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Tuesday question! Boat edition

Pat McRotch

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3.0 mercruiser dieseling. Fucked with timing a bit yesterday with no luck.
Carb or??
It's my uncles poontoon boat, just trying to help him out a bit.
TIA.
 

Pat McRotch

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How old is the fuel? What do the plugs like? Have you pulled plug wires to see if you have a dead cylinder or ignition issues?

1) Don't know, I'd have to ask him. He takes care of his shit so I assume he drained the tank after the last use of the year.

2) i didn't pull plugs last night

3) didn't pull plug wires either.

Boat ran fine when parked. I'll ask him these questions when he calls me back.
 

Pat McRotch

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Fucker ain't answering his phone. I'll be back with more info shortly.
 

rockdog57

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Mercruiser distributors are different than pretty much everything out there in that era. The timing needs to be set with the engine at or under 700 rpm. You set it at 8 degrees advance and tighten her down. The distributor advances thru the little brain box tied to it with I think 4 wires. There is no advance inside the distributor. It’s all done electronically thru the little box. If you have it idling above I think 750 rpm the box has already started to advance the timing.
 

Pat McRotch

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Fuel is from a few months ago, with stabil in it.
Engine has 240hrs.
Compression test was done when he bought it, 1yr ago. Compression was good.
Plug wires look good, haven't looked at the plugs.
 

Pat McRotch

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Mercruiser distributors are different than pretty much everything out there in that era. The timing needs to be set with the engine at or under 700 rpm. You set it at 8 degrees advance and tighten her down. The distributor advances thru the little brain box tied to it with I think 4 wires. There is no advance inside the distributor. It’s all done electronically thru the little box. If you have it idling above I think 750 rpm the box has already started to advance the timing.

That's good to know. Thanks for the input.
 

Pat McRotch

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Uncle found a couple loose wires. I asked, "to what?"
him: fuck if I know but it's good now! throwing a timing light on it now since we fucked with the distributor..

He says it shuts off fine, starts fine. All is good.

Thanks for the input dickbags! :smokin:
 

DozerDan82

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Mercruiser distributors are different than pretty much everything out there in that era. The timing needs to be set with the engine at or under 700 rpm. You set it at 8 degrees advance and tighten her down. The distributor advances thru the little brain box tied to it with I think 4 wires. There is no advance inside the distributor. It’s all done electronically thru the little box. If you have it idling above I think 750 rpm the box has already started to advance the timing.

I put an HEI on my Merc 4.3, 1/3 of the cost and got rid of that hassle.
 

rockdog57

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I put an HEI on my Merc 4.3, 1/3 of the cost and got rid of that hassle.

How did you hook up the shift interrupt? Without that you can’t get the boat in neutral very easy. The neutral interrupt stops the ignition from firing for a split second taking pressure off of the gears allowing the shift to neutral to happen easy. If you research thunderbolt ignitions you might be surprised how they work. I was all ready to ditch mine until I studied how they work. Not trashing on your decision. If it worked for you that’s great!
 
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How did you hook up the shift interrupt? Without that you can’t get the boat in neutral very easy. The neutral interrupt stops the ignition from firing for a split second taking pressure off of the gears allowing the shift to neutral to happen easy. If you research thunderbolt ignitions you might be surprised how they work. I was all ready to ditch mine until I studied how they work. Not trashing on your decision. If it worked for you that’s great!

Thunderbolt ignition..... isn’t that out boards???
 

DozerDan82

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How did you hook up the shift interrupt? Without that you can’t get the boat in neutral very easy. The neutral interrupt stops the ignition from firing for a split second taking pressure off of the gears allowing the shift to neutral to happen easy. If you research thunderbolt ignitions you might be surprised how they work. I was all ready to ditch mine until I studied how they work. Not trashing on your decision. If it worked for you that’s great!


Mine is a 4.3 I/O Have not had it in the water yet ha but I know it goes from F-N-R Not sure, buy I know it dropped in (ish) and fired up.
 

toomany

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How did you hook up the shift interrupt? Without that you can’t get the boat in neutral very easy. The neutral interrupt stops the ignition from firing for a split second taking pressure off of the gears allowing the shift to neutral to happen easy. If you research thunderbolt ignitions you might be surprised how they work. I was all ready to ditch mine until I studied how they work. Not trashing on your decision. If it worked for you that’s great!


I did the same for the 4.3 in my boat.

Works just fine at any speed that you want to be switching directions. I got the boat free from the previous owner because it "needed a motor". Turns out ignition was bad. Looked into it and once I found out how much it was for the "correct" parts, an Ebay HEI ended up in there for $60 and I was on the water. I carry a spare module and coil just in case.
 

rockdog57

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I did the same for the 4.3 in my boat.

Works just fine at any speed that you want to be switching directions. I got the boat free from the previous owner because it "needed a motor". Turns out ignition was bad. Looked into it and once I found out how much it was for the "correct" parts, an Ebay HEI ended up in there for $60 and I was on the water. I carry a spare module and coil just in case.
No doubt about it, merc is proud of their stuff! $600 for an ignition module is insane. If mine does burn up I’ll be figuring a different ignition is gonna get installed.
 

DirtRoads

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$60 automotive HEI isn't supposed to be installed on a boat. There are protections on marine distributors/starters/alternators that are supposed to keep you from blowing yourself up if you have a fuel leak and fill your engine compartment with fumes. YMMV, I'd probably run it.
 

evernoob

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It does around here to buddy, so yes.

Dieseling is a known problem with specific known steps. You already did one, timing.

1. Timing
2. Idle screw set too high
3. Carb not shutting due to buildup on the carb/worn out
4. Carbon deposits in the head
5. Valve got a hot spot or stuck open, again deposits
6. Engine running too hot for another reason

The last reasons are related to pre-detonation, probably because of carbon buildup. So it gets too hot b/c too high compression, a hot spot forms in the combustion chamber and keeps igniting the mixture without spark.

So, you checked the timing. Then you check the operation of the carb. He already checked and sees the spark shuts off when the ignition is off, of course.

Then you either use a chemical engine cleaner to clean out the gunk, barring that, take off the head and clean it out.

Source: 10th Grade small engine shop
 

junkytj

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$60 automotive HEI isn't supposed to be installed on a boat. There are protections on marine distributors/starters/alternators that are supposed to keep you from blowing yourself up if you have a fuel leak and fill your engine compartment with fumes. YMMV, I'd probably run it.

They have marine HEI distributors. That's what I ran when I changed my malfunctioning thunderbolt (Used a DUI). It was an I/O and I never had issue with changing gears at all. I don't recall how it was wired other than by the directions with the exception of the lanyard interrupt wasn't in their directions. I noted that in my review on summit for the unit, but there are so many versions, I don't know if that was worth the trouble.
 

DirtRoads

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They have marine HEI distributors. That's what I ran when I changed my malfunctioning thunderbolt (Used a DUI). It was an I/O and I never had issue with changing gears at all. I don't recall how it was wired other than by the directions with the exception of the lanyard interrupt wasn't in their directions. I noted that in my review on summit for the unit, but there are so many versions, I don't know if that was worth the trouble.

Yep, I priced one out for my Malibu with a 351. Shit wasn't near $60 haha. I think it was like 3-400 or something ignorant like that.
 

DozerDan82

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$60 automotive HEI isn't supposed to be installed on a boat. There are protections on marine distributors/starters/alternators that are supposed to keep you from blowing yourself up if you have a fuel leak and fill your engine compartment with fumes. YMMV, I'd probably run it.

Oh - yes I am well aware about proper venting. not overly concerned with it. I like to live dangerously!
 
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