1979 90 HP Mercury outboard Flooding issues

My Mercury outboard was having some issues last year with accleration and hesitation during throttle (it would die/bog down at half throttle). I took it to a reputable Marine shop and the guys there were very helpful. They told me that one of the switch box's were bad (power head) and that I should replace both of them. I took the boat home and ordered the parts and replaced the SB's, the rectifier and the water pump just to be on the safe side. I took it out this last week and the boat did not want to start right away (as opposed to sitting in my driveway with the hose hooked up). After some coaxing I finaly got it to start and it ran fine. The next day the boat started and ran fine but would not pull a skier unless I choked it until it was at half throttle and then released the choke. I took it back to shore and opened up the needle valves on the 3 carbs 1/8 of a turn each counter clockwise(I marked the original spot just in case) and it ran flawlessly the rest of the day. The next day it wouldn't start and was now flooding fuel out of the vent hole at the top of the bowl in the top carb and the bottom carb as well. I reset it the carbs back to original and it still wouldn't work. I proceeded the pull the top carb off to see if the float was sticking, but I really couldn't tell. I can get the engine to start in Neutral and half throttle just fine, but when I put it back in drive it dies. Will a rebuild of the carbs fix this issue? I am fairly mechanical, but I want the job done right and I don't mind spending the 3-4 hundred dollars to fix it the first time. Any help or suggestions would be greatly appreciated. I learned about the carb adjustment from my last post (last year). Thanks again.

Re: 1979 90 HP Mercury outboard Flooding issues

Any time that an idle mixture adjustment is needed on a two stoke engine that has previously ran fine, then it is time to properly clean the carbs as the fuel/oil residue from NON- use has already begun to restrict fuel flow AND can cause a float needle valve to not seal, thus your carb's are flooding.

Count the # turn IN on each idle mixture screw until each is very lightly seated, write it down so you can return them to this same position once finished. It will save you some time later once it is running again.

Clean and rebuild each carb. It is highly recommended to use rebuild kits, replacing gaskets and the needle valve, cleaning alone without replacing the valve might not cure the flooding.

Re: 1979 90 HP Mercury outboard Flooding issues

What Charlie said. Also inspect the floats. The originals can disolve from the ethyl in the gasoline we now have. Make sure the little springs on top of the floats are intact.

Re: 1979 90 HP Mercury outboard Flooding issues

Thanks for the advice. I bought the entire boat a few years ago from another military member ($500) who was moving to Germany and I have since talked to him about the problem. He said that he had never acomplished any major maintenance on the fuel system, so I think it is time to get the carbs rebuilt. I will be dropping the boat off on July 30th and when I get it back and test it out I will update this thread. Thanks again.

Re: 1979 90 HP Mercury outboard Flooding issues

The fuel leaking out the vent hole is a good indicator the floats are sticking. Its worth replacing them when you do the carbs.

Re: 1979 90 HP Mercury outboard Flooding issues

Winged Wheel, Leaking carbs could be an indication of bad floats or sticky floats. Of course bad inlet needles and seats are just as likely or probably more likely. That is why I recommeded he inspect the floats. If he replaces just the floats, and the inlet needles are bad, the problem will not be fixed. It is easy to inspect the floats, but difficult to inspect the needles/seats.

Re: 1979 90 HP Mercury outboard Flooding issues

Chris, I was just suggesting that when he does a carb rebuild, that replacing the floats also is a good idea. I usually don't believe in just"cleaning" a carb. If I'm pulling it off I always rebuild it.

Re: 1979 90 HP Mercury outboard Flooding issues

I called the Marine shop and they are running anywhere from 4-5 weeks behind. I have been reading my Seloc Mercury Manual and it seems fairly straight forward on the rebuilding of the carbs and timing and synchronizing. I have looked at the parts from this website and they are fairly inexpensive. I am going to order 3 rebulid kits, 3 new floats and a rebuild kit for the fuel pump as well. All this will cost me around $76. I will keep posting as to my results. I will start rebuilding them sometime in the next 2 weeks and if there are any hints, tips or tricks to any of this, please advise me before I start. I will also be taking a lot of pictures to help with the reinstall and for future use. Thanks for all the help and advise, please keep it coming in.

Re: 1979 90 HP Mercury outboard Flooding issues

A couple of things. Set the compound float levers carefully. They should be parallel to the carb bowl top, when it is inverted. There is a copper gasket under the inlet needle seat. Replace it.

The main and idle restrictor may be hard to remove from the carb body. just blow them out with some gumout jet spray, and forget it. Make sure you blow out the small holes drilled in the barrel of the carb. These are for idle fuel flow.

If you remove the brass pipe plugs, reseal them with some silicone caulk.

Re: 1979 90 HP Mercury outboard Flooding issues

Awesome tips.Thanks again for all of your help and knowledge. I feel really good about doing this. I have rebuilt several automotive carbs before and dozens of small engine carbs and the principles seem the same...get everything clean and new again and the fuel will flow like it should. My only hesitation with doing all of this was the timing and synchronization. Once again I have timed my fair share of auto's, but I have never worked with multiple carbs. I will do my best and the great thing is that I have this forum to keep coming back to, with people who have done this all before. Thanks again.

Re: 1979 90 HP Mercury outboard Flooding issues

Look on here for a "link and sync" thread. that will help tremendously.

Re: 1979 90 HP Mercury outboard Flooding issues

Ok, so I started rebuilding the carbs today and I noticed that my carb is a lot different from the one pictured in the manual (seloc) and the one pictured with the carb rebuild kit, I double checked to make sure that it is the correct kit for my carbs 18-7021 (sierra) for my WMK 27-2 carbs (Mercarb 13685676 1 1/4) "back drag". I found that my carbs do not have an inline screen filter on top. Do I need to install a good inline filter? When I removed the needle and seat, the seat has rubber in the middle, at the bottom and this was falling apart pretty bad, the new one looked a little cheaper but I don't have a choice now, I have to use it. Other than that everything seem to go pretty smooth except for what "Chris 1956" said was true it is impossible to remove the main jet and main nozzle (I was able to remove the idle tube), so I have the first one soaking in Berrymans chem dip. There is a winged piece of plastic that is in the throat of the cab and the main nozzle is holding it in place, since I can not remove the main nozzle I am having to selectively and cautiously (as to not melt that plastic wing) keep the carb submerged only up to that point, of course I will flip the carb and resoak the other side to insure the entire carb gets cleaned. I am going to start to rebuild the rest of the carbs and the fuel pump tonight and I should be done by tomorrow or Sunday, Monday at the latest...NFL starts this weekend. Go Broncos!

Re: 1979 90 HP Mercury outboard Flooding issues

You should have the backdrag carbs. The only difference is the carb cover. Under the brass fitting that allows gas into the carb, there is a screen. Clean or remove it. The main fuel strainer in the fuel pump will be adequate.

A seperate water seperator is a good idea. An inline fuel filter is OK, but not as good. Use 3/8" fittings and fuel line.

You may leave the jets in for soaking. Blow them out with air or gumout jet spray.

The original inlet seats were rubber/brass. The new seats are all brass, and the needles are ss with neopreme tips. Don't mix old and new.

Re: 1979 90 HP Mercury outboard Flooding issues

That is correct about the original seats and needles. When I got them all apart (one at a time) I noticed that the rubber under the brass seats, the rubber was starting to deteriorate and each one was worse than the last. I have finished rebuilding all of them (took lots of pics, but don't know how to post them) and rebuilt the fuel pump. Now it is on to the Link and synch portion. I obtained a procedure from this forum (FAQ/Clams Canino) it seems straight forward, but I think I need to identify everything on my motor that is asociated with this process. I think the two screws directly beneath the flywhell are used for the first and second pick ups, but I am not positive. If you have any suggestions or know of a better procedure, please advise. Thanks for the response all the information is greatly appreciated.

Re: 1979 90 HP Mercury outboard Flooding issues

Hey KD, Does that motor have a distributor ignition? If so, the set screws (throttle stop, max spark advance, idle stop) are on a plate on top of the distributor. The idle pickup timing is adjusted via the brass collar on the midsection of the distributor. There are two 5/16" stainless bolts that hold the collar tight.

Re: 1979 90 HP Mercury outboard Flooding issues

No it does not have a distributor, it is the thunderbolt ignition (two switchboxs and a coil for each cylinder). I think that the two screws under the flywheel are for the vaccuum advance, the one on the left is connected to a rod that is connected to a plastic connector that is connected to (I am assuming) some part at the stator/trigger area, the other screw (to the right of the first) screws down on a "stop" and I think that this one is for max advance. I am waiting on a dial indicator to ensure that my pointer is in the correct spot. I am going to pick up some new fuel hoses today at 9am and begin installing the carbs, once this is done my friend is coming over with his dial indicator and I should have a big chunk of this done by 4pm. I will post again tomorrow morning; as I work form 0000-0800. I am in the Air Force stationed at Travis AFB. Thanks again for everyones help, I will have more questions later...I guarantee it. One more question, why does Merc. use zip ties to hold down fuel line connections? Is there a better replacement? It seems like this would cause a leak, can I use squeeze clamps instead or will these rust out?

Re: 1979 90 HP Mercury outboard Flooding issues

Zip ties are the best (and cheapest) way to clamp hoses. You may use ss clamps. That motor does not have a vacuum advance. The trigger moves as the throttle is opened. There should be adjustments for idle pickup, max advance and throttle stop, as well as idle stop.

Re: 1979 90 HP Mercury outboard Flooding issues

Well, I didn't get as far as I would have liked, but, after some running around I was able to get the carbs on, new fuel lines on (zip ties) and verify that the timing pointer is set correctly. Today I anticipate being able to do everything up to the point where I have to take the boat to the lake and set the WOT adjustment. I am hoping sometime this weekend I will be able to get this completely finished and maybe still be able to water ski one last time. As the work gets closer to completion I am always nervous about whether or not all my work has fixed the problem...we shall see.

Re: 1979 90 HP Mercury outboard Flooding issues

Ok, I finished setting the timing and at the time the carb lever touches the throttle cam (1st throttle pickup), the timing is at 3-5 BTDC and the carbs are just engaged, but not open (all the tension is gone and any further advance on the throttle opens the carbs further), * should the carbs be open at all at this point? on the side of the butterfly inside the throat there is about a 1/16th" gap between the wall and the butterfly opening. Then when the max timing is set to 21BTDC there is about a 3/16" gap. Should the carbs be open more than this and if so how much?. Like I said I am following Clams Canino's thread on "Timing and Sync of Merc Inlnes (to 1988)", but he doesn't say how much the carbs should be open during this procedure and I would like to get it right. Thanks again for all of your help it is greatly appreciated.

Re: 1979 90 HP Mercury outboard Flooding issues

Update, the timing is done and the boat starts up fantasticly, but now I cannot adjust the idle speed because when I follow the instructions in the book (Seloc) it tells me to hook up to one of the - terminals on any of the coils, but when I do there is no read out on the tachometer. I took the tachometer (hand held) and hooked it up to my wifes VW and it works just fine. Is there another place to hook up my tach (it does not have an input for an in dash one)? I am afraid to hook it up any where else until I get some advice. Thanks again for all of you help.