750 Edelbrock issue

[Hysteric]

It needs a higher float level than the Carter 750 because the primary booster flow is later due to the fact that the booster not being at the vena contracta like it should the mains starts later. I did a test a while back where I compared the correct booster with the Eddie booster and I cant remember if its 500rpm or 1500 rpm difference I saw before the Eddie came on. Setting the float level higher will cause the mains to come on sooner on the shorter length booster.

 

[Bewy]

If by higher float level you mean the float itself is higher [ with n/s closed ], in the E carbs it is lower.
The fuel level in an E carb is lower than what it was in the original Carter AFBs.

 

[rumblefish360]

He means it so there is more fuel in the bowl.
More fuel in the bowl for a higher level of fuel will cause the mains to come on sooner and run richer even more so on the shorter length booster.

He is dead nuts on.

I started down this math and then stumbled onto a speed talk thread (IIRC) about this. It was awesome finding out I was right in the little I had uncovered and reading on about what else I had not discovered yet was simply awesome. Great work by the fellas over there.

I wonder about the 800 Edelbrock @Hysteric
And words on those?

 

[Hysteric]

If by higher float level you mean the float itself is higher [ with n/s closed ], in the E carbs it is lower.
The fuel level in an E carb is lower than what it was in the original Carter AFBs.

It should be higher on the 750 by the fact that the booster sits higher than it should in the venturii. Vacuum and air flow (bleed) is what raises the fuel level up and out of the booster but the greatest depression is at the smallest part of the venturii also known as the vena contracta. So if you move the booster away from the point of fastest moving air higher there's less signal so the air flow has to be greater before you get enough vacuum present to lift the fuel. The vena contracta is at different heights on the 600 and 750 so require different length boosters. They skimped and only used 1.....the 600 for both.

800 looks to be fine. As a matter fact Joe Sherman stated he used them on engines up to 550HP and they got better mileage than a Holley.

 

[rumblefish360]

The vena contracta is at different heights on the 600 and 750 so require different length boosters. They skimped

BINGO! Just what I had found out as well. At the time, I did t understand the full effect there was. I had collected more than just a few Oder Carter AFB & AVS carbs.

Under the boosters (AVS has the primary only) I noticed different holes in the tubes and different orifice openings and some closed off. This was making me confused. VERY! Shortly there after I discovered that AFB carb thread.

I had tried talking with the Federal Mougal tech line. All I got was a pompous know it asshole that couldn’t answer a single question directly but mostly said;

“It is a sophisticated calibration done by the factory engineers that is well over YOUR head to understand the complexities of finite fuel calibrations & delivery of ….” Yadda yadda yadda yadda yadda….

800 looks to be fine. As a matter fact Joe Sherman stated he used them on engines up to 550HP and they got better mileage than a Holley.

Thanks
I have a 800 AVS. (1st gen, not the improved booster model.) I have a little bit of a reservation on installing it on a 340 that isn’t a power house. I picked it up for a big block street machine targeted for approximately that HP level, as I don’t really have a great need to exceed such levels on this particular build for the street. (It’s on the back burner for now anyway.)

 

[Hysteric]

“It is a sophisticated calibration done by the factory engineers that is well over YOUR head to understand the complexities of finite fuel calibrations & delivery of ….” Yadda yadda yadda yadda yadda….

There is more truth in this than people would like to admit. That's why old Holley's work so well.......The less you use the better.

Its all about the vacuum the carb see's. And the carb only see's the vacuum the engine creates.

 

[rumblefish360]

There is more truth in this than people would like to admit. That's why old Holley's work so well.......The less you use the better.

Its all about the vacuum the carb see's. And the carb only see's the vacuum the engine creates.

I agree. There is more than what meets the eye.
I just wasn’t thrilled with his crappy attitude and responses. He was a dick about the matter.

 

[Hysteric]

I just wasn’t thrilled with his crappy attitude and responses. He was a dick about the matter.

What's new. Same **** happens here and people get over it and go back to being civilized don't they not? We have to see truth even when we don't like the way it comes or who delivers it.

 

[rumblefish360]

Live voice is different than text in many cases, but yup, you are correct!

 

[Hysteric]

Case in point this engine shows exactly what I mean. It will depend on how much vacuum your engine makes and how well the carbs vacuum reference is matched to your engines requirements.

http://wright-here.net/files/articles/phr_1109_sbo/phr_1109_sbo_ocr.pdf

"The intake port is way smaller than the original. , think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.91square inch~ es]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers. he claims they were almost at those numbers by .200-inch lift. Just perfect for limited camshaft and rpm range applications.

They made 1.37 HP per cube with only 195 cfm peak flow. They made 2.2 HP per cfm truly remarkable when you think about it. Its at 316 CI and uses an 800 carb.

Its making very good torque for a small cube engine with a small port and a big carb. Now if you hogged those ports out to 180 cc what do you think the vacuum difference would be for the same rpm that the carb would see? If nothing changes in the short block the pistons draw on the port at those rpms is now less is it not? The piston now has to displace a greater area. So what happens to the vacuum the carb see's now and how does the calibration now affect the fuel delivery? How do you compensate a lower vacuum reference now? You play with calibrations......Or you could go to a smaller carb could you not?

Here's a good thread with so much insight it's required to be read many many times over to be really understood.

emulsion question

Now what happens to the vacuum at the T/slot when you put a bigger carb on? Then think about why Mopar used a spread bore design and you realize you get the best of both worlds.

 

[racerhog]

I did. It was a bunch of gunk from the tank pumped through. fouled plugs etc. I replaced plugs ,opened carb and cleaned out got it back up and going. I just had it running the other night and it was a "cold start" in the 40s here in Pa. Once I got gas pumped up through the lines it started up. The car is going back together so it doesnt get started every day

Glad you got it fixed !!!! Cheers

 

[Rat Bastid]

Case in point this engine shows exactly what I mean. It will depend on how much vacuum your engine makes and how well the carbs vacuum reference is matched to your engines requirements.

http://wright-here.net/files/articles/phr_1109_sbo/phr_1109_sbo_ocr.pdf

"The intake port is way smaller than the original. , think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.91square inch~ es]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers. he claims they were almost at those numbers by .200-inch lift. Just perfect for limited camshaft and rpm range applications.

They made 1.37 HP per cube with only 195 cfm peak flow. They made 2.2 HP per cfm truly remarkable when you think about it. Its at 316 CI and uses an 800 carb.

Its making very good torque for a small cube engine with a small port and a big carb. Now if you hogged those ports out to 180 cc what do you think the vacuum difference would be for the same rpm that the carb would see? If nothing changes in the short block the pistons draw on the port at those rpms is now less is it not? The piston now has to displace a greater area. So what happens to the vacuum the carb see's now and how does the calibration now affect the fuel delivery? How do you compensate a lower vacuum reference now? You play with calibrations......Or you could go to a smaller carb could you not?

Here's a good thread with so much insight it's required to be read many many times over to be really understood.

emulsion question

Now what happens to the vacuum at the T/slot when you put a bigger carb on? Then think about why Mopar used a spread bore design and you realize you get the best of both worlds.

LOL. If you don’t mind welding, epoxy and a ton of work to make 435 that’s great.

 

[Hysteric]

LOL. If you don’t mind welding, epoxy and a ton of work to make 435 that’s great.

And yet you IGNORE the FACT that it does it with only 195 cfm peak air flow and only a 145 cc port

They can do with 195 cfm and 145 cc what takes you 250 cfm and 160+ cc to do.

 

[Dan Georgino]

I am in the process of tuning my 340 with 750 edelbrock. It will idle at 800 rpm and then the idle gets low, if I rev the throttle it returns for a while then does it again, this is sitting in neutral in the garage. I am suspecting a problem with fuel pressure, however I am wondering if anyone else has had or seen this problem with Eddy carbs. The only vacuum ports I am using are PCV and vacuum advance, car has manual brakes. There isn't any vacuum leaks, car is pulling 16 in hg on a vacuum gauge. I am thinking my next step is check fuel pressure, fuel filter, and then get into fine tuning with jet kit at some point. The exhaust is "smelly" no matter how I set the carb rich or lean.

Your idle throttle butterfly is set too far open. Reset the opening again.

 

[rumblefish360]

LOL. If you don’t mind welding, epoxy and a ton of work to make 435 that’s great.

For a class CID limited/camshaft limited engine, that’s pretty darn good.

 

[Rat Bastid]

For a class CID limited/camshaft limited engine, that’s pretty darn good.

It is. It wasn’t built for a class, it was built for a dick slapping contest. Welding the exhaust ports? Yeah, that’s cheap. Then all the export in the intake port and all that port work was cheap too. It wasn’t a cost effective build. Hysteric thinks everyone should drop 5k plus on porting junk iron castings. I was far over that 20 years ago.

 

[Hysteric]

Hysteric thinks everyone should drop 5k plus on porting junk iron castings.

Yeah porting junk heads always cost 5-10K don't they........to get 195 cfm.

 

[rumblefish360]

Ohhhhh boy, let’s not do this again in THIS thread fellas. We can always go back to the other thread!

 

[Hysteric]

Ohhhhh boy, let’s not do this again in THIS thread fellas. We can always go back to the other thread!

I agree. There is no place here for any technical discussion. Lets go back to what these guys do best....Dick slapping

 

[Rat Bastid]

I agree. There is no place here for any technical discussion. Lets go back to what these guys do best....Dick slapping

Says the chief dick slapper. Who in their right mind would do that much work on that head? Evidently you’ve never done it or you’d see how dumb it is. But keep thinking you are the only guy here who can make a head flow. What a joke.

 

[Hysteric]

Who in their right mind would do that much work on that head

I guess some one who can make power with very little air flow......Guess that's not you.

Evidently you’ve never done it or you’d see how dumb it is. But keep thinking you are the only guy here who can make a head flow. What a joke.

Wait.....That head doesn't flow.......But its making power........

 

[Rat Bastid]

I guess some one who can make power with very little air flow......Guess that's not you.


Wait.....That head doesn't flow.......But its making power........

I’m smart enough to not reinvent the wheel. What you consider power I consider street car stuff. I know you want everyone to think you can do port work, but you can’t. If you did, you’d be smart enough to not bother with junk iron heads unless it’s a class rule. It’s stupid. Stupid is as you do.

 

[Hysteric]

I’m smart enough

Obviously by what you post you're not.....

I know you want

Sure you do.....

 

[rumblefish360]

OMG!
Just drop it fellas!

 

[Dartswinger70]

Its amazing what people will put on their cars...........I have never seen build up like that on a carb transfer slot and throttle blades.

Honestly its gas tank gunk.(old, bad/varnish gas) Now most will replace the tank I took a chance went for it and got to deal with the aftermath. Now it runs fine. I told the wife "the car sat for years the first time I had it in the road, i didnt replace the tank then..." I may replace the tank yet but i dint want to stop what i was doing which was to get the car running, but not on a gas can like it was. I know being cheap but I survived. Now one thing I also had done is put a heat spacer between the carb and intake, i suspect the gas was flashing off between starts. I had to long crank after hot shutdown before it would start.