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1975 mercury 1150 115hp really hard starting and bogs

blair683

New member
Hi, I have a 1975 mercury 115hp (inine 6 cylinder) outboard engine it is extremly hard to start to the point that the battery is almost dead by the time it starts. Once it starts it idles great and runs wide open great but you have to ease on the throttle real slow because it will die if you just crack it wide open real fast. The weird thing is the primer bulb (brand new) will not pump up hard. One thing I noticed about the fuel pump is you can blow right threw it ( I dont know if your supposed to be able to or not) when you pump the primer bulb it will pump gas right into the carbs. I figured the gas wouldnt be able to make it through the fuel pump until the engine is cranking. I looked at the diaphram in the pump it looks good (no holes that I can see) but are these symptoms of a bad fuel pump? Any help is greatly appreciated!
 
That is normal for the fuel pump. Sounds like you need to rebuilt the carbs. Replace the needle and seats and use new gaskets when reassembling. Check the floats for fuel intrusion and proper adjustment.
 
The so called " primer bulb " is nothing but a manual fuel pump.----------------It pumps fuel right through the check valves in the pump and fills the carburetors.--It saves the starter motor having to do that.-----------------So that part is all normal.------If the bulb does not go hard, then you may have a hole in the fuel pump diaphragm or a leaking float valve in a carburetor.---------------Excessive cranking will ruin your starter and that gets expensive, so best to find out why the starting problem.....Perhaps your starting procedure can be improved ??----------Let us know how you try to start in some detail.
 
Ok so here's an update. I bought a rebuild kit for the fuel pump and installed it I tore the bowls off the carbs and looked at the floats everything looked fine and clean but still the same problems. I didn't want to tear into the carbs to much because of the fact that there's alot of jets and screws and I was afraid to get something out of adjustment. My starting procedure is as follows. Pump the primer bulb a few times, turn the key on, hold the chock button and start cranking with the fast idle all the way down, after much much cranking it fires so I turn the fast idle up a bit and it fires up and runs. Please note I have tried alot of other procedures this one just shows the most success. Thanks for all the great info and please add any advice. I wonder if it something with the ignition system?
 
Throttle only handle must be all the way up and more.--------It needs throttle plates open a bit, so that choke plates can do their job.
 
Sorry I havent replied in awhile, I have been busy with work and such. So heres an update. I rebuilt the fuel pump and cleaned the carbs and still the same problem. Finally I pulled the distributor cap off and all the contacts were badly corroded. I cleaned them all up and sure enough she fires right up everytime with the fast idle throttle all the way open! Seems to run great on the garden hose I havent had a chance to goto the lake yet. I am going to stop at the dealer after work tomorrow and get a new cap, rotor button, plugs, and wires. Does anyone know what the best plug is to run in these or should I just run what it calls for stock. So after all that I would appreciate help with my next problem. My power trim works great going down but when I try to put it up it will go for a few seconds and stop then you have to wait a few minutes and will go up a little more and stop. It will repeat this process until its all the way up. It does the same thing if I jump it at the selonoid with a piece of wire. Does anyone know what the problem could be? I really appreciate all the great information thus far it has saved me alot of time and money.
 
I do not think you want to replace the distributor cap !!---------May not be available and just a bit pricey if it is.
 
I do not know if its the original pump or not ill have a look at it and let yins know if there's any brand or writing on the pump. Thanks
 
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