81 Carb Gurus

[big2bird]

Gerry,
I set the float to .420" per Lars. My understanding is the solenoid height is 1.305" with a gauge. The solenoid travel is 4/32", and the idle bleed is adjusted to obtain 30* at idle. (The idle bleed gauge is approximate till test run.) The TPS has been adjusted to .56 volts at curb idle. Idle mixture is 3 1/3 turns out.

What I do not understand is the rough idle it appears to have, even though I nailed the 30* at idle.
I am going to have a gauge machined, set the solenoid, adjust the travel to 4/32", set the dwell at 30*, and see if that refines it out.

 

[big2bird]

17081228 = automatic tranny / Federal Models

17081217 = MANUAL TRANNY / Federal Models

17081218 = Automatic tranny / California Emmissions

These numbers imply either that there were no California-Emmissions equipped with a MANUAL, or the Corvettes with manual transmission were OK with the State Government of California.:confused

I thought the 2 after the year code was 49 state, and 5 is the Kalifornia code.

 

[GerryLP]

I thought the 2 after the year code was 49 state, and 5 is the Kalifornia code.

I got the numbers from my Corvette Interchange Parts Manual, but none of these books are 100% correct, so you could be right; however, some of the check digits in part numbers apply to some model and not others. Perhaps the notes at the end of you literature/Book will clear things up.

 

[GerryLP]

Gerry,
I set the float to .420" per Lars. My understanding is the solenoid height is 1.305" with a gauge. The solenoid travel is 4/32", and the idle bleed is adjusted to obtain 30* at idle. (The idle bleed gauge is approximate till test run.) The TPS has been adjusted to .56 volts at curb idle. Idle mixture is 3 1/3 turns out.

What I do not understand is the rough idle it appears to have, even though I nailed the 30* at idle.
I am going to have a gauge machined, set the solenoid, adjust the travel to 4/32", set the dwell at 30*, and see if that refines it out.

Did the Dwell needle varied on you? It should "hunt" small distances back and forth. If it is steady, then I would run the engine a little longer. Just like being on a traffic jam. Let it idle in drive until it gets to operating temperature really good. Also, make sure you follow the 6-cylinder scale. I have had the best results when adjusting the air valve no more than an 1/8 of a turn at a time.

It is tempting to go half a turn, but the air valve has to "consume" [adjust] either air or fuel from the previous adjustment, so if you turn large amounts of the screw, you'll end-up chasing your own tail.

Roughness usually equals air leak. Just double-check everything.

I have to make sure that everyone understand that the air valve adjustments are done in drive if an automatic transmission, so please, block the wheels. At least two wheels if stock L81 and all four if crate motor (with higher HP) in place. Lets be safe, people!

If after all this, the needle won't hunt or vary, then re-adjust you idle mixture screws. Additionally, If you changed your curb idle, then you just changed your TPS reference point. If the needle still won't hunt, then check your TPS again. I have gotten up-side-down and lost my way, so the best method to find your way sometimes is to start from square one. Remember, dwell higher than 30 deg = lean tracking. Under 30 degrees = rich tracking.

 

[big2bird]

I got the numbers from my Corvette Interchange Parts Manual, but none of these books are 100% correct, so you could be right; however, some of the check digits in part numbers apply to some model and not others. Perhaps the notes at the end of you literature/Book will clear things up.

http://www.carburetion.com/quadnumber.htm

 

[big2bird]

Did the Dwell needle varied on you? YesIt should "hunt" small distances back and forth. If it is steady, then I would run the engine a little longer. Just like being on a traffic jam. Let it idle in drive until it gets to operating temperature really good. Also, make sure you follow the 6-cylinder scale. I have had the best results when adjusting the air valve no more than an 1/8 of a turn at a time. Yes

It is tempting to go half a turn, but the air valve has to "consume" [adjust] either air or fuel from the previous adjustment, so if you turn large amounts of the screw, you'll end-up chasing your own tail.

Roughness usually equals air leak. Just double-check everything.

I have to make sure that everyone understand that the air valve adjustments are done in drive if an automatic transmission, so please, block the wheels. At least two wheels if stock L81 and all four if crate motor (with higher HP) in place. Lets be safe, people!

If after all this, the needle won't hunt or vary, then re-adjust you idle mixture screws. Additionally, If you changed your curb idle, then you just changed your TPS reference point. If the needle still won't hunt, then check your TPS again. I have gotten up-side-down and lost my way, so the best method to find your way sometimes is to start from square one. Remember, dwell higher than 30 deg = lean tracking. Under 30 degrees = rich tracking.

I have a frien making the gauge for me. I will re-check everything, then if not happy, start on the vacuum leak procedure. I may even pull it, as I believe the secondary wind up is too tight. Arggghhh!!!

 

[GerryLP]

I wonder...would a photo copy of my tool come-out actual size?

That way we could compare them...

 

[big2bird]

I wonder...would a photo copy of my tool come-out actual size?

That way we could compare them...

My friend has the original GM gauge. .170" ID, ,220" OD, closed on one end, 1.305" length

 

[big2bird]

 

[GerryLP]

I must admit...I am not sure what that square rubber piece with the old-fashioned can opener is...

Below are the tools that I have. The Thexton 362 I got from:

ETW Corporation
Tukwila, Wa

They are on the web.

View attachment 14255

 

[big2bird]

I must admit...I am not sure what that square rubber piece with the old-fashioned can opener is...


View attachment 14255

That's because I just found out that is a tool for throttle bodies.:L

 

[GerryLP]

That's because I just found out that is a tool for throttle bodies.:L

So perhaps it will come handy for our 1982 Vette owners counterparts...:L

and 84 owners too...

 

[big2bird]

Well. I had two gauges made. The one on the right is GM replica, the one on the left is Big Bird designed.

 

[big2bird]

Gauge in place

 

[big2bird]

Gauge shows solenoid too low

 

[big2bird]

Final settings. Float .420, solenoid ht 1.305", travel 4/32", idle mix 3 1/3 turns, Idle bleed 30* M/C dwell. Runs pretty good, but still a slight miss at idle. Off to chase another goose. I believe I have eliminated the carb. Capped all vacuum lines, no change. Next is possible new plug wire or new plug. Argh!!

 

[GerryLP]

Good job!

Do the pump shots seem to be lagging? or too short?

Wait...wait. Did you say miss? I took it as hesitation.

You know what worked for me to chase down the miss in my L81, After I verified everything else ignition-wise, I found some information on the D.I.U. (or is it D.U.I.) website. Their research had shown that a common miss on HEI ignitions was the random grounding of spark on the two screws that hold the rotor. They use nylon screws to hold their rotors on their HEI units.

So, I went to Home Depot (I love that place ), and their nylon screws are cheaper by half, and you don't have to wait for UPS to skip Saturday and show-up on Monday.

And that's how I got rid of the miss in my stock distributor. You ought to try it. s

 

[big2bird]

Good job!



Wait...wait. Did you say miss? I took it as hesitation.

You know what worked for me to chase down the miss in my L81, After I verified everything else ignition-wise, I found some information on the D.I.U. (or is it D.U.I.) website. Their research had shown that a common miss on HEI ignitions was the random grounding of spark on the two screws that hold the rotor. They use nylon screws to hold their rotors on their HEI units.
s

I have a DUI dizzy in mine. Complete with nylon rotor screws. I appreciate the help. Keep thinking. I am looking for a defect in an everything new situation. Argh.

 

[big2bird]

See Gerry, It's not for lack of spending money or time.

 

[big2bird]