Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

[mspehr11]

I have 1983 Mercury Outboard, 6 cylinder, 3 cycle, 90HP engine,


Engine starts and idles well,

In Neutral, engine revs up to full potential, alot of smoke generated, blue tint to smoke,

In drive, engine accelerated well but once throttle past half way the max speed is capped and engine feels slugish as though it is towing a load

If feels as if it wants to go but can't, leaking gas into water

I have changed the gas and cleaned the carbs with carb spray,

Please give me a direction,

Mark

 

[Barnacle_Bill]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

Carbs need to be taken apart, thoroughly cleaned and reassembled with new gaskets and needle & seats. Spraying carb cleaner does nothing for the internal workings.

 

[jethrosixxx]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

You could try an aux tank heavily dosed with Sea Foam. It worked for me clearing a clogged pilot jet. Your Milage May Vary!!

 

[Chris1956]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

Mark, Perform a compression test. All cylinders should be 120+PSI. Next put a timing light on each plug wire in turn and see that each fire consistantly. If these two tests fail, post back the results. Now run the motor at fast idle on the muffs for a while and examine the spark plugs. If any are real clean, you have water intrusion.

Remove the brass hex head plug at the base of the side bowl of the carb, and carefully give the main jet a blast from the gumout can. Repeat for all three carbs. Install brass plugs and test motor in water. If it still bogs down pump primer bulb to see if it improves. If no improvement, put timing light on plug wires and see if you still have spark at high speed. If you do, carbs are most likely culprit. If no spark, stator is likely culprid. Check ADI ignition troubleshooting procedure on CDI Electronics website.

 

[mspehr11]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

Thank you Chris for your reply

I have done a Compression Test, they read as follows

Plug 1 115 PSI Plug = clean with little fluid on head
Plug 2 110 PSI Plug = Thin flim of fluid on head
Plug 3 120 PSI Plug - Clean
Plug 4 120 PSI Plug - thin film
Plug 5 120 PSI Plug with little fluid on head
Plug 6 120 PSI Plug with little fluid on head

I have removed the Hex nut and sprayed the jets with carb cleaner, I will try to put the boat in the water tomorrow to test it,

I have purchased carb fluid cleaner, my next step would be to remove the carbs, disassemble and soak overnight, am I at risk of screwing up the pin and needle settings?

Thanks

Mark

 

[udunit1966]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

We're having exactly the same problem. When the boat 1st hits the water it goes all out 40+ MPH for about a minute or so , then it does the bog down thing and we can't get it to go again. This happened twice. Pull it out the 1st time, cleaned carbs (spray), new fuel, cleaned filter. Ran great for about 1 minute again then bog city . It looks like fuel is dripping from the top carb. Floats all work ok. I was thinking of going to a marina for help but the dutch in me is still looking for the cheaper solution. Let me know how you make out and any additional help would be great!

 

[mudskip]

Re: Mercury Outboard 90hp 6 cyl 2 stroke - Bogs down past half throttle

I have a srt8 six Merc (1974) has a Manual Fuel Pump, I was having a problem just like you and it was because fuel was leaking through one of the diaphragms. rebuilding the fuel pump was easy, and the quicksilver (mercury) kit was under 20 bucks... I also did as one of the fellows mentioned before and got kits (plural) for my carbs as my model has 3...just watch the linkages...I know it sounds goofy but I usually take a picture with my digital camera to help with reassembly. Also I can't express how invaluable my Clymer outboard shop manual has been to me over the years. The last thing I will mention is that Mercs run such hot plug wires (old thunderbolt systems) that when you try and attempt WOT the wires can ground out when the Stator pushes higher amps/voltage at higher RPMs, unlike most standard plug wires, Mercs old thunderbolts use copper cores, not carbon filiment like the newer 4 strokes & such. I am a green horn on here but I hope you find a solution.... nothing worse than seeing your boat on land.