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Author Topic:   Mercury 90 hp 6 cyl ignition problem
usatracy posted 08-08-2006 02:02 PM ET (US)   Profile for usatracy   Send Email to usatracy  
I have a 1984 90 hp 6 cyl that I got off Ebay. Tried it on the lake and it has a noticable power drop off around 3,000 rpm. Sounded like a cylinder fell off due to ignition or dirty carbs. Brought it home and found that top cylinder 1 was not firing all the time (using a timing light) and cylinder 5 does it too but not as often (both come off switchbox 1).
Swapped the coils out, no change, swapped the two switch boxes around, problem stays at cylinders 1 and 5. No change at all.
At idle number 1 fires for about 2 to 5 seconds, then the engine shudders and 1 does not fire for one half to 2 seconds and then engine speeds up as 1 fires and the cycle repeats. At 2800 to 3200 it seems to be doing the same thing, won't hold rpm as a cylinder, probably 1, drops in and out.
Does this mean I have a bad stator ?
What about the triggers, could they cause this problem?

Stator tested out as
Blue to Red should be 5400-6200 ohms was 7.45 kU on my meter which I guess is 7450 ohms
Blue white to Red white should be 5400-6200 ohms was 7.03 kU on my meter
Red to Gnd should be 125-75 ohms, was 164.2 on my meter
Red white to Gnd should be 125-75 ohms, was 163.2 on my meter

Has 150 to 155 psi on all cylinders

Fuel does not seem to be a problem, no pump or strainer or dirty carbs.

usatracy posted 08-08-2006 05:30 PM ET (US)     Profile for usatracy  Send Email to usatracy     
When I disconnect the two yellow wires from the stator to the rectifier, the problems go away at all rpms, so is my rectifier the only bad component ?
Binkie posted 08-13-2006 10:42 AM ET (US)     Profile for Binkie  Send Email to Binkie     
Sounds like you know more about your Merc than most people here.
When I had a problem with my Mercury, I would always go to John`s Old Mercury Website,
They have a question and answer board,with many knowlegeable members that know all there is to know about Mercs, and you will get a definate answer to your problem


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