mercury 150hp problems

[tigershark95]

hi,
have a 1977 mercury 150 hp ob, i-6
has 130 psi in each cylinder,
can run the boat anywhere from 5 minutes to 1 hours, runs great
if i shut it off, restarts easily, put in foward and apply gas it dies. but will
restart everytime. if i pull the cover and manually apply throttle it will sputter
if i spray carb. cleaner into the carbs, especially the top carb. it clears up right away, and will stay that way until the next time i stop, same things again. engine runs cool, water pump work great.

i have replaced the gas tank, hose, fuel filter, gas lines,

any suggestions would be great

thanks

 

[emckelvy]

Re: mercury 150hp problems

Sounds like maybe it's a touch on the lean side. You can try adjusting each carb's idle mixture screw approx 1/8 to 1/4 turn CCW (richer mixture) and see if that helps. The idle mix screws are slotted, on the upper right side of the carbs as you're facing them.

Best way to adjust idle mix is to get the motor nice & warmed up, idle in gear and adjust each carb idle mixture screw for best idle. Then turn each mixture screw approx 3/8 to 1/2 turn CCW. This probably will result in a tad lumpier idle, but Inline Sixes like to run on the rich side or they'll stumble upon acceleration.

The ideal adjustment is as lean as the motor will tolerate and still be able to cleanly accelerate to WOT.

If you can't achieve a satisfactory adjustment, perhaps you'll need to do the "Link 'n Synch" of timing and carb linkages that's frequently discussed here. Just do a search and you'll find all the info for that.

HTH..........ed

 

[curtis63]

Re: mercury 150hp problems

I have the same problem you do. I just discovered a work around yesterday.

1. Start the engine and put it in gear and accellerate up to 1000 rpm.
2. Push the Choke button for about 1 second until the motor almost dies.
3. Wait for the idle to recover after the choking.
4. Increase the speed up to 1500 rpm, or until the engine seems to sputter again and immediately push the choke button for another second.
5. Wait for the idle to recover after the choking.
6. Increase speed a little more, up to 2000+ rpm.
7. If it sputters, repeat steps 5-6 over and over until it starts going.
8. More likely, by this time, you'll be able to fully accelerate and the motor will hum right along as fast as you want to go.

So, that's my work-around for the problem. I'm going to go try and adjust the idle speed as suggested by the other replyer.. This should work for you though until you can get your idle speed adjusted.

If anybody has any other suggested fixes, please let me know. It almost felt like the choke was getting stuck until I pushed the choke button a couple times, but I have no idea what the actual problem is, just how to work around it.

Hope this helps out,
Curtis

 

[curtis63]

Re: mercury 150hp problems

hi,
have a 1977 mercury 150 hp ob, i-6
has 130 psi in each cylinder,
can run the boat anywhere from 5 minutes to 1 hours, runs great
if i shut it off, restarts easily, put in foward and apply gas it dies. but will
restart everytime. if i pull the cover and manually apply throttle it will sputter
if i spray carb. cleaner into the carbs, especially the top carb. it clears up right away, and will stay that way until the next time i stop, same things again. engine runs cool, water pump work great.

i have replaced the gas tank, hose, fuel filter, gas lines,

any suggestions would be great

thanks

I think my engine has the same problem you were having. Did you ever get yours fixed? What did the solution end up beng.

I was on the lake yesterday and figured out how to work around the problem I was having. Here's what I did:

1. Start the engine and put it in gear and accellerate up to 1000 rpm.
2. Push the Choke button for about 1 second until the motor almost dies.
3. Wait for the idle to recover after the choking.
4. Increase the speed up to 1500 rpm, or until the engine seems to sputter again and immediately push the choke button for another second.
5. Wait for the idle to recover after the choking.
6. Increase speed a little more, up to 2000+ rpm.
7. If it sputters, repeat steps 5-6 over and over until it starts going.
8. More likely, by this time, you'll be able to fully accelerate and the motor will hum right along as fast as you want to go.

Let me know what the actual problem was with your motor so I can fix mine right and not have to work around the problem anymore..

Thanks,
Curtis

 

[Ed R]

Re: mercury 150hp problems

That old motor has no idle adjustments! pull off top carb, and clear out pick up tube!

 

[curtis63]

Re: mercury 150hp problems

That old motor has no idle adjustments! pull off top carb, and clear out pick up tube!

Thanks for the quick reply.. I'll give it a try. I'm totally new to boats, but I bought a maintenance guide for my engine, so hopefully I'll be able to figure out what 'clear out the pick up tube' means. Any more specific help would be greatly appreciated !!

Thanks again,
Curtis

 

[KenStone]

Re: mercury 150hp problems

I think I have a related problem, but now worse. my start was a lil spit and sputter but then a quick whip lash lauch, now my motor is hung wide open in idle. we have step by step went down the fuel line and checked repaced and cleaned all but carbs and today when we changed the spark plugs 4 cyl was worse than the others so they concluded we needed to take the carbs out and shine them up that the floats where hung up caused by gunk. I hate buying other peoples problems.. LOL

 

[emckelvy]

Re: mercury 150hp problems

That old motor has no idle adjustments! pull off top carb, and clear out pick up tube!

What are you talking about?? This motor has THREE carbs and EACH carb has an idle mixture adjustment!

If they are adjusted too lean, you'll get the exact symptoms these guys are talking about.

If you don't adjust the idle mixture on an Inline Six to be slightly rich at idle, likely it's going to bog off the line and be hard to start.

If you try and adjust the mixture and there's no change in idle speed no matter how you turn the screw, time to tear the carb(s) apart. Otherwise there's still tuning to be done!