Mariner Manual questions- idle rpms all over

[ksgoosekillr]

Have 91' mariner 90hp 3 cyl. Serial 0DO80511

managed to find a service manual online that is for 0D283222 and above... so one up from the one I need.

My question is this Im chasing a bad idle issue where after a link and sync the idle mixture screws do not seem to change much in the way of causing the engine to stumble. In fact more the opposite leaning the screw out is causing the engine to run better. Making me chase the issue. Planning to rebuild the carbs and fuel diaphragm more for my piece of mind this week. Have a bad regulator that im replacing this week, checking the stator this evening.

I have set my timing to what is called out in the manual above (hoping that its similar to my engine). idle mixture screws are set at 1, 1-1/2, 1-1/2. I checked compression on cylinders with throttle closed 115/112/108. All within %10 of each other. A little on the low side but I assume opening the throttle would increase those numbers a bit. No matter what I do to each idle mixture screw I cant seem to make the engine stumble. So instead left the idle mixture screws at that setting at adjusted 1/8 turn at a time based on idle to hole shot, then reset idle rpms after each adjustment to the 600-700 rpms in gear. However it seems after a short run that it never settles back to my last setting range and instead seems to always drop rpms. Hence the reason I am looking into the carbs, stator, fuel pump, fuel filter. Need to check pickup tube in tank as well.

Aside from what Im checking out above and the reed block (not to thrilled about breaking it down for that) anything else I should check out? plugs are new NGK BUZHW-2s. Spark is strong.

what about differences in manuals from this one to the one I need? I assume there cant be too many variances then again I have noticed a few things that are different in the link and sync diagrams.

 

[ksgoosekillr]

If anyone has manual 90-136452 and can tell me what stock carb settings are for 1-2-3 it would be greatly appreciated. Also the timing specs. Worried there are difference between the manual I have and my engine.

 

[ksgoosekillr]

found the actual manual. In case anyone else has this same engine and is wondering:

stock settings 1-1/2 for all three carbs
2 degs at idle
28 deg at max rpms

THIS DOES DIFFER from the manual one model range up which called out for carb 1 to be 1/2 -1 turn vs 1.5 and timing specs of 4 deg idle, 24 deg max.

 

[ksgoosekillr]

Here is what I have checked so far, just covering my bases to see if I have missed anything:

Stator: measured low on idle winding, replacement coming
fuel pump: new diaphragm kit coming
Coils: measured good
Trigger: measured good
Carbs: new carb rebuild kit coming, i must say though these were the 3 cleanest carbs ive ever worked on. Whoever did the work before me though was special, all screws to bowl were not tight, missing gaskets on drain plugs.
Regulator: new replacement coming
Plug wires: all 3 tested good for continuity
Plugs: new
Inline fuel filter: new

 

[Texasmark]

If your manual mimics the later model engines, proper final setting of the low speed jets is a smooth, strong hole shot....that is (example) boat coming out of the No Wake Zone, at idle, firewalling the throttle with best trim position (trial and error before you start tweaking the carbs)....open each just enough to accomplish that, diddling all 3 in unison. If you open one a tad and nothing happens, put it back where it was and go to the next one. If you have been through all 3 and nothing changed, then you must be at the performance limit of your rig.

Expect this to take awhile.