Need help with carb adj on Edelbrock-350

[Villengineer]

I have a 1405 (manual choke version) on my '65 F-100 that has the exact same problem. The previous owner had put it on and could never get it tuned right. I figured that I might have better luck. However, this is my first "carter" carb, lots of Holley and Autolite experience, and I have decided that after being fully disgusted with trying to tune the Edelbrock carb that my solution is to replace it with a Holley.

 

[HarryVanderpool]

With the engine OFF , look down the throat while giving it full throttle with your hand . It should have a strong steady stream of fuel out of both jets which will continue to spray for a second or two after you hit the throttle stop . If you are only getting a dribble , the diaphram , check ball or spring is faulty . Is the carb a vacuum secondary type ? If it's a double pumper then it's really to big for a 350 . What size cam has it got ? Big cams cause low manifold vacuum , when you stomp on the loud pedal manifold vacuum drops to zero , air speed slows and the engine takes a crap . Is the manifold dual plane or single plane (single plane should not be used on the street just like big cams) A 350 running at 5000 rpm's (being honest) with a volumetric efficiency of 80% needs a carb of 405 cfm . So the formula is :-350cubes X 5000rpm = 1750000 divided by the constant 3456 = 506.36 - 20% lost eficiency = 405cfm .

Wow, thats interesting.
I learned to size carbs out of a book called, "Racing Engine Preparation"
I compared my formula to yours, and got the same result!!

350 cubes

Times:

Half of your desired full HP RPM: 2500 (every other revolution is an intake)

Times the constant: .0005787

Equals= 506.36

Times Volumetric Efficency .80 (in your dreams )

= 405.09

Holly used to make a really killer 390 4 barrel.
Otherwise, a 500 should be just fine.

 

[SPIKER]

it has been a long time since I messed with mine, (carter AFB) but basically same carb. so far all good info. I have mine on a 400 ford bored 30 over with all EB cam intake and misc.

others said right. I got the tuning kit. which comes with all new metering springs rods seats ect. it also comes with directions which was a great help.

bog like you describe is usually a lack of fuel getting into the intake from the carb when vacuum is low (Wide Open Throttle) until AIR Velocity picks up: this is a classic ACCELERATOR PUMP problem. Move the linkage that is attached at right front cornet pump to shorter through, (closer to pivot point) on the top part of the linkage. If you have a adjustment at the gas pedal linkage then make sure it gives as much movement as possible. Carters/eldelbrocks carbs use a plunger type pump not a diaphragm pump. make sure the fuel is squirting in like mentioned above and that the float level is set right.


The kit has other springs & Rods that can help set mid upper rpm range fuel flow vs lower rpm low position flow.


chime in if you need more help
mark

 

[skargo]

I forgot, part of the problem is you can not adjust the secondaries. Edelbrock addressed this with their AVS series of carbs.

I still think a properly built q-jet is the way to go on a GM vehicle, from what friends have told me.

It's funny, nowadays people pay good money for q-jets, when back in the day that was the first thing you pulled of and tossed into a corner

 

[Treemonkey1000]

the Edelbrock Performance series of carburetors are basically the old Carter AFB design, nice carbs. The accelerator pump issues are fairly common and not too bad to replace but the top of the carb must come off.

Generally it's very easy to tell if the accelerator pump is the problem. Do this with the engine off. There needs to be fuel in the carb at the proper level, open the choke plate and with a flashlight, look down the primary side of the carb while slowly opening the throttle, you should be at half-throttle by the count of "one-thousand-one, one-thousand-two". This is what you're looking for, there should be a continuous stream of fuel squirting out of the pump nozzles as soon as you start to open the throttle. If the accelerator pump is worn, you'll get little or no fuel out the nozzles the first 10 or 20 degrees of rotation of the throttle and then the stream will start to get stronger the further you open the throttle, if this happens, it's new pump time.

This procedure only works if the float level is correct and you're testing on level ground. One other area that they should look at is the carburetor base gasket, between the carb and manifold. You could get the Performer manifold with a square flange or a spread-bore (think Rochester Q-Jet) flange. The Edelbrock carb he has is a square base and could be fighting some small vacuum leaks if it's bolted up to a spread-bore manifold. A small spacer plate (spread-bore to square flange) can be used if this is the case.

You can see both style of carb flanges here:

Edelbrock.com - Manifolds - Chevrolet - Performer - Small Block

 

[sixdogs]

Well, it's either fixed or very close to it.
I came home and checked for fuel at the carb and had it just right. Then I moved the plunger linkage from the longest linkage to the shortage linkage and it made a huge difference. Not quite perfect so I moved the linkage to the middle positon and, as far as my test run took me is perfect. I mean perfect.
Now, i need to put more mileage to really check on but the plunger rod was the solution.
Prior to asking you guys I switched thermostats, changed the intake manifold gaskets because that's what Edelbrock? told me. I also jerked with the timing a dozen times and canged air filters to a bigger one.
I love Edelbrock stuff so I'm Ok with this. Whatever; it's fixed.
Thank you all for making my '34 coupe roadworthy again. I have been trying to figure this out for quite a while.

 

[Eagleview]

Carters/eldelbrocks carbs use a plunger type pump not a diaphragm pump.

Yes , i should have said plunger not diaphram . A little tip for anyone with Leather cups on the pump plunger on older carbs . Soak in oil overnight before installing , they last and work much better .

 

[Eagleview]

Wow, thats interesting.
I learned to size carbs out of a book called, "Racing Engine Preparation"
I compared my formula to yours, and got the same result!!

.

Thats pretty cool , two different formulas and the same result . That means i have been correct twice this millenium .

 

[skargo]

Well, it's either fixed or very close to it.
I came home and checked for fuel at the carb and had it just right. Then I moved the plunger linkage from the longest linkage to the shortage linkage and it made a huge difference. Not quite perfect so I moved the linkage to the middle positon and, as far as my test run took me is perfect. I mean perfect.
Now, i need to put more mileage to really check on but the plunger rod was the solution.
Prior to asking you guys I switched thermostats, changed the intake manifold gaskets because that's what Edelbrock? told me. I also jerked with the timing a dozen times and canged air filters to a bigger one.
I love Edelbrock stuff so I'm Ok with this. Whatever; it's fixed.
Thank you all for making my '34 coupe roadworthy again. I have been trying to figure this out for quite a while.

Congrats sixdogs!

 

[RobJ]

.

I still think a properly built q-jet is the way to go on a GM vehicle, from what friends have told me.

It's funny, nowadays people pay good money for q-jets, when back in the day that was the first thing you pulled of and tossed into a corner

We used them on a lot of cars and learned the tricks. Most dealt with the secondary...
Adjust acc. pump link
change out metering rods on the secondary.
loosen the butterfly springs in the top secondary (for that ba-wa kick in sound)
And the one with the most bang for the buck...The secondary fuel wells were very small and gas starvation was a problem. Very small holes filled the wells from the main bowl. We would drill out the holes to allow them to refill faster. An electric pusher pump and a good fuel pump also helped.
We also took out the small filter in the front of the carb.

Loved the quadrajets.

Rob