Force 120hp 1999 erratic revs

[Paulboater]

Started motor before and idles OK but whe revs are applied it can do what it wants 3000 -6000 rpm and gives me no control eventually it will slow down but can idle on any thing between 800 - 1500. then apply revs slightly it can go ok or of the scale.
carbs clean - new needle valves - mix ok - plugs ok
all help appreciated Thanks Paul

 

[kandil]

Re: Force 120hp 1999 erratic revs

How about the fuel pump or the timing?

 

[waylonh]

Re: Force 120hp 1999 erratic revs

Sounds like a broken reed.

 

[john from md]

Re: Force 120hp 1999 erratic revs

You may have a vacuum leak between the carbs and the crankcase and/or a loose/broken reed.

Did you use new seals when you put the carbs on last time?

Regards,

John

 

[Paulboater]

Re: Force 120hp 1999 erratic revs

Thanks for all replies very helpful, Yes did put new seals on the carb and have checked hoses etc. will check the reeds now Thanks Paul

 

[RRitt]

Re: Force 120hp 1999 erratic revs

was it doing this before you rebuilt the carbs? Did this start immediately after the carbs were rebuilt? If this is a new problem that started immediately after rebuilding carbs then I think the carbs should be double checked. If you're in the vicinity it wouldn't be a bad idea to look at your mercury reed valves. Some models and years of mercury made reeds are prone to cracking which will initiate the self-destruct sequence.

 

[dalotel]

Re: Force 120hp 1999 erratic revs

mercury made reeds are prone to cracking which will initiate the self-destruct sequence.

I've had reeds break before, no self-destruct occurred. Mercury didn't make anything prone to break, it's operator error. Redline on the inline 4 is stamped right on the engine, 5250rpm, and if he's slamming the tach at 6000rpm, gee, broken reeds. No further damage should result, $60 fix.

 

[IMPATIENT 1]

Re: Force 120hp 1999 erratic revs

I've had reeds break before, no self-destruct occurred. Mercury didn't make anything prone to break, it's operator error. Redline on the inline 4 is stamped right on the engine, 5250rpm, and if he's slamming the tach at 6000rpm, gee, broken reeds. No further damage should result, $60 fix.

where'd you get the reeds so cheap? all i can find for my 1998 force 120hp is reed blocks for 88bucks, can't find just stock petals

 

[Frank Acampora]

Re: Force 120hp 1999 erratic revs

The engine is not "redlined" at 5250 RPM. That is the RPM at which it makes its rated horsepower. The operating range is 4500-5500 (if it is like earlier Force models) and in reality because there is no valve train to "float" like in a four cycle engine, the engines could probably run well in excess of 10,000. But I would not try it. Hell! My little 2 liter 4 banger Chevy is redlined at 7000.

I do however, run MY 1989 125 at 5900-6000 on my 14 foot flat bottom. Can't go fast without going fast.

REEDS don't break from running the engine at 6000 RPM. They are good to at least 20,000 but in reality, the efficiency of intake decreases and inefficiency of spitback increases markedly after 6000. In other words, They are always slightly open; at higher RPM they can't react fast enough to seal the crankcase and pump a full charge into the cylinder. That's one of the reasons the top RPM operating range is so similar in all makes of two cycle outboards.

Stock reeds are spring steel and break from material fatigue, and that's a quality problem--although Merc would never admit to it.

Boyeson reeds are plastic and they RECOMMEND periodic replacement due to material fatigue.