1987? 90hp tower of power mercury bogs out when in the water

[racerone]

If your motor has a belt driven distributor it is NOT an 87 model.---Post serial # or a picture !!

 

[Chris1956]

OK, sounds like carbs need cleaning, new gaskets, new floats and new inlet needle and seats. The gasket sets and floats are pretty universal, but use your serial number to make sure you get the correct inlet needle and seats.

 

[james shilling]

I did not find any sort of screen or filter inside of the carb cover or under the brass fuel line.. I believe my boat to be a 1978. mercury 900, I cannot find anything that matches my serial numbers. I believe the motor mout is an old one off some other mercury engine as the numbers dont match anything. is there somewhere else on the engine that I may be able to locate the actual serial numbers? When I took the carbs apart I checked the needle & seat, and was within tolerance for the float. I did not know about the idle screw I will relook at carbs again tomorrow. I did find more sediment inside the bottom of the float bowl, I think that you are correct that some sediment must be clogged inside the idle mixture screw. will look into that tomorrow.

 

[racerone]

Pictures of your motor will help.

 

[Georgesalmon]

NO ACETONE in the fuel!!!

As you have found out running good on muffs is not an indication of anything. You have a fuel problem. All new hoses, new fuel pump kit, and carbs rebuilt with carb kits and adjusted properly will likely help you out a lot. That little screw on the carbs needs to be started at about 1.5 turns out and then backed out a little at a time until the motor accelerates. Compression test is also mandatory first as already mentioned.

 

[roscoe]

Better to diagnose before spending money on parts.


How did the compression test turn out?

What is your serial number?

 

[60sboater]

Why not post the numbers off the transom mount even if they seem to not make sense. Someone here may be able to decode them and/or post pics of the beast. Keep at until it is back to normal because those inline sixes are fun when they growl.

 

[james shilling]

SUCCESS!!!! Thank everyone for your help, it was truly appreciated. Took carbs all the way apart, did not appear overly dirty. put in new floats and checked drop and heigth adjustments to factory settings. When I started engine a whole bunch of tan fluid came shooting out of the exhaust? When it dried it appeared to almost be like glue. I believe this to be the contaminants in the fuel and carbs and once the cleaner ate away at it it got flushed out of the system. The boat runs great!!! Took it out on the lake today and it screamed fast!! Was alot of fun, did burn up the whole tank of gas. I also installed another inline filter inbetween the fuel pump and carbs. The other filter I had installed was between tank and bulb and fuel pump. For those people who question acetone in the gas, acetone is one of the main components in the chemical makeup of carb cleaner, read the contents of the can. acetone will eat threw crap! Well boat runs fine this will be my last entry probably. I will follow up with photos. For those people interested in the serial number it is 3619029 mercury 6 cyl model 900, 90hp the date I found on the black box says 1978. The cowl is black and blue and white mercury lettering, the front is red and black with thunderbolt ignition sticker on it.

 

[Chris1956]

There is no question that acetone is a powerful solvent. The question is whether it will keep the oil in the fuel from lubricating the motor. If not you will end up with a very clean motor, without any compression, and possibly ruined bearings.

It is best to use the acetone when cleaning the carbs on the workbench, and keep it out of the motor fuel.

 

[Metalman423]

I just had the same problem with my 78 mercury 900. It's your carbs bro. The high speed jets are stopped up and not letting it accelerate. Also I would recommend rebuilding the fuel pump and check your timing. All of those were contributors to my "land boat". Hope this helps bro.

 

[Chris1956]

Metalman, Clogged high speed jets are not the usual issue for acceleration issues in inline Merc motors. Normally the idle jets will clog long before the high speed jets, in an inline carb. When they do, the idle circuit cannot supply enough fuel for the motor to accelerate enough to activate the high speed jets. As you know, carbs work on Bernoulli's principle. Carbs are designed so that as the air speed thru the venturi increases, different parts of the carb are called upon to provide fuel to atomize into the airstream.

I suppose it is possible for the high speed jets to clog, and the idle circuit to be clean, but it would certainly be usual. Someone should take a perfectly running inline motor and intentionally clog the high speed jets and report the results.