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Eratic tach

J

jclays

Regular Contributor
Starboard tach started dancing

Starboard tach started dancing today. Heading through the marina at 1000rpm on both engines. After a while the starboard tach was reading 1600 rpm. The engines did not speed up. only the tach on the starboard side. She went down to 1000 a bit latter. As I exited the marina to open water I started to bump up the throttles. Both reading 1600 rpm. A few minutes latter the starboard jumped to read 2200 rpm but the engines did not. Bad Gauge? Ground condition?
 
"Had a similar problem (hi

"Had a similar problem (higher rpm tach than engine) last month. I replaced the condenser and coil (on an OEM distributor - non electronic) and problem went away. Not sure which one solved it, but I'd try the less expensive condenser first."
 
"I had the same issues with an

"I had the same issues with an erratic tach. On the back of most tachs is a switch that allows the tach to be used on 4/6/8 cylinders, I moved that switch back and forth to clean the contact internally and then put back to the original setting. The tach has worked fine since then.

Timmy"
 
I have experienced the same as

I have experienced the same as Timmy. Rotating that switch thru the 3 settings a few times corrected the erroneous reading I was seeing on one of the tachs.
 
Sameo as Timmy and Erich on my

Sameo as Timmy and Erich on my Port tach. Couldn't believe such an easy fix would actually work for me - BUT IT DID!! (do you know how much room there is on the backside of the insturment panel on a Carver 350 Mariner :eek:)
Nice to get an easy one once in a while.
 
"That's how we fixed the d

"That's how we fixed the damper plate...
wink.gif


Since we are talking tachs... Mine are not readng correctly or so I believe. Two years ago I added on of those swing needle sync indicators to help get both engines close to the same rpm to help eliminate some accidental "steerage" since one side may be faster then indicated.

At most tach readings, the port side is 200-300 rpm higher but the swing needle gauge is telling me it is centered and they are about even.

Do those things get the same signals as a tach would to operate? Is there any hint of accuracy?

One thing is that you can hear the hum of the engines start that sinusoidal rhythym once they get in the "zone" Something must be right . Once you get to 3000 or so, you cant hear anyway so it is hard to tell. Any opinions?"
 
"I love my sync indicator.

"I love my sync indicator.

They are driven by the same thing the tach uses - the "low" side of the ignition coil. Every one that I have seen is "accurate" when they work. They differ from a tach in that they produce a differential rather than a single ended signal.

The sound being "in the zone" is know as beat frequency - the lower and slower it becomes, the closer the engines' rpms match.

Do your tachs have the CAL hole in the back?"
 
"Yes they do have a calibratio

"Yes they do have a calibration adjustment aside from the 4,6,8 switch but I never knew what I would be calibrating them against. I love the way that swing needle gauge works. It is ON CENTER when that BEAT FREQUENCY really kicks in. You can hear and feel it , at that point its almost as if you dont need to look at the indicator.

I would think I am not calibrating the tachs to match at one point as the rpms would have no bearing. I do have a laser tach but at 3000, I don't feel very comfortable hanging inside the hatch cover trying to take a measurement. At idle, I'm good."
 
"Jeff,
I'd be happy to se

"Jeff,
I'd be happy to second that nomination, however, if memory serves (which doesn't happen that often anymore:eek:) you suggested this a couple of weeks ago (I think that's where I read it first) - right?
Marlin"
 
"I'm going to have to do t

"I'm going to have to do this click bakc and forth on my starboard tack, looks almost the same at low speed but off by about 200 at cruise )port 3200 (correct) and starboard 3400 (wrongo)"
 
"I'd like to know why we h

"I'd like to know why we haven't heard from the original poster, James Smith. We are making all sorts of recommendations and no reply since his first post on 9/6/09. Hello Jim...where are you?

Erich"
 
"marlinmike,


Please show

"marlinmike,


Please show me the post so I can give credit to the original poster of this idea


Timmy

"Jeff,
I'd be happy to second that nomination, however, if memory serves (which doesn't happen that often anymore:eek:) you suggested this a couple of weeks ago (I think that's where I read it first) - right?
Marlin""
 
Sorry ive been MIA haven't

Sorry ive been MIA haven't been on the water much since I posted. Works picked up right now. I will try operating the switch behind the tach if I can get to it. Also I have been wondering about the condenser as I posted originally. Will try them and see.
 
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