1986 merc 35/40 hp outboard issues

[mickyryan]

I figured id post this here to broaden audience.
1986 merc 2 cyl 35/40 hp .
carb clean and working well
timing checked it is spot on hi and low rpm as per manual
135 compression on both cylinders.
good spark on both cylinders.


1, why is rpm 2500 on muffs only but 1100 on water

sometimes it wants to stall sitting after about 3 minutes of running under 1500 rpm
will idle across water at 1500-2000 rpm for awhile

when trying to get it to take acceleration if i raise outdrive a bit it will take acceleration however if i leave outdrive down it bogs and stalls at 1400- 1500 rpm in gear

at 3000- 3200 rpm the boat sounded great harmonics were singing on engine but 3k seems awful low rpm for a outboard, tach might be off as i have been having issues figuring out exactly how many poles this engine has the book says 4 or 12 im befuddled!.at 4 the tach seems correct at low rpm.

appears to me this is a back pressure problem however i don't know what would be causing it.
i wondered if engine was sitting too low in water but water is about 9 inches from bottom of engine and it is spitting out of the 2 bypass holes for exaust just under the engine at top of the mid unit..

 

[GA_Boater]

2500 on muffs and 1100 in the water - Assuming neutral, it's all about back pressure. My Merc runs about 1100 on muffs in neutral and 800 in the water and drop to about 7-750 in gear.

Has the idle mixture screw been adjusted in the water and in gear?

I think you have 12 poles, but what is the serial number to confirm?

 

[jimmbo]

Sounds like might running on only one cylinder, As for the high Idle speed.
You say the time is correct for both WOT and Idle...There is no Idle Timing Spec. Retardation of the Timing is how the Idle Speed is set. If you adjusted the Pickup timing thinking you were setting Idle Timing, you will need to go thru the Sync Process to get the Relationship between the Carb and the Spark advance correct.
What Service Manual are referencing? If not Factory, then toss it and get the Factory Manual

 

[mickyryan]

On front of engine it says 3 btc@300 rpm i checked with throttle closed anit was 3- 4 btc then slamming throttle to max i checked wot timing to 29 as per label i never had to adjust anything but idle mixture screw and the throttle screw for idle , with boat tied off in gear i made those adjustments, let me know if i errored in some way

 

[mickyryan]

of course the timing check was with plugs out cranking only

 

[mickyryan]

when i got back home i was flushing and thats when i realised almost 1 k. Diff between water and muffs