Carb Question?

« **on:** June 18, 2011, 01:47:33 PM »

Im running an Indmar 454 with a 750cfm edelbrock carb with mechanical secondaries. I have a holley 750cfm with vacum secondaries. Want opions on the use of the 2 carbs. mechanical secondaries vs vacum. Which gives the better performance.

« **Reply #1 on:** June 18, 2011, 03:12:16 PM »

Quote from: Hddaddy on June 18, 2011, 01:47:33 PM

Im running an Indmar 454 with a 750cfm edelbrock carb with mechanical secondaries. I have a holley 750cfm with vacum secondaries. Want opions on the use of the 2 carbs. mechanical secondaries vs vacum. Which gives the better performance.

Two ways to look at this.

The first is, the vacuum secondaries will have a hard time getting to WOT on a jet because of the incredible load on the engine at WOT.

The second is, lower vacuum levels can be achieved with the mechanical secondaries and proper tuning becomes mega important.

At the end of the day, if you run it hard, the mechanical secondaries will out run the Vac/sec....On the other hand, the vac/sec will be easier to drive and may afford a bit more fuel economy, but wont be anything to write home about.

I guess it really depends on what you are trying to achieve...

I am also assuming this is a jet, since you did not say.

GT

« **Reply #2 on:** June 18, 2011, 03:47:43 PM »

Jet it is, when I bought the boat it had the holley 750 with vacum secondaries on it. I switched it to the edelbrock 750 with mechanical secondaries. Just wasnt sure if it was a good thing or not. Its a jet so fuel economy i dont think can ever be a big factor. Just want the best performance.

« **Reply #3 on:** June 18, 2011, 03:55:41 PM »

Quote from: Hddaddy on June 18, 2011, 03:47:43 PM

Jet it is, when I bought the boat it had the holley 750 with vacum secondaries on it. I switched it to the edelbrock 750 with mechanical secondaries. Just wasnt sure if it was a good thing or not. Its a jet so fuel economy i dont think can ever be a big factor. Just want the best performance.

I really hate to sound ignorant, but here goes..... $:-\$

What carburetor made by Edelbrock has mechanical secondaries?...

Hope I am not making myself look like a moron....Hate it when I do that....

GT

« **Reply #4 on:** June 20, 2011, 08:38:22 AM »

Quote from: GT Jets on June 18, 2011, 03:55:41 PM

I really hate to sound ignorant, but here goes..... $:-\$

What carburetor made by Edelbrock has mechanical secondaries?...

Hope I am not making myself look like a moron....Hate it when I do that....

GT

This is what I was told regarding the edelbrock carb. Hey if its not then its not. Your a better tech guy then me. Value all opinions. So, would it be better for me to put the holley back on?

Carb info straight from edelbrocks website; "EDELBROCK MARINE SERIES 750 CFM, ELECTRIC CHOKE CARBURETORS
CALIBRATED FOR PERFORMANCE
Designed and calibrated for optimum marine performance in small-block and big-block V8 engines with Performer RPM, RPM Air-Gap and Torker II manifolds and with Performer manifolds on large cubic-inch engines. Comes with: Metering Jets - Primary .113, Secondary .107; Metering Rods - .071 x .047; Step-Up Spring - orange (5" Hg)."

« **Reply #5 on:** June 20, 2011, 07:36:09 PM »

Quote from: Hddaddy on June 20, 2011, 08:38:22 AM

This is what I was told regarding the edelbrock carb. Hey if its not then its not. Your a better tech guy then me. Value all opinions. So, would it be better for me to put the holley back on?

Carb info straight from edelbrocks website; "EDELBROCK MARINE SERIES 750 CFM, ELECTRIC CHOKE CARBURETORS
CALIBRATED FOR PERFORMANCE
Designed and calibrated for optimum marine performance in small-block and big-block V8 engines with Performer RPM, RPM Air-Gap and Torker II manifolds and with Performer manifolds on large cubic-inch engines. Comes with: Metering Jets - Primary .113, Secondary .107; Metering Rods - .071 x .047; Step-Up Spring - orange (5" Hg)."

I was not trying to offend...Just so ya know...

That is what used to be a Carter AFB, then owned by Weber then purchased by Edelbrock. There is actually nothing really wrong with them per se' but where it says 5"hg is the vacuum rating for the secondaries.

It is definitely a vacuum secondary carburetor....These carburetors are very tune able, it just goes back to what you are trying to do...

GT

« **Reply #6 on:** June 24, 2011, 02:22:39 PM »

No offense taken, just looking for advice. Whats the best way to tune this carb? Seems to be working, only complaint is at idle its keeping my rpms around 1000 to 1500.

« **Reply #7 on:** June 24, 2011, 02:44:21 PM »

Quote from: Hddaddy on June 24, 2011, 02:22:39 PM

No offense taken, just looking for advice. Whats the best way to tune this carb? Seems to be working, only complaint is at idle its keeping my rpms around 1000 to 1500.

I assume that you have messed with the idle screw and have had no luck getting to idle down? If so check for a vacuum leak, around the manifold, carb base plate or a missing cap off of one of the vacuum ports on the carb itself. an easy way to do that is spray carb spray around all of those mating surfaces with a (NOT HOT) running engine and listen for either the rpm's to increase or decrease. if that happens then you have found the source of the leak.

Hddaddy

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