Carburetors - Gary's Musings

[Gary Lewis]

The following discussion was originally in the New Member's section under Darth Vader, which is Bill/85lebaront2's truck.  Therein I said "In Bill's case his background means he's the most qualified person around on carbs.  But I'll still argue with him about Holleys and Carterbrocks.    As yet he's not risen to the bait, but Jim/fljab did, as show below....

[fljab]

Gary Lewis wrote

In Bill's case his background means he's the most qualified person around on carbs.  But I'll still argue with him about Holleys and Carterbrocks.  

I've always messed with Holleys, but am interested in going Carter or Edelbrock on Big Whitey eventually, so Bill's advice there would be great. I am no expert at all on carbs, but like many of us, have some shade tree messing around back in the day.  Other than rebuilding the Carter 1 bbl on the '81, I really haven't done that much with them for some time now as anything made in the last 30 yrs is pretty much all EFI, including my motorcycles.

[Gary Lewis]

I think the Holley's are best for max power, and Carters/Edelbrocks for daily driving - for two reasons. First, in my experience the Edelbrocks come out of the box jetted closer to how I want one. Rusty had a stock Holley 1460 on him when I got him, and the MPG was poor. So I installed an Edelbrock 1406 and not only got better MPG but better part-throttle acceleration. Later I installed an air/fuel ratio meter and found that the Holley was very rich, even though that it had stock jetting. But the Edelbrock's air/fuel ratio was very close to what the engine wanted and provided a much more "crisp" feeling. However, it gave away some power at WOT. Yes, I could probably have tuned the Holley's AFR to get it closer to what the engine needed, especially since Holley's have more things to tune, but why when the Eddy was essentially there out of the box?

The other reason is reliability. In my experience Holleys are prone to problems because they hold gas in with gaskets or fabric. In my youth the bowl gaskets were made of cork, and when the carbs ran dry the cork shrank and you had a leak. Today the better kits have gaskets that don't shrink, but you can still have problems if a ham-handed "mechanic" has over-tightened the bowl screws and warped the bowl or main body. In addition, there's the design flaw of no check valve in the vacuum passage to the power valve. Holley admitted it was a flaw by installing a check valve on newer carbs, and kits are available to fix it on older ones. But forums all over the place have people writing in who have blown power valves due to one backfire because many of the carbs out there have not had the check valve added.

To me the choice is simple - if I'm racing I'll use a Holley, but for my daily driver I'll use an Eddy. Or, the newer Street Demon, which is similar to a Carter or Rochester.

[fljab]

Gary Lewis wrote

To me the choice is simple - if I'm racing I'll use a Holley, but for my daily driver I'll use an Eddy. Or, the newer Street Demon, which is similar to a Carter or Rochester.

I was looking at the Street Demon carbs on the Summit site; they have 625 cfm versions similar to this one:

https://www.summitracing.com/parts/dem-1900/overview/

They look interesting, but again, I know little about it.  I'm still looking for a good used dual plane intake and having no luck locally, but for now I'll be happy to get the stock setup running better.

[Gary Lewis]

I have the 750 CFM version of that carb with the polymer bowl to keep the gas cool. But it is on Dad's engine and that is at Tim Meyer's shop, although it will be delivered on Sept 15th, so I don't have any experience with it yet.

However, Tim has dyno'd the engine extensively and says that the carb performed very well. In fact, it gave almost as much HP as a 780 CFM Holley.  But the small primaries that give such good part-throttle performance don't do as well on the top end as the larger ones on a Holley. And the huge secondary that makes up for the small primaries can't meter as precisely as the smaller individual secondaries of a Holley.  Again, if I'm going racing (boogity, boogity, boogity) I'll run a Holley.

[Gary Lewis]

Guys - Should this carb discussion be moved to a new thread out on the main page?  Maybe "Gary's Thoughts On Carbs" or somesuch?  Doesn't seem to belong here.

[fljab]

Gary Lewis wrote

Guys - Should this carb discussion be moved to a new thread out on the main page?  Maybe "Gary's Thoughts On Carbs" or somesuch?  Doesn't seem to belong here.

Sure, might be good to get it as a main topic.

[Gary Lewis]

Ok, does this work?  (Wow, that was easy!  I just created the new thread, got its permalink, and put that in the proper field in the Move dialog on your post.  And it moved not only that post but all that followed.  )

So, Jim, should I now delete my question to you, your response, this response to you, and your to-be response?  

[ArdWrknTrk]

This is the other Jim.

I just tore down a 650 cfm Edelbrock 'Thunder' AVS today.
Seems pretty simple, but all the linkages are a little fiddly.

I'm used to Holley's and use the blue gaskets so i don't have "fabric" or any of the leaks Gary alludes to.

I guess I can give a full report when my fuel line comes in next week.

I think Demon is OK,  having learned to put my issues with Barry Grant behind me.

[Gary Lewis]

Jim - I think you know, but the Street Demon is a completely different design than the other Demon carbs, which are similar to Holley's. But the Street is a Carter-style carb, designed by an ex-Carter engineer about 10 years ago. Kind of a cross between an AVS and a Thermoquad.

[ArdWrknTrk]

Yes, I do know.

Just making the point that I've finally gotten the bad taste out of my mouth from past association with the name.

Your carb has plastic bowls.
I guess that means no corrosion when this crap sold for fuel comes apart after sitting for a week or two in humid weather?

[Gary Lewis]

I hope that's the case.

[fljab]

You have the choice of getting aluminum or composite bowls:

https://www.summitracing.com/parts/dem-1901/overview/


https://www.summitracing.com/parts/dem-1900/overview/

[Gary Lewis]

Yes. I chose composite to keep the gas cooler. Today's gas easily percolates and the composite bowl helps by insulating the gas from the heat of the engine.

As said, the designer had been an engineer with Carter until it folded, and he borrowed the best stuff from their various carbs, and the polymer bowl came from the Thermoquad. The TQ was a good carb, but ham-handed mechanics wreaked havoc by over-tightening the screws and deforming the bowl.

[85lebaront2]

That's why I went to EFI, no percolation issues. Maybe our new president will do away with the damned ethanol in gas. It was done to help the grain farmers and all it did was drive up the cost of food and cause problems with fuel systems.

[Gary Lewis]

Yes, the ethanol is a big issue.  It is amazing what it does to the rubber lines in the old trucks.

[85lebaront2]

You should see what it does to small engine carburetors. We have a station that carries non-ethanol mid grade and that's what people here use for small engines, marine use and agricultural use (the ones that still have gas powered tractors).

[Gary Lewis]

We have several stations that carry straight gas in several grades, and that's what most people use for small engines. And all the marinas I've been to only carry straight gas.

I sure wish they'd change that law.

[Edward Michael]

Ordering a new carb and wondering how your 750cfm is working out.
Is this a significant performance and fuel increase over the 625cfm that was mentioned?

[Gary Lewis]

Edward - Is that to me?  My 750 CFM Eddy is working great.  No problems with it at all.

But that's on a non-stock 460.  What engine do you have?  (Hint: If you'd put that info in your signature we wouldn't have to ask.)  A 600 to 650 CFM carb is a better choice for a 351, if that's what you have.