5.7 thru hull exhaust

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mattman21

Cadet
Joined
Sep 3, 2003
Messages
18
Re: 5.7 thru hull exhaust

I still don't see how that relates at all to the fact that it's fine out of the water but acts up when it's in the water. Could it be possible that there is backpressure while in the water that causes timing to be messed up a bit?
 
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mattman21

Cadet
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Sep 3, 2003
Messages
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Re: 5.7 thru hull exhaust

Thanks for the replies Don S, I wasn't trying to be contradictory as Kagee seems to think I was, I'd just like to see how that wouldn't make a difference. Just call it logical or analytical thinking or whatever. I'm starting to think maybe after all it wasn't the flappers, but it's gotta have something to do with the boat being in water and not, because it acts totally different...
 
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marlinempress

Petty Officer 3rd Class
Joined
Apr 25, 2004
Messages
84
Re: 5.7 thru hull exhaust

oops sorry I wrote that from a different computer with a different login. I forgot to add that the engine is a 350 fuel injected with a holley tbi 2d thingie. It also has an edelbrock high-rise intake manifold. I replaced the points and wires and everything last season but never set them with a dwell meter, just a feeler gauge. Could that possibly cause such a symptom that changes in and out of water?
 
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Darrendude

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Nov 16, 2004
Messages
145
Re: 5.7 thru hull exhaust

One difference is when the boats in the water there is a load on the engine and there is not a load when on the muffs. I agree it sounds like a timing or fuel delivery problem . Have you checked your fuel filter lately?
 
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marlinempress

Petty Officer 3rd Class
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Messages
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Re: 5.7 thru hull exhaust

I haven't checked the fuel filter lately. Is there much more of a load even when it's in neutral in the water?
 
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trog100

Senior Chief Petty Officer
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Dec 1, 2004
Messages
751
Re: 5.7 thru hull exhaust

darren has hit the nail right on the head..<br /><br />"One difference is when the boats in the water there is a load on the engine and there is not a load when on the muffs"<br /><br />in the water it has to shift a bloody great boat.. on the muffs it dont shift bugger all.. come on dudes thinking caps on.. he he <br /><br />i think its a fuel starvation problem..<br /><br />trog100<br /><br />ps.. "Is there much more of a load even when it's in neutral in the water?"... errr.. now u really have me baffled.. he he.. never noticed that one.. whoops..<br /><br />out of curisosity how does it behave when it is under a real load in gear and shifting the boat..???
 
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marlinempress

Petty Officer 3rd Class
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Apr 25, 2004
Messages
84
Re: 5.7 thru hull exhaust

When it's in the water, it'll act the same way in neutral and in gear. It'll be ok until about 2000 rpm then it bogs.
 
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Darrendude

Petty Officer 2nd Class
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Nov 16, 2004
Messages
145
Re: 5.7 thru hull exhaust

I would wager its a plugged fuel filter. At least thats the cheapest thing it could be. Check both of them if you have 2. One maybe after it comes out of the gas tank and the other is in the fuel inlet coupler at the carb, as far as I know . Does it have a 2 or 4 bll carb? a 4bll at 2000 rpms, the secondaries start opening up and whoosh , it sucks gas hard. You will never get the secondaries to open up on the trailer or in idle. Thats assuming it has a 4 bll carb.
 
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trog100

Senior Chief Petty Officer
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Dec 1, 2004
Messages
751
Re: 5.7 thru hull exhaust

its a bit odd that it behaves the same way under load and not under load.. any kind of engine misfire problem should get noticably worse when a load is applied..<br /><br />hard to describe what an engine sounds like when the throttle is opened and the mixture weakens off.. i can do it physically but writing it.. he he he<br /><br />basically as u open the throttle air has to go in.. it cant fail to.. if the gas aint going in as well u get a kind of big prolonged "gasp" with no increase in engine rpm.. hold it long enough and u might get a backfire thru the carb.<br /><br />so.. is "bogs" a big "gasp" or more of a spluttery hesitant misfire finally clearing and the engine rpm going up like it should do.. ????..<br /><br />u have to laff.. he he <br /><br />trog100
 
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marlinempress

Petty Officer 3rd Class
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Apr 25, 2004
Messages
84
Re: 5.7 thru hull exhaust

it's more of the prolonged "gasp" with no increase in engine rpm. I actually do get backfires through the carb if I hold it for too long too. I know the timing is set right and the advance is working 'cause I just set it at the beginning of the season. Although I'm not sure the contacts are set just right, I replaced them as well and only set them with a feeler gauge, not a dwell meter. Trog100 it sounds like you're onto something with that description of my bogging, it fits it pretty well. That'd be wonderful if it's just a fuel filter problem, but I still fail to see the correlation between in and out of water differences with the fuel filters. I've messed with the mixture on the ECU when it's having troubles too and it doesn't seem to affect much.
 
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newport dave

Chief Petty Officer
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Nov 21, 2004
Messages
458
Re: 5.7 thru hull exhaust

Were both the exhaust shutters accounted for? I think you said that you had found one and pulled it out, but what about the other one?<br /><br />It could be still be in the intermediate housing or the outdrive causing an exhaust restriction. That would explain the performance issues.<br /><br />What about the "not doing it on the hose" thing?<br />Maybe the shutter is stuck in an area where it is submerged when the boat is in the water , and not when on the hose, and it is reacting differently as far as the amount of exhaust blockage that is created.<br /><br />Dave
 
Bondo

Bondo

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Messages
71,110
Re: 5.7 thru hull exhaust

I actually do get backfires through the carb if I hold it for too long too.
Click to expand...
That's running Lean........<br /><br />You've also Got to deal with the Ignition...... Either get it Right,.... or Swap it out to Eletronic.............<br /><br />There's Many reasons for the difference in being In the Water, or On the Hose.............<br /><br />Maybe the filter is So Plugged that it flows better in the Trailer Attitude, rather than the Floating Attitude...... Who Knows........<br /><br />Muffs Are a great diagnostic Tool....... But, No... On the Muffs is Not the same as Floating...............
 
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marlinempress

Petty Officer 3rd Class
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Messages
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Re: 5.7 thru hull exhaust

hmm, ya know I never even considered the fact that it backfires through the carb due to a lean condition. It's got two fuel filters, a small plastic one before the pump and a large metal one between it and the throttle body. I actually wouldn't be real surprised if they're a bit plugged, it had sat for a while before I got it and did some work on it, but I never replaced the filters. That's also a good point you bring up newport dave, I hadn't thought of that. No I haven't accounted for the other flapper, and I have no idea if it's still there or what. I tried a little today to get the riser and exhaust boots out of the way to see, but the riser wouldn't budge even after kicking it and the rubber boot dealies are kinda stuck around the pipes. Does anybody know where to get an electronic ignition for a good price on this motor? It's a 5.7 260hp gm omc 1986, I believe the dist. cap is a screw-down type.
 
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trog100

Senior Chief Petty Officer
Joined
Dec 1, 2004
Messages
751
Re: 5.7 thru hull exhaust

not many manuals go into "bogs" "gasps" or "hesitant splutters" do they.. he he he<br /><br />its amazing what a bit of common language turns up..<br /><br />assuming your timeing is vaguely right.. that carb backfire can only be caused by a weak mixture.. what happens is this.. the mixture fires but burns so slowly thats its still going off when the piston gets round to its next induction stroke.. as the inlet valve opens the still expanding hot gases whoosh up thru the carb probably setting fire to the incoming mixture as well.. hence the bloody great flash..<br /><br />and.. flame-arrestor or not.. my logic tells me this flash would be more than enough to set of any leaky gas vapours which might be hanging around that engine compartment.. which if true does kinda make a mockery of all the special marine spark-free electrics that everyone goes on about so much..<br /><br />course my logic could be wrong.. he he<br /><br />it sometimes is...<br /><br />trog100<br /><br />ps.. now running with the ignition timeing well retarded might well help this carb backfire along.. but just imagine just how far retarded u would have to be to cause it.. forget ignition timing and concentrate on weak mixtures first and foremost..
 
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Laddies

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Messages
12,218
Re: 5.7 thru hull exhaust

Marlin, it sound very much like the throttle position sensor is not working or misajusted, thats what controls your mix off idle
 
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marlinempress

Petty Officer 3rd Class
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Apr 25, 2004
Messages
84
Re: 5.7 thru hull exhaust

yeah I thought of that a while ago and have set it correctly to within one-hundredth of a volt. Thanks for the suggestion though. I'll definitely have to look into replacing the fuel filters and think about getting the electronic ignition conversion.
 
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marlinempress

Petty Officer 3rd Class
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Apr 25, 2004
Messages
84
Re: 5.7 thru hull exhaust

oh yeah is there any way to test the TPS to ensure it's working correctly?
 
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Laddies

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Messages
12,218
Re: 5.7 thru hull exhaust

Usally if you connect it to a VOA and advance and retard the throttle lever, the meter needle will jump around like a bad fuel gauge, not move smoothly like it should
 
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