77 merc 150 bogs in gear but not in neutral

[checkmate150]

77 mercruy 150 hp serial number is 4750174. Boat has sat for about 5yrs. Took it out yesterday, it started and ran great for about 5 minutes, had it wide open and up to 40mph. Shut it off to fish for 30min started back up and would not go over 6mph, every time I tried to throttle up it would stumble and kill the engine if I didnt back it off. Put new plugs in it and fresh 91 octane fuel/ marine oil and tried again. Same results, ran great for a few mintues then bogged out again. If I put it in neutral im able to rev up to 5000 rpms no problem but absolutely cannot in gear. I think it may need the carbs cleaned out after sitting so long. Thought i'd ask the experts, thanks in advance.

Neil

 

[narvlebenoit]

Re: 77 merc 150 bogs in gear but not in neutral

Cleaning the carbs would be the first thing after sitting that long and check for bad or just change fuel lines.

 

[aerox]

Re: 77 merc 150 bogs in gear but not in neutral

Just to make sure check that nothing got tangled in the prop because we used to have the same issue.

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

thanks for the quick response, i'll check the prop tonight, o and I replaced the fuel line from the tank to the engine with a new primer ball yesterday, but it still could be the lines that feed the carbs

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

I looked at the prop and can't see anything hanging out of it, its hard to tell if theres anything under it, should I pull the prop off and check inside? The prop spins freely.......

 

[arsenalpsu]

Re: 77 merc 150 bogs in gear but not in neutral

77 mercruy 150 hp serial number is 4750174. Boat has sat for about 5yrs. Took it out yesterday, it started and ran great for about 5 minutes, had it wide open and up to 40mph. Shut it off to fish for 30min started back up and would not go over 6mph, every time I tried to throttle up it would stumble and kill the engine if I didnt back it off. Put new plugs in it and fresh 91 octane fuel/ marine oil and tried again. Same results, ran great for a few mintues then bogged out again. If I put it in neutral im able to rev up to 5000 rpms no problem but absolutely cannot in gear. I think it may need the carbs cleaned out after sitting so long. Thought i'd ask the experts, thanks in advance.
Neil

WOH---first off never rev your engine over 1500-2000 out of gear unless you you'd enjoy rebuilding your engine. I'd say it's either a loose connection or broken wire in your ignition system or you need to rebuild your fuel pump. Does it slowly get worse or just all of sudden cut out? If it sudden I'd check all my connections, if it still does it than get an OEM book and start testing for faulty parts- if it's gradual loss of power than i'd rebuild the fuel pump.(easy to do)

 

[Chris1956]

Re: 77 merc 150 bogs in gear but not in neutral

It is very likely dirty carbs, however, take a compression test and spark test to rule out those issues. That motor should have a distributor, so check the plug wires for arcing to ground, when accelerating. Also, check wiring harness for bad wiring. You can burn out the trigger or switchbox, if some of the wires short. Each are $200+ .

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

Heres some pics of my fuel pump, I bought the pump used because the previous owner deemed the old one bad and lost it. This doesnt look good but im not positive its the problem. I will order a rebuild anyways. The screen has some small junk on it. I pull tested and inspected the wiring for shorting out and found nothing out of the ordinary. I'm going to order new plug wires and carb kits also.

Neil
http://i114.photobucket.com/albums/n246/crazyhausk1500/DSCN2523.jpg
http://i114.photobucket.com/albums/n246/crazyhausk1500/DSCN2524.jpg

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

http://i114.photobucket.com/albums/n246/crazyhausk1500/DSCN2532.jpg

In the pic the black piece with the round hole in it was found behind the valve and the brass piece that holds it up was unthreaded and blocking the main jet (bottom hole). I think this is my problem. I still have ordered carb kits and a fuel pump rebuild kit.

 

[lathehand]

Re: 77 merc 150 bogs in gear but not in neutral

I also have a 1977 150 hp merc number 4750278 only 104 numbers away from yours.I hadsimular problems with mine .I rebuilt the fuel pump;cleaned the carbs and also changed the gas lines added a water seperator and she runs like new again.

 

[CharlieB]

Re: 77 merc 150 bogs in gear but not in neutral

Boat has sat for about 5yrs.

Neil

Reviving an engine that has been parked for a long time, it is advisable to clean the fuel tank, lines, etc.

Also the water pump impeller should be replaced to ensure you do not suddenly lose cooling and overheat the motor due to 'brittle' impeller blades breaking.

Oil tanks have been known to accumulate 'sludge', cleaning the system and refilling with fresh TCW-3 is far more cost effective than a rebuild.

While none of these may be your immediate problem, who knows what gremlins are lurking under that cowling just waiting to rear their ugly head?????

 

[Chris1956]

Re: 77 merc 150 bogs in gear but not in neutral

Chrckmate, I have one of those blown 1500 laying around, so I am pretty familar with them. I did not understand you post about the carb. The black plastic thing is the carb venturi. It sits on top of the main nozzle.

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

The main nozzle came unthreaded and fell down in front of the main jet ( gravity), thus blocking the jet and also not pulling fuel up. I had to order carb gasket kits because the old gaskets were spent. They came in yesterday and I put the carbs back on and also rebuilt the fuel pump yesterday with a new pump kit. I took it out to the lake last night and the same thing happened as before. It would bog or die at around 6mph when i tried to take off, I didnt look at rpms- sorry. I ordered smaller main jets anyways( had .080, goin with .076)they will be here tues, but Im still not convinced thats the problem because like I said in my first post the boat took off like a champ at first then just lost all power as the day progressed. Im starting to think it may be my spark plug wires, which my Dad had a problem with his boat once having similar symptoms and the problem being the wire between the cap and coil. I cannot seem to find a spark plug wire set anywhere locally or online. All I have found are individual plug wires from cap to plug for $22 a piece

As another member has posted loose electrical or shorting to ground so I guess that would be my next step. Thanks for the help so far. I really do appreciate.

Neil

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

Reviving an engine that has been parked for a long time, it is advisable to clean the fuel tank, lines, etc.

Also the water pump impeller should be replaced to ensure you do not suddenly lose cooling and overheat the motor due to 'brittle' impeller blades breaking.

Oil tanks have been known to accumulate 'sludge', cleaning the system and refilling with fresh TCW-3 is far more cost effective than a rebuild.

While none of these may be your immediate problem, who knows what gremlins are lurking under that cowling just waiting to rear their ugly head?????

The tank, lines from tank to engine, and primer ball, and lines from pump to carbs and carb to carbs have all been replaced as of last week.

Im not sure what oil tanks your referring to being its a 2stroke, but the lower gear oil level (plugs just above the prop and just under the prop) is full, and I plan to change it tomorrow anyways.

Neil

 

[Chris1956]

Re: 77 merc 150 bogs in gear but not in neutral

Try oldmercs.com for sparkplug wires. They were $6/ea, but you need to cut to size and install the boots and springs yourself.

Bogging on takeoff is a classic symptom of lean idle mixture. Hit the choke when you try to accelerate. if it is better, richen the carbs 1/8 turn at a time to dial the correct mixture in. Top carb runs leanest, so richen that one first, followed by a test and then richen the mid carb and test etc.

You should stick with original factory sized jets, unless you are over 5000 feet in elevation. Those motors like to run rich at high speed, and it keeps them cool and healthy.

 

[CharlieB]

Re: 77 merc 150 bogs in gear but not in neutral

Forget the oil tank, your motor does not have an auto-mix system, you must be pre-mixing your fuel yourself.

But one of my other points was COOLING, how old is the water pump impeller?

A weak or failing cooling system will cause $$$$$ damage.

Once the motor is to temp, how is the 'P' stream?

Place your hand on the exhaust side cover, is it cold?

How hot is the other side of the motor and the cyl head? Careful of the old plug wires, they can BITE!

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

Forget the oil tank, your motor does not have an auto-mix system, you must be pre-mixing your fuel yourself.

But one of my other points was COOLING, how old is the water pump impeller?

A weak or failing cooling system will cause $$$$$ damage.

Once the motor is to temp, how is the 'P' stream?

Place your hand on the exhaust side cover, is it cold?

How hot is the other side of the motor and the cyl head? Careful of the old plug wires, they can BITE!

Yes I mix the oil and gas. I have no idea how old the impeller is. I will order one tomorrow. New plug wires will be here tuesday. Tonight I took the distributor cap off and it looked ok, not dirty, or worn or corroded. When the cap was off I turned the distributor housing by hand while touching the center of the cap and yes I got bit!! So it seems the spark is there but??? A friend has a tool that hookes on the wires and tells how many volts are on the plug wire while its running so if I get the tool I will check each individual wire this weekend. Also I will temp gun the exhaust cover and head temps and report.

Neil

 

[checkmate150]

Re: 77 merc 150 bogs in gear but not in neutral

UPDATE- I finally took it to a boat mech after doing a compression test he asked for. I came up with 105- 115 psi on all cylinders. He ran it and everything checked out until it started running like crap and he did a cylinder leak down test. Number 3 and 4 are low. He suggests resleaving them both to the tune of about $800 for everything.

 

[CharlieB]

Re: 77 merc 150 bogs in gear but not in neutral

WHO ran it?

Where you there?

Tell him that you can't afford it as yet and TAKE IT HOME!!!!!!

Re-test Compression again and post each cyl''s #

Check those carbs again, they may have the factory screens in the fuel inlet, there was a Service Bulletin long ago advising to remove those screens as they could plug up, reduce fuel flow to that carb and melt the pistons in those 2 cyl's.

$800 is suspiciously low for a rebuild.

Look up the parts, do the math and you will soon see.

Two cyl liners + machining

Two pistons + SIX sets of rings

Gaskets and Seals

Bearings?

What is is hourly labor rate?

Can you now understand why I get suspicious?