Carb Tuning Help

[65Guy]

I have an edelbrock 1405 on my 350. I set the fast idle at about 900 rpm and when i put the truck in drive it almost goes dead at like 600 or 700 rpms. Does this sound like a tuning problem with the carb or is it a timing thing with the motor. I havent checked the fuel pressure yet but i know that these carbs can run rich if the fuel pressure is too high. Help please.

[EVBuilder]

What is the timing set at? Are you running a mechanical or electric fuel pump? Are there any vacuum leaks? One tip for setting idle mixture, hook up a vacuum gauge to an active idle vacuum port and tweek the idle mixture screws until maximum vacuum is reached. Sometimes if idle mixture is too rich it will pull the RPM down under load. Without knowing what the timing is set at and what cam you are running its hard to say what it should even be. I have the same type of carb on a 400 sb and mild RV cam with static timing set a 8 deg. BTDC. If you're running a hotter cam you may need more. another good thing to know is what the total timing is and when it comes in. This can be checked by using either a timing tape or a programable timing light. If you buy a timing tape make sure you order it for the right diameter balancer or it wont be accurate.

[Sick5]

Wow never knew the part about using a vacuum gauge to set the mixture screws.
ive always (on edelbrock) screw in all the way and then 2 1/2 turns out
....
so one more time make sure i gets this right hook up vacuum guage turn screw till i get the must sucktion?
what should the timing be set for a stock 305



dam sorry 65GUY didnt mean to jack it but very interested in this myself
elertrical fuel pump for me

[EVBuilder]

Yes thats a good baseline to get started but to get it fine tuned that is method I use on all brands of carbs. My favorite carb for any application is the late 60's early 70's era Q-jet. I drag raced them and ran them on the street they are bullet proof. Also if you know what list number to look for are available up to 850 CFM.

[EVBuilder]

Electric fuel pumps have a tendency to run too much pressure so a regulator and gauge are invaluable. Also some carbs can handle more line pressure than others. Q-jets for example dont like pressure above 8 psi. while Holley's can handle more. With my limited experience with the Carter AFB/ Edelbrock carb I am not sure what their limit is.

[Sick5]

Originally Posted by EVBuilder

Yes thats a good baseline to get started but to get it fine tuned that is method I use on all brands of carbs. My favorite carb for any application is the late 60's early 70's era Q-jet. I drag raced them and ran them on the street they are bullet proof. Also if you know what list number to look for are available up to 850 CFM.

well i have a 1406 eld wich is a 650 i think
im going to start looking for a cam not sure what cam is right for me!

[EVBuilder]

As for your timing question Sick5... If the engine is stock refer to your manual and then try advancing it 2 degrees at a time until the performance falls off or spark knock becomes an issue. If the engine is not stock then its probably going to be trial and error until its right. But most stock engines like between 4 and 8 degrees BTDC. When tuning for drag racing we never look at static timing i.e. timing at idle. the total advanced timing is what to check and also when it comes in. the factory puts really heavy springs in the mechanical advance so it may never reach total timing. Mr. Gasket makes an advance curve kit that comes with a variety of springs to change the RPM of when the total timing comes in. A tip for that too, don't use the weights they tend to bind just change the springs.

[Sick5]

Thanks
you should make a quick tips thread

[65Guy]

I decided to go with tbi and the carb had a float problem. thanks for all the help guys.

[EVBuilder]

Cam selection can be complicated. There are many considerations to take into account. They include rear axle gearing, rear tire diameter, intake manifold, fuel economy, emissions laws in your area, vacuum requirements such as power brakes, driving conditions, Also a cam that would be quite mild in a 350 will be wilder in a 305. Exhaust is also something may need upgrading afterward. Timing chain and gear sets can change the way a given cam performs also. There are three location timing gear timing sets that can alter the cam timing by 4 degrees in either direction from how the cam was ground. Advancing the cam gives it better performance in the lower RPM while retarding it will do the opposite. Another distributor trick few know about is end-play. The factory set up can have over .050" of end-play, being that the gears are helical if the distributor shaft can travel up and down it will also rotate a few degrees, Mr. Gasket makes a distributor shim stock kit that you can eliminate this play. I like to clamp the distributor housing in a vice and put a dial indicator on top of it. Then check the play that it has. After that drive out the 1/8" roll pin with a drift punch and add the appropriate amount of shim to bring it down to .005" this will greatly stabilize the ignition timing over the entire RPM band.

[Sick5]

Originally Posted by EVBuilder

Cam selection can be complicated. There are many considerations to take into account. They include rear axle gearing, rear tire diameter, intake manifold, fuel economy, emissions laws in your area, vacuum requirements such as power brakes, driving conditions, Also a cam that would be quite mild in a 350 will be wilder in a 305. Exhaust is also something may need upgrading afterward. Timing chain and gear sets can change the way a given cam performs also. There are three location timing gear timing sets that can alter the cam timing by 4 degrees in either direction from how the cam was ground. Advancing the cam gives it better performance in the lower RPM while retarding it will do the opposite. Another distributor trick few know about is end-play. The factory set up can have over .050" of end-play, being that the gears are helical if the distributor shaft can travel up and down it will also rotate a few degrees, Mr. Gasket makes a distributor shim stock kit that you can eliminate this play. I like to clamp the distributor housing in a vice and put a dial indicator on top of it. Then check the play that it has. After that drive out the 1/8" roll pin with a drift punch and add the appropriate amount of shim to bring it down to .005" this will greatly stabilize the ignition timing over the entire RPM band.

Wow
well at time i have a 305. i do have a 350 from 1993 burban that im thinking of parting out... im going to try that vacuum trick in a bit