Edelbrock carb question
Thread Starter
7th Gear
Joined: Nov 2001
Posts: 7
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From: Usingen
Edelbrock carb question
Hi everybody,
during the last year i used an Edelbrock 600cfm carb on a 350 engine with a Performer Intake, runs good, gas mileage is ok, it has a smooth idle but in the bottom end i miss somewhat of power. So i've got an Edelbrock 750cfm carb completely rebuilt and now the idle is a bit rough regardless of adjusting the idle screws lean or rich, but on the bottom end till nearly 3000 rpm this carb makes a lot more power than the 600cfm, above 3000 rpm it seems to be the same with both carbs.
So i would like to know if anyone of you have experience with a Edelbrock 750 carb how to get a smooth idle and maybe a little more power in the upper rpm's?
Thanks a lot.
Fried
during the last year i used an Edelbrock 600cfm carb on a 350 engine with a Performer Intake, runs good, gas mileage is ok, it has a smooth idle but in the bottom end i miss somewhat of power. So i've got an Edelbrock 750cfm carb completely rebuilt and now the idle is a bit rough regardless of adjusting the idle screws lean or rich, but on the bottom end till nearly 3000 rpm this carb makes a lot more power than the 600cfm, above 3000 rpm it seems to be the same with both carbs.
So i would like to know if anyone of you have experience with a Edelbrock 750 carb how to get a smooth idle and maybe a little more power in the upper rpm's?
Thanks a lot.
Fried
Le Mans Master
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From: Hoosier
Cruise-In III Veteran
Re: Edelbrock carb question (fhal01)
So you're saying the bottom end is better with the 750? Interesting.
I have the 600. Three things to look at.
1-Make sure that your throtle blades don't expose more than 040" of transistion slot. The rough idle may be too much gas, and that's why the adjustment screws aren't making much difference.
2- Your linkage is probably the original from the Q-Jet? Edelbrock carbs use more lever travel than Q-Jets. You'll need to shorten the cable cover to get more cable movement or buy and install a Lokkar brand cable.
3- Edelbrocks don't like more than 6 psi fuel pressure. The stock type pumps deliver 7 to 9 psi. I use a regulator on mine.
The reason you see the same power above 3000 rpm is the vacuum secondary. The carb is only delivering what the engine vacuum says it needs.
I have the 600. Three things to look at.
1-Make sure that your throtle blades don't expose more than 040" of transistion slot. The rough idle may be too much gas, and that's why the adjustment screws aren't making much difference.
2- Your linkage is probably the original from the Q-Jet? Edelbrock carbs use more lever travel than Q-Jets. You'll need to shorten the cable cover to get more cable movement or buy and install a Lokkar brand cable.
3- Edelbrocks don't like more than 6 psi fuel pressure. The stock type pumps deliver 7 to 9 psi. I use a regulator on mine.
The reason you see the same power above 3000 rpm is the vacuum secondary. The carb is only delivering what the engine vacuum says it needs.
Instructor
Joined: Jul 2002
Posts: 132
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From: Virginia Beach Va.
Re: Edelbrock carb question (fhal01)
For what its worth, check your float adjustments, Edelbrocks carbs for some reason don't have the floats right. Are you using ported or manifold vacuum? Try swapping it out and see if it makes any differance. :flag
Thread Starter
7th Gear
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From: Usingen
Re: Edelbrock carb question (biltogo)
Thanks for quick response.
Yes, it's no joke the 750 gives more power from idle to nearly 3000 rpm, i've checked it changing the carbs (which takes only a few minutes) and drive a few miles with both of them.
The cable is already modified to get the full lever travel. The floating needles and seats are new and working fine, i've also adjusted the floats exactly like it's described in the user manual.
What i don't know is the fuel pressure delivered from the pump, i will check this as soon as possible.
Thanks.
Yes, it's no joke the 750 gives more power from idle to nearly 3000 rpm, i've checked it changing the carbs (which takes only a few minutes) and drive a few miles with both of them.
The cable is already modified to get the full lever travel. The floating needles and seats are new and working fine, i've also adjusted the floats exactly like it's described in the user manual.
What i don't know is the fuel pressure delivered from the pump, i will check this as soon as possible.
Thanks.
Le Mans Master
Joined: Mar 1999
Posts: 6,744
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From: delmont pa
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Cruise-In II Veteran
Re: Edelbrock carb question (fhal01)
go to http://www.edelbrock.com/automotive/eps_intro.html :chevy
Thread Starter
7th Gear
Joined: Nov 2001
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From: Usingen
Re: Edelbrock carb question (Tominator)
The engine is completely stock, just the intake is an Edelbrock Performer which has been pocket ported to match gasket and head ports, timing is at 28 degrees at 2400 rpm.
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Drifting
Joined: Jun 2001
Posts: 1,809
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Re: Edelbrock carb question (fhal01)
Trying to think through this one, so above 3000 RPM it really drops off. Please explain in more detail, does it seem like above 3000 does it spudder or seem to be running lean.
Once you hit above 4000 does it seem like not much is happening?
I'm just trying to determine if your sec. are not opening or if you need more jetting in the secondaries.
See the Edelbrocks are famous for not giving much in the higher RPMs, but with bigger jets in the secondaries they can rev really well.
Once you hit above 4000 does it seem like not much is happening?
I'm just trying to determine if your sec. are not opening or if you need more jetting in the secondaries.
See the Edelbrocks are famous for not giving much in the higher RPMs, but with bigger jets in the secondaries they can rev really well.
Thread Starter
7th Gear
Joined: Nov 2001
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From: Usingen
Re: Edelbrock carb question (Tominator)
The behavior is like that:
cruising with about 2600 rpm, then push the pedal down it goes quite good up to 3600 rpm, then it takes a long long time to reach 4800 - 5000 rpm, but without any pinging or spuddering.
Is there any way to check if the secondaries open or not?
cruising with about 2600 rpm, then push the pedal down it goes quite good up to 3600 rpm, then it takes a long long time to reach 4800 - 5000 rpm, but without any pinging or spuddering.
Is there any way to check if the secondaries open or not?
Drifting
Joined: Jun 2001
Posts: 1,809
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Re: Edelbrock carb question (fhal01)
The first thing I would check is the fuel filter to make sure it is not partial clogged.
To check if the sec. are opening do a search of the topics, someone had mentioned a very easy method one time but can't remember it exactlly. Think it had something to do with putting a paper clip by the sec. and then test drove it and then checked to see if it moved. [but be sure to tie it to something so it doesn't fall into the engine] Your problems sounds more like too small of jets though.
If it's not the sec. then you will need to rejet the sec. not a big job at all. Buy a tuning kit [can't think of the name] from a parts store for your 750 and then increase the secondaries size, go up a couple of sizes.
This should make it rev higher, then keep increasing the size till it revs where you want it too.
Once thats out of the way you can start working on the idle, with the other parts that come with the kit.
[Modified by Tominator, 1:19 PM 4/8/2003]
To check if the sec. are opening do a search of the topics, someone had mentioned a very easy method one time but can't remember it exactlly. Think it had something to do with putting a paper clip by the sec. and then test drove it and then checked to see if it moved. [but be sure to tie it to something so it doesn't fall into the engine] Your problems sounds more like too small of jets though.
If it's not the sec. then you will need to rejet the sec. not a big job at all. Buy a tuning kit [can't think of the name] from a parts store for your 750 and then increase the secondaries size, go up a couple of sizes.
This should make it rev higher, then keep increasing the size till it revs where you want it too.
Once thats out of the way you can start working on the idle, with the other parts that come with the kit.
[Modified by Tominator, 1:19 PM 4/8/2003]
Melting Slicks
Joined: Aug 1999
Posts: 3,123
Likes: 13
From: Hollywood, Florida
Re: Edelbrock carb question (fhal01)
Very good thread with alot of good, helpful info!!
My Edelbrock 1405 (600CFM) also runs STRONG till about 3500-3800, then seems a bit flat.
A Performer intake and 268H Comp cam (single profile) are the only engine mods.
I'll try rejetting the secondaries a couple steps up.
I changed the primary metering rods and springs which made a world of difference, now I'll work on the "back side" :p:
[Modified by shoptek, 5:25 PM 4/8/2003]
My Edelbrock 1405 (600CFM) also runs STRONG till about 3500-3800, then seems a bit flat.
A Performer intake and 268H Comp cam (single profile) are the only engine mods.
I'll try rejetting the secondaries a couple steps up.
I changed the primary metering rods and springs which made a world of difference, now I'll work on the "back side" :p:
[Modified by shoptek, 5:25 PM 4/8/2003]
Le Mans Master
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From: Hoosier
Cruise-In III Veteran
Re: Edelbrock carb question (shoptek)
You can check if the scondary circuit opens by
1-using a pencil, depress the weighted vacuum door. If it moves and returns feeely it will when you're driving.
2-pull the throtle lever full back, the secindary blades should start to open about midway and be fully vertical all the way back.
If you're using a stock cam, I think what you see above 3500 rpm is normal. But changing the secondary jetting to experiment can't hurt anything.
1-using a pencil, depress the weighted vacuum door. If it moves and returns feeely it will when you're driving.
2-pull the throtle lever full back, the secindary blades should start to open about midway and be fully vertical all the way back.
If you're using a stock cam, I think what you see above 3500 rpm is normal. But changing the secondary jetting to experiment can't hurt anything.
Thread Starter
7th Gear
Joined: Nov 2001
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From: Usingen
Re: Edelbrock carb question (biltogo)
Now i've news about the rough idle with the 750, today i started playing around with the idle mixture screws and the air screw according to the Edelbrock owners manual. Finally i got a smooth idle with 2 3/4 turns on the mixture screws and then adjusted the air to 750 rpm. With the 600 carb the mixture screws need only 1 1/2 turns to get the correct idle, so now i can say the 750 was too lean as the reason for the rough idle.
Now i will order some larger jets to check the secondaries, hope they're comming soon (sometimes it's a bit hard to get those parts here in Germany)....
Now i will order some larger jets to check the secondaries, hope they're comming soon (sometimes it's a bit hard to get those parts here in Germany)....
