40hp won't start without alot of throttle

bluerdg

Cadet
Joined
Jun 8, 2009
Messages
11
97 model yr Force 40hp. Best I can tell is the insulation on my cowling drooped and caused enough friction on the plastic cap over the nut on the flywheel to melt it off. Strange that there's no mark on the insulation but glued it back. Long story short I found the top of the cap on the butterfly in the carb after trolling back to the ramp. Took it home, wiped out the carb and she fired up. I ended up doing a few minor adjustments to the throttle cam, but all seemed good. Took her out this past weekend and it started fine but had nothing with a load on the prop. Full throttle won't push it past 3k when it's normally at 5100 or so. I've reset the throttle cam(mark just touching the butterfly arm) Pulled the carb and adapter (reeds and reed plates are clean and tight) found a little fine debris in carb bowl, but all appears to be good, fuel filter isn't clogged. It will fire but won't start unless I give it about 1/2 throttle. Dies immediately when I put it back in neutral. Pumping the bulb doesn't seem to change anything. I can adjust the throttle and it acts like it would run the tank dry. I've had muffs on and eased up through the throttle to about 4000-4500 with prop engaged and disengaged, but she won't do that pushing the boat. I'm much more familiar with car motors, this feels like a fuel issue, but I'm not sure what to check next on an outboard.
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,744
Re: 40hp won't start without alot of throttle

start by checking the spark and compression on both cylinders.
 

bluerdg

Cadet
Joined
Jun 8, 2009
Messages
11
Re: 40hp won't start without alot of throttle

It ended up being fouled plugs, or a combination of excess oil and plugs on the way out. I'd checked them first thing, one had a little oil and the other was dry, but they looked normal. Best I can surmise is that the cap restricted air flow enought to reduce combustion and allow oil to build up in the cylinders (answers the choked issues I had). A weeks worth of overthrottling it to get her started to troubleshoot probably didn't help, as the oil had just fowled the plugs compounding the issues. I pulled the plugs yesterday to see if I could get a look at the valves and valve chamber and they were soaked. Put in a new set and she fired up like a champ, produced a cloud of smoke for about 30 seconds that should have alerted fire depts in other states, but it quickly cleared, she settled into idle right at 1k and just purrs now.
 
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