1405 Edelbrock Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevy55 · 07-21-2002, 01:28 AM

What kind of vacuum should I be running at idle on the timed vacuum port and the manifold vacuum port?

bigjimzlll · 07-21-2002, 01:43 AM

that depends on a lot of things..mainly your cam profile and timing..alot of other things will effect vacuum...head gasket...valves...the 1405 is ste up from the factory a little rich, richer than the 1406..my small block has a bout 12 inches of vacuum at idle..if your having problem with hesitation or bogging the problem probably lies in the springs...if you go to www.edelbrock.com it may help...also they have a help line thats real good

chevy55 · 07-21-2002, 01:56 AM

Is it normal for both ports to read close to the same amount of vacuum? Timed port reads 6in and the manifold reads 8in.

Longhorn Man · 07-21-2002, 02:00 AM

At an idle, your timed vac should be about 0

chevy55 · 07-21-2002, 02:13 AM

Both ports act like manifold vacuum. Tried timing it, disconnected the vacuum advance and plugged and set the timing but when I connected the timing advanced. Could it have been crap from the fuel tank getting inside the carb or caused by the many intake backfires I have had? I don't know what to do. I might pull off the carb and check it out and if nothings wrong I will check out edelbrock's web site.

mikep · 07-21-2002, 02:42 AM

how about a little more background on the motor and build. Did this backfiring thing just start ? what sort of cam? New build or is it a new problem with an old motor?

Whats up?

chevy55 · 07-21-2002, 01:21 PM

It has just been rebuilt, it has a 216 degree duration. The intake backfires were caused by me not having the timing advanced enough

mikep · 07-21-2002, 01:40 PM

216 isnt much for duration and you should have more like 16-18 inches of vacuum at idle if not more. Are you sure you are using the right balancer/timing mark combination? I know two guys who arent and they swore they were until we figured out the problem. How much initial advance are you running? How much total? How far out are your mixture screws? Dont be afraid to go into a LOT of detail about your engine build, timing procedures, cam setup etc.

chevy55 · 07-21-2002, 05:46 PM

I am using the same balancer. From my experience the timing sounds like it is almost right on. It starts right up without a problem. With the distrubutor advance line plugged I had set it at 14 degrees advanced. When I plugged in the advance it jumped up to about 17 or 18 even at idle on both the timed and manifold vacuum ports. The mixture screws were turned five turns, it does diesel when I shut it off. However when we lean the idle mixture screws it will either intake backfire or it won't start. We put my carburetor on my brothers truck and it worked fine so I know it is not that. I think that there is a vacuum leak on the intake manifold. I might try and change the gaskets since it is easy to get to and I have enough time. Even with the carburetor as rich as it is if I give it full throttle from idle it will intake backfire.

mikep · 07-21-2002, 06:47 PM

Are you using an EGR valve? Sounds like you have a horrendous vacuum leak somewhere. What manifold are you using. Might want to check the manifold for cracks. That still wouldnt explain the timed to port vacuum thing though. That just shouldnt happen although with your really low idle vacuum something is wacky. I'd yank that manifold off and inspect it carefully even under the heat shield if its OEM.

Longhorn Man · 07-21-2002, 07:08 PM

It sounds to me like the primarys are open a little at idle...can't explain why, but that's what it sounds like.

bigjimzlll · 07-21-2002, 07:13 PM

andy might be on to some thing...disconect your throttle cable and see what happens...i think you have a vacuum leak also...my mixture screws are about 2 1/2 turns out....are you running a spacer?

chevy55 · 07-22-2002, 01:21 AM

When we put the carburetor on my brothers truck he had the screws about 2 turn out. I went ahead and changed the manifold gaskets, it is a new weiand excelerator without a spacer, threw the carb back on it with the same settings at about 2 turns out and it fired up. Now I have good throttle response considering the fact that it the timing I am sure is off and the rocker arms aren't adjusted right, that is a job for tomorrow. Changing the manifold gaskets did the trick. Thanks to all for the help. What a relief!!!!!!!!!!!!!!

07-21-2002, 01:28 AM	#1
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	1405 Edelbrock Questions What kind of vacuum should I be running at idle on the timed vacuum port and the manifold vacuum port? __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

07-21-2002, 01:43 AM	#2
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	that depends on a lot of things..mainly your cam profile and timing..alot of other things will effect vacuum...head gasket...valves...the 1405 is ste up from the factory a little rich, richer than the 1406..my small block has a bout 12 inches of vacuum at idle..if your having problem with hesitation or bogging the problem probably lies in the springs...if you go to www.edelbrock.com it may help...also they have a help line thats real good __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

07-21-2002, 01:56 AM	#3
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	Is it normal for both ports to read close to the same amount of vacuum? Timed port reads 6in and the manifold reads 8in. __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

07-21-2002, 02:13 AM	#5
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	Both ports act like manifold vacuum. Tried timing it, disconnected the vacuum advance and plugged and set the timing but when I connected the timing advanced. Could it have been crap from the fuel tank getting inside the carb or caused by the many intake backfires I have had? I don't know what to do. I might pull off the carb and check it out and if nothings wrong I will check out edelbrock's web site. __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

07-21-2002, 02:42 AM	#6
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	how about a little more background on the motor and build. Did this backfiring thing just start ? what sort of cam? New build or is it a new problem with an old motor? Whats up? __________________ No truck :-(

07-21-2002, 02:00 AM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	At an idle, your timed vac should be about 0

07-21-2002, 01:21 PM	#7
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	It has just been rebuilt, it has a 216 degree duration. The intake backfires were caused by me not having the timing advanced enough __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

07-21-2002, 01:40 PM	#8
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	216 isnt much for duration and you should have more like 16-18 inches of vacuum at idle if not more. Are you sure you are using the right balancer/timing mark combination? I know two guys who arent and they swore they were until we figured out the problem. How much initial advance are you running? How much total? How far out are your mixture screws? Dont be afraid to go into a LOT of detail about your engine build, timing procedures, cam setup etc. __________________ No truck :-(

07-21-2002, 05:46 PM	#9
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	I am using the same balancer. From my experience the timing sounds like it is almost right on. It starts right up without a problem. With the distrubutor advance line plugged I had set it at 14 degrees advanced. When I plugged in the advance it jumped up to about 17 or 18 even at idle on both the timed and manifold vacuum ports. The mixture screws were turned five turns, it does diesel when I shut it off. However when we lean the idle mixture screws it will either intake backfire or it won't start. We put my carburetor on my brothers truck and it worked fine so I know it is not that. I think that there is a vacuum leak on the intake manifold. I might try and change the gaskets since it is easy to get to and I have enough time. Even with the carburetor as rich as it is if I give it full throttle from idle it will intake backfire. __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

07-21-2002, 06:47 PM	#10
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Are you using an EGR valve? Sounds like you have a horrendous vacuum leak somewhere. What manifold are you using. Might want to check the manifold for cracks. That still wouldnt explain the timed to port vacuum thing though. That just shouldnt happen although with your really low idle vacuum something is wacky. I'd yank that manifold off and inspect it carefully even under the heat shield if its OEM. __________________ No truck :-(

07-21-2002, 07:08 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	It sounds to me like the primarys are open a little at idle...can't explain why, but that's what it sounds like.

07-21-2002, 07:13 PM	#12
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	andy might be on to some thing...disconect your throttle cable and see what happens...i think you have a vacuum leak also...my mixture screws are about 2 1/2 turns out....are you running a spacer? __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

07-22-2002, 01:21 AM	#13
chevy55 Registered User Join Date: Nov 2001 Location: Mesa, AZ Posts: 105	When we put the carburetor on my brothers truck he had the screws about 2 turn out. I went ahead and changed the manifold gaskets, it is a new weiand excelerator without a spacer, threw the carb back on it with the same settings at about 2 turns out and it fired up. Now I have good throttle response considering the fact that it the timing I am sure is off and the rocker arms aren't adjusted right, that is a job for tomorrow. Changing the manifold gaskets did the trick. Thanks to all for the help. What a relief!!!!!!!!!!!!!! __________________ 1955 Chevy Shortbed Stepside 2nd Series. http://community.webshots.com/user/chevy55truck

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