79 140hp MERC runs great but won't pull up waterskier....

[140hpMERC]

I have a 79 140 hp on a 16 sidewinder boat and it runs great at high speed but the thing is that i cant even get a skier up out of the water when before i had it rebuilt i have pulled up 5 of them. The 3rd piston seased so i had it rebuilt. ever since then i couldnt pull up a water skiier, they say 2 change the prop but it the same prop that has been on it since day 1. it seams to be bogging down when i try 2 get them up and ideas????????????

 

[jimmbo]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Compression check, link and sync check, and idle mix adjustment.

 

[CharlieB]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Ditto.

The idle mixture is still just a bit too lean for the additional load of the skiers.

Turn the idle mix screws out an eigth turn each (six of them) and try again. It may take two times depending on how far off they are.

 

[jimmbo]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Ditto.


Turn the idle mix screws out an eigth turn each (six of them) and try again. .

Since there are only three single bbl carbs on this engine where are the three extra idle mix screws?

 

[wasp]

Re: 79 140hp MERC runs great but won't pull up waterskier....

charlieB and Jimmbo,

I am having the same problem. If I adjust the idle mix screw to help the throttling what will it do when trying to start.

 

[jimmbo]

Re: 79 140hp MERC runs great but won't pull up waterskier....

In theory, no to little affect.

 

[Chris1956]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Merc, Those inline sixes neet to be propped corectly to allow them to rev up enough to get to their powerband. My '77 Merc 1500 with a 21 pitch prop would pull two skiers. With a 23 pitch prop it would plane, but not get above fast idle with a skier.

I suspect the power of your motor is down 10% or so after the rebuild, so you are now below threshold with a skier.

 

[CharlieB]

Re: 79 140hp MERC runs great but won't pull up waterskier....

I didn't notice the year, was thinking of later V6, instead of your stacked 6.

Same difference, idle mixture must be rich enough for acceleration.

In the water, in gear, at idle, adjust idle mixture to best idle speed PLUS 1/8 turn. Slam throttle WOT, ANY hesitation/cough/sneeze/bog at all then further open idle mix screws an additional 1/8 turn, repeat test.

 

[j_martin]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Even with a screamin' Demon XR4, I prop down to pull skiers. I also use a ventilated prop, which lets the engine spool up before it grabs at hole shot time.

I use 2 high fives, 24 inch for fishin' (Fast fishin' no doubt) and 22 inch for skiing. If I ever ding the 22, I'll replace it with a 20 for skiing.

Torque is what beats up a short stroke motor, not RPM's.

hope it helps
John

 

[140hpMERC]

Re: 79 140hp MERC runs great but won't pull up waterskier....

The boat is going to the machanic tomorrow and i will tell him the sugestion and will post the result i know the compression should be 148 when new it is now 142 would that make a difference?

 

[j_martin]

Re: 79 140hp MERC runs great but won't pull up waterskier....

You just had a bunch of guys tell you that the inline 6 needs to spin up to develop enough torque to pull it out of the hole. Slightly tired shouldn't keep you from skiing. If the compression is even, it's probably the gauge that changed.

Lower pitch, ventilated prop will let it take off like a slingshot.

John

 

[BM]

Re: 79 140hp MERC runs great but won't pull up waterskier....

Yes, but hang on.... He stated that since rebuild it won't pull a skier yet nothing in the setup has been changed. So that rules out prop or any other issue more or less.

I would have a look at your WOT timing. After rebuilding it your mechanic may have been over zealous in knocking back the timing as a 'bang" safeguard. If he pegged it back too far you will lose grunt.

Those comp differences are insignificant. Where did you get 148psi from? As far as I know Mercury have never released compression readings for their engines.

Cheers

 

[140hpMERC]

Re: 79 140hp MERC runs great but won't pull up waterskier....

I got the 148 psi from what the machanic has said 2 me

 

[140hpMERC]

Re: 79 140hp MERC runs great but won't pull up waterskier....

And at 50 mph i am doing 4500 rpm
the fastest i have ever had the boat was 63 mph and that was right before the engine blew

 

[emckelvy]

Re: 79 140hp MERC runs great but won't pull up waterskier....

I'm having trouble believing the 50 mph with a prop that will only achieve 4500 rpm. Something is terribly out of whack, either the speedometer is wildly off or the tach is reading low.

Is 50 mph per GPS or speedo? How about when you hit 63 mph? What were the water conditions and do you have power tilt-n-trim?

I had a Super 16 'Winder years ago with a 1350 Merc. It was absolutely scary with a Stiletto prop and would do a hair over 50 but start chine walking. It was also turning close to 6000 at the time.

You'd have to have a seriously-modified hull to be able to survive a true 63 in a Sidewinder.

And you're not making any power with that 140 at 4500 rpm.

More Questions:

What's the pitch on the prop?

When the shop rebuilt the motor, were the pistons hi-dome or low-dome and what did they put back in it?

What was the total spark advance before they readjusted it?

What's the total spark advance now, has anyone verified its setting since the rebuild?

Anyway, a bit more info might help bring the problem to light.

Note on the compression values; agree with previous post, the values (long as they're not extremely high or low) are irrelevant as long as they are even with the others. If all cyl's are reading 142 psi and you know the compression tester is accurate, nothing wrong with that! One thought, I'd expect slightly lower readings if hi-dome pistons were replaced with low-domes.

HTH........ed

 

[140hpMERC]

Re: 79 140hp MERC runs great but won't pull up waterskier....

yes i do have a power tilt and trim and i have always thought that the tach was a lil off. and as regards to the 60 well that a guess cause the speedo top out at 60mph and i was below that. it was the scariest thing i have ever done the boat was rocking side to side and when it would rock to the left i would turn the wheel right and visversa so a TRUE 63 i have no idea but it was fast enough the change my white seats to brown.

 

[140hpMERC]

Re: 79 140hp MERC runs great but won't pull up waterskier....

the pitch of the prop is 21 and i will get you more answers to your question as soon as i find them out