Throttle Problem

[Summer breeze]

Having read through hundred of posts on this and other sites i need to post a fresh thread as i am having real trouble locating a problem

I am running a 60hp mercury outboard from 1991/2

starts and runs fine, regularly serviced and it keeps coming back from the garage with "there is nothing wrong we can find"

problem is, on opening throttle, as you push forward past 3\4 on th way to WOT the engine bogs down. it is like the engine is starved of fuel. the revs drop off and the boat falls almost of the plane. now that is similar to may issues i have read on here.

the issue is that if i keep pushing the trottle the engine comes back to life and will run at max\optimum revs and sits comfortably on th plane at full speed.

any ideas what this "trough" in the throttle curve may be and how i might rectify it.

thanks in advance
glenn

 

[markcw]

One thing to try is a tool i have heard off, and used for dagnostic fault finding, it a device you place on the spark plug and run the engine it then shows via a led light the spark trace to the plug and engine. it may help i showing up a coil-ht lead-plug or distributor fault

Another thing to do is replace all the fuel filters and check internal fuel line for degradeing off rubber hoses or blockages, an air leak into the fuel supply hose could give you a problem. may also be a carb issue as you have full trottle jets in most carbs.
Years ago i had a very similar problem on a merc inline V6 O/B after lots of work checking earth connections, voltages around engine, turned out to be the Secondary stator coil in the flywheel wheel had an intermitent fault, had to be replaced and it did cure the problem, thing ran suppper fast and smooth.

secondary stator coil is used from 1/2 throttle to full, thing is it can only get checked with a special tool.


just a few ideas.

mar

 

[tinkicker0]

Does it do it when the throttle is pushed forward slowly or just when quickly?

 

[Summer breeze]

Happens every time. If pushing forward slowly or thumping it.

If I back off to past the point where it happens it will happen again on the way back up even though I'm already up on the plane at poss 15-18 knots.

 

[tinkicker0]

Happens every time. If pushing forward slowly or thumping it.

If I back off to past the point where it happens it will happen again on the way back up even though I'm already up on the plane at poss 15-18 knots.

If its a slide carb, I'd recheck the needle position, air corrector jets and the emulsion tube for blockages to the air bleed holes. If its a fixed jet carb, I'd be checking the float height.