Dunzvett81
Well-known member
What is a Dwell meter and where could I get one?
thanks
thanks
Dwell meter ?
- Thread starter Dunzvett81
- Start date
twiget
Well-known member
A dwell meter is used to set the points on an old distributor. I doubt your '81 has points though. GM went away from points in distributors back in the mid-70's.
Jason
Jason
- Thread starter
- #3
Dunzvett81
Well-known member
thanks, I am asking because I recieved a code # 23 which is mixture control soleniod and upon reading previous posts, members talk about hooking up a dwell meter to the green connector to obtain the reading.
paul67
Well-known member
This is a dwell tachometer but you need a code reader.
- Moderator
- #5
I know very little about engines....
I do know that you use a Dwell Meter to setup parts of the timing/air & Carb on the 1981
I also know that the Dwell has to be set on the 6 cyclinder operation 
Hopefully someone will be along with the proceedure. If you are looking at Code Readers, be sure it can read the 1981 Codes and has the correct pin connection... I bought one off eBay years ago, and it is now a paper weight :eyerole
If you haven't purchased a GM Shop Manual, I highly recommend getting one, eBay or aftermarked vendor, here again, be sure it is the geniue GM 1981 Corvette Shop Manual # ST-364-8T
Bud
I do know that you use a Dwell Meter to setup parts of the timing/air & Carb on the 1981
I also know that the Dwell has to be set on the 6 cyclinder operation Hopefully someone will be along with the proceedure. If you are looking at Code Readers, be sure it can read the 1981 Codes and has the correct pin connection... I bought one off eBay years ago, and it is now a paper weight :eyerole
If you haven't purchased a GM Shop Manual, I highly recommend getting one, eBay or aftermarked vendor, here again, be sure it is the geniue GM 1981 Corvette Shop Manual # ST-364-8T
Bud
- Thread starter
- #6
Dunzvett81
Well-known member
Thanks for the help.
Jay
Jay
Jay,
Like Jason said, that was the original purpose for distributors with breaker points. The dwell determines the length of time the contacts were closed (to build the voltage level in the coil, and when the points opened, the rapid collapse of the magnetic field in the coil triggered the current).
However, like Bud posted above, the dwell meter is used on the L81's to set the air valve to the correct range (one tries to get it as close to 30 degrees as possible). I guess GM designed to use the dwell meter. The system is set-up to indicate a relatively rich condition with a dwell reading below 30 degrees and a relatively lean condition with a dwell reading of higher than 30 degrees.
The connection with the mixture is that, if for some reason, you are pretty far from 30 degrees from either direction, the procedure has you check your mixture control screws at the base of the Rochester carburetor for correct setting (3 -1/3 turns out from light bottoming).
This check is time consuming, for one should only turn the air valve 1/8's of a turn at-a-time, and then one has to wait for the adjustment to reflect on the dwell meter. If you go through the adjustments too quickly, then you end up chasing the needle of the dwell meter. Also, Bud is right about the scale - place it on 6-cylinders. With L81, you have to get your engine nice and warm, so even if you had it running 20 minutes, but turned it off for 5 minutes, then make sure you let it idle for at least 2 minutes to ensure the computer is cycling all the switches / settings like it is supposed to. One way to tell, is by noticing that the dwell meter's needle hunts (or varies small distances). If it is dead solid (not moving), then wait some more time.
Most dwell meter instructions tell you to disconnect the ground before starting or shutting off the engine. What I do is clamp it to a rubber hose near your ground, and when you are ready to check or adjust your air valve, then connect it to ground.
I hope this helps explain it.
GerryLP:cool
Like Jason said, that was the original purpose for distributors with breaker points. The dwell determines the length of time the contacts were closed (to build the voltage level in the coil, and when the points opened, the rapid collapse of the magnetic field in the coil triggered the current).
However, like Bud posted above, the dwell meter is used on the L81's to set the air valve to the correct range (one tries to get it as close to 30 degrees as possible). I guess GM designed to use the dwell meter. The system is set-up to indicate a relatively rich condition with a dwell reading below 30 degrees and a relatively lean condition with a dwell reading of higher than 30 degrees.
The connection with the mixture is that, if for some reason, you are pretty far from 30 degrees from either direction, the procedure has you check your mixture control screws at the base of the Rochester carburetor for correct setting (3 -1/3 turns out from light bottoming).
This check is time consuming, for one should only turn the air valve 1/8's of a turn at-a-time, and then one has to wait for the adjustment to reflect on the dwell meter. If you go through the adjustments too quickly, then you end up chasing the needle of the dwell meter. Also, Bud is right about the scale - place it on 6-cylinders. With L81, you have to get your engine nice and warm, so even if you had it running 20 minutes, but turned it off for 5 minutes, then make sure you let it idle for at least 2 minutes to ensure the computer is cycling all the switches / settings like it is supposed to. One way to tell, is by noticing that the dwell meter's needle hunts (or varies small distances). If it is dead solid (not moving), then wait some more time.
Most dwell meter instructions tell you to disconnect the ground before starting or shutting off the engine. What I do is clamp it to a rubber hose near your ground, and when you are ready to check or adjust your air valve, then connect it to ground.
I hope this helps explain it.
GerryLP:cool
paul67
Well-known member
Jay,
Like Jason said, that was the original purpose for distributors with breaker points. The dwell determines the length of time the contacts were closed (to build the voltage level in the coil, and when the points opened, the rapid collapse of the magnetic field in the coil triggered the current).
However, like Bud posted above, the dwell meter is used on the L81's to set the air valve to the correct range (one tries to get it as close to 30 degrees as possible). I guess GM designed to use the dwell meter. The system is set-up to indicate a relatively rich condition with a dwell reading below 30 degrees and a relatively lean condition with a dwell reading of higher than 30 degrees.
The connection with the mixture is that, if for some reason, you are pretty far from 30 degrees from either direction, the procedure has you check your mixture control screws at the base of the Rochester carburetor for correct setting (3 -1/3 turns out from light bottoming).
This check is time consuming, for one should only turn the air valve 1/8's of a turn at-a-time, and then one has to wait for the adjustment to reflect on the dwell meter. If you go through the adjustments too quickly, then you end up chasing the needle of the dwell meter. Also, Bud is right about the scale - place it on 6-cylinders. With L81, you have to get your engine nice and warm, so even if you had it running 20 minutes, but turned it off for 5 minutes, then make sure you let it idle for at least 2 minutes to ensure the computer is cycling all the switches / settings like it is supposed to. One way to tell, is by noticing that the dwell meter's needle hunts (or varies small distances). If it is dead solid (not moving), then wait some more time.
Most dwell meter instructions tell you to disconnect the ground before starting or shutting off the engine. What I do is clamp it to a rubber hose near your ground, and when you are ready to check or adjust your air valve, then connect it to ground.
I hope this helps explain it.
GerryLP:cool
Interesting! I learned something today.
- Thread starter
- #9
Dunzvett81
Well-known member
Gerry: Thanks for the explanation, very good info! appreciate all the help. Everytime I come to this forum I learn something new.
Paying it forward...A few years ago, I was more on the receiving end of help end, and now, if I can help, then I am most glad to offer my help!
But one cannot know everything. I still learn a lot from our members just the same.
GerryLP:cool
But one cannot know everything. I still learn a lot from our members just the same.
GerryLP:cool
Jay,
In the link below, you'll find several images of pages for the SD-100A AC-Delco "Domestic and Imports Tune-up Specifications", and on page 120, you'll have the basic tune-up specifications; page 126 has the TPS adjustment procedure; Page 138 and page 139 have the idle mixture adjustment and air valve adjustments (respectively); Page 140 covers situations in which you find an identifying letter on the air valve adjustment screws; and page 155 has the carburetor adjustment values. Let me know if you don't find it, for perhaps I meant to load the particular page and forgot to do it.
http://corvetteactioncenter.com/gallery/showgallery.php/ppuser/752/cat/500
In the link below, you'll find several images of pages for the SD-100A AC-Delco "Domestic and Imports Tune-up Specifications", and on page 120, you'll have the basic tune-up specifications; page 126 has the TPS adjustment procedure; Page 138 and page 139 have the idle mixture adjustment and air valve adjustments (respectively); Page 140 covers situations in which you find an identifying letter on the air valve adjustment screws; and page 155 has the carburetor adjustment values. Let me know if you don't find it, for perhaps I meant to load the particular page and forgot to do it.
http://corvetteactioncenter.com/gallery/showgallery.php/ppuser/752/cat/500
- Thread starter
- #12
Dunzvett81
Well-known member
Once again thanks for all that info Gerry. That is some really good reading. I thinks my next buy will be a 81 corvette shop manual.
The L81 shop manual is a must. But you can supplement it with the SD-100A, and the 9D-5-1 (E4ME Carb manual). These do not repeat the information from each other 100%, so you'll find small bits of information which expand the understanding in the carbs.
The 9D-5-1 you can find on e-bay sometimes, but there was a vendor who sold it by download electronically, and it was not to bad to peruse. The best way is to print-it, and remove the few advertising pages they embedded into the electronic file OR get a pdf file editing program and you can remove the excess pages. Good luck!
The 9D-5-1 you can find on e-bay sometimes, but there was a vendor who sold it by download electronically, and it was not to bad to peruse. The best way is to print-it, and remove the few advertising pages they embedded into the electronic file OR get a pdf file editing program and you can remove the excess pages. Good luck!
- Thread starter
- #14
Dunzvett81
Well-known member
As it turned out I had a dwell meter in one of my older tool boxes I found. 
I hooked it up and found that I was running very rich at about 20 degress. I adjusted the air valve (this took some time, like others said it took patience) but it paid off. I was able to get it right around 30 degress. Thanks for all the help!
I hooked it up and found that I was running very rich at about 20 degress. I adjusted the air valve (this took some time, like others said it took patience) but it paid off. I was able to get it right around 30 degress. Thanks for all the help!
Jay,
I am glad that it worked-out fine.
GerryLP:cool
I am glad that it worked-out fine.
GerryLP:cool
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