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Madmax305 09-02-2012 04:53 PM

Which Carb?
Help me decide which carb for my set-up. I have a 1967 el camino with a th350, 4.10 gears, 3000 stall, 350sbc. It has about 9.2 compression, RHS 64cc vortec heads, LT headers, msd pro billet HEI dist and a comp magnum 286h flat tappet cam. I have been having problems with my Holley street avenger 670 vac sec carb. I would like some suggestions on which Edelbrock carb to buy. The carb will need vac secondaries and electric choke. The performer series 600 or 750cfm or the Thunder series 650cfm? This is a street cruising car only, no track time.

scott420p 09-02-2012 04:58 PM

I have run the 750 edelbrock on an s10 with a th350 3.89 a 3000 stall, 202 160 461 camel humps hei and a very similar cam with absolutely no problems. I actually had to upgrade from the 600 edelbrock. The edelbrocks are pretty simple to tune also.

Madmax305 09-03-2012 09:04 AM

Are there any problems with these carbs and Lopey cams? Will there need to be additional adjustments to the carb to get it to run right with high lift/duration cams?

cdminter59 09-03-2012 11:10 AM

which carb
Adjust your initial timing so you don't use the carburetor's curb idle screw to open the throttle plates to far to uncover the idle transfer slots. Start with around 16* initial timing to get the engine to idle around 950 rpms. If you don't get instructions with your carburetor go to Edelbrock's website for tuning instructions. You will need a vacuum gauge to tune the carburetor. Before installing the carburetor adjust the idle transfer slots to about .020. Here is the technical data on tuning your Holley 670 Street Avenger . Doesn't matter which carburetor you have both will have to be tune to your engine.

F-BIRD'88 09-03-2012 12:52 PM

You will need 24 to 26deg of idle base timing for that 286H-10 cam to idle sweet.

recurve the distributor to allow this and 34-36deg at max advance. (10deg mechanical advance curve)
Get a 4.5" power valve.

No amount of carb monkeying or swapping carbs will work untill you give the engine the generous amount of timing it needs at idle.

The 670 SA holleys are intended for very mild cammed motors.
It will cost more to dial in this carbs fuel curve than getting a real deal 750 cfm hi perf carb.
Once the spark curve is correct the 670AS carb may or may not need the IFR and or the IAB fine tuned.
The WOT power jetting will probabily need correcting to.

A 750 (any 750) will make more power and run better on that motor in every respect.
Get the 750 eddy or the 800 thunder series.
The 800 AVS thunder carb IS NOT TOO BIG.
If you get the version with electric choke start your calibration tuning
using the base line of the manual choke version.

Or get a 750 holley Not a avenger series. Can be VS or double pumper.
The street advenger series carbs are for mild camed motors.

Find a good used 650-700 DP holley and upgrade it using the proform HP body
Or find a used 3310 750VS and upgrade that using the proform 750VS HP body kit.

The vastly better performance and tunability of the HP carb body outways the lack of a functional choke.

Do not be afraid of a DP holley . It will be good on gas and responsive as hell once upgraded and dialed in.

The avenger series holley are notabley lame on perf motors.
Thats why they cost less.

F-BIRD'88 09-03-2012 01:11 PM

If you prefer a tame running motor with a smooth idle and excelent idle off idle driving response why not change the cam?
A cam like the Comp Dual energy 265DEH will probabily suite your driving style and purpose
a whole lot better. It will still go like hell.
1.6 rockers gets you high lift and short snappy duration with this cam.

265-269 211-221 110lsa .471" .495" lift when using 1.6 rockers.

This cam matches your lil 670 carb a lot better. strong power to 5500rpm
very resposive at low speeds. good on gas.

Your 9.2:1 compression is lame. You are 1 whole compression ratio shy of what the Comp Magnum 286H-10 cam likes best ...You could supercharge that thing.
You would really like a weiand 144 blower on it.
Cures all throttle response issues instantly. LOL

Start by correcting the distributor advance curve with 24 to 26deg initial base at idle.
huge difference. work form there.

F-BIRD'88 09-03-2012 02:16 PM

Update. Everything is fine now. I drove the Elky for about 30 minutes and pulled out the dizzy. It slipped out with no issues. It turned out my manifold bolts were really loose, all tightened up and no more engine wobble issues or black smoke. I wound up with 16' initial with 38' total, all in by 3000rpms. I changed to the lightest springs, wow, it really made a difference on the torque. All is good....

Your quote:

A search of your olds posts indicates you ahve had many issues with basic faults like vacuum leaks.
etc etc. No amount of money spent on numbourous new carbs will cure a simple manifold vacuum leak or a simple ignition fault like a bad engine/body ground or low ignition supply voltage etc.
Or simply not giving the cammed up motor the amount of inital timing it needs at idle to burn the fuel correctly at idle.
Lack of idle timing on the comp 286H-10 cam will result in the carbs throttles being too far open at idle .
Won;t matter how many carbs you buy and try.
Start with 24 to 26deg base idle timing. Get the primary and sec throttle positon correct on the carb.

Make sure the advance curve is on the base of the curve at idle. SHould not move untill 1100rpm.

Timing must not drop off when idleing in gear.
Super light advance springs give a inconsistant idle.
You will need a custom 10deg advance bushing for the MSD small cap distributor.
18deg at idle will not be enough.

Ported vacuum will work the best for this one.

Madmax305 09-12-2012 10:49 AM

Thank you for the replies...Update, I have ordered an Edelbrock 800 thunder series carb and a custum set of 10* and 14* bushings for the MSD dizzy, ($33 for the two bushing, WOW). I will keep everybody posted on the progress....:)

Madmax305 09-15-2012 03:53 PM

OK, I put the new Edelbrock 650 carb on and installed the new 10* advance bushing in the MSD distributor. I tried to adjust the base to 24-26* but the starter bucks and I can't get the motor to take that much base timing. The most I can get is about 16-18* before the starter bucks and will not crank the engine fast enough to start it...

Any other options? What about hooking up to the manifold vacuum vs ported vacuum to help add 10-12* to the base. Would this help me achieve the 24-26* initial timing? :confused:

F-BIRD'88 09-15-2012 04:07 PM

Fix the starter first (heat shield, remote ford solenoid, battery, cables ground)
Then install the interupt toggle switch. its easy. make sure the OEM starter brace is installed.

What about hooking up to the manifold vacuum vs ported vacuum to help add 10-12* to the base. Would this help me achieve the 24-26* initial timing?

This works on manual trans cars that idle with no load but not auto trans cars that have to idle in gear.
This pulls the manifold vacuum down at idle in gear which causes the timing to drop off.

You need a solid non wavering 24-26deg at idle, in gear, that does not jump around.

To test your starter disable the spark and kick the motor over when hot. If the motor still cranks slow with no spark the starter or cables or battery is fubared.
if the starter will crank the motor while hot, while spark is disabled, use the interupt switch for hot starts.

The motor and headers will idle cooler and much cleaner with this increased idle timing. But you will still need a starter heat shield.
The starter motor and or the starter solenoid may already be cooked from excessive header heat and lack of shielding . In that case the only cure is to replace it.

the new style small body starters 97ish LT1 gen II corvette motor allow much more air gap from the hot headers (still need a shield) and have a gear reduction drive. GM finally got their act together with the starter motor hot crank issue.

The simple $10 ignition interupt toggle switch works. If your starter brace is missing, get one.

Madmax305 09-15-2012 04:12 PM


Originally Posted by F-BIRD'88 (Post 1590995)
Fix the starter first (heat shield, remote ford solenoid, battery, cables ground)
Then install the interupt switch. its easy. make sure the OEM starter brace is installed.

OK, I already have the remote ford solenoid installed, I have the oem starter brace, I will install that. What is the interupter switch?

F-BIRD'88 09-15-2012 04:38 PM


Originally Posted by Madmax305 (Post 1590996)
OK, I already have the remote ford solenoid installed, I have the oem starter brace, I will install that. What is the interupter switch?

Get a single pole single throw (SPST) toggle switch (10 to 15amp rated) and install it on the dash. Wire it into the 12V+ power wire to the distributor.
All you are doing is switching off the spark momentarily for hot cranking to take the cranking load off the hot starter.
Crank it over 1-2-3 count and throw the switch and it will fire.

If using a MSD box (or most other boxes) the switch goes on the small red power switching wire that controls the box on off.

You will also find this switch useful for cranking/turning the motor for valve lash setting etc And as a simple anti theft device.

F-BIRD'88 09-15-2012 04:39 PM

NEVER EVER operate a GM starter motor without the brace installed.

F-BIRD'88 09-15-2012 04:48 PM

You can also get and install a auto cranking-start retard box to retard the spark during engine starting.
But try the simple interupt switch. No more burned out starter motors.
Do you have a (Moroso) starter heat shield and (Thermotec) starter heat wrap?
They really help keep the GM starter alive. Does not take long to cook a GM starter with headers.

Some of the start retard boxes are "universal"- stand alone type and work with any ignition (like HEI).
Some only work with a spark box like the MSD-6.
Many but not all add on spark boxes have this start retard function,,, built in
Pretty much any ignition retard box (nitrous, blower, towing etc) can also be used as a start retard.

F-BIRD'88 09-15-2012 04:58 PM

Within a short time you will find using the interupt switch, second nature when starting your car.

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