fires with plugs out, but not with them in?

O

outboardnut

Petty Officer 1st Class
Joined
Oct 27, 2006
Messages
323
Hi Everyone.
Thank you for letting me pick your brain.
I'm piddling with a 1975 85 HP Johnson.
It fires 1/2" gap with the plugs out, but when I put the plugs in it doesn't fire at all.
Only difference is a slight drop in RPM that the motor is turning over.
Anyone have any clues?
 
iwombat

iwombat

Captain
Joined
Jul 12, 2006
Messages
3,767
Re: fires with plugs out, but not with them in?

Sounds like you need new plugs.

Maybe you can describe your test setup a little better though.
 
E

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: fires with plugs out, but not with them in?

You need 300 RPM. The fact that it fires with no load generally tells you that the ignition system is OK and that the problem is in the starter system: battery; battery cable; solenoid; or, grounds.

Rarely, the symptoms lead you to the stator.
 
O

outboardnut

Petty Officer 1st Class
Joined
Oct 27, 2006
Messages
323
Re: fires with plugs out, but not with them in?

Ok, maybe I'm going a little to slow.
I can't tell an RPM with the plugs in because it has no spark....but it "sounds" OK.
However I just took the plugs out and put a tach on it......and it is only turning over 350 RPMS with the plugs out.

So........I'm going to work on getting the girl to spin around a little faster!

Thanks!
 
HighTrim

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: fires with plugs out, but not with them in?

As Ezeke already mentioned, Ill be willing to bet that your trouble is in the starter system. Go over all your connections with a file, then re tighten. Check all your wiring for nicks, cuts or abrasions, or check to see if it crunches when you flex it, and replace as needed. Ensure your battery is fully charged and load tested. A voltage drop test could isolate a faulty component, connection or section of wiring if you have a MM.
 
F

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: fires with plugs out, but not with them in?

350 RPM should be plenty if it is accurate. '73 models were plagued with stators that melted down and caused that same problem. The green stators that replaced them were ok. You might want to take a good look at the stator to see what's in there.
 
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