Mercury 9.9HP won't accelerate

I need help troubleshooting a problem and I need answers to a few questions.

The problem: 9.9HP mercury won't accelerate. Starts great and ildes great and will even run great at low RPM, but when you try to accelerate the engine falls flat on it's face. I've had the carb. rebulit checked the fuel line and put new gas in it. No help. So I took my service manual and started following the troubleshoot steps. I first disconnected the low oil switch, because the way I understand it, it will not allow the engine to rev up. I then checked all the resistance valves according to the book, and all where fine. I checked the stator coils,primary and secondary and the 5K ohm plug cap, the trigger coil. I was going to do the voltage checks, but I don't have a meter that will read Peak vaules, I guess I could use my Oscope. So then I put my timing light on and found the idle and low rpm to be dead on 5 degrees BTDC, but when I started to accelerate the timing never advance. Any ideas

Question # 1 How do I determine what year the motor was manufactured? The only number I can find is the serial # 0H000254.

Question # 2 I think the DCI unit/ Switch box might be the problem, but I'm not sure about the part number, because I can't cross reference the number I found at www.mercruiseparts.com over to CDI's part number. The number I came up with was 825667T, which superceded 825667.

 

By the way it's a four stroke. Sorry I left that out.

 

o ,ring in the carb ,,that is what it sounds like

 

I agree sounds fuel related. Check the fuel line connection. They sometimes get loose and allow air to leak.

 

Update: I took a can of dust off and held it upside down and srpayed the CDI switch box and the motor speed up, only to die a few seconds later. I'm going to replace the CDI box. And I found out that the part # is 825667T. The only place to get this part is OEM. The cheapest price was boats.net.

 

probably be cheaper to have a pro look at it with some diagnostic equipt,and narrow it down ,did some dustoff get to your carb?longliner

 

Check exhuast to see if plugged.

I had a weedwacker (line trimmer) doing the same. It turned out mud wasps had built a nest in the muffler.

Just a thought.

Take care.

Tim

 

No, the dust off didn't get into the carb.

 

Exhaust fine.

 

Might be your computer.. 4 strokes are tricky.

 

i have a4 stroke yamaha high thrust with same problem my internal fuel filter disintergrated and clogged port only when throtling up

 

Some Of The Engines Also Have An Overheat Sensor, So Also Disconnect That To And See If The Engine Runs Better If So Replace The Sensor If Not The Only Thing Left To Limit Rpm Is The Cdi Box
If Everything You Tested Did Test Good.
I Had This Samething On A Couple Engines Were All Was Good Till Trying To Go Over 2500 Rpm Most Of The Time The Resolt Is Low Oil And The Oil Presure Switch Is The Cause (add Oil And Try Not To Embarrass Fisherman In Front Of Wife)

 

i havnt had it out yet since i got another boat i plan on using the 9.9 as a kicker and will check it out before i put it on other boat thanks for your reply let you know how it works