Help please, Merc 260's 2bbl vs 4 bbl

OK, WTF??!!!

I pulled the boat, which went poorly, but that's another story, pulled both drives off, and checked the drive ratios. They are exactly the same!!! I marked the prop to the casing with soapstone, marked the yoke, turned the driveshaft 1.5 times, and BAM - the marks lined up perfectly. Did them both twice, same results.

ERRRRR!!!! Insanity is starting to set in. This is really starting to piss me off!

Any other ideas? Anybody?
 
are you sure the 2bbl mtr is a 350 or is it poss. it's 305
 
26sxl - The 2 bbl motor could possibly be a 305 - but then I'd be in real trouble, since it's the one running stronger and using less fuel.

To any and all: Last night I put a vacuum gauge on the questionable motor. Pulling about 18 inches but the needle vibrates badly. Not by more than 1 or 2, but it's constant and very, very quick. I pulled off 1 plug wire at a time, needle dropped equally and idle got rougher on all except 1 cylinder. I swapped the plug wire with another plug at both ends to see if the symptom followed the wire. Vacuum dropped to 16, and pulling either wire did nothing, so I switched them back. Vacuum stayed at 16, but the idle smoothed out, and now pulling either wire effects no change in vacuum reading or idle. Again, I say WTF?

I ordered a new set of plug wires. Here in WI, nobody stocks any parts, ever. Tonight I'll check the timing for about the 10th time, make sure I've got the right spark plugs in there and that they're gapped correctly. I've read a lot of troubleshooting stuff about what the vacuum readings mean, and it sounds like the shaky needle indicates ignition problems in general, and specifically plug gap. The slightly low reading could be timing too. My timing light is about 100 years old, maybe I'll borrow a better one.
 
Check the type of plugs you are using, be sure they are the correct reach for the type fuel you are using. Most people use AC MR43T or equivalent on the older 5.7s. There is a newer style plug that has a longer reach, supposed to help with burning the newer alcohol blended gas. Champ number is RV15YC4 (I've never liked Champs though). Check with a local mechanic and see what they are recommending. May want to see if both engines are running the same plug type too.
 
I was about a 1/2 step ahead of you. Did some research on plugs today. It had Autolite 145's in it, gapped to .045, I put in Autolite 25's, gapped to .035 per sparkplug411.com (or something like that), a few forums I saw concurred. Should've called the dealer, but didn't. The 25's are longer.

I thought maybe I was onto something here. Also THINK I might have had 2 plug wires crossed, but not sure. Started it up, steady vac gauge at 20, timing at 8.5 degrees, and the idle increased to around 1200. Aha! Got it, right?

Turned the idle down to 700, it got a little rough, the vac gauge dropped to 16 and shaking like crazy. Turned the idle back up bit, to about 950, the vac gauge is still shaky and only at about 16. Right back to WTF?

Got a charter Saturday, with a full, heavy boat, and pretty far offshore. Don't want to make it any worse, that's for sure.

ERRRRR!!!!!
 
More on plugs: Pulled the new Autolite 25's back out, gapped 'em all to .045, where they came stock. That made the vac needle shake even more violently. Pulled them back out, re-gapped them back down to .035, vac gauge settled down a little, but not as steady as it was the first time, not even as good as with the old plugs.

Why does it seem like every time I do something that makes it worse, then reverse it, it never goes back to the original, better state?

And Scorpio - if I had access to a local mechanic that I trusted, you really think I'd be doing all this BS myself? (that's meant lightly!) I'm not saying there aren't any around the Milwaukee area, I just don't know any. The only answer the dealers give me is "schedule an appointment and we can look at it". Every non-dealer shop I know of has a bad reputation.

Maybe I'll try those Champion plugs tonight. Thanks!
 
I know how you feel, I always find that if I want it done right I have to do it myself. Too many shops claim to be experts but turn out to be learing as they go on my dime.
Just curious, what condition is the dist. cap and rotor? A friend just had an issue with his boat stalling at idle and turned out to be a burnt cap, looked great on the outside acording to the mechanic (lol).
 
Was at the dealer today picking up the plug wires so I bought Mercruiser numbered Delco plugs, and happened to talk to their Mercruiser Master Tech who was behind the counter getting something. He recommended the stock Delco's gapped at .035, so I bought them, put them in, absolutely no change. So now I've got new wires, new plugs, new cap and rotor, timing at exactly 8 degrees BTC, a rough idle until almost 1K rpm, 16 inches of vacuum with the needle shaking very badly.

But my "good motor" somehow managed to fill completely with water and lock tight. That was a pleasant surprise when I went to start it last night! Really long story, but I got it fixed - just need to install exhaust shutters, which apparently the previous owner didn't think were necessary.
 
This is a long sad story for sure. After reading through it all, I got to say its time to start over from the beginning. Take what you know (ie: the drives and props are the same) and go through the trouble shooting process.

Your prognosis is the 4brl engine is weak on power. Presumed over fueling via flow scan results. Vacuum gage fluctuating (this is not normal, has got nothing to do with ign syst, everything to do with valve system. compare to the good motor). Look at the plugs and see how things are burning, compare to good motor.
 
I think the differance may not be all that abnormal. Think of it if you had a 1980, pre vortec, and a 1997 (with vorted) Chev pick up trucks. All things equil, rear end, 1/2 ton, auto trans etc, the 80 is good for about 12-14 mpg and the 97 about 18-20 mpg. Now if you drop the 97 to a 305 the power is about the same as the 80 and the mpg gets even a larger differance.

The fluxuating vac gage at idle is not normal though but may or may not be effecting things at higher rpms under a load depending what is causing it.
 
to check if vortec heads.see if the intake bolts go stright down or are angled.Vortecs are stright up and down.The newer 2 BBL motors are 250HP.true at the flywheel.the old engines were overrated.Are the secondaries open at the RPm with the huge burn?would make a huge difference.the new engines also have a higher RPm rating too I think then the originals.The vacuum guage bouncing around could be a carb problem too.I have seen the new ethanol gas causing lotsof issues with carbs.may need a rebuild.check the advance on the timing too to make sure its working.
 
Thanks Jongus and Collector. The one motor, the 2bbl, the one with perceivably more power, burning less fuel is most definitely Vortec. No doubt about it. And yes, the secondaries on the questionable motor are wide open under load - hence the massive fuel burn. Haven't had time this week to do anything more. Will water test it tomorrow with changes posted earlier.

I think at this point, if it doesn't improve, I'll just hunt down another identical Vortec over the winter. I haven't seen any of the 2bbl 5.7's out there used or aftermarket new or remanned though, everything is 4bbl. Merc does list them, so I know they made them. The2bbl manifold isn't available even through them.
I REALLY wish that the drives had mismatched gears!
 
Just remember the 350's have quite a bit more torque than the 305's ..
 
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