8,000 RPM's????

[biggie]

1987 Donzi Minx #13- Fairly stock vortec 350, alpha 1 gen 1 outdrive and 23p quicksilver. Mercruiser ignition and thunderbolt 4 coil...New Livorsi monster mega rim gauges...I checked the calibration on the tach, checks out for a v8. But I can't for the life of me figure out why I'm spinning 8k? Someone point me in the right direction. I had the power package built by RPM in Fort Walton Beach, FL and they said that the compression is 10:1 but I should only be making power around 5,000 rpm's...I'm lost

[mattyboy]

more info needed

how fast are you going
what drive and ratio
and what size prop?

have you verified with external tach or device like a timing gun with a digital rpm read out?

[biggie]

I'm running 58mph by GPS, I believe it's 1.47 if I'm not mistaken. Currently I'm running the 23p quicksilver mirage.

[biggie]

I'm running 58mph by GPS, I believe it's 1.47 if I'm not mistaken. Currently I'm running the 23p quicksilver mirage.

oh and no I haven't verified by external...should I take the boat to the engine builder to have him check it?

[mattyboy]

running those numbers
58 mph
1.47.gears
23 pitch with 10% slip

you are at about 4400 rpms

does everything else seem ok no burning rubber smell I thought a spun hub but not at 58 mph

the tach senses a pulse of grounds from the dist check all your grounds and your dist wiring your numbers beside the rpm seem to be right in a 350 minx's wheel house so I would say you have a tach issue if I held a ground on the "sender" lead on the tach I would peg it so a flaky ground could give you a high reading . I would see if you could borrow a tester

how are your idle and midrange rpm readings?

[Morgan's Cloud]

I often have problems with my spectacles and mistake a '5' for an '8'

[biggie]

Roger that I'll check the tach and dial down to a 21p hydro q4. Thanks for the input.

[joseph m. hahnl]

They have a 10 pole/5 pulse and 12 pole/ 6 pulse and use a Duetsch Connector Harness . I'd start with verifying what pulse you have on the tach . You also need to confirm if it's voltage triggered (negative terminal on coil) or current triggered (positive side of the coil). I'm sure the installation instruction indicate which side. If you just hitched up the DCH to the existing wiring you may have overlooked it.

[BUIZILLA]

where is the tach lead wire connected? on the coil (which side?) or the distributor?

[mattyboy]

a wiring diagram for a merc

http://www.lgdonziclassic.com/pdfs/merc.pdf

usually a gray wire in the merc setup to the sender on tach should go to the - side of the coil and bridged to the ground going into the Dist on a can style coil and a points/breakerless ignition setup

[johnnywhale]

I didn't think a tach could work on the positive side of the coil? Isn't it uninterrupted? Only after the resistance of the coil do you get a pulse when the module / points / etc complete the circuit to ground.

[johnnywhale]

Never mind, found this:
https://www.msdignition.com/page.aspx?id=3300

Might help

[mattyboy]

didn't realize Livorsi had so many different tachs and ways to connect them

this page may help you need to know what model tach you have scroll down to T

http://www.livorsi.com/tools.htm