Loss of top end 5.7 ltr 2bbl

HeadnSouth · May 16, 2005

I recently did a tune up on my 98 2brl 5.7 ltr Merc w/ IV thunderbolt ign. Plugs, cap, rotor, wires and a carb kit. The boat idles rough and has lost approx. 1500 or 10 mph rpm on the top end with a load. I've checked the timing and it varys 4+- degrees at idle, its been adjusted and readjusted but I still have no TE. The sensor in the dist cap was replaced still NG. Someone mentioned carb adjustments and the thing is when I did the carb kit the wrong kit (5.0 not 5.7) was sent but I did not figure that out until I made adjustments. DOH! And I haven't been able to get the correct ones yet. Sierra was no help.

Carb # 8612458103 I'm not sure where to look next until I can verify the carb settings. I've looked around and found some merc manuals but #24 cannot be found to check my settings. Anybody have a working link? Thx

JB · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Howdy headnsouth. Your Mercruiser is not an outboard, so I will move this to the Mercruiser forum. Good luck.

HeadnSouth · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

DUUUHHH! I tend to read to fast. My bad, I had the merc part at least.

Don S · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Time for a compression test and check the exhaust manifolds & risers for water leaks.

HeadnSouth · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

The engine only has 230 hours on it and has only been in fresh water. Its run great until I fixed it.

Don S · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Hours on an engine don't mean squat in a boat. The constant sitting doing nothing does more harm than actually taking it out and using it. If it's only started this since you "Fixed" it, I guess that tells you where to look now, doesn't it. Sure hope you use a new base gasket each time you pull the carb.

HeadnSouth · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Sure did use a new gasket. But without the carb float settings I'm SOL.

John_S · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

My Merc manual doesn't have your carb part number, guessing yours is a vortec engine. The Mercarb in my manual, has the same settings for 5.0 and 5.7L. The setting below are for a 43mm Mercarb '98-01, from Seloc manual: Float Level = 11/32 Float Drop = 15/16 Pump Rod = Middle hole Choke Setting = 2 marks lean Choke Unloader = 0.080 idle Mixture = 1 1/2 turns Float Weight = 9g max Primary Jet = 1.65mm Power Valve = 0.90mm Venturi ID = 475 As far as timing, are you sure you have T4? A '98 should have T5. If you have a T5, make sure you follow the procedure, and ground the correct lead, otherwise it will be trying to adjust timing on its own. If you do have a t4, I'd check the distributer for end play. From reading posts, another common tune-up error, that causes loss of topend, is plug wire swapped on 2 cyl. Highly recommend getting the Merc manual for engine and drive.

Don S · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

This is where you have to be real careful with Mercruiser stuff, especially the carbs. The best thing to do is go by engine serial number to get the proper manual and parts. A perfect example is what John shows, now, if you have a 97 engine (very possible if it's an early 98 boat and they had some 97 packages left over and had to get rid of them) the float level would be 9/16" not 11/16. The float drop would be 1-1/32 not 15/16" and you would have a 35mm carb not a 43mm. So you really need to make sure what you have.

HeadnSouth · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Thanks for the help. From what I had read previously I assumed it was a IV, a diagram that I have of a IV is identical. But I just removed a sticker from the cowl that was covering a V.

With so many different models and stuff it makes it very confusing. Could you please explain what is (I believe)called the "Base Timing Mode" for setting the ignition timing? Thx again and do I need both volumes of manual#24?

Don S · May 16, 2005

Re: Loss of top end 5.7 ltr 2bbl

Without a serial number from your engine, don't buy any manual yet. Book 24 may not be the one you need. Look at the metal tag just above the starter on the back of the block. get that number and we can verify which manual you have and a few other things. Never ASSUME you have a 98 engine because you have a 98 model year boat. It may still have been built in 97 with 97 parts. Service mode is only on Thunderbolt V ignition systems. You say you have TB IV, so you don't have a base timing mode at this point.

HeadnSouth · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

I went to mercs web site and according to my engine # service manual# 24 is the one for me. I'm currently checking around for a used <$$$ manual. I've heard mixed reviews on the seloc manuals and would rather the merc. 90-861327 1 SERVICE MANUAL MERCRUISER 5.7L ALPHA Serial Number: 0L079244 Model Number: 4311025LS John S appears to be right on with the V ignition, and that explains the knock sensor on the engine. IV doesn't have a knock sensor but does have the knock module. Like I mentioned above after removing a sticker from the cowl it uncovered a the TB V Not sure if the merc number for the carb will help but here it is. Carburetor # 861245 8103 Carburetor Mercruiser # 3310-861245A1

John_S · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

Don is correct, you need to make sure you have the correct engine. I assumed you didn't have a '97, only because the carb part number didn't match my Merc manual, which does cover the '97 2brl, but not the '98 one. A '98 should have vortec heads, too. My manual maybe wrong, for it does show a 43mm on 5.7 for '97 (both the Merc & Seloc). It does have different a couple of different settings, including what Don said. Here is the link to the 454 manual on T5 timing. The timing procedure looks to be the same for the '97 Merc manual, but I didn't check every word: http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

John_S · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

HeadnSouth, From what look-up I can do on serial number (nowhere as good as what Don has), it looks like you have a '98. Also your description having a knock-sensor and knock module falls inline. My '97 2brl does not have those. Good news is, you have a vortec and more hp.

HeadnSouth · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

Thanks guys, Urock sure wish boatfix would get the ALL pdf files working.

Don S · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

Yep, the manual 24 is the one you want, and you do not need the suppliment. It's for the 6.2L. Here is the timing instructions from book 24 for the Thunderbolt 5 ignition, and your's should be set at 10° BTDC @ 650rpm.

HeadnSouth · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

Thanks Don. I was wondering where the timing lead was located. I'll be putting on the ear muffs as soon as get home today.

HeadnSouth · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

Well I'm one step closer to getting it all ironed out. Did the timing as instructed and it still ran rough.

So as Don pointed out its something I did. He must be psychic. Pulled the plugs to visually check whats going on and found them all black and sooty but one which was looking straight out of the box. mmmm no spark to # 8 Pulled the wires and added a bit of dielectric grease to both ends while I was inspecting the all new wires and #8 wire was looking pretty crappy. Fired the engine up pulled #8 and there was no difference. So back to sierra for a replacement.

PS: the carb specs that John posted where the same that I had set them for. Hopefully with the new set of wires I'll be good to go.

Don S · May 17, 2005

Re: Loss of top end 5.7 ltr 2bbl

You might try changing that spark plug from one cylinder to another. Could be a bad plug causing it not to fire, not the wire. This is assuming (that word that go you into trouble with the Thunderbolt IV ignition) you have good compression on that cylinder. And please tell me you haven't put Champion spark plugs in it...... Please!!!!

HeadnSouth · May 18, 2005

Re: Loss of top end 5.7 ltr 2bbl

Did a resistance test and it showed 16.26K ohms in a 2'wire. (8mm silicone from sierra) Ran a continuity check and it came up zip. All using a fluke meter. Inside the boot of the cap side it was rusty looking and nasty. The rest of the wire boots looked ok. I did the TB IV troubleshooting when I started the search for the cause and everything checked out ok. Haven't looked to see if there is a diff. in the IV and V check but I'd be willing to bet its a bad wire.

Ps: I used NGK's

Loss of top end 5.7 ltr 2bbl

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