Logo
FULL SITE MENU

71 Merc 80hp stalls in gear

M

medicineman

New member
" I bought a 71 merc 80hp from

" I bought a 71 merc 80hp from my brother last year. He skied behind the thing then put up the boat and let it sit 4 years (2 outside under tarp).

I bought it took it to a marine mechanic and had him go over it. Replaced the water pump, impeller, rewired the head, checked compression, and rebuilt carbs. The mechanic got it started, runs in neutral, dies when put in gear. He pulled and checked carbs, and timing, both OK.

He told me to take it to another Merc specialist(he is OMC) he was clueless. Bottom line is I paid him part of his bill, now will owe this other mechanic his money, and I am getting in deep.

The help I need is this. What could be the culprit? Fuel pump was working, appears to be getting enough spark(ran 15 min in neutral), idles at 1000rpm. If this other mechanic decides to start from the bottom up should I stop him? Can't see putting $1500 in this old motor. Where should I concentrate my money, fuel pump, coil, new gaskets? "
 
" Medicineman,

I fin

" Medicineman,

I find it hard to believe that a mechanic wouldn't have figured this out, but my guess is that the idle is just too low. In the book I have (86 merc 115, but the concept is still the same) it says the engine should idle between 650 and 750 when it's in gear in the water. I set mine to idle at about 850 in gear, it gives me more confidence that the engine will not stall out in any condition. When the engine is in the water, in neutral, it idles at about 1100 and out of the water, on a flush attachment, it idles around 1400.

You don't want it to idle too high, as it will cause excess wear on the lower unit, but try adjusting the idle up until it idles at 1200 in neutral in the water, then put it in gear and give it a shot. One thing to note is that there is a bit of play in the linkage, so at a givin setting you may have + or - 100 RPM's. Once you get it to idle in gear, get it adjusted so that it idles at a reasonable speed in gear and you should be all set.

Lets hope it's not this, but there is an off chance that the lower unit is seized up for some reason, and it causes the engine to stall when it is put in gear. To check for this, pull the spark plugs out (to eliminate compression), put it in gear and turn the flywheel clockwise by hand, the prop should turn... if you cannot turn the flywheel at all with the engine in gear, take it of gear and try - if you can turn it then, you most likely have a lower unit issue.

Jon "
 
" Check compression, check for

" Check compression, check for missing bleed inserts.Check adjustment of the low speed jets. "
 
"Well, Guys thanks for the inp

"Well, Guys thanks for the input.

The mechanic called today and said the "trigger was defective and firing sporadically, also the carbs were leaking gas. Said the trigger was $385 plus labor, and that there was no rebuild on the carbs as far as he could see(not torn down yet).

I called the previous mechanic and gave him the update and he said yes I rebuilt the carbs and the fuel pump, take them apart and look at the new parts. Stated he checked the trigger early in the rebuild and it was working OK.

Funny thing is I trust both these guys. I guess I am in for a $1000 ride. My question here is has anyone ever had a trigger go bad, and how did it act, cost to fix?

Another thing the new mechanic said, that the comprssion in the cylinders is off, 1-130, 2-155, 3-135, 4-133lbs. He said this will cause it to idle rough. I am no genious, but is 20lbs a big deal?
He said he is going to "fog" the cylinders for a day, and try to brake the rings loose. Suggests a ring job if the compression doesn't even out. I feel the ring job is unnecessary, What's your thoughts?"
 
You can remove the bypass cov

You can remove the bypass covers and do a visual inspection of pistons and rings.
 
"Medicineman,

Trigger and s

"Medicineman,

Trigger and stator coils can be difficult to diagnose, even when you have the proper meter for the job. The price for the trigger seems high to me. You can price a trigger at www.seilermarine.com, or any number of marine parts warehouses. I think the price should be about $180 for a new unit, but I could be mistaken.

The uneven compression is probably due to heavy carbon, which can cause the reading to be higher than normal. This would explain the 155 psi figure.

"
 
You must log in or register to reply here.
Back
Top