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1988 Donzi 17' Open Bow w/ 3.0L Mercruiser 4 Cyl

C

Crex619

New member
Good Evening folks,

I'm the new proud owner of a 1988 Donzi 17R (believe that's the model). I bought it knowing it needed a "tune up" but not quite sure what all that entails typically. Here's a list of things I've done so far:
Plugs/Wires
Cap/Rotor
Fresh Oil/Filter Change
Fresh Gear Oil Change
Rebuilt Carburetor (2 bbl) with new gaskets, float, and needles.
New Battery

The issue I'm noticing is a bit of roughness from the engine. Currently I can't put it all the way back to center (neutral) without it dying. I've adjusted the fuel mixture needle to recommended spec, and adjusted the idle screw. If I have it running about 1000rpm it runs fairly smooth, but doesn't seem to want to die, just at anything lower than 1000rpm. I'm not 100% sure what the typical idle speed for these engines are, but aside from that I'm not sure why the boat is dipping so hard and dying when in center position. If I'm quick about it I can get it to go from neutral (acceleration) to in gear (reverse or forward) and it'll pick up the rpms again. Thinking it could have been the gas, I did bypass the current setup for a fresh bit of fuel. I work on cars typically, but I know I/O's aren't that much different, but I wanted to throw this out here just in case I'm missing something simple.

Thanks in advance!
 
I've adjusted the fuel mixture needle to recommended spec, I'm not 100% sure what the typical idle speed for these engines are, Thinking it could have been the gas,
Click to expand...

Ayuh,..... The air screw "Spec" is just a starting point, further adjustment is done by ear, 'n results,.....

Most all I/O motors idle at 650/ 700 rpms,......

I hope you used fresh gas since the carb rebuild, as the old gas probably just dumped more crap into the fresh carb,....
 
If this has the A drive, you will also have what's called an SI or SA.... (shift assist or shift interrupt).
There will be a micro switch that is operated by a mechanical cam device.
Resistance felt by the lower shift cable's outer jacket is what operates the cam.
The SI or SA is primarily there to assist in shifts from gear back into neutral..... but may occasionally misbehave during shifts into gear.
The cam/micro switch system may be out of adjustment.

By the way....... Dog Clutch shifts need to be made quickly and decisively.

As Bill says..... idle speed should be around 650/700 RPM.


.
 
bondo said:
Ayuh,..... The air screw "Spec" is just a starting point, further adjustment is done by ear, 'n results,.....

Most all I/O motors idle at 650/ 700 rpms,......

I hope you used fresh gas since the carb rebuild, as the old gas probably just dumped more crap into the fresh carb,....
Click to expand...

Yup, all fresh gas (considered Seafoam as well). I've moved the screw both ways roughly 2.5 turns, keep going further?
 
At 1000 rpm you are no longer using the idle circuit of the carb, which is why it smooths out. Your "rebuild" needs a rebuild in all likelihood as your idle circuit is clogged up.

And get a repair manual, read it, and follow the directions and you'll be in better nick.
 
Ayuh,.... That's it,..... It shouldn't move, at All, except when shiftin' Outa gear, 'n only In the water,.....

If it moves at any other time, the odds are the lower shift cable is beat,....
 
bondo said:
Ayuh,.... That's it,..... It shouldn't move, at All, except when shiftin' Outa gear, 'n only In the water,.....

If it moves at any other time, the odds are the lower shift cable is beat,....
Click to expand...

So, it doesn't move at all thus far. Whether it's in gear or not.
 
If that is a picture of your interrupter/cut out switch then I see a real problem.

The metal arm on the switch should have a small roller on it.

I dont see that in the picture.

see image and respond if this is so...image_54142.jpgimage_54142.jpg
 
I noticed yesterday that the roller and switch arm are missing.

However, in the absence of that roller/switch arm, the micro switch is not being activated.
That would appear to eliminate the SI or SA from being the culprit regarding the engine stalling during a shift.
 
RicardoMarine said:
I noticed yesterday that the roller and switch arm are missing.

However, in the absence of that roller/switch arm, the micro switch is not being activated.
That would appear to eliminate the SI or SA from being the culprit regarding the engine stalling during a shift.
Click to expand...

Of course you did................Mr Wizard!
An no it does not because as the side of the V notch moves it could hit the arm of the switch and could make the switch or he is over shifting and going into the opposite gear causing a stall
 
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So I've poked around with that switch because I didn't know what it was at first, figured it was some type of kill switch. Can confirm it works as such because I'm able to depress the switch and it kills the engine. No contact appears to be made between the arm and the switch while moving from idle to throttle or vice versa.

I also tried messing with the mixture screw on the lower right of the carb, but didn't appear to have any affect so I set it back to 2 turns back from bottom.
 
kghost said:
YOU ARE SOL

Those switches are extremely difficult to come by..............

Good luck
Click to expand...
I'm sure someplace like Digit-Key or Mouser has them. Maybe under a different manufacturer or part number but without doubt there's a cross reference. Pretty common.
 
o2batsea said:
I'm sure someplace like Digit-Key or Mouser has them. Maybe under a different manufacturer or part number but without doubt there's a cross reference. Pretty common.
Click to expand...

So I've found a few by cross referencing part numbers and such, but my overall question is what does this microswitch do exactly that would cause it to bog down/die when going to center neutral?
 
The actual shifting takes place in the lower gear case.

You have a forward gear and a reverse gear. A pinion gear is in constant contact with both forward and reverse gears so they are spinning all the time.
A clutch dog moves (is what gets "shifted") to engage one or the other. The clutch dog is what is attached to the propeller shaft and causes the prop shat to spin when engaged with either forward or reverse gear.

Due to the design of the clutch dog teeth and the same teeth on the gears there is a centrifugal force that makes the separation from either forward or reverse gears very difficult when spinning and even more difficult at higher than idle speed rpm.

The Shift interrupter/cut out switch momentarily kills the ignition to allow the gears to separate (interrupts the centrifugal force if you will). This occurs due to the resistance created on the SHORT shift cable when trying to separate the gears, the SHORT shift cable resistance in turn causes the V notch to move.

The roller on the end of the switch sits in the middle of the V notch when in neutral or full forward or full reverse. When you try to go from either forward or reverse back to neutral (ONLY), when under load it causes the V notch to move thus actuating the switch causing the ignition to momentarily "cut out".

Shifting from gear back to neutral should be done somewhat quickly. If you shift to slow back to neutral the engine can stall.

Now if the short cable is bad (too much resistance all the time) or out of adjustment it will activate the switch when shifting INTO gear as well so the cable must be in good working order and the adjustment/set up must be correct.
 
The actual shifting takes place in the lower gear case.

You have a forward gear and a reverse gear. A driven pinion gear is in constant contact with both forward and reverse gears so they are spinning all the time.
A clutch dog moves (is what gets "shifted") to engage one or the other. The clutch dog is what is attached to the propeller shaft and causes the prop shat to spin when engaged with either forward or reverse gear.

Due to the design of the clutch dog teeth and the same teeth on the gears there is a centrifugal force that makes the separation from either forward or reverse gears very difficult when spinning and even more difficult at higher than idle speed rpm.

The Shift interrupter/cut out switch momentarily kills the ignition to allow the gears to separate (interrupts the centrifugal force if you will). This occurs due to the resistance created on the SHORT shift cable when trying to separate the gears, the SHORT shift cable resistance in turn causes the V notch to move.

The roller on the end of the switch sits in the middle of the V notch when in neutral or full forward or full reverse. When you try to go from either forward or reverse back to neutral (ONLY), when under load it causes the V notch to move thus actuating the switch causing the ignition to momentarily "cut out".

Shifting from gear back to neutral should be done somewhat quickly. If you shift to slow back to neutral the engine can stall.

Now if the short cable is bad (too much resistance all the time) or out of adjustment it will activate the switch when shifting INTO gear as well so the cable must be in good working order and the adjustment/set up must be correct.
 
.......................
kghost said:
Due to the design of the clutch dog teeth and the same teeth on the gears there is a centrifugal force that makes the separation from either forward or reverse gears very difficult when spinning and even more difficult at higher than idle speed rpm.

The Shift interrupter/cut out switch momentarily kills the ignition to allow the gears to separate (interrupts the centrifugal force if you will). This occurs due to the resistance created on the SHORT shift cable when trying to separate the gears, the SHORT shift cable resistance in turn causes the V notch to move.

Centrifugal force has zero to do with this!
The dog clutch teeth are machined in a way that they are not parallel with each other.
They are machined in a fashion as to not be parallel, and in what you may think of as being "dove tail" cut, or perhaps mildly ramped.
The dove tail profile creates interference, of which is what holds engagement, and is what prevents unwanted disengagement, while under load.
The prop thrust, at engine idle speed, is enough to prevent easy disengagement..... hence the need for the shift interrupt system as you have explained very well.

But again, it has nothing to do with centrifugal force!
Click to expand...



.
 
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Moron

The teeth are not machined they are cast, First off

And again due to your 10000000000% lack of knowledge of Mercruiser you are wrong again


Mercruiser does not use any "dovetail" design..................WTF! Go the F away!

I wont even begin to describe the design of the mercruiser clutch dog and corresponding teeth on the gear


You dont deserve to know................



Dont waste everyone times with your spew..............what an idiot!
 
kghost said:
The teeth are not machined they are cast,
Click to expand...
Are you suggesting that the dog clutch gears and sliding sleeve are cast components?

If so, that makes 4 items whereby you have been incorrect lately!



I would love to see a casting like this, and more importantly, one that would hold up under these strenuous conditions:

merc dog clutch sliding sleeve.jpg


Components like these begin from selected materials, often in billet form, and are then fully machined into their final profile.



.
 
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Gee that looks like a dovetail to meeeeeeeeeeeeeeeeeeeeeeeeee

Who cares what you think, what you find or anything you post.

Go to the Swedish fish forum and spew to them, they obvious enjoy your junk!
 
So some good news in an update. Toyed around further with the engine, and with curiosity I removed the shift levers (?) and there was the rest of that shift interrupter. The previous owner must have reassembled it incorrectly, and put the roller under shift levers. So on a side note a new issue has arose. When I try to move to WOT it bogs, and dies. Tried playing with the mixture screw, but nothing seemed to change. (To clarify, I have never really worked on a carbureted engine, primary FI, so forgive me if I'm missing something obvious)
 
Reporting in after doing some further investigation/work on the engine. Finally put it in the water this weekend and ran it up and down. Initially it ran well and response was good. I've noticed I have no mid throttle, either barley anything or full throttle no in between. If I'm in neutral I can go through the entire rev band, but once it's in drive the mid band wants to just die.
 
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