Merc 5.7L LX with Governor???

[Mjust]

Ok so ive looked at the Weber/AFB Carter 4BBL carb and cant find a Governor anywhere and from what im told there isnt one. Ive had people drive my boat and they tell me that there is a governor installed somewhere cause when it hits 4000RPMs it bounces the motor back to 3900RPMS over and over till i back off the gas. It sounds like a car with a rev limiter installed on it. Where else can a governor be installed on a boat???

 

[John_S]

Re: Merc 5.7L LX with Governor???

If you have a Thunderbolt V ignition there is a rev limiter but it is around 5000rpms, not 4000.

 

[Don S]

Re: Merc 5.7L LX with Governor???

What year is your 5.7, what ignition system do you have, are you SURE the tach is correct.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

So my tach can be off 1000RPMS?? Doesn't seem like it could be possible cause it good at idle. My boat has Feria gauges and the RPM Tach has a dial on the back to set it to the correct engine size. I have it set to a V8 but the boat originally did have the Merc 1996 4.3L in it so im wondering if something didn't get changed when they upgraded the engine to the 5.7L LX. Its a lot of motor for a 18 foot open Bow, my boat weighs 2200 LBS and I have a 21" Pitch on it and the Alpha one is a 1.62 gear ratio. With two people in it I can get it to plane out but if more than two I have to have people sit in the front to get me down to plane. I was thinking of adding a hydrofoil to the alpha one to help get it planed faster and reduce cavitation. Any thoughts??

 

[Mjust]

Re: Merc 5.7L LX with Governor???

Im not sure on the engine year but the serial on it starts with 0K so Im thinking it a 96 motor. How can I tell what ignition the boat has??

 

[Don S]

Re: Merc 5.7L LX with Governor???

What is the rest of the SN, they used the OK numbers in 96 and 97.
If you changed that 18 foot boat from a 4.3L to a 5.7L and still can't plane it out with 4 people, you have some serious problems somewhere, and it is NOT in need of a hydrofoil.
Do you know how to use the trim ?

 

[Don S]

Re: Merc 5.7L LX with Governor???

Just realized something. You have the 1.62 Gear ratio, that is for a V6, not a V8. You should have the 1.47 and even then the 21 pitch prop may not be enough.
Since you are using that prop with the 1.62 drive, you ARE hitting the rev limiter, and your tach is off, and you will have a hard time planing cause you don't have the speed.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

The funny thing is I dont have to trim, I just leave it all the way down and the boat goes and when planed it takes off like a bat out of hell till I hit 4000RPMs at WOT. When i take off and get on the gas the rear of the boat digs deep and pulls the bow almost straight up when I have people sitting in the back seats. The motor sounds like it has plenty of power and tourqe and runs really good, the boat just doesnt respond like I think it should. I can only trim up a little bit after I get it planed out and maybe get another 100RPMS till it hits what sounds like a rev limiter. The previous owner had like a 18 or 19 pitch prop on it at one time and he said it worked good but he had the rev limiter issue so he went to a bigger prop which he said reduced the problem but didnt take it away.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

How much would I be looking in cost to gear down to the 1.47 then?? Or could I go with a 24 Pitch or a 4 Blade prop to help?? Also another thing is I noticed the Distributor Cap has a 90 degree hose fitting coming out of it, it that a vent for water??? or should there be a hose hooked up?? The distributor cap is a merc.

 

[Don S]

Re: Merc 5.7L LX with Governor???

If changing prop pitches worked, Merc wouldn't have different gear ratio's.

That fitting on the cap is just a vent. No hoses go to it.

You need to get a tach that will read properly. After you get the right gear ratio, and tach, you will have to prop the engine to get 4400 to 4800 rpm at WOT. Then you will have to learn how to use the trim. If it's trimmed all the way down, you are just plowing the nose thru the water, not actually planing.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

BTW the lake in Texas I run on is at about 700' above sea level if that matters any. How much does it cost to have a gear change done??

 

[Mjust]

Re: Merc 5.7L LX with Governor???

When i put all my info into the prop selector on merc's website it recommends a 23 pitch for my motor with a 1.62 ratio and a alt of 700' above sea level. going from a 13.75 x 21 to a 14 x 23 is going to make it even harder for me to take off and plane isnt it??

 

[erikgreen]

Re: Merc 5.7L LX with Governor???

I don't know what a re-gear will cost, but I suspect you'd be better off buying an SEI sterndrive with the correct 1.49 ratio for about $1300, then selling your old leg to recoup some of the cost.

I believe re-gearing a sterndrive is one of the nastier, pickier jobs you can do to one, and it can't be done without special tools and lots of time.

Erik

 

[tommays]

Re: Merc 5.7L LX with Governor???

i am thinking some trim tabs should be the first thing on your list

And 18' with a V-8 has gotta be pretty stern heavy



Tommays

 

[John_S]

Re: Merc 5.7L LX with Governor???

Are you using the ICM from the 4.3L? or did you buy a new one for a V8? They are expensive purchased new from Merc, so might have tried to get by with it. It maybe the root of your problem. I am not sure how the rev limiter works, but here is my simple calc: 5000rpms X 6 cyl = 30,000 pulses per minute, divide that by your actual 8 pulses a min = 3750 rpms. Close to 4K, especially with tach error.

A V6 advance curve will not be ideal for a V8, either. The module will be mounted to the distributer or exhaust elbow. Most have the advance curve labeled on it like: V8-22A If you do have a V6 module, start watching ebay to save yourself a couple hundred bucks.

PS: I believe the 4.3L T5 does not use a knock sensor. To stay with T5, you would need a T5 V8-22A that was for the (pre-vortec) 5.7L or 5.0L alpha 2brl. The 5.7LX and 350 mag had the knock sensor and you would have to wire up or change the harness. Alternatly, you can go to a T4, which doesn't have a rev limiter.

 

[slia67]

Re: Merc 5.7L LX with Governor???

Tach could be set up for a V6 too.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

Are you using the ICM from the 4.3L? or did you buy a new one for a V8? They are expensive purchased new from Merc, so might have tried to get by with it. It maybe the root of your problem. I am not sure how the rev limiter works, but here is my simple calc: 5000rpms X 6 cyl = 30,000 pulses per minute, divide that by your actual 8 pulses a min = 3750 rpms. Close to 4K, especially with tach error.

A V6 advance curve will not be ideal for a V8, either. The module will be mounted to the distributer or exhaust elbow. Most have the advance curve labeled on it like: V8-22A If you do have a V6 module, start watching ebay to save yourself a couple hundred bucks.

PS: I believe the 4.3L T5 does not use a knock sensor. To stay with T5, you would need a T5 V8-22A that was for the (pre-vortec) 5.7L or 5.0L alpha 2brl. The 5.7LX and 350 mag had the knock sensor and you would have to wire up or change the harness. Alternatly, you can go to a T4, which doesn't have a rev limiter.

What you are saying does make a lot of sense, I didnt own the boat when the 5.7L LX was installed so im not sure about the ICM. Ill have to run out to the lake and see what is in it.

 

[Ro-Tator]

Re: Merc 5.7L LX with Governor???

Sounds like Don's hit the nail on the head yet again.
Right now, it's the equivalent to drivin' a corvette in second gear and wondering why it won't go faster (?)

 

[John_S]

Re: Merc 5.7L LX with Governor???

Take down any part numbers on the modules, just in case the timing curve is not readable or on there. A common curve for the 4.3 is V6-14.

Do you have any mph (preferably gps) numbers to go with your wot runs?

Even if this is your issue, I think you have a different problem with getting on plane. As others have said, you could just be stern heavy and some tabs would help. I'd also check to make sure the trim is actually coming all the way in on the outdrive.

 

[Mjust]

Re: Merc 5.7L LX with Governor???

Take down any part numbers on the modules, just in case the timing curve is not readable or on there. A common curve for the 4.3 is V6-14.

Do you have any mph (preferably gps) numbers to go with your wot runs?

Even if this is your issue, I think you have a different problem with getting on plane. As others have said, you could just be stern heavy and some tabs would help. I'd also check to make sure the trim is actually coming all the way in on the outdrive.

No the speedometer doesnt work and I dont have a gps but am looking into getting one. From instinct and past boating id say the boat is doing mid 40's at top speed. As for trim tabs. do i need to by the electric ones or will the stationary ones be ok?