Dual quad setup

[39chevy]

I running dual Edelbrock 550 square bore quads with progressive linkage on an Offenhouser mainfold on my 348 with an Isky 268/268 hydralic cam. My question is in regards to setting up the carbs. Most advise to shut down the idle circuits on the front carb, but I have mine set up with the idle adjusted like the primary carb. it seems to idle a little better and doesn't have the flat spot, but it is reallty a ***** to get started even in sunny Southern California. What do you guys recommend?

 

[mac1]

Both carbs should have an idle circuit. Maybe your getting confused with disconnecting the choke on the front carb. When I ran progressive linkage I to had a difficult time starting my car even on warm days, just a few minutes after shutting it off. I found flooring the gas pedal a few times before firing her up helped, but I eventually switched over to direct linkage and it now fires up immediately. I'm sure more knowledgeable people will have more to say on this. Hang in there.

 

[1958 delivery]

I would look at mixture rich/lean and timing as the reason for hard starting.

 

[32witha409]

39,

If you turn in the idle mixture screws on the front card, make sure that the throttle butterflys on that carb are shutting tight. If they pass any air you will have a dickens getting the motor to start or idle right. I believe it if fairy common to have the secondary carb in a progressive setup nothave a operable idle system. Just my take on the question.

Robert

 

[39chevy]

More info

Mac, no, I only have a choke of the rear (primary) carb. The choke plate is removed from the secondary carb. My hard-start problem sounds the same as yours. This is a weekend only car. I think I can set up my progressive linkage to run both carbs at once. I'll give that a try. Do you experience any bog when snap open the throttles?

Delivery, I adjusted the carbs using my limited old scholl knowledge...lean out the idle jets until RPM drops and turn back in a little, adjust idle RPM and do it again until it idles where you want it. Any timing or jetting settings you can recommend?

 

[39chevy]

Btw

That 32 with a 409 is looking good. I made good use of the Offy rocker covers I purchased from you last year.

 

[MRHP]

carb

Ditch the progressive, set idle screws on both carbs, set idle mixture screws on both carbs, and should run good. If not you have another problem. Fuel boiling in carb, fuel draining back due to faulty fuel pump, or improper timing come to mind as starting problems.

 

[1958 delivery]

No recomendations per se, but I have noticed that, as an example, on my car I know the center (idle circuit) carb is overly rich due to high float level. It starts and runs like a dream when cold and below 160 temp, just touch the key and it fires up instantly. But when the engine temp is higer it'll be hard to start and often requires holding the pedal on the floor to start quicker, which allows more air to offset the rich condition. I don't use it often enough to bother re-adjusting the float level, just lazy!

 

[mac1]

Going from progressive to direct linkage was an easy transition for me.
Do what MRHP says and you'll be happy. You'll have great throttle response and it should start better. You'll will have to learn to take it easy on the gas pedal
though

 

[Fathead Racing]

New Edlbrock and Carter AFBs are identical carbs. Under the carb use either a 1" spacer with open plenum or Edlbrock #2732 plate. The new carbs will develop a vacuum leak under the carb without this. Adjust each idle mixture screw out one turn and each throttle in 1.5 turns. Adjust each idle mixture screw to obtain maximum vacuum and then adjust throttle screws equally to obtain idle speed. DO NOT adjust idle mixture screws all the way in on the front carb.Use the lightest metering rod springs that does not surge at highway speeds ( usually 5" to 7" below idle vacuum- if engine idles with 12" vacuum try 5" springs first in both carbs). I run my dual quad 409 with progressive linkage and have no issues.

 

[oil4kids]

Dual quad 409s I believe are really 4 cylinder motors running on the the rear 4 cylinders unless you have both carbs dialed in perfectly. I put together a 4 inch stroker years ago, dialed in the carbs, as best i could with vac guages and corvair multicarb flow meters, new carters mind you, did one pass and pulled the intake off to look at the motor, the machine shop assembly grease was still on the intake valves on the front 4 cylinders 1,3,2,4

swapped the front and back carbs, ran the same, maybe its just the design of the intake having raised runners in the rear

I dont know if the dual quad Offy manifold suffered from this.

 

[CHEV601234]

"Dual quad 409s I believe are really 4 cylinder motors running on the the rear 4 cylinders unless you have both carbs dialed in perfectly."

no offence, but you don't have ANY odea what you're talking about. A 2x4 car is running on the primaries of the rear carb most of the tiem with an even fuel distribution to all Eight! Someone desogned the intake that way. These cars werre designed to drive around town, not jus ton the race track./

"the rear four cylinders"????

 

[1958 delivery]

Why would direct linkage vs progressive have any effect on how the engine starts?

 

[MRHP]

It has absolutely nothing to do with starting. Everything to do with throttle responce and drivability. My car was a pooch in the lower rpm with progressive linkage. Straight linkage gives a more even fuel distribution. In my opinion progressive linkage makes for a lazy engine around town. I could never tell a difference gettin' after it. Of course, this is my opinion. I am sure others will have the opposite recommendation! :stooges

 

[1958 delivery]

OK, I thought his question was about difficulty in starting the engine.

 

[rstreet]

I have no problems with starting my 2X4's and have NO chokes:eek: and with progressive linkage, both carbs "working" and no drivability problems. I use the minus two jetting/metering rod system as recomended by Edelbrock and Ronnie. Also Ray "Fatrides" adjustment system is about as good as it gets on mine. I have done some work on my 948 distributor but that was more for driveability and over heating then starting.
robert

 

[Garbageman]

I run a setup very simalar to yours and have no problems. I set my carbs up based on information from Curt Harveys website, which is no longer availabe, but it is the same advice the Ray "Fatride" stated earlier. Pump the pedal a couple of times and turn the key, if it doesn't fire stop pump again and it will fire. After it has fired I have no more long starts the rest of the weekend.

Paul

 

[oil4kids]

Chev60,......


if you doubt my statement, put in a brand new set of spark plugs, run your 09 for a 1 minute at 1500 rpm and pull the plugs, they will tell you the story, back spark plugs wet, front plugs look almost new

and by the way the "someone" who designed the dual quad intake was Fred Frienke who also designed the z11 intake

 

[MRHP]

Yes, I also have divorced chokes on both carbs. Give it a couple of pumps and it will start when cold. When hot, just turn the key.If you have a hard start when hot, your timing, starter/battery, or fuel boiling in the carbs are the most probable culprates. How hot do your carbs get. I'll bet fuel boiling into the intake making for a rich condition.If this is the case, an insulator gasket would be needed under the carb. Do you have the crossover open in the intake? If you are running manifolds, is your heat riser working properly? Both of these raise the temp of the intake and aggrivate a hot start condition.If you only have a cold start problem, a choke or some foot pumping should do the trick.

 

[39chevy]

No hot start

MRHP - no I don't have a hot start problem. Once I fianlly get it started it will start right up all day long. I'm running shorty block hugger headers, I have the crossover blocked off at the heads, I'm using a Holley electric fuel pump regulated down to 5 PSI, I have phenolic spacers under the carbs, I am running 5 BTC initial timing with 28 degrees all in at 2200 RPM on a Mallory distributor with fully centrifical advance (no vacuum) converted to pointless ignition with a Pertronix conversion kit. I have new plugs and Taylor plug wires. The engine only has about 5 or 6 hours on it since rebuild. I've never dynoed the setup and I would like to get it on a dyno to get it tuned. Anybody around SoCal know of someone who can help me out?