omc 3.0 L 400 series questions

wvwarlock

Seaman Apprentice
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Jul 30, 2008
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44
good afternoon every one..

first of all let me thank everyone for all the help and assistance so far as it has been a big help.

i finally got the boat on the water this weekend after weeks of troubles and turmoil. but after a day on the water it was well worth all hassles to get to that point.

i only experienced a few minor glitches that i hope to resolve this week before going out again so here goes:

1. speedometer is very erratic. at full throttle it varies between 22 and 42. where does the speedometer hook up and what do i need to check?

2. tachometer does not work at all. any idea where the tach should hook to and any suggestions on what to look for?

3. mystery gadget... mounted on transom near stringer. it is plastic with a cable running up back of boat and through the back. any ideas???

4. prop is a 13 1/4 inch 17 pitch might there be a better size??


boat is 1983 starcraft css 181
motor is omc 3.0 l model 302STHRCTR
drive is a 400 series stringer model 982740
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: omc 3.0 L 400 series questions

#1 is answered by #3 . . . :D The plastic thingy is a Pitot tube. It allows water into the "cable" which is actually a hose that runs all the way up to your speedo. The water compresses the air in the hose which the gauge reads, it is actually a pressure gauge that is indexed to show corresponding speed. They are notoriously inaccurate, but when right some are dead on. The little plastic thingy is usually hinged and needs to be down. Also, the hose and pitot itself need to be free of any stuff, weeds, gunk etc. You could remove it from the speedo head and shoot some air through it to see if it is clear. [Edited out]

#4 should be dead on if it is anything like mine was. Need the tach to confirm.

#2 usually driven by a lead from the coil. should be a gray wire I think . . .
 
Last edited:

wvwarlock

Seaman Apprentice
Joined
Jul 30, 2008
Messages
44
Re: omc 3.0 L 400 series questions

i will check but i thought the plastic piece that pivoted kad a cable connected to it running up through the black tube on the back.
 

QC

Supreme Mariner
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Mar 22, 2005
Messages
22,783
Re: omc 3.0 L 400 series questions

Does the plastic thing have a hole in the tip/end? Or is it fat and squatty on the end. Could be a transducer for a depth sounder . . . Either way, what I describe is how the speedo works . . .
 

chiefalen

Captain
Joined
May 18, 2008
Messages
3,598
Re: omc 3.0 L 400 series questions

I would like to know where is the passage in the stringer out drive to run a pitot tube?

Maybe you can post a picture, would help alot.
 

Uraijit

Banned
Joined
Feb 5, 2008
Messages
884
Re: omc 3.0 L 400 series questions

The tach is connected to the negative side of the coil.

Try connecting a battery charger to the tachometer. Your tach should give you a reading of 3600 RPM. If you don't get anything, the tach is bad. If you get the 3600 reading, check your wiring back to the coil. There should be a signal wire connected to the negative side of the coil.
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: omc 3.0 L 400 series questions

I would like to know where is the passage in the stringer out drive to run a pitot tube?.
Yeah, that was a mistake, I remembered after I posted that my old stringer powered boat didn't even have a speedo . . . All I could remember at first was that it didn't have a transom mounted pitot, so I . . . well . . . I forgot . . . :redface: Thanks for the challenge as I was going to correct and well . . . I forgot . . . :rolleyes: :)

Try connecting a battery charger to the tachometer. Your tach should give you a reading of 3600 RPM.
Is that true no matter what the switch on the back of the tach is set to?
 

Uraijit

Banned
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Feb 5, 2008
Messages
884
Re: omc 3.0 L 400 series questions

For a 4 cylinder, it will be 3600, 2400 for 6ers, and 1800 for an 8 cyl. ;)
 

chiefalen

Captain
Joined
May 18, 2008
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3,598
Re: omc 3.0 L 400 series questions

Warlock post a picture. But could be a fishfinder transducer.
 

wvwarlock

Seaman Apprentice
Joined
Jul 30, 2008
Messages
44
Re: omc 3.0 L 400 series questions

i will get back home tomorrow and then post a pic. thanks again
 

wvwarlock

Seaman Apprentice
Joined
Jul 30, 2008
Messages
44
Re: omc 3.0 L 400 series questions

i got to looking at the item, and it is a pitot tube. it moves very stiffly so i may need to replace it. should it move freely?
 

QC

Supreme Mariner
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Mar 22, 2005
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22,783
Re: omc 3.0 L 400 series questions

No. It needs to stay down while running at speed . . .
 
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