i have a couple carb questions, i have a healthy 305, (10-5-1 comp, summit polished intake, 48000 vlt coil, 467 lift cam, 222* duration) i have 2 carbs, first is a carter 500 cfm. It rus descent, but has a lot of hesitation off the line and has no high end power. the eldelbrock 600 i have doesnt stumble off the line, but after you punch it has a huge miss, gos miss, etc. but then you let off and nail it and it runs great. I am new to tuning carbs, i can take them aprt and put the together, but dont know about jets, metering rods, accelerator pumps, etc. what could these problems be? how could i get the idle-2500 miss out of the 600?(by the way after 2500 it runs great) how could i go about tuning it? oh and i have another? what do metering rods do? thanks

 

I'll bet that "Summit Polished Intake" is of the Single Plane Design.
These intakes are not famous or their low rpm throttle response.
That combined with the camshaft you are using tend to not be happy till it gets above 2000/2500 rpm.
Some things that will help tune out this drivability problem are
1. Try a larger accelerator pump shooter and or adjust the
linkage for more pump volume.
2. Try recurving your distributor for more inital timing but the same total mechanical timing. like 12 to 14 deg inital and 32 to36 total.
3. Be sure the vaccum advance is plugged into "ported vacuum"
on the carb. (If it's plugged into full manifold vaccuum it may bog when you step on it. {timing actually retards when it should be advancing}.
4. Get a high stall converter. Like about 3000+ rated stall.
This will allow your 305 to wind up into it's power band when you accelerate, bypassing the very low rpm which single plane
intakes don't like.
5.. Change to a more street friendly dual plane design intake.
An Edelbrock Performer or performer rpm or a Weiand Stealth.
Will have much better low rpm response and much better street manners.
6. If any of the internal surfaces of your intake are in any way polished, you will have lots of drivability and throttle response problems. The plenum and ports should be rough. "As cast".
7. Be sure that some exhaust heat can get up to the passage under the plenum. This heat helps the fuel vaporize and greatly
reduces the warm up time.
But before you try any tuning, check for and repair any vacuum leaks.!!!!
Hope this helps....

 

its dual plane idle- 5500 powerband, the cam is also idle to 1500, where could the vac leak be, i checked the lines, its no the carb, ive had it off and on so many times, my timing is at 8*-30* right now.

 

The 500 Carter may have been calibrated for a dual quad
setup (rods and jets) They then would be too lean on a single carb setup. You could check the Carter catalog for stock jetting
for the different Model 500cfm carbs to see if this is the case,
and start with a single carb calibration as a baseline.
As for the immediate stumble on acceleration check the
size of the accelerator discharge nozzles and the linkage adjustment.
Also check the spring preload adjustment on the secondary velocity valve. It may be too loose causing the secondaryies
to flop open too soon.
For the Edelbrock 600 first be sure to start with stock jetting for that carb model as a baseline. The different jetting calibrations for the different model carbs are stated in their catalog
and online. Again work with the accelerator pump discharge nozzles and linkage adjustments for the best throttle tip in performance. Then work with the air door tension to get a smooth secondary transition.
Some sources for vacuum leaks are
Intake to head gasket, Power brake booster and lines,
Any air conditioning vaccuum lines, transmission vaccuum
modulator and lines. Carb baseplate to manifold gasket or adapter plate. Fuel vapour canistor vaccuum purge lines or controler. Vaccumm leaks can be hard to find but you won't ever get the carb right if you have one.
Edelbrock has an "Owners Manual" for you, to guide you through the tuning process step by step. Get one. This book is also relevent to a Carter AFB. (The exact jet/rod combinations may not, but the method is the same.)
Your carb may be infected with dirt. Mostly from not using a fuel filter. One of the internal fuel passages may be clogged with dirt
This can only be cured with removal and rebuilding the carb.
The metering rods work in combo with the primary jetting to control the air/ fuel ratio during different modes of operation.
They are controled acording to engine vaccuum and load
by manifold vaccuum acting against a spring loaded power piston.
Basicly the rods are down in the jet at idle and cruise (lean)
and up out of the jet when at wot low vaccumm (power rich).
They have progressive steps that allow an exacting progressively richer mixture as they are raised up out of the jet
according to engine load. (manifold vaccuum).
Their are many possible jet/ rod/ power/spring calibrations
possible with the available parts. This makes it a much more exacting carb than a holley, but also much more likely to be out of wack. The stock rod/jet is almost always the best place to start.
Note: You do not need ever available rod and jet to tune your carb. There is a group of relevent rods and jets that will tune your carb to your motor. They are available in kits from Edelbrock and
Carter.

 

i had the same problem with my 1406, i did change the acceleration pump link to the upper hole and hessitation is now GONE, try it bro.
Fern.

 

thanx, ill try that