2001 Mercury 150 Saltwater Series (carb) midrange bog after extended running.

[Jon1229]

Hi,

I have been trying to trouble shoot this problem for almost a year now. I have a 2001 merc 150 that runs great for hours, but eventually starts to bog at midrange rpm. If I run the motor continuously for 3 or 4 hours, I can only drive around idle rpm or WOT. Anything in the middle bogs. This ONLY happens after the motor has been running for hours.

Things I’ve tried:
New plugs
New plug wires
New Stator
New Trigger
New cdm modules
New Main Harness
New Power-pack
Carb rebuilt about 18 months ago.

My thought was that something was getting hot, but after replacing everything, the symptoms persist. Any help is appreciated.

 

[Dukedog]

was this problem there before and/or after you did tha carbs???

 

[Jon1229]

was this problem there before and/or after you did tha carbs???

The problem didn’t start until maybe 8 months after the carb rebuild.

 

[Dukedog]

if you have done all that other stuff (mech. fuel pump not mentioned) tha carbs are 'bout tha only thing left... sometimes a carb rebuild last years, sometimes weeks.... jmo.

 

[Jon1229]

if you have done all that other stuff (mech. fuel pump not mentioned) tha carbs are 'bout tha only thing left... sometimes a carb rebuild last years, sometimes weeks.... jmo.

I actually just bought a fuel pump rebuild kit a few days ago, just cause I haven’t rebuilt it in almost 3 years. I figured it might be time. If that doesn’t work, it looks like I’ll be tearing down my carbs again.

Thanks

 

[Texasmark]

The problem I see with the above comments is its midrange, not WOT. So what in a fuel system would clog at midrange only, and only after hours of operation? And is it the whole engine or are you loosing a cylinder....and how could the cylinder workfine for hours, then clog, then increasing RPMs correct itself. Good luck on answering that one.

I thought about a piece/speck of (black) fuel line floating around the high speed jet area but if that were the case and WOT flushed it out, why would it consistently return at mid range.......mind boggling.

A thought: Possibly spark advance linkage binding. At low speed you essentially have no advance and you have put full pressure on the linkage in that direction. At midrange you are putting mild pressure on it. On WOT operation you are putting full pressure on it in the opposite direction. Might disconnect the remote control cables and watch the spark advance arm movement vs your manually moving the throttle lever linkage in the engine. Is it a smooth transition from min to max or seems to bind till you get to WOT. You'd have to do this on the water when it acted up to get a good reference I'd think. Stator may be binding. I guess the same could be said about the carb linkage but I doubt that.

Other thing is you might remove the cowling and go about your business normally. When you get to your time slot does it still do it. Could be heat related binding. Good luck.

 

[Jon1229]

The problem I see with the above comments is its midrange, not WOT. So what in a fuel system would clog at midrange only, and only after hours of operation? And is it the whole engine or are you loosing a cylinder....and how could the cylinder workfine for hours, then clog, then increasing RPMs correct itself. Good luck on answering that one.

I thought about a piece/speck of (black) fuel line floating around the high speed jet area but if that were the case and WOT flushed it out, why would it consistently return at mid range.......mind boggling.

A thought: Possibly spark advance linkage binding. At low speed you essentially have no advance and you have put full pressure on the linkage in that direction. At midrange you are putting mild pressure on it. On WOT operation you are putting full pressure on it in the opposite direction. Might disconnect the remote control cables and watch the spark advance arm movement vs your manually moving the throttle lever linkage in the engine. Is it a smooth transition from min to max or seems to bind till you get to WOT. You'd have to do this on the water when it acted up to get a good reference I'd think. Stator may be binding. I guess the same could be said about the carb linkage but I doubt that.

Other thing is you might remove the cowling and go about your business normally. When you get to your time slot does it still do it. Could be heat related binding. Good luck.

Thanks! I hadn’t thought about that. It’s definitely a possibility and next time it acts up, I’ll absolutely test it out