions?
 
I can not see or hear your motor !---Model # is ?-----So provide the compression test information / results.------Does spark jump an actual gap in air of 3/8" or more.-----And does the tell tale hose come off the side of the block or the top of the block ?-----Water pump impeller changed ?----Oil injection in service and tested ?-----Or mixing at 50:1 in your tank ?
 
racerone said:
I can not see or hear your motor !---Model # is ?-----So provide the compression test information / results.------Does spark jump an actual gap in air of 3/8" or more.-----And does the tell tale hose come off the side of the block or the top of the block ?-----Water pump impeller changed ?----Oil injection in service and tested ?-----Or mixing at 50:1 in your tank ?
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It's a J70TLETS compression was 93, 95, 93. VRO definitely oil is being injected with the gasoline. Have not tested spark. The fuel lines and priming bulb look pretty old. I'll probably change those. Carbs "look" clean but, ya never know if there could be a bit of crud in a jet.

Like I said, it seems to be improving. Tach on the panel does not look to be telling correctly at low rpm. Seems to be a bit happier slightly past the first detent in gear. Maybe igle speed adjustment?
 
I notice that inside the cowling all the fuel lines are 3/8. But, from the tank to the bulb and bulb to engine, 5/16" . Fuel line is not looking great anyway, I see no logical down side with changing all out to 3/8". Is there?
 
Recheck compression with another gage known to be accurate. If the numbers you posted are real then your motor needs rebuilding. Compression should be at least 110. If you don't know anyone with a gage some auto parts stores loan tools.
 
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