'99 Johnson 70 - operability issues at low speed

JPTL

Seaman
Joined
Sep 20, 2003
Messages
51
After fresh plugs, clean gas, clean carbs, and carbs synced, the engine idles fine but seems to load up at slow speeds, as though the mixture is too rich or oil fouling.
The oil injection system was disabled by the p.o. and I've been premixing at 50:1.
I was told that the injection system is designed to meter the oil at a lower rate at low speeds (somewhere in the 100:1 range) and at a higher rate at high speeds (somewhere in the 50:1 range). I've also been told that Johnson triples from this era can be finicky when it comes to low speed operation.
Could this be the problem - too high an oil ratio at low speeds causing loading/fouling?
This engine never runs at sustained high speeds - mostly puttering around at or near idle speed.
Question to folks out there with disabled oil injection systems:
Has anyone run their premix at 75:1 without adverse effects?
Thanks!
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,043
The results of a compression test are required here !----Not a good idea to go to a 75:1 mixture.
 

jakedaawg

Rear Admiral
Joined
Jun 26, 2012
Messages
4,275
As racer states a compression test is a must. A spark check with a an open air gap checker set to 7/16" would also be helpful. I believe you will find either weak spark on one or end up finding a heavy float/bad needle seat on one.

I GUARANTEE you that it has nothing to do with the oil ratio at 50:1. In racing/high speed and also in heavy use/commercial operations we run these at 25:1 all day every day!
 
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