5.7L Merc Carb Issues

Jay Gadsby

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Joined
Jun 26, 2010
Messages
22
Hey Gents,

I am the proud papa of an 86 Searay Pachanga II with a 5.7L Merc/Alpha One. Recently I removed the can system (my step father did this on his Pachanga with no issues, and other people have as well). I replaced the cans with a 90* 4" mandrel bent exhaust tube. Fits great. But thats not the problem. (I hope)

The problem is, now it suddenly wont idle. The idle with the cans was low to begin with (500ish) so I raised the idle to the standard 650-700rpms as per the owners manual. The engine has trouble starting and I must give it gas, even if its warmed up. Then it will stumble and stutter until I pump the throttle once or twice. At this point it will idle all darn day, when given the juice it will jump up through the RPM range with no issues at all. If I shut it down and try again, same same. I recently purchased the boat, and the owner did not provide with service records. The boat ran flawlessly on the water, easily hitting max rpms (and a speedo reading of 59mph) Would the muffling system cause all this issue? I have seen others run without it, but there is not a whole heck of a lot of Pachanga info floating around on the intraweb. Please someone help!! Oh, for the most part I am a DIYer, and dont have any issues, however, I dont have a lot of carb experience. I will be pulling the plugs to see how bad they look in a few.
 

Alpheus

Lieutenant Commander
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Aug 3, 2009
Messages
1,759
Re: 5.7L Merc Carb Issues

Check the choke and make sure its not sticking.

How old are the plugs and wires?
 

Jay Gadsby

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Joined
Jun 26, 2010
Messages
22
Re: 5.7L Merc Carb Issues

Carb is a little dirty but not bad.

bad3d5a2.jpg



The plugs are a little black, but they dont smell all that rich and its not a gross amount of carbon or anything.
8513c00c.jpg


So yeah, if someone has some insight on this please share :) I am in the Army, so I like to do things my own usually without having to rely on paid assistance if you get my drift.
 

John_S

Rear Admiral
Joined
Jun 21, 2004
Messages
4,269
Re: 5.7L Merc Carb Issues

Did you do the idle mixture adjustment? You usually go back and forth with the idle speed for a few laps.
 

Jay Gadsby

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Joined
Jun 26, 2010
Messages
22
Re: 5.7L Merc Carb Issues

Check the choke and make sure its not sticking.

How old are the plugs and wires?

Young sir, I honestly could not tell you how old they are. They look very new (as do all the filters and such) The boat only has 300 hours on it.
 

Alpheus

Lieutenant Commander
Joined
Aug 3, 2009
Messages
1,759
Re: 5.7L Merc Carb Issues

Looks mean nothing as far as the outside of the carb. Its the inside that will kill ya.

I had a carb that looked exactly like that on the outside, and yes the engine ran when I gave it lots of throttle.

DSC02531.jpg


Check your filters,fuel pressure,cap,rotor.

Sounds like either a choke malfunction, well plugs in the carb are leaking or your plugs are just old and loading up...

If you want to rebuild your carb its cheap and easy.

http://forums.iboats.com/showthread.php?t=362542
 

Jay Gadsby

Cadet
Joined
Jun 26, 2010
Messages
22
Re: 5.7L Merc Carb Issues

Did you do the idle mixture adjustment? You usually go back and forth with the idle speed for a few laps.

I did not touch the mixture at all, I just adjusted up the idle since it was a little low to begin with. And then only by 200 rpm or so.
 

Jay Gadsby

Cadet
Joined
Jun 26, 2010
Messages
22
Re: 5.7L Merc Carb Issues

Looks mean nothing as far as the outside of the carb. Its the inside that will kill ya.

I had a carb that looked exactly like that on the outside, and yes the engine ran when I gave it lots of throttle.

DSC02531.jpg


Check your filters,fuel pressure,cap,rotor.

Sounds like either a choke malfunction, well plugs in the carb are leaking or your plugs are just old and loading up...

If you want to rebuild your carb its cheap and easy.

http://forums.iboats.com/showthread.php?t=362542

I think I am going to go crazy and do a big tune up anyhow. The boat is new to me with no records so it cant hurt. I will try and get it done this week (we have a 3 day weekend this coming one, so I want to enjoy my new toy). Looks like some late nights maybe. Carb, I guess I could try, whats the worst that can happen, I need to buy an Edelbrock? lol. After making that joke, I realized, that is a to-do mod for the future anyhow. hmmmmm.
 

Alpheus

Lieutenant Commander
Joined
Aug 3, 2009
Messages
1,759
Re: 5.7L Merc Carb Issues

the mixture screws are for idle only. Here is how I adjust them.

If you are planning on doing hole shots or pulling people and want to get up on plane as fast as you can. follow this procedure.

1 get engine up to normal operating temp making sure that the choke is open full.

2 Turn you air mixture screws all the way in till they just bottom out and turn them out again 2 turns.

3 adjust your idle to around 600 to 700 rpm, or as low and stable as you can get it.

4 You can do this by ear,vacuum gauge or with a tach.
Turn your air mixture screws out until you start to here or see (tach or vacuum gauge) the engine rev just a little and just when it starts to bog down a little turn in until max RPM is achieved. Do this with both needles one at a time.

If you are looking for better fuel economy and are just spending your days cruising around and not at WOT all the time follow the first 3 steps accept this time turn your needles in till the engine revs a bit and the starts to bog and turn out till you are at maximum RPM.

5 After your needles are set return the idle of your boat to around 700-750 RPM

The reasoning on this is just that the mixture curve is a little small but you can choose which end you want to run at. For hole shots you want to be at the rich end just for that little bit of extra fuel before the carb switches to the primary circuit. And for cruising you can run a little on the lean side as not to waste the extra fuel dumping at idle it also dosen't carbon up the plugs as fast.
__________________
 

Jay Gadsby

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Messages
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Re: 5.7L Merc Carb Issues

now, I am doing all this at the house hooked to a hose since the lake is 30 minutes from me and I am doign this after work. You say Max RPM, am I to rev this thing to 4600rpm or are you speaking of the 650-700 cap on the idle as being max. Sorry for the dumb question, I am just not all that well versed in the carb world (and its making me feel like an idiot right now)
 

John_S

Rear Admiral
Joined
Jun 21, 2004
Messages
4,269
Re: 5.7L Merc Carb Issues

now, I am doing all this at the house hooked to a hose since the lake is 30 minutes from me and I am doign this after work. You say Max RPM, am I to rev this thing to 4600rpm or are you speaking of the 650-700 cap on the idle as being max. Sorry for the dumb question, I am just not all that well versed in the carb world (and its making me feel like an idiot right now)

You don't touch the throttle during this procedure. It is the max rpm you get by turning the mixture screws. We are talking <100 additional rpms from the default adjustment.

Make final idle speed per manual, on the water, in gear.
 

Jay Gadsby

Cadet
Joined
Jun 26, 2010
Messages
22
Re: 5.7L Merc Carb Issues

You don't touch the throttle during this procedure. It is the max rpm you get by turning the mixture screws. We are talking <100 additional rpms from the default adjustment.

Make final idle speed per manual, on the water, in gear.


Thats a check, roger and a hooah. Just wanted to clarify. Thanks!
 
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