Merc 3.0L Carb EST - Timing/top end power

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OK, I'll admit up front I've got a number of things to look at - and things I haven't checked yet, but interested in leveraging your collective knowledge to minimize boat down time.

​I have a 1990 Shamrock 17 with the original Merc 3.0L. I have a Rochester 2 barrel and an upgraded EST ignition.

​My ignition is missing the second plug (the one which has the wire that you cross for setting timing and the shift interrupt). When looking at the EST, the plug on the left (the one that comes from the coil) is there, but the one is broken off - you can see three pins. My timing is at about 4BTDC at idle and does not seem to change with acceleration. In that, I lack top end power. I can plane, and I get about 27mph out of the boat, but it feels like there is a top end I am not accessing. In that, my tach is sticky and I don't know what I am really getting, but I think I am topping at 3500rpm or so. Resistance checks of the coil get readings that are off from the manual, but again, it runs fine...just not great. No knocking or pinging. I bought the boat 6 months ago, changed the fuel filter, cleaned the carb with a toothbrush and cleaner, but haven't checked plugs or compression or fuel pump output. I did have an issue a month ago where I would get a good hole shot, get to 28mph and then fall off after a minute to 24. I found that I had a kinked fuel line and assess that the boll of the carb had slowly been losing level at WOT due to the kink. I fixed the line and am back to a steady 28 or so. Either way, I feel the advance isn't advancing. Unrelated, but does anyone know if there should be a cap on the vacuum test port for the carb? Mine is uncovered (you can stick a finger on it and feel suction, but its not covered. Is that messing with my idle at all? Does it risk foreign material contamination, or is it just a bypass venturi?

​Yep, I need to check compression, plugs and fuel pump output, but I don't really see anything that points to those. Just trying to understand the impact of not being able to put my EST in test...does it just affect my accuracy of setting timing? Should I set it to 12BTDC? Is there a way to test the distributor part of the EST? What advances my timing, is it my coil? If so, does an inaccurate rpm reading lead to an inaccurate advance? I don't sense RPM off the tach...assuming it is coming from the coil or somewhere else.

​Again, we are operational, heading out for a 20min cruise later today, just trying to figure out where to efficiently go with this project.

Thanks in advance,
PJ
 

Scott Danforth

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if your ignition isnt advancing, fix it.

EST is electronic (Electronic Spark Timing) to fix an EST that doesnt change the advance curve with RPM, you pull it, toss it and replace it.
 

alldodge

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You need the right side plug to set timing and also to make the EST work. One of the wires is supplies 12V and the other 2 pins are jumped together during timing. Search for Delco EST timing tool
https://www.amazon.com/Sierra-International-18-5516-Distributor-Timing/dp/B015E8S7X4

The long wire gets connected to 12V by jumping the two wires together on the shift interrupter. Once timing is set, keep the plug installed and cut the loop wire. It can be jumped back together if needed again. Then reconnect the wires back on the interrupter.

The manual for 1990 should be 1 BTDC
Now if you had breaker points (being a 1989 maybe) timing was at 6 BTDC

NOW THE PUZZLE QUESTION
I'm thinking you have a 1989 motor which use to have points. If (The big IF) this was the case, then the shift interrupter supplies a ground and not 12V to the distributer. If this is the case then the EST will not work unless rewired.
 

Silvertip

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And no -- you should not have any ports open to manifold vacuum. That causes a lean condition that causes idle issues and can burn valves and pistons.
 
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I've found an est kit on amazon, but looking at the shift interrupt pig tail, I can't imagine where that would go to. Does it go to the shifter?
Trying to avoid buying a new est and going, "where does this wire go? "
Appreciate the point that if timing doesn't advance than I need a new timing circuit.
 

alldodge

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First we need to know what has changed with the motor. Did it use to have points or something else?

The long wire on the EST plug goes to the shift interrupter. If yours is supplying a ground then the ground needs to be removed and 12V needs to be connected to one side. The other side gets connected to the pig tail.

If the motor use to have points then the interrupter switch needs to be changed from a Normally Opened (NO) to a Normally Closed (NC).
 

fishrdan

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Good info AD, except for:

If the motor use to have points then the interrupter switch needs to be changed from a Normally Opened (NO) to a Normally Closed (NC).

The shift interrupt switch still needs to be wired NO. Applying 12V to the pigtail wire stumbles the ignition while the engine is running - while shifting out of gear.
 

fishrdan

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I would... get an advance timing light and see if the ignition is advancing as it should. $30 at Harbor Freight. Cheaper than throwing parts at something that you don't know is broken.

Check that the timing is at 10-12* at idle, then advances to 26-28* at 2800RPM. (Those numbers are out of memory, check the manual.) I would also check to see if the ignition is advancing smoothly, from idle up to 2800RPM.

Timing for EST ignition is 1* while in base timing mode, then 10-12* when the timing shunt is removed. (1* depends on year some were 1* BTDC, 1* ATCD, etc, what does the engine sticker say?)

Vacuum port on the carb? Have a pic? Is that port for the fuel pump's sight tube. If someone plugged off the sight tube port on the fuel pump, it could cause the engine to run poorly at high RPM and not achieve WOT. Don't ask how I know..................
 
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Yes sir. So, I checked timing a month ago (led to really starting to look at this!) And it was not advancing. All the marks down there are pretty rusty, but pretty sure I got this little dot somewhere in the middle of the jagged metal plate....and it ran ok. I don't have a shunt and that plug receptacle is broken off on the est. I revved at idle and did not see the dot move. If I'm getting spark (it is running), should I bother with the coil or just the est. Also, some people online say that a velvet drive doesn't need a shift interrupt....so I could in theory do I just use that port to get timing set?
I'm inclined to buy an est and a shunt and go from there, does that seem logical? On old motors I've had before, coils tend to outlast distributors.
The vacuum port is on the front of the carb by the choke and pointing down on an elbow. It is threaded and about a half inch in diameter. I have put a vacuum gauge on that port to set mixture, but am never getting above 13in or so and am about 5 turns out on each of the two mix screws to get there. Vacuum is also not very sensitive to adjustment. When I pull the vacuum Guage off, I currently don't put a port cover back on, but will get one. My slight exploring to this point makes me think (based on a finger over the hole) that it will stall.
Today I will recheck idle timing (not base...no shunt) and look for advance, look to see if there is a shift interruptor on the transmission and cover the vacuum port. Assuming no advance I will order an est.
 

alldodge

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The Merc carb would not have a vacuum port on it, wonder if you have a carb off a car

Its not the coil
 

fishrdan

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I don't have a shunt and that plug receptacle is broken off on the est. I revved at idle and did not see the dot move.

The EST module has an electrical connector broken off it? That's where I would start, replace the obvious broken parts.

Velvet drive? This Mercruiser 3.0L is in an inboard boat, not an I/O boat? I'm not a inboard guy so have no clue about needing/not needing a shift interrupt switch, but guessing it's not needed.

Post a picture of the carb port you're referring to. On a sterndrive 3.0L Mercruiser, there is a clear yellow "sight tube" going from the fuel pump to carb, so if the fuel pump ruptures if dumps the fuel into the engine. That's the port I was talking about, sounds like you have a different port...
 
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Ok, so a couple revisions.
1. I don't think this carb port should be covered. It's on the underside of the choke and putting a finger on it makes rpm go down. Pic attached.
2. There is some advance. The timing marks on the pulley are illegible, but I think I am in a goodish place and there is some advance. There are 5 spikes on the timing band, I think they are 18 btdc, 12, 6, 0, 6. I am at about 6 to 12 btdc and with rpm increase, the mark does move left - past the 18 mark. Sorry I didn't catch that when I first checked it. It's not a lot of movement, maybe an inch.
I can rev all the way up in neutral, but fall short under load. I think if I buy a shunt I can set timing better, but that doesn't resolve dodges point that the right plug is needed for the est to work. I have no shift interrupt switch, just one lever into the tranny.
Next is compression and fuel pressure
 

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alldodge

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My apologies and say I was wrong you do not need the plug to have it work correctly, but you do need it to time it correctly

The tube your looking at is to warm the choke from the manifold heat. There should be a tube going from it to the manifold. Many replace the choke with a electric one

Velvet drive trans
 

fishrdan

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It looks to me that you have a Mercruiser (old) 140HP, not a (newer) 3.0L, pretty much the same thing, but there are differences. Or maybe it's a cobbled combination. The fuel pump and carb are from a 140HP, but the distributor is from a 3.0L and valve cover looks 3.0L. There can be issues swapping parts between these engines, and maybe that's what you're dealing with. The adapter plate between the carb and manifold does not look stock...

Are the spark plugs taper seal or gasket seal?

I have a 140HP and used an EST from a 3.0L without issue, but tried a 3.0L fuel pump and it wouldn't perform and had start issues. Slightly different bolt location for the fuel pump between the 140HP and 3.0L as I remember, pump arm wasn't hitting the cam correctly. (If you have a 140HP this is not an issue.)

AD mentioned the carb's heat stove choke, which connects with a bent metal tube, to a port on the manifold. Does you manifold have a 1/4" (approx) tube that goes directly through the manifold to-bottom, open both ends. This tube is what connects to the choke's threaded port.

Wire brush the timing tab and see if you can get a better reading. Snap a pic of it with your phone so you can blow it up. Google 140HP and 3.0L timing tab, to see if you can find one that looks like the one you have. Need to get your timing set correctly for the EST ignition, it needs to be between 10-12* at idle while out of base timing mode.

Fix your tach so you know what the WOT RPM is, needs to be 4200-4600 for a 140HP, 4400-4800 for a 3.0L.

140HP heads and manifolds are different than 3.0L. If you have a mis-matched head and manifold it can affect performance. Check out this link to see the different heads/manifolds used for GM 4cyl marine engines. You may want to check the engine serial number and manifold number, to see if it reveals anything.

http://greenbaypartsworld.com/marine...ld-gaskets.jpg
 
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Fishrdan, thanks for the wealth of info. Among other things, I am perplexed as to why I can't get the engine to go into base timing. I replaced the timing module (flat plate with the two plugs) and bought the timing shunt. Hooked it up to 12v and plugged it in but saw no change in timing with it hooked up of not.
I guess I am trying to fix this and learn how it works all at the same time. I don't have a shift interrupt, so I either have no voltage to the timing plug (nothing connected) or 12v and a jumper. My assumption is that base timing is that depressed state used during the shift and that I really need to set to 10 to 12 at idle (which is where it sounds best.
Someone on here had a link to a manual for the 3l ignition systems. Going through it, it has diagnostics for the coil. Resistance checks for my coil (and a brand new one) are good on ground checks and in resistance from supply to plug post, but a couple of the 40 ohm internal reads don't come up. The consistency between old and new confuse me.
Boat is running real rough, stumbling under accel, surging, losing power (power comes back by spraying carb cleaner in the carb), etc. This weekend I plan to pull plugs, check compression and put timing back at 12 btdc at idle. I may change the coil since I have a new one. Looking in the dist, it's pretty oily...I will try to pull the cap and clean it (on the chance I am leaking in there.
I've been ignoring fuel and carburation. I could put a bottle on it to rule out the pump, but am a believer that the problem is electrical.
On that, I replaced the 12v plug from ignition to the coil and assess I am getting good current. I have not done resistance checks between coil and dist (two timing wires) but they look good. I don't feel leakage from any plug wires.
It's a new boat to me, and there are a lot of things needing improvement. ....but it did run all summer! Some have made a comment that if you can't set base timing g then that's the problem. Is that true on what is likely an 89 3l with est back fit? If this was a points boat, the hunting at a steady throttle would point me to the carb, I think, but as I have found nicks in wires, loose connections and a wet engine after running (my flywheel spits water all over the electrical bus, coil, starter, dist - encapsulation and shielding planned for the winter ) I think I need to look at grounds and supplies.
Previous owner said coil, dist, plugs all new this spring. ...wires and plugs look it. Inside of the dist is dirty and coil is rusty. Going to get at that and look at grounds and check plugs. Wire brush, photo of timing tab complete. Any other advice?
 

alldodge

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if your ignition isnt advancing, fix it.

EST is electronic (Electronic Spark Timing) to fix an EST that doesnt change the advance curve with RPM, you pull it, toss it and replace it.

I think Scott had your answer in post 2
 

Bondo

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Boat is running real rough, stumbling under accel, surging, losing power (power comes back by spraying carb cleaner in the carb), etc.
the hunting at a steady throttle would point me to the carb,
I've been ignoring fuel and carburation.

and a wet engine after running (my flywheel spits water all over the electrical bus, coil, starter, dist - encapsulation and shielding planned for the winter )


Ayuh,...... Welcome Aboard,.... Why O Why would you ignore the Obvious that yer diagnostics says is the Problem,..??..??

'n why o why would you shield, 'n encapsulate, insteada just Fixin' the water leak,..??..??
 
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Appreciate all the help and fixing things as fast as I can!
Water on the engine is due to a very shallow bilge and if there was any rain, there is standing water in the bell house which gets slung up on the engine upon starting. Not fun, might have to find a pump that keeps level lower.
Copy on Scotts answer. Timing is advancing (poor measurement previously) just not going into base mode.
There is some est troubleshooting in mcm service manual 13 (pg 24) that I plan to do next.
Thank you
 
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