Greetings, I have a question regarding the 1975 tach. Ever since I have had the car the tach will read around 4k when I start the car in the am, even while idling. After running for a little while it seems to settle down and read correctly. I am wondering if it could be the circuit board behind the gauge itself.

______________
Daytona Yellow '75 350 Muncie 4 spd

What does the tach do when you turn the key off? They normally go up to somewhere around 4000rpm with the key off, then it should come down to 0 with the key on, engine off. If yours is kinda stuck at 4 until it runs for a while, it may well be the tach meter itself...it may have some dirt, or something sticky on the guts. Normally, I would suggest you try bypassing the tach filter first, but since you've already swapped the distributor, that won't help. Assuming your MSD has a tach output that is to be connected to the factory tach wire from the original distributor, I would say bypass the filter anyway, and run the tach output from the MSD directly to the tach input wire by the dist.
If the tach is still funky. then you get to rip into the dash. Check the wire from the dist to the tach board for continuity. Then check for battery voltage, and ground at the board. Flip the board over and look for any burnt, of corroded areas. If all of that checks out, then it's likely your tach itself is bad.







|UPDATED|11/23/2015 11:45:27 AM (AZT)|/UPDATED|


______________

Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks for the reply Joel, thats what I ended up doing. I removed the tach filter and went directly from the MSD tach output to the brown wire after the filter. I still have to get into the dash to replace the board, but it now works as it did before. Basically in the morning it will float at somewhere below 0 at idle to around 3.5 - 4k while running.. at any rpm. Then once I have driven about 20 miles it seems to read correctly, so I am assuming the board could use replacing. 

______________
Daytona Yellow '75 350 Muncie 4 spd

You want to adjust both the idle speed, AND the idle mixture screws on the carb. Normally, the idle will change as you adjust the mixture screws, depending on how far off they are to begin with. Start with the carb adjustments, and then go to moving the dist around for the highest vac reading. Then...go back to the carb....then back to the dist....rinse and repeat. Some times it only takes a few minutes, sometimes a lot more. It really all depends on how close, or how far it is from "just right" when you start. You have to take into account fuel quality, ambient air temps, humidity, etc. to get it dialed in perfectly. That being said, as long as it starts and runs well HOT, with no hiccups, it's good enough for me. One trick to see if you have too much timing for a HOT engine is to rev it up to around 4500-5000rpms(in park/neutral), and shut the key off while your foot is still on the gas. Once it dies, crank it up...if it kicks back, take a couple of degrees of timing out until you can do this without it kicking back when starting. You want it to be able to start reliably when hot. This keeps the battery happy,and can keep from snapping the nose of the starter off, especially on big blocks.
hth


______________

Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

As an update to the original post regarding the tachometer and the MSD Ignition. I ended up just running the tach wire (Brown) directly to the MSD tach output and it works fine. No tach adapter is needed. Just wanted to add this in case someone else has the same question.

______________
Daytona Yellow '75 350 Muncie 4 spd