Engine dies when trim down

[fbriggs]

Ok so here is my problem. Have a 70 hp merc 3 cyl that on muffs runs perfect, once in water only way it will idle is with trim up, as you start to lower engine the further you get under water the lower the rpm goes. When all way down engine dies after 10 sec or so. If I start to raise engine it stays idleing.
Idle set at 850-900, timing at 8 degrees, carbs new, linkage and sync adjusted, timing advances correctly.
Have had someone tell me to bump up timing, tried but have to go all the way to 15 degrees before engine works and stays idleing, just not sure if I should leave timing that far advanced.
Any suggestions.

 

[racerone]

It is NOT PERFECT on the hose.-----It only SOUNDS perfect to you because the engine is not doing any work.--It will run nice on 2 of 3 cylinders.--------Start with a compression test.----Post your numbers.----Test spark on all leads.

 

[fbriggs]

Engine rebuilt recently only a bout 50 hours on motor at that time compression was an even 150 and spark jumps my tester set at 1/4". But will recheck to make sure.

 

[fireman57]

There are guys here that are great on both OMC and Merc but there is a forum for Merc only. Might get a better response there, or maybe not.

 

[Joe Reeves]

There are guys here that are great on both OMC and Merc but there is a forum for Merc only. Might get a better response there, or maybe not.

Ditto..... Wrong forum.

 

[GA_Boater]

Ditto..... Wrong forum.

Moved to the Merc outboard section.

When you say trim up, how far up are you trimming?

And do a drop cylinder test. Pull each plug wire to see if one has little or no effect.

 

[Sea Rider]

How about using the factory timing advance and carb synch specs along increasing a tad the idle rpm and checking if motor still dies when triming up. Will be a good idea to retorque the cylinder head, exhaust covers gaskets back to factory specs, will surely find them bit compressed and with less torque from were originaly torqued to.

Happy Boating