MERCURY 125HP CARBURETORS

WHEN TOWING SOME ONE WAKE-BOARDING THE MERCURY 125HP IS REVING AROUND 2200RPM.<br />BUT WHEN THE WAKEBOARDER CARVES THE OUTBOARD LOADS UP AND FALLS UNDER THE 2000RPM AND THEN IT DROPS DOWN TO 2 CYLINDERS SO THEN YOU GIVE IT MORE THROTTLE AND IT TAKE OFF GIVING THE WAKEBOARDER A VERY HARD TIME TO STAY ON.<br />THIS IS WHY I WANT TO KNOW IF THERE IS ANY WAY OF REMOVING THE CARBURETORS WITH NO IDLE JETS AND FITTING OTHERS WITH IDLE JETS?

Re: MERCURY 125HP CARBURETORS

As another poster pointed out, if you enabled idling on the other two cylinders, the overall idle would be too high.<br /><br />That said, there might be a way by playing with the syncronization to get the timing at idle to back off a bit, to to get it back down. I think it's cousin, the 3 cylinder 90, idles on all 3.<br /><br />What might stand in the way, is if the idle stabilizer circuit will detect too little advance and do something to compensate, thwarting your attemts to get it to idle down.<br /><br />Lastly, are you sure it's propped correctly? If it's hovering around 2000 at wakeboard speeds, and the wakeboarder can load it down like that, dropping to the next pitch down would help in both areas.<br /><br />My own boat is powered my an older mercury of similar hp and propped for it's intended use. I'm sure it wakeboards closer to 3000 than 2000, and it doesn't load down too much.<br /><br />-W

Re: MERCURY 125HP CARBURETORS

Note: The parts list for the 125 shows a different main jet in *each* carb too. (to compensate for missing idle circuit and?) <br /><br />You'd need to resolve this as well, Check your parts lists as they used a few different carbs on the 125's. <br /><br />This doesn't sound like a job for an amateur by any means. <br /><br />My only experience with one of these motors is that I rebuilt one that ran without water and pulled #1 sleeve loose from the block. (not pretty) However, since it was running great before it melted down, I use liquid electrical tape to hold all the tuning "as is" and reassembled it without re-tuning. I never had to play with the tuning.<br /><br />-W

Re: MERCURY 125HP CARBURETORS

I'm afraid your motor is not appropriate for your application. They are great at trolling, and they perform very nicely at top end. They are simply crappy skiboat motors. Your story is repeated time and time again, and your only real solution lies with a different motor. Your salesman shouldn't have sold it to you in the first place.<br /><br />The problem is that they idle on two and run-out on four. They have a difficult time in the transition which occurs around 1800 to 2200rpm...about where you ski at. It's not a flaw, it's a characteristic.<br /><br />The motors were designed with fishermen in mind. It'll troll smoothly for long periods, and it'll get you to your favorite fishing hole in a hurry. But for skiing, they're just not well suited.

Re: MERCURY 125HP CARBURETORS

Willy , you'd think with enough "motivation" there would be a work-around?<br /><br />I mean if the 8 cylinder looper can idle on 8, and the 3 cylinder can idle on 3 - then it would follow that the 4 *could* be made to idle on 4 with enough fiddling. At $250 bucks a carb and the risks involved rejetting the thing, I'd be leery of taking it on however.<br /><br />I'm gonna ask the Scream & Fly guru's about this, my own curiosity is aroused now... LOL<br /><br />-W

Re: MERCURY 125HP CARBURETORS

In the meantime, I think propping way down is the answer. You want to get your rpm's up (out of the transition zone) and keep your boat speed down.

Re: MERCURY 125HP CARBURETORS

I agree that short of replacing the motor, propping down for wakeboarding is the most practical way to solve your dilemma.<br /><br />I had a similar experience with my Seaswirl Spyder with 4.3 Cobra; it had plenty of power for boarding, but was hard to control. Ended up with a 15 pitch Gil Marine 6-shooter prop which had excellent grip, and the pitch was low enough that the motor wouldn't drag down at all when you made a hard cut.<br /><br />It was still good enough to run over 40 but of course you have to watch the full-throttle revs.<br /><br />You'll probably find you use less fuel, too, as a lower pitch prop will get your motor up in a more suitable rpm band rather than cycling back and forth.<br /><br />Try dropping down about 4" in pitch from where you are now and see how that works.<br /><br />There should be a suitable 4-bladed prop that'll work well for you, you'll like the added 'traction' when you're coming around to pick up a downed boarder. Or check out the Gil 6-shooter, it's great in this application.<br /><br />Happy Wake Jumping........ed

Re: MERCURY 125HP CARBURETORS

So far I've gleaned 2 pieces of additional data.<br /><br />1. There is a kit available to let it idle on 3.<br /><br />2. There is a harmonic issue at low rpm that precludes a safe idle on 4.<br /><br />I cannot verify theese. But it makes sense.<br /><br />-W

Re: MERCURY 125HP CARBURETORS

I hesitate to offer this, but if you were to take the throttle plates from a similar model that idles on all cylinders, you might be able to get the idle speed down. That would mean 4 throttle plates from either a 75Hp or 90Hp. I wouldn't hazard a guess as to which. The plates on the 4-cylinder have rather large holes in them for idling. Of course, you'd need two more carbs that have the adjustable idle needle, I think the #1 carb. But then you have to consider jetting which could cook a piston if you were to guess wrong.<br /><br />But the reason they actually went to idling on two cylinders is because that was the only way they could get a smooth idle out of it. The 75's idle rather poorly, the 90's idle awfully. The 4-cylinders must've been real shakers!

Re: MERCURY 125HP CARBURETORS

Yep,<br /><br />I just heard from a guy in FonDulac and he said to FORGET trying to get it to idle on four, dangerous rattles result. Period.<br /><br />That's good enough for me. Oh! and when propping it down, DON'T let it go over 5400, the cranks snap.<br /><br />If you ask me they're a worthless POS compared to the Tower of Power - for that HP range anyway.<br /><br />-W