Timing
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Timing
So I had asked a question about carb tuning a while ago and I got the answers I needed.
http://forums.corvetteforum.com/c3-t...-question.html
But now I have a new question that is related but more specific to timing. I checked my dwell last night and it was 36*, so I set it to 30* (spec is 28-32*). This increased my idle speed by about 200 RPM...so I adjusted the idle speed screw back to spec. Then I went to check my timing, so the first thing I did was unhook the vac advance hose from the port on the carb and plug it. When I did this, the engine's idle speed increased by about 200 RPM and evened out somewhat. In essence the car ran "better" with a vacuum leak, and conversely if I put my finger over the port on the carb without the vac line hooked up it dropped the idle speed considerably, similar in effect to covering the top of the carb with your hands to starve it of air...am I supposed to let the port on the carb draw air as I set my timing? Something rubs me the wrong way.
http://forums.corvetteforum.com/c3-t...-question.html
But now I have a new question that is related but more specific to timing. I checked my dwell last night and it was 36*, so I set it to 30* (spec is 28-32*). This increased my idle speed by about 200 RPM...so I adjusted the idle speed screw back to spec. Then I went to check my timing, so the first thing I did was unhook the vac advance hose from the port on the carb and plug it. When I did this, the engine's idle speed increased by about 200 RPM and evened out somewhat. In essence the car ran "better" with a vacuum leak, and conversely if I put my finger over the port on the carb without the vac line hooked up it dropped the idle speed considerably, similar in effect to covering the top of the carb with your hands to starve it of air...am I supposed to let the port on the carb draw air as I set my timing? Something rubs me the wrong way.
Instructor
Joined: Mar 2013
Posts: 108
Likes: 1
From: Georgia
No
You pull the hose from the dizzy and put a screw in the hose or remove it from the Carb and put a plug over the carb port.
What you did causes the carb to run leaner and most times it will cause the car to increase the RPMs. If the exhaust mornally smells rich, you need to adjust the air/fuel mixture on your carb. It is a two step process. Read your manual and it should explain how it is done.
You pull the hose from the dizzy and put a screw in the hose or remove it from the Carb and put a plug over the carb port.
What you did causes the carb to run leaner and most times it will cause the car to increase the RPMs. If the exhaust mornally smells rich, you need to adjust the air/fuel mixture on your carb. It is a two step process. Read your manual and it should explain how it is done.
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Thanks, yes familiar with the mixture adjustment from the manual. I'll try to adjust my mixture first, I do believe it is quite rich. Then I'll attempt to time, then adjust mixture again to make sure all is well in the neighbourhood.
Last edited by Brcmpbl; May 9, 2013 at 06:35 PM.
Burning Brakes
Joined: Sep 2006
Posts: 851
Likes: 10
From: Palm City, FL
Set the curb idle speed
Perform the idle mix screw adjustment procdure as normal except checking RPM instead of highest vaccum... for highest RPM you can get.
When done, adjust the curb idle back to what you had it prior to adjusting the mix.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
I did was unhook the vac advance hose from the port on the carb and plug it. When I did this, the engine's idle speed increased by about 200 RPM and evened out somewhat.
Burning Brakes
Joined: Oct 2000
Posts: 877
Likes: 59
From: Minneapolis, MN USA
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Adjusted carb mix last night, was set at 4 full turns out on both screws. A lot. Seated screws and backed out 3 turns each, hooked up vac gauge and found that best vac I could get was 1/8 turn or so in from 3 turns.
Now need to sort timing, that's for tonight.
Have Lars' papers...for those asking here, you can email him at v8fastcars@aol.com (I think that's correct anyway, been a while).
Next week the N11s go on!
Now need to sort timing, that's for tonight.
Have Lars' papers...for those asking here, you can email him at v8fastcars@aol.com (I think that's correct anyway, been a while).
Next week the N11s go on!
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Burning Brakes
Joined: Oct 2000
Posts: 877
Likes: 59
From: Minneapolis, MN USA
Have Lars' papers...for those asking here, you can email him at v8fastcars@aol.com (I think that's correct anyway, been a while).
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
I believe Lars' e-mail address is:
v8fastcars@msn.com
I could be wrong, too, though. Give it a try. Remember to be respectful. He deserves it.
Scott
v8fastcars@msn.com
I could be wrong, too, though. Give it a try. Remember to be respectful. He deserves it.
Scott