Edelbrock 750cfm Carburator secondaries won't open

[The_Handier_Man1]

From: west coast redneck  (Original Message)
Sent: 6/18/2005 8:46 PM

I have a possible problem with my 750 edelbrock carb.Electrick choke.It's 2 years old.I was so happy when I replace the old Carter carb.It started great & ran great But it seemed that i didn't have as much power as before but I just overlooked that until yesterday.I was running it with the air cleaner off . It seemed nomatter how much I floored it I didn't see the larger barrels open up.It's looking like I've been running on 2 barrels since I bought it.With the engine offI can open thethrottle full & the other barrel can open freely.When I open the larger barrels with the engine off No gas comes through the jets .Is this normal.?Any lelp or suggerstion from you carb people would be great.



From: HeavyHaulTrucker
Sent: 6/18/2005 9:35 PM

Redneck, first I am going to refer you back to a previous discussion from when nvdesertrat0775 was having trouble with his Edelbrock -- 40 mph uphill?? -- specifically, check out from Message #26 down.

The cure to that particular problem was that he needed to install the proper Edelbrock linkage adapters.  This may sound like a silly question, but did you also install the Dodge throttle adapter and re-adjust the transmission throttle linkage?  This is something that you might want to look into, since if the linkage is all the way to the rear and the secondaries do kick in then you should both hear and feel the engine roar and begin to pull the hills harder.

Just a guess, but this seems to have become a common error that we make when installing the Edelbrock carbs.  But in answer to your original question, while it is common to not see any fuel flow in the secondaries when the engine is off, the secondaries should open up at about 3/4 throttle with the engine running.  You might want to check the choke adjustment -- it is adjustable, and that may have something to do with your problem.  But I just have a feeling that you also failed to use the proper adapters in the linkage.

John



From: Liv42dayOK
Sent: 6/19/2005 8:56 AM

Can the secondaries be checked for proper operation while the vehicle is in park, or must it done while driving?

- CuriousSob



From: west coast redneck
Sent: 6/19/2005 12:32 PM

Hi I'm hopefully going out today with a buddy to verify what  I think I'm seeing when I'm driving.Can't really do it when it's in park without really revving it out.I've briefly floored it in park & no response of the secondaries.When the engine is off I can put the throttle down & open the secondaries.When I do that no gas comes out the secondary jets.? Are they supposed to.?



From: west coast redneck
Sent: 6/19/2005 12:50 PM

Hi again HHT.I tried going to the Up hill site.They only showed the last 16 of the 100 or so. Couldn't figger out how to get back to number 26.When I push previous it goes back to to previous discussion being a different toppic. I know it's probably some thing very easy.



From: west coast redneck
Sent: 6/19/2005 1:08 PM

Desregard the last statement. I figured it out.Thanks



From: denison
Sent: 6/20/2005 11:42 AM

With most 4 barrel carbs there isnt any "throttle" pump for the secondaries to squirt fuel in as the throttle is being opened. The Holleys that do have such a throttle pump for the secondaries are called "double-pumpers", and they Always have mechanical linkage to open the secondaries.
I Think the general rule is, if the secondaries are opened by vacuum, there will not be a throttle pump.
If the secondaries are opened by a mechanical linkage, there might be a throttle pump for them too.
Some 4 barrel carbs have had a vacuum operated valve to keep the secondaries from opening when the vacuum in the intake is too low - so they wont open when the engine is turning too slowly. BMW did this on their 3.5 liter V8s in the 50s.
I dont know about Edelbrocks.



From: west coast redneck
Sent: 6/20/2005 8:47 PM

Thanks Denison..That makes allot of sense. I had the carb installed by our local shop so I've left it there for him to take a look. So maybe it's possible that if it only opens up on revs or  I haven't revved it up enough.? The Vacuum gauge sits around 3 or 4 & when I accelerate it goes to 15 or 20 .Is this normal.?I also noticed that they disconnected one of the hoses that goes to a container & eventually back into the fuel system.The front left Vacuum port of the carb was capped.??Hope this gets figured out .Going camping & fishing for Halibut way out in the open  outside of port Renfrew, Vancouver Island after work Fri..Curious,has there ever been a Vancouver Island Jam.Lot of cool camping up here & I don't mean the temp.



From: denison
Sent: 6/21/2005 11:46 AM

If that edelbrock has vacuum operated secondaries, there would be a vacuum diaphram on the side of the carb that was about 2 inches in diameter I think. In such a set-up the primary butterly would have to be open far enough to "un-latch" the secondary butterfly mechanism. So its not the engine rpm that is involved per se, but the vacuum difference between the bottom and the top of the carburetor.
I would presume that even with the engine shut off, if the secondaries are mechanically operated on that carburetor, they would open when you rotated the primary throttle shaft all the way open. Its possible there would be a vacuum diaphram to prevent this from happening with the engine stopped, but like I say, I dont know Edelbrocks.
With the 2 or 3 vehicles I have driven that had 4 barrel carbs and vacuum gauges (installed by me) - the impression I got was that vacuum operated secondaries opened about the time the vacuum gauge had dropped to zero. Not that vacuum gauges are very accurate, especially for comparing one engine to another.
The only time I have been able to see secondaries open, was while driving along with the engine cover and air cleaner removed, getting up above 35 mph, and putting the gas pedal to the floor. I had a flashlight rigged to shine down into the secondary throats, and was able to lean over and glance down and see that they had really opened. I wasnt able to see whether fuel was squirting in though, as I still had to steer the motorhome, but my helper said the fuel below the venturis looked like a garden hose was turned on down there. Also, you should only look down after the throats have opened, and from as far above the carb as you can get, and wear goggles - to avoid getting eye damage from a backfire.
With the air cleaner off, even if the engine cover is on, I imagine you would be able to tell a difference in "tone" between the primary inlet hiss, and the secondary inlet howl.



From: SmallDiscoveries1
Sent: 6/21/2005 1:35 PM

I had this old corvette that would scream at high RPMs. Oddly enough, it had very little midrange and would even bog down. Any guess as to why? I don't know the technical terms, but when the carb would not kick in the remaining 2 barrels, I gave it a little mechanical help. I put a small bolt and nut in the arm that the lingage pulls down that was to open up all 4 barrels. The bolt was put about 1/2 down where the linkage slides and would catch at about 1/2 throttle. Being a 4 speed, it worked out quite well until the intake was changed. It did fine at low rpms, bogged in the middle and screamed at high rpms.

For some reason, the wheels liked to spin when I released the clutch. Smile.



From: west coast redneck
Sent: 6/21/2005 8:35 PM

Boy I can see my gas mileage going down  .It sure howls now.I guess it was a combination of 2 things. One was with the change of carbs the foot pedal  fully down didn't actually put it  all the way down .Made the bolt shorter.The other has something to do with the throttle arm needing to be higher or lower.When I dropped the rig off I put the trucker guys email with my note. He said that was a great help.So to everyone thanks again. Now to Halibut  & beer.!!



From: OldEdBrady
Sent: 6/21/2005 9:07 PM

Going fishing, Hunh?  Well, if you ever forget your license (or don't have one), keep this in mind:

A guy went fishing.  A game warden came up to him and said, "Doing a little fishing, hunh?"

The guy didn't have a license, so he replied, "Nope. just drowning some worms."



From: west coast redneck
Sent: 6/21/2005 10:05 PM

Good one. I'll have to change that to baby octopus though.!!!!



From: west coast redneck
Sent: 7/2/2005 3:19 PM

Thanks for all the help. I'm on all 4 barrels now.Great to have the power back again.Put a large K& N air filter on just because.Had a great fishing trip. In all 6 Halibut,6 grey cod, & 1 ling cod.



From: Liv42dayOK
Sent: 7/2/2005 4:12 PM

Glad to hear you have your power back!  Question:  What was the cause and the cure?

- Sob



From: west coast redneck
Sent: 7/3/2005 8:08 PM

Eh Sob.The cause was basically the mechanic not following through on the installation the first time. It was a combination on the throttle adjustment by the carb & the foot pedal wasn't going all the way down. Had to shoten a bolt.Somehow out of this I still had to pay an hr labour though.



From: mightybooboo
Sent: 7/3/2005 11:21 PM

An honest garage should have fixed it on their dime,not yours,if they did a poor install.My guy backs up  his work,I think all  mechanics should,but maybe I just dont understand what mechanics go thru?

BooBoo



From: denison
Sent: 7/4/2005 10:26 AM

A lot depends on the service manager or ownership, even the economy and the business neighborhood. You have to be compete to survive, and if the garage on the next block is skimping on work, overcharging, etc.; then you can be really upright and maybe go broke, or you can conform to the norm. I have a friend who was a service manager in various facilities. He had to deal with dealership owners who were close to bankruptcy, (or a nasty divorce) and made it clear the service department was going to save all of their jobs or else. That would be when he would make the grand gesture and quit! He could afford to do that, having inherited plenty of oil company stock from his family. Most people cannot.
We had a family friend who was an honest and skilled mechanic, and I could recommend him to people asking me for an honest mech. I would also tell them to go to the service manager of the service station and give positive feedback, if they wanted him to be able to afford to stay honest. His hourly pay did not include any vacation time, nor health insurance, nor sick leave or retirement benefits, being for a gas station. He got his hourly pay - period.



From: MacD22C
Sent: 9/15/2005 5:55 PM

Hi,
  I would call the carb techs at Edelbrock, they should know.
John



From: MacD22C
Sent: 9/15/2005 5:59 PM

Here is the number, they helped me, then I got my 1411, 750 CFM from Jegs ($281 +adapter kit).
Edelbrock Tech Line Only: 800-416-8628

John