I recently installed a edelbrock 600cfm on my stock chevy 305. I cant seem to get the choke to keep it running when cold whether I adjust the choke to rich or lean. Does that mean the carb is too rich for my 305?
Can’t speak to that carb model, but on my truck’s autolite 2100 the choke plate is fully closed before starting the engine , then slightly open when the engine starts up and is cold idling. I’m guessing it is open about 1/10 to 2/10 of an inch. Don’t have the specs in front of me, but the specs say to use a drill of a certain diameter to use as a gauge to set how far the choke plate is open during cold operation. How far is your choke plate open when this is happening? Either too little or too much will cause poor idle performance when cold with carbs.
Edit: The “choke pull off” is what causes the choke plate to open once the engine starats. Faulty choke pull offs (usually due to a split diaphram in the vacuum motor) used to be a common reason for poor cold idling. Ray and Tom used to joke on the show that in the early days pretty much any complaint from a caller about cold idle, they’d say “faulty choke pull off” … lol …
Its completely shut when cold but the edelbrock is a little different than an autolite. It actually has a air passage hole on top of the choke plate. Its an Edelbrock 1405 thats converted from manual to electric choke.
You’ve gone above my carb pay grade I’m afraid. Hopefully somebody here has some direct experience w/that model of carb. What if you experimented with manually opening the choke plate at various amounts while cold idling to see if that helped? I seem to recall Ray suggesting to a caller with this problem to place a stiff piece of cardboard (I think) over the choke opening and move it around to create varying sized apertures as a trial and error method of setting the proper choke opening.
Are you pretty certain the warm mixture setting is otherwise correct? If the warm mixture is set incorrectly it might be impossible to set the cold mixture correctly using the choke plate.
The carburetor is fine for a 305 so that’s not the issue.
I assume you mean the engine is stumbling bad and/or trying to die upon cold startup?
The reason why could be due to the fact that the carburetor does NOT have a choke pull-off diaphragm. Unfortunately, that’s the way they’re made so it takes some tinkering to make them tolerable. I can’t speak as to how you’ve done various adjustments.
The choke PO is designed to open the choke flap about 1/8" immediately upon cold startup and from that point it opens gradually as the choke heater warms up. Without the choke PO it basically overchokes itself.
The choke blade does open about that far after the engine runs for about 10 seconds and then dies. Then I have to pump the gas alot to get it to stay running. George may be onto something when he mentioned idle mixture.
Is it on the fast idle cam?![IMG_0650|690x366](upload://2j37V Photo is a Weber, the Edelbrock may be different but similar.
That’s pretty much exactly how the 2100 works. On the 2100 there’s one other adjustment not shown in that image that controls the choke plate angle vs the cam angle.
That looks the same as my carb. Ill check the position of the cam tomorrow when its cold.
How does the truck run after it is warmed up? The fact that you have to use the accelerator pump to keep it running makes me think it is not too rich. If it was my truck I would convert it back to manual choke. I never liked automatic chokes anyway.
It runs and idles perfect when warm. Secondaries operate like they should. Its just a bear to start.
The choke pull-off is inside the choke housing. If you find that it is running lean with the choke set, the choke pull-off setting can be adjusted by bending the choke rod. Be careful, adjust in 1/32" increments until you find that it is not too lean or rich to operate cold.
The adjustments are shown in this manual;
The choke conversion information below shows the vacuum port that must be opened during the conversion to supply vacuum to the choke piston.
Thanks! Alot of useful info there.
I agree with Nevada_545. I’m familiar with the old vacuum diaphragm operated external choke pull-offs but not the ones that are internal to the choke housings, but the pull-off needs to be set richer.
The Edelbrock manual is a real ++++ Nevada and if the OP has the patience and insight to get the carburetor adjusted correctly he will likely be happy with the performance. It often seems easier for a beginning DIYer to rebuild his first engine correctly than his first carburetor though.
Over the years customers have brought me cars and trucks that someone had attempted make some performance modifications which didn’t quite work out. A common problem was installing severely oversized Holley carburetors and my best solution to that was installing the correct size Edelbrock which performed like an OE carburetor. I seem to recall they cost less than $130 back in the good ole days.
fyi, a recent issue of Hot Rod magazine has a multi-page article on the Edelbrock’s son, who ran the company successfully for a long time despite taking over the head job while still pretty young and inexperienced. Oct or November issue I think.
Yeah I remember my Quadrajet had that pull off. I’m not too familiar with the pull off in the choke housing on an edelbrock. I’ll study the diagram further.
Turns out I had the fast idle linkage installed wrong. Fires right up everytime now.
Actually, what you describe is a lean condition, not a rich one. Pumping the pedal to keep from stalling means the choke is opening too quickly or the base tuning in the carb is lean. If i runs OK when warm, the choke is opening too quickly. You might need to add a resistor inline to the choke so it doesn’t get so much current to open that quickly. Since you have an Edelbrock carb, is it on an Edelbrock manifold? And does that manifold have heat passages from the exhaust ports below the carb to warm it up? And did you use the gaskets WITH those center ports open? You block those off for better power but they make the engine hard to warm up in the winter if they are blocked.