Need Carb tuning 101 class

68conv4sp · May 27, 2008

My 302 w/ Edel 170cc heads and a mild cam (.469/.469 lift) has an Edel 500 cfm Performer. It runs very strong from idle to 5000 rpm. The only issue that I would like to fix is that it bogs when I suddenly floor it. Any gradual throttle increase is fine. I have never touched a carb before...

10secgoal · May 27, 2008

Buy a Holley.
Your pump shot is off, or your secondaries are opening too fast. Either on an Edelbrock has very limited tuning capabilities.

67coupestang · May 29, 2008

??? im not an expert but the edel's are adjustable. the accel shot is limited there are only 3 holes of adjustment... the secondaries, you have to change out the springs on either side of the air inlet. they dont control how fast the secondary plate opens, thats done on vacuum alone, but they control how fast fuel gets shot in to the secondaries. then you can change the needles/jets for more/less flow try this: http://www.carcraft.com/techarticles/carb_tuning/index.html

68conv4sp · May 29, 2008

Thanks, Coupestang. The pictures complement the written article I have on this subject. I am going to lengthen the pump shot (from middle hole to top hole) and see if that helps the momentary bog that happens when I floor it. Will report results tomorrow.

Shamus O'toole · May 29, 2008

The Edelbrock is a good cruiser carbs. If you looking for performance go with a Holley stlye carb.

wild70stang · May 29, 2008

You might want to check your choke. I have a 500 cfm AFB and while the choke opens up and if I try to rev the motor it bogs, but once its fully open it doesn't hesitate.

Fast63 · May 29, 2008

10secgoal said:
Buy a Holley.
Your pump shot is off, or your secondaries are opening too fast. Either on an Edelbrock has very limited tuning capabilities.

Well, an edelbrock is a mechanical secondary carb, so of course the secondaries are open the instant to mash on the throttle. It does have an air valve (which does not completely cut off air to the secondaries) that has very limited tuning capabilities. However, no engine should require that air valve to be tuned at all.

But about the pump shot, I assume you mean it has limited tuning capabilities because there are only 3 holes in the pump shot arm to tune with? Yes, that is true, however you can bend the rod attached to it any way you want to in order to adjust it. Yes, it is kind of hokey, but it does open up tuning capabilities.

I also completely disagree with O'toole that holley is better for performance. I have not found that to be the case on my street machines.

Keep rocking with the edelbrock, put the pump shot arm to the hole closest to the carb, and see how that works out. No one can argue that the edelbrock will get you better gas mileage

68conv4sp · May 31, 2008

Well, the change on the pump shot stroke did not solve the momentary flat spot after sudden acceleration.

zookeeper · May 31, 2008

I hate to say it, but the Edebrock carbs just aren't all that tuneable. I watched one hardcore Edelbrock carb owner try for weeks to get the bog out of his street/strip car at the drags. He refused to notice that every other car at the drags had a Holley and that there may be a reason for the overwhelming majority. Try as he might, it never got better, the car never got quicker until he finally borrowed a box-stock Holley and oddly enough, cured the bog. If I were you, I'd call Edelbrock and see what they recommend, or save for a Holley.

Fast63 · Jun 1, 2008

zookeeper said:
I hate to say it, but the Edebrock carbs just aren't all that tuneable. I watched one hardcore Edelbrock carb owner try for weeks to get the bog out of his street/strip car at the drags. He refused to notice that every other car at the drags had a Holley and that there may be a reason for the overwhelming majority. Try as he might, it never got better, the car never got quicker until he finally borrowed a box-stock Holley and oddly enough, cured the bog. If I were you, I'd call Edelbrock and see what they recommend, or save for a Holley.

How much horsepower was he running is my question. They are limited to being able to handle a certain amount of horsepower, that limit I don't know, but I would venture a guess to say that 800hp is out of the question with an edelbrock carb.

But once again, you are wrong that edelbrocks are not that tunable. Is he even aware of different size pump shot nozzles and tuning beyond the 3 holes on the pump shot arm?

The only tuning that a holley has for advantage over an edlebrock is with a double pumper and having that extra shot into the secondaries. Other than that, there is no difference in their tuning ability.

zookeeper · Jun 1, 2008

Sorry, didn't mean to cause a total meltdown. But if Edelbrocks were THAT good, they'd still be called Carter's and everyone would use them in drag racing, circle track and on the street. As it is, you'd be hard-pressed to find even one fast Edelbrock-carbed car anywhere. It's like the Loch Ness monster, everyone thinks it exists, but nobody's actually seen one.

Fast63 · Jun 1, 2008

zookeeper said:
Sorry, didn't mean to cause a total meltdown.

LOL!! What does that mean?

What do you mean if edelbrocks were that good, they would still be called carters? Edelbrock bought carter's design, why would they still call it carter? That is just bad business.

Anyway, who knows why people don't use edelbrocks in racing? I think they are stupid for not doing so. But many classes are limited to using the same carburetor or type/size, and I don't know why edelbrocks aren't allowed, I would like to know that myself. Personally, I run better times at the track with the edelbrock every time.

Next time (if ever) you go to a very large car show, like Hot August Nights for example, take a gander at all the guys running superchargers. 9 out of 10 on average are running an edelbrock according to my count, and about 7 out of 10 N/A cars were running edelbrocks as well.

68conv4sp · Jun 1, 2008

Easy guys. So, back to the issue at hand - I'm willing to buy a new Holley or Edel (about 10 years old w/ a little shaft play). Its about $360 for a 0-80570 570cfm w/ vac secondaries and electric choke. Do you think I'd need to adjust it from its factory settings? I have a 9.5:1 302 w/ Edel Alum heads (170 cc runner, 1.6 & 1.9 valves), and I never wind it above 5000 rpm.

zookeeper · Jun 1, 2008

68conv4sp said:
Easy guys. So, back to the issue at hand - I'm willing to buy a new Holley or Edel (about 10 years old w/ a little shaft play). Its about $360 for a 0-80570 570cfm w/ vac secondaries and electric choke. Do you think I'd need to adjust it from its factory settings? I have a 9.5:1 302 w/ Edel Alum heads (170 cc runner, 1.6 & 1.9 valves), and I never wind it above 5000 rpm.

Quite honestly, no. Holley carbs are tyically a touch rich at idle, and while it's no fun to run in a closed garage, it makes the car much more driveable, and makes great throttle response. If it were my car, I'd lean towards an 1850, 600CFM Holley w/vac secondaries, but that's just because I've always had great luck with these carbs.

jikelly · Jun 1, 2008

Wow 104 tomorrow.

Um, the eldelbrck carbs are very tuneable and I especially like that you can take the carb apart to get to the jets without emptying the fuel bowls.

Ill dig up some old threads on carb tunning for you tomorrow.

68conv4sp · Jun 2, 2008

Zoo, are you currently using the 600cfm Holley and what are your motor specs? I'm in Northern CA as well - Monterey area.

jik, thanks for the carb tuning info.

biggyfan1 · Jun 2, 2008

Holley +6

S-Car-Go · Jun 2, 2008

The problem may be in the age of the carb, not the brand. 10+ years is a long time for a carb if it is untouched.

With the motor off and air cleaner off, are you getting a good pump shot? How is the rest of the tune? Timing? Plug color? All the Eddys I've had also want a little stiffer spring under the rods.

I like that 80570 if you are going to buy a new carb. It is a 1850 (just polished) vac secondary.

What transmission and gears?

jikelly · Jun 2, 2008

Take a look at the edelbrock tuning threads I bumped to the top. You can read through that stuff there and then let me know if you have any questions. I'm pretty good at screwing stuff up so I can tell you what not to do.

zookeeper · Jun 2, 2008

68conv4sp said:
Zoo, are you currently using the 600cfm Holley and what are your motor specs? I'm in Northern CA as well - Monterey area.

jik, thanks for the carb tuning info.

No, my car currently has a pair of 390cfm Holleys on an original Shelby intake. I've used Carter carbs (same as Edelbrock) in the past on a '65 I used to own, and while they were good carbs, I went back to Holley carbs on pretty much every car I've owned or worked on. Maybe that's my reason for being quick to recommend them, is that nearly 30 years of experience running one, two or three Holleys has proved to me how well they work and how easy they are to tune. I've never really had problems with Carters, but don't see them being as easy to tune, nor did I have much luck buying parts for the Carters I had. If you're just looking for good street performance, it's hard to go wrong with ANYTHING Edelbrock sells, they make and sell great parts, but if you're more oriented towards the hot rod end of the scale, (IMHO) Holley is the only game in town. Also, I'm a little farther north, I actually live near Eureka, Ca.

Need Carb tuning 101 class

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