357 Mag Bravo 4V Reman, Just Installed, 325HP, WORSE then old engine @ 260HP!!! ??

[Orbitter]

No Title

Here's some pics of the spark plugs. I swapped with new ones to see what, if anything would change. No change that I noticed.
Plug for cylinder 7 is much different then the rest. Some are slightly tan and some very white while
#7 cylinder's plug is very black except for the very tip of the insulator.

Please read the notes on the photos for details.
I should also mention, I removed the spark arrestor and silly cover with flames on it so don't freak out. It's back on now.

edit: to mention another thing. I pulled each plug wire off while idling. 1 of the wires when pulled made so little difference that I'm not really sure it did or not. Just a guess because I didn't keep track of it unfortunately but I assume that was cylinder 7.
There were 2 other plug wires that when pulled had very very little effect but it was noticeable. I assume that was probably cylinders 3 & 6. The rest had all the same effect, made a noticeable difference in sound and a small change in RPM.

 

[HT32BSX115]

Almost appears that the distributor advance curve and/or camshaft is all wrong for this engine..............................

You absolutely sure the spark plug wires are going to the right plugs in the right firing order?

 

[Orbitter]

Almost appears that the distributor advance curve and/or camshaft is all wrong for this engine..............................

You absolutely sure the spark plug wires are going to the right plugs in the right firing order?

I'm not. That is something I am going to check in the morning. Could very well be 2 hooked up backwards which would also explain the 2 plugs on cylinders 3 & 6 that almost look like they are brand new.

 

[NHGuy]

To give you all a little background on the carburetor size issue. If the carb is vacuum actuated it acts like the primary size bore until there is enough suction -demand to pull open the secondaries. I think Mercruiser started with the 750s because GM used them. Then never changed.
OP, seems like you are getting somewhere. Good for you, might be nearing the solution.

 

[achris]

Just watched your video. Yes, definitely something off around the carburation.. Check out and report what carb is on the engine. You can hear the engine 'roaring' for fuel until it hit's about 2800, then it does take off. Definitely a sign of too much air and more enough fuel...

 

[Orbitter]

While I was down in the engine bay during take off, I moved the choke butterfly closed a bit to make it richer while we were trying to plane and it didn't improve. Held my hand over the intake slightly so block off air and enrich the mixture and it didn't help any. Any restriction to airflow did not improve power to get on plane, only made it worse.

 

[HT32BSX115]

While I was down in the engine bay during take off, I moved the choke butterfly closed a bit to make it richer while we were trying to plane and it didn't improve. Held my hand over the intake slightly so block off air and enrich the mixture and it didn't help any. Any restriction to airflow did not improve power to get on plane, only made it worse.

Wonder if the jets are a little too aggressive......

And having said that, 2 plugs that don't appear to even be firing (what'd the other 6 look like?) still makes me wonder if a couple of wires are crossed or if the the ignition is still in the "base" mode, wasn't timed in the base mode or the Knock sensor is defective (and indicating a continuous knock retarding the timing......etc)

 

[Orbitter]

Wonder if the jets are a little too aggressive......

And having said that, 2 plugs that don't appear to even be firing (what'd the other 6 look like?) still makes me wonder if a couple of wires are crossed or if the the ignition is still in the "base" mode, wasn't timed in the base mode or the Knock sensor is defective (and indicating a continuous knock retarding the timing......etc)

The others were ok, except for cylinder 7's plug which was very sooty! Aside from the very tip of the insulator, the rest of the plug including the threads was all covered in black soot.

 

[sub2010ss]

That port on the distributor is a vent, not a vacuum port. The wire over the valve cover that has a small black plug in it is how you ground out the ignition system to set the timing and adjust the idle. The other two wires are for an alpha 1 gen 2 shift interrupt switch which I am guessing the bravo doesn't need.

 

[Orbitter]

That port on the distributor is a vent, not a vacuum port. The wire over the valve cover that has a small black plug in it is how you ground out the ignition system to set the timing and adjust the idle. The other two wires are for an alpha 1 gen 2 shift interrupt switch which I am guessing the bravo doesn't need.

Thank you.

 

[HT32BSX115]

The others were ok, except for cylinder 7's plug which was very sooty! Aside from the very tip of the insulator, the rest of the plug including the threads was all covered in black soot.

Sounds like that cyl is not making much HP............

 

[Tail_Gunner]

Just watched your video. Yes, definitely something off around the carburation.. Check out and report what carb is on the engine. You can hear the engine 'roaring' for fuel until it hit's about 2800, then it does take off. Definitely a sign of too much air and more enough fuel...

Could be but but running that hard at low rpm and no popping then it comes on strong at around 2600 rpm...I believe that the timing is all in at that rpm (advancing), It sounds very much like a timing issue and if i saw this right no trim tab's absolute must with that boat and weight. Sorry about the prop pitch push i had no ideal a 2.20 gearing could raise pitch that high. Its not unheard of to have a timing module fail rare but ti happen's...Who set the base timing it seem's a little bit retarted.

 

[HT32BSX115]

the base timing it seem's a little bit retarted.

Retarded timing would absolutely make it wimpy out of the hole....................

Having said that, I still think 26p might still be a tad "tall" for that boat/engine/drive.

With everything running "just right", you still want that thing right at 5200 at WOT (if 5200 is max RPM)

Don't prop it to run up against the REV limiter. The module model number will determine the REV-limit RPM.

 

[Eric 3.7LX Alpha 1]

Well checking the timing will be the cheapest option, I'd throw a light on it at idle and advance and see what the numbers look like. Go from there.

To check advance timing, you have to get a hold of an advance timing light.

What kind of ignition do you have in her? In some you have a procedure to do first to check timing....

 

[Orbitter]

It's got a Thunderbolt V Ignition.
And yea, I am unfamiliar with how to check & adjust it as you can't simply spin the dizzy.

 

[JustJason]

The others were ok, except for cylinder 7's plug which was very sooty! Aside from the very tip of the insulator, the rest of the plug including the threads was all covered in black soot.

You know what causes soot? Read post 31.....

 

[NHGuy]

I think Jason makes a good point. If you'd like we can walk you through checking and setting the valve adjustment. An over tight setting will cause lost compression and valve leaks. Eventually it would cause damage around the valve seat.

 

[Orbitter]

Yea, if you can. Or point me to a good video on the subject that is applicable to my engine.

 

[HT32BSX115]

Since you have the plugs out, screwing a compression gage in there will not take long. crank the engine with the throttle wide open and ensure that the compression is adequate for all 8

Adjusting the timing is not rocket surgery either. www.boatfix.com/merc/techbk/95/95hgb4.pdf

Instructions are there for several different ignition systems including Tbird-5 and the advance curve is shown for the 350

 

[Orbitter]

For clarification, It doesn't directly state initial timing for 357 Mag Bravo 4V on there. But does state that for Thunderbolt IV and then 2 graphs/specs without an ignition type specified and then at the bottom the Thunderbolt V graph. Am I correct in assuming that when I ground the wire for setting the module into base mode, I then adjust the timing to 0 degrees? Or with that wire grounded, do I adjust it to 8 degrees?
Or is the "MCM 5.7L Bravo" listed on page "4B-13" my engine, just slightly different name?