79 7.5 merc problems

[dperkins8694]

I have had my 79 7.5 merc for about 2-3 years. Got it from my father-in-law who only ran it once and it set for 7 years with fuel in the carb. At first the little engine that could ran great, then it started not getting up to speed. So this winter I rebuilt the carb, spring came put it in the water ran great for 2 minutes and then back to the way it was running. So I decided to check the compression and noticed I was leaking water from the rear of the engine. So I replaced all the gaskets. Checked for spark from both plugs, the lower plug was not getting any spark. Tested the coils and everything pointed to the switch box, replaced that yesterday, great spark starts better than it every did. Now for my problem, its not peeing. I had it in a 40 gallon trash can, did not let it run long 2 maybe 3 minutes, the engine was not getting hot. I was able to hold my hand on the block without removing. Drained the can and forced water through the muff hole and the water filtered through. Filled can again, no peeing. Prior to the gasket change as soon as you stated it it would start peeing. Am I not allowing enough time for the water to push through? I dont want to burn anything up. Any help would be appreciated, thanks.

 

[7920hpMercury]

Re: 79 7.5 merc problems

Great little motors!
Few suggestions:

drop the lower unit and hook a hose to the copper intake pipe in the mid section, crack water flow open and see if you get good water flow. If not, you have a restriction in the passage somewhere.

put the lower unit in a bucket and chuck the drive shaft to a large drill and spin it clockwise maybe 1000rpm, should get a good water flow out the discharge.

Last if this checks out, see if your idle relief holes for the exhaust are plugged up. These holes or hole is right below your lower cowling in the back and plug up with exhaust goop. When plugged, the exhaust goes out the prop hub and right into the water intake. Particularly noticeable in a barrel. You can rod out these holes and spray some solvent or pull the powerhead off and clean out. These holes are to allow the gases out when idling.

Good luck.

 

[dperkins8694]

Re: 79 7.5 merc problems

Thanks will give it a try. Just dont understand why it stopped all of a sudden, and why I can force the water trough with a muff.

 

[dperkins8694]

Re: 79 7.5 merc problems

ok I took the lower unit off and I have a question. The water tube that goes to the water pump to the brass pipe, should that be tight where it dont fall off? The connection going from the tube to the brass pipe is very loose. To the point it just came off. ?? have not tried step 2 and 3, just thought that tube looked really bad. Thanks

 

[green4themoney]

Re: 79 7.5 merc problems

do you mean the tube that seats on top of the pump housing? that is your water tube guide, that just sits on to of your pump and helps you line up the copper tube (water pipe) with the pump housing properly when you re-assemble the LU. the water tube is initialy sealed with a rubber seal lower in the water pump housing. Did you say the water tube came out of the tubeguide/ pump housing? or did the water tube guide simply fall off?

 

[dperkins8694]

Re: 79 7.5 merc problems

I see what you mean, its just a guide. The one that was on there is in bad shape, is it ok to use a auto fuel hose?

 

[dperkins8694]

Re: 79 7.5 merc problems

found the problem, the impeller was toast. Replaced impeller and its running great. Knock on wood, lol. Thanks for the help.