1985 Johson 90HP breaking up while running

[mick3446]

I have a 1985 Johson 90HP that runs great for the first 10 to 15 min at top speed than it starts to break up(sputter rev up and rev down) but never stops. Once I shut it down is runs fine for a while...it may break up again or it may run fine the rest of the day. I also notice when I park it for a day or so I have fuel and oil leaking from the bottom of the crawling on the mid section. Carbs have been cleaned and rebuilt...everything is put back together correctly. ( I hope)

 

[emdsapmgr]

Re: 1985 Johson 90HP breaking up while running

Weak ignition components tend to break down when they heat up to normal operating temperatures after 10-15 mintues of running. I'd check the spark on each plug wire with an inductive timing light to see if you still have fire on all 4 wires. Regarding the oil/fuel leak, I'd check to see if the powerhead base gasket has failed. When it goes, a black, oily substance leaks down onto the exhaust adapter and down onto the midsection. A fairly common (nuisance) failure on these older models. It also can emit exhaust fumes into the cowling which gets re-ingested into the carbs. If this is the problem, the powerhead must be pulled to replace that gasket.