constant alarm 87 merc

70hp 87 merc #B145621, I took it out and alarm is a steady on, starts fine but once you put it in gear and a little gas the engine dies. Pumping water fine, change oil lines and is flowing freely. I disconnect oil sensor and alarm shuts off but engine still kills. runs great hooked up to muff in gear with some rpm's going. i do not have a manual-probably should get. from what i've seen on past posts is heat sensor related? it was fun pushing the boat on the trailor with a stiff mississippi current

Thanks
quillKing

Re: constant alarm 87 merc

The engine is stalling because the carbs are dirty, there it not a safty shutting it down. The horn blowing is probably the oil sencor.

Re: constant alarm 87 merc

Thank you, Laddie. Do you think this is something i can rectify with a simple cleaning? SeaFoam? or do you think the carbs should be rebuilt with a kit? I appreciate your help, and this forum was a nice find for a person like myself.
Thanks!

Re: constant alarm 87 merc

I have never used SeaFoam on a engine to clean carbs it's a band aid at best, you may not need kits just gasket sets but the only way to properly clean a carb is to remove it and clean it. Unless you like the loading and unloading and other frustrations that poor performance can cause.

Re: constant alarm 87 merc

I will give that a try-thanks-. do you think it is just a coincidence then that the oil alarm and crappy running(engine killing) both occured on the same boating venture? appreciate your help!

Re: constant alarm 87 merc

Yes.

Re: constant alarm 87 merc

If your oil alarm is going off, you should mix oil in the main gas tank at 50:1 till you figure it out.

If the oil alarm and performance issues occurred at the same time, the next step is to do a compression test (after you oil the main gas) to see if any damage is done internally. Then go from there.

Until you know the condition of the main mechanical parts of your engine, all other "tune up" items are useless.

hope it helps
John

Re: constant alarm 87 merc

It does help and I appreciate your insight. I will p/u a compression tester. Good idea about premix. buddy of mine in Nisswa recommended that too.

Thank you.

Re: constant alarm 87 merc

quillKing said:

It does help and I appreciate your insight. I will p/u a compression tester. Good idea about premix. buddy of mine in Nisswa recommended that too.

Thank you.

Click to expand...

Well, i picked up a comp tester. took out top plug and it was plenty wet-with gas/oil, bottom pug was the same and the middle one wa not as wet-maybe more normal? for the 1st time (owned this one for over 3 years) i removed the carb cover. there was a noticeable amount of oil pooled in the cover, teaspoon maybe. carbs appeared dirty with standing oil. is this normal? I cannot run the muff, hose froze and did not do cmp test. thing is one day fine, next this. the carb cleanning sounds like a must? don't hope for bad compression.
Thanks Laddies & John-appreciate it!

Re: constant alarm 87 merc

Hello again. I checked compression and all 3 cylinders were fine. I cleaned the carbs and they were very dirty. Fired right up when I put the carbs back together, but not on the water yet. It is pumping water fine out of the tell tale. This engine has a water discharge above the top cylinder to the right as you look behind it. The hose is clear and there was no water going thru it. I believe this tube is for my gauge on the dash. The water gauge appears to be measuring water, but no water is going thru, bit once I disconnect this hose from the engine water jets out! But will not travel thru the line. Is air in the line blocking ot from reaching the gauge.
I also want to take off the lower unit and replace the impellar. My manual says take off the bolt facing the back of the stern. I have two bolts-in doing this will it then free the lower unit from coming apart? I took off the four main bolts and the bolt in the far back side of the lower unit. I last took off a lower unit on a 76 65 hp many years ago. I just received my manual and having a hard time with what unit is mine and which one isn't. Do I need to disconnect the shift linkage bolt that is tucked way underneath the motor under the cowling.
As always, thank you for your assistance. (it's starting to warm up in these parts!

Re: constant alarm 87 merc

The hose is clear and there was no water going thru it. I believe this tube is for my gauge on the dash. The water gauge appears to be measuring water, but no water is going thru, bit once I disconnect this hose from the engine water jets out! But will not travel thru the line. Is air in the line blocking ot from reaching the gauge.

Click to expand...

The water pressure gauge works the same way as a speedometer on the boat. The water does not travel thought the hose. Instead, the water pressure at the far end of the hose pushes against the air inside the hose and compresses it so that the air pressure is equal to the water pressure (equilibrium). The gauge at the dash measure the air pressure in the hose and shows the water pressure value on the gauge. I guess the water would travel into the hose only as much as is needed to compress the air, which is not much.

Re: constant alarm 87 merc

Thank you for that information.
If any one knows anything about my question regarding the two bolts facing the back side of the stern and if removed will free up the shift linkage to remove the lower unit. 1987 70hp Merc. #145621
Thanks!