Mercury 90 inline 6 newbie - loads of questions!

[Little Terry]

Hello everyone.

My first post here, so apologies if i come accross as being a bit clueless - that will be because I am!

My mate and I have just aquired a small shakespeare boat that has a Mercury 90 outboard on it. We are trying to re-commission the outfit to use for a few fishing trips. However, we have not owned a boat before and our experience is limited to a few charter trips for wreck fishing etc on someone elses, rather larger than ours, boat!

The engine is a 6 cylinder inline 2-stroke motor as far as we can see. There does not seem to be any form of ID plate on it (unless we are looking in the wrong places). The casing suggests that it is a Mercury 90 'power trim'.

There are some casting numbers on the cylinder head.......1023 5068
There are some casting numbers on the intake side of the block, between the carbs..........971-7328

That seems to be all!

It has three 1bbl side draft carbs.

We have had the motor turning over by shorting out the starter solenoid and it spins freely. There is a good spark and plenty of fuel getting to the carbs (it runs out of the air intake on each carb) but the fuel doesn't seem to be getting into the bores. We got it to fire last night by removing the plugs and squirting a little gas in manually. It ran well on that for a second or two then stopped again.

Is there some sort of safety device that would shut off the fuel from the bore? Or is it just sticking floats in the carbs? The dash is very basic and just has an ignition toggle switch and two buttons - one is an electric choke device and the other presumably is for the starter, but that doesn't seem to work. There is also a switch that has a thick black, two-core cable running to it - the seller told us to pull that out and put a clamp behind it to stop it going back in (I presume that its some sort of 'dead-man' switch that should be connected to the drivers wrist).

The guy we bought it from seemed very surprised that it wouldn't run (and we know him well, and is unlikely to be lying). He used it on a local boating lake last summer and it has been sitting still since.

Any help would be greatly appreciated. I am reasonably experienced with car engines, but know nothing about boats (so far)!

Thanks in advance,
Mark.
I will try to post a pic of the motor later.

 

[Chris1956]

Re: Mercury 90 inline 6 newbie - loads of questions!

Mark, The serial number should be on the transom bracket, in the front. It will tell you the year of the motor. Look it up by serial number at maxrules.com

It is no newer than 1988. Fuel mix is very likely 50::1.

The motor will probably start for you if you choke the daylights out of it. Newer inline six motors have fuel enricheners rather than choke plates.If you have any doubt that the carbs are clean, you should clean them. The cylinders will score if the motor is run too lean.

 

[turbinedoctor]

Re: Mercury 90 inline 6 newbie - loads of questions!

If there is fuel coming out of the intake side of the carbs you probably have stuck floats. You should consider rebuilding the carbs and while you are at it replace the floats. While you are ordering or going to the dealer to get the carb kits pick up a Mercury Maint. Manual for this motor as well. It costs more then the Clymers or Seloc's but it is worth it if you plan on doing the work your self. I too have a 90 inline 6 and started with limited knowledge of 2 stroke outboard engines but they are easy to understand if you have a good manual to go along with it.


Does yours have the choke plate in front of the carbs or a soliniod with tubes running to the intake manifold? They are cold nature but once it starts and warms up a bit they start with a touch of the key.


Durwood

 

[oldgradywhite]

Re: Mercury 90 inline 6 newbie - loads of questions!

Rebuild the Carbs and replace all fuel lines this e85 it killing the fuel systems on our motors! I have this motor if I were you when rebuilding the carbs buy a small ball bearing and block the rubber tube that goes from one side of the carb to the other. This tube is call a back drag tube it was a fuel saving idea that mercury put on its carbs after the gas shortages in the 70's. Todays fuel it to thin for that motor if you run it as is you are taking a real risk!

 

[turbinedoctor]

Re: Mercury 90 inline 6 newbie - loads of questions!

I agree with OldGrady on replacing the fuel tubing also, to make sure it is rated for ethanal fuels. We have E10 in our area, I think e85 would be a bit to much for these outboards since Mercury only recommends e10. The diaphrams in the fuel pump may not be able to handle the higher stuff.

As to the back drag tube, I will disagree with OldGrady on that. I still have mine installed and haven't noticed any problems with it yet. I do have the larger jets in my carbs to make sure it runs on the rich side instead of the lean side. The timing is adjusted to about 18 degrees instead of the 20 degrees that the manual calls for. These motors last longer this way.

 

[Little Terry]

Re: Mercury 90 inline 6 newbie - loads of questions!

Does yours have the choke plate in front of the carbs or a soliniod with tubes running to the intake manifold? They are cold nature but once it starts and warms up a bit they start with a touch of the key.

Durwood

We have the choke plates in front of two out of the three carbs. We plan to have another look at it this week and will let you know how we get on.

Thanks for the advice so far.

We cannot find any plate or serial number anywhere on the motor, casing or bracketry. Is there any other way of identifying the year?

Mark.

 

[madgadget]

Re: Mercury 90 inline 6 newbie - loads of questions!

Mark do you have a fuel primer bulb? if not get one, my motor (I6 140hp) started a million times easier with one. Also, get one of those pump spray things and put some fuel in it, spray it into the carbs and see if it fires that way...

 

[Chris1956]

Re: Mercury 90 inline 6 newbie - loads of questions!

Mark, The last year for choke plates was 1983. Two choke plates is normal.

You can try to match the block numbers on the starboard side of the block with the numbers on the crowleymarine.com web site. Start with '83 and work backwards.

BTW - Depending on what parts you want, those motors shared a lot of parts over the years. For carb parts, see if there is a WM number on the carbs.

 

[jeff_smith_0423]

Re: Mercury 90 inline 6 newbie - loads of questions!

Not uncommon for them to not have a transom bracket serial #. I owned an '86 that had a plastic printed mercury marine decal that was supposed to have the # on it. I located my serial # on one of the freeze plugs. Starboard side of the engine, aft of all of the electronics, obfuscated by a plug wire. If it hasn't been rebuilt, the engine serial# should be stamped on that plug.

 

[rosser1]

Re: Mercury 90 inline 6 newbie - loads of questions!

by the time you get your motor to run good you will know it well, even if it has been setting for a little while and ran sometime this summer. you need to clean or rebuild carbs, if you and your mate have had it running for a sec or two then there are a few things right with it. prime it up if carbs leak a little thans ok, just floded but a lot is a stuck float. keep a check on battery, it is the life of the solenoides and if battery is weak it will not spin starter fast enought and then motor will not turn fast enough to start, yes it may turn over but it has to be fast for it to crank. if your having to jump solenode and not useing key, there is a saftey in key that may not let it start unless using key to crank. and you may have to trace problem back to that. make sure fuel mix is new and no water is in the gas or tank. another common problem. fuel and spark and enough spinning rotation and it should putter, then you can start from there. good luck and let us know how it goes.

 

[OldMercsRule]

Re: Mercury 90 inline 6 newbie - loads of questions!

Sorry this reply is a bit late.

One other way to tell what vintage the engine could be is the distributor (or lack thereof). If the engine has six coils and no distributor it is at least a 1979 or newer. If it has a distributor and a single coil it is 1979 or older.

The serial numbers are usually on the starboard side of the block on the 1979 and older black blocks.

The engine bracket also changed in 1980. The pre 1980 brackets had screw type clamps and the newer 1980 and later clamps required through bolts.

If it is a "franken Merc" it could be a combination of the above as the powerheads 1972 on up would bolt to the later midsections without any known issues.

Hope this helps. JR