Tuning an Edelbrock carb

[Mike Van Veghten]

Barn -

Good question.

The shortcommings are the lack of proper fuel flow at booster ventury caused by the relitivly low air pressure drop while going thru the ventury.
Just comes down to a lower than ideal vacuum signal at the boosters. Then if you have a spacer under the carburetor...that makes things worse...again, more lower booster signal.

Can it be "compensated" for, not really (blower!)....can it be "masked"...yes.
By - larger jets..or smaller needles (Edelbrock)....or stiffer springs (Edelbrock)..or richer idle adjustment..or higher fuel pressure..or higher float adjustments.
A manual transmission will also somewhat mask the lack of proper carb. function.
Overall..the fuel economy suffers, drivability suffers.

If you've got the R2+ cam, a good flowing intake manifold, big valves AND good porting to go with the big valves(!), higher compression and 3.55 (or lower) rear axle gears...then, you can make "good" use of a larger carb.

Otherwise...not the best you could do.

Mike

[bige]

If you are dumping raw fuel it is possible to dilute the oil or even wash it away; that would be the only "damage" I can think of if you continue to drive with the problem you're having.

ErnieR

[52-fan]

Wow, lots of comments after I last checked my post last night! I will not get to tackle the carb for a few days so we won't know how this turns out for a while. As far as the carb size, I just remembered that my 340 Cuda had a 750 Thermoquad on it and ran fine. Of course, again we're dealing with higher compression, bigger valves and cam, and small secondaries for normal cruising.
I just finished talking to the most experienced mechanic here at work and he thinks the fuel pressure may well be the culprit. This guy is a real mechanic and has drag raced with AFBs and other carbs. He even offered to help tune this carb if we can't get it right so I am feeling pretty good about this project.

1952 Champion Starlight, 1962 Daytona. Searcy,Arkansas

[Dick Steinkamp]

quote:Originally posted by bige

Too big a carb is not causing the problems the poster is describing and it would be ashamed for him to spend another $300 to fix something that can be done with some diagnostic time on the present configuration.

I would agree, Ernie...but I don't believe even with a lot of time (and some money) tuning a 650 CFM carb on a mild 289 Stude that it will ever run as good as a properly set up 500 CFM on the same motor. My guess is there will still be some noticeable driveability issues after setting the 650 up as well as can be done...certainly not to the extent that is being experienced now, however. In the end, it may be worth investing the time to set up the 650 and putting up with a few remaining issues rather than spending the money for a smaller carb.

[bige]

My guess is there will still be some noticeable driveability issues after setting the 650 up as well as can be done


[/quote]

From experience with two low performance applications, a 307 Chevy and a 318 Duster the 600 ( no 650 Edelbrock ) will perform with no driveability problems at all when it is set up properly. The Chevy is gone but the Duster is a project still waiting in the wings. Right now it even has a 1 inch spacer on it to adapt the E Carb to the spread bore Thermoquad manifold that's currently on the car. It runs very well and is very responsive. The engine is a bone stock, small valve 318 with single 1 7/8" exhaust.

In both applications the secondaries needed to be leaned out, considerably. The primary jetting was left alone but a fatter rod was used on the Duster and the Chevy got dropped to a .095 jet in the front. I also changed the springs to the next highest tension for better throttle response while in cruise mode.

Also, in the poster's case we don't know which 600 carb he has. The 1406 is jetted leaner out of the box than the 1405 with .098 jets as opposed to .100.

Hopefully, there will a post after the problem is solved.


ErnieR

[Dick Steinkamp]

quote:Originally posted by bige
( no 650 Edelbrock )

Edelbrock lists one here...

http://www.edelbrock.com/automotive_new/mc/carbs_acc/thunder.shtml

Here's their application guidelines...

http://www.edelbrock.com/automotive_new/mc/carbs_acc/carb_app_chart.shtml

They do recommend a 650 CFM for engines as small as 283 CID, but "off road, high performance".

[Mike Van Veghten]

I've had a heavilly modified Holley, 650 double pumper on a 262 cu.in. street engine that worked out very well also.
But...what I had was NOT this combination of parts!! My daily driver 259 inch Stude has had a two barrel, a 500 cfm, a 600 cfm and a 650 cfm carburetor on it.
It has a 500 cfm Edelbrock on it. Why...it works the best on all accounts...not just some accounts.

Mike

[bige]

Dick,

I should have qualified my no 600 statement a little. The Thunder series are relatively new and I just assumed that a fairly common Performer series would be a $50 carb obtained on a swap. I could be wrong but I would be surprised if it was a Thunder series with an adjustable air valve. If it is I will gladly swap him the 500 I have on the shelf in the garage (G).

Mike,

I don't disagree with you...but to make someone think that their car will not run satisfactorily with a properly set up 600 is just not true. For some people 90% of perfect works when the costs are low. And when 90% feels like 100% perception becomes reality. In fact isn't that what the factory did in the first place with the 2 barrel on your 259? They put together a combination that worked well enough in most situations and kept the cost down. I'm just proposing the same thing to a person who got a bargain on a carb and is looking to make it work well enough to enjoy his car.

So, yes the 500 is the best, but I would be willing to bet if I had that car in my driveway for a couple of hours and set it up the customer would be thinking of other ways to spend $350+ dollars rather than for a carb.(G)

ErnieR

[Flat Ernie]

I tend to agree that a larger carb can be tuned reasonably well. Mike's correct in that it reduces the pressure drop and states that a spacer makes it worse - I would put it to you that only an open spacer makes it worse, a 4-hole spacer will actually help increase the signal strength to the venturi. I've managed to tune a few "too big" carbs using "flow management" devices like stubstacks & 4-hole spacers.

500 would likely be better, but the 600/650 should be made to work reasonably well.

Daddy always said, if yer gonna be dumb, you gotta be tough & I'm one tough sumbitch!

[Flashback]

I guess the bottom line with me is: Why should you have to "tune" a carb. on a stock engine, when you can simply bolt on a carb. designed for it? It's kind of like buying a pair of shoes too big and then asking how much paper are you going to have to stuff in the toe to make them fit. Is it the looks? I know you can find a carb. for a lot less than I have heard quoted. Have you eliminated the fuel pump pressure being a problem?

Tex in Alabama
53 C Coupe

Tex E. Grier

[bige]

quote:Originally posted by Flashback

I guess the bottom line with me is: Why should you have to "tune" a carb. on a stock engine, when you can simply bolt on a carb. designed for it? It's kind of like buying a pair of shoes too big and then asking how much paper are you going to have to stuff in the toe to make them fit. Is it the looks? I know you can find a carb. for a lot less than I have heard quoted. Have you eliminated the fuel pump pressure being a problem?

Tex in Alabama
53 C Coupe



Tex E. Grier

What's the big idea throwing logic into this conversation?

[Flashback]

I'm sorry, I forgot myself for a moment. Old age you know. I always liked to stick a 650 Holley on a stock 265 or 283, all the while taking off a good working carb. BUT, it looked good, ha-ha!!! LIKE THAT CAR of yours.

Tex in Alabama
53 C coupe

Tex E. Grier

[barnlark]

Ernie,
I don't have you to tune this carb for me, but it sounds like it would be a good idea... I DO have a four hole 1" spacer on it and after my friends went through it and changed some springs, etc. it really feels very responsive and after my new fuel pump it feels better than ever. I haven't checked fuel useage yet since it's on the fiirst full tank, but this all started for me when I had an original WCFB and left it at a well known and respected vendor to be rebuilt. He lost it and never found it, or at least never told me if he did. Never got reimbursed either. I got a great deal on this 600 Competition and will use it for the summer until I find a 500 when I can afford it, if that is the best carb in the long run for my stock early '62 289 engine. If it strands me on the way to Lancaster, I'll allow all to remind me "I told you so"...

quote:Originally posted by bige

Dick,

I should have qualified my no 600 statement a little. The Thunder series are relatively new and I just assumed that a fairly common Performer series would be a $50 carb obtained on a swap. I could be wrong but I would be surprised if it was a Thunder series with an adjustable air valve. If it is I will gladly swap him the 500 I have on the shelf in the garage (G).

Mike,

I don't disagree with you...but to make someone think that their car will not run satisfactorily with a properly set up 600 is just not true. For some people 90% of perfect works when the costs are low. And when 90% feels like 100% perception becomes reality. In fact isn't that what the factory did in the first place with the 2 barrel on your 259? They put together a combination that worked well enough in most situations and kept the cost down. I'm just proposing the same thing to a person who got a bargain on a carb and is looking to make it work well enough to enjoy his car.

So, yes the 500 is the best, but I would be willing to bet if I had that car in my driveway for a couple of hours and set it up the customer would be thinking of other ways to spend $350+ dollars rather than for a carb.(G)

ErnieR

[Allan Songer]

I've got to choose a carb for my warmed over R1 in the next few weeks and I've really become enamoured of the Barry Grant Demon carbs. They're pretty much Holley 4150/60 clones but REFINED and really REALLY nicely made. Anyone here have any experience with them? They make both a 525 and a 575 and I was thinking either one would suit my purposes pretty well. They run about $75-$100 more than the Edelbrock but in terms of quality I think they're probably worth every penny.

[bkz81]

The few Demons that I have seen run were junk. Edlebrock were still far superior.