So here is the story. I bought my wife a rebuilt 75 duster with a 360. The engine was rebuilt, but I have no specs. The little build data that I have is that stroke is original, heads appear stock, intake manifold is stock, edelbrock 600 cfm carburetor, stock mopar ignition, and 727 torque flight with stock converter.The problem, idleWhen sitting at a stop light the car invariably dies. I have the ignition set at 34 degrees BTDC at 3500-4000 rpm. To get good air fuel ratio (with a fast wide band air fuel ratio meter) I had to back the idle screws out almost all the way. I cannot get a good idle in neutral that is much below 1000 rpm, and unless the idle is 1100 or more it will not idle stopped in gear. With the idle at 1000 I am drawing about 15-18" of vacuum as idle goes down the vacuum starts to go down. I have been to my wits end and back. I found and replaced a bad vacuum advance canister, replaced plug wires. The spark plugs are a nice tan, and look nearly new. Next I plan on checking top dead center is properly marked. I think this will be pointless, but next I think I will have to pull the engine and check the degree on the cam shaft. I am also contemplating putting in a higher stall torque converter. I am at my wits end the car is fun, but does not throw me back in the seat. I didn't want to build this car, I just wanted something for my wife to drive.any advice would be greatly appreciated.
when sitting at a light, in gear and at idle, do u have around 10 degrees advance? advance it until it pings some and then back her down a little. maybe u have a vacuum leak. if the cam is in late idle will suffer, but if u lighned up the dots the mopar cam is in the ballpark. if your cam is advanced u will have more low end and less top end, if retarded less low end and more top end
I had to back the idle screws out almost all the way. I cannot get a good idle in neutral that is much below 1000 rpm, and unless the idle is 1100 or more it will not idle stopped in gear.you did not say if its a brand new carb... do you have some carb spray.????do you have compressed air and an air nozzle...take the idle mixture screws out.. spray carb cleaner spray into the idle mixture screw holes.. then follow up with a blast of compressed air.. try it a few times.. see if the idle circuits start responding...if its a brand new just out of the box carb.. call edelbrock.. you might have debris in the idle feed restrictors. the idle feed idle transition restrictor is where the drill is sticking.. the idle air jet is out on the bench. you might also have the throttle blades set wrong.. having the idle holes uncovered too far..lastly... DO YOU HAVE a PCV valve hooked up??? it allows a known amount of air into the intake and allows you to close the primary throttle blades farther. early AFBs actually had an idle speed screw / idle air bypass right where the PCV hook up is on at the front of the carb.. so you might want to verify you have the proper size of PCV valve installed.. aftermarket manufacturers have been packaging them by shape not flow rating like they should be..
12-14 degrees at about 1000 rpm. I am going out to clean idle air jets and check transfer slots now. Thanks
I adjusted the throttle plates to where .060" of the transfer slot was exposed. I got that number from my How to Rebuild and Modify Carter/Edelbrock Carburetors. I also cleaned out the idle jets with carb cleaner and air. I initially set the idle screws to 3 turns open. This combination ran, but would not idle. I have checked for vacuum leaks every way I know how (starting fluid at all joints, propane, even blowing smoke in the intake manifold with the engine shut down). Is there a way to check cam specs without removing the engine from the car and searching for numbers on the cam? The more I work on this problem the more I believe some one put a cam that was way to wild for the rest of the build in the engine. I am going to finish removing all vacuum lines, and plugging them in a search for vacuum leaks. Is it possible a 600 cfm carburetor is just too small?
You should be able to pull the cam out without taking the engine out, but you do have to disassemble a bunch of stuff on the front end. I'm guessing who ever built the engine put it in right but who knows, as an electrician I've seen qualified people do stupid crap. Though if nothing else seems to be the problem that may be the case so I would check if all else fails. Did cleaning the idle air jets work or did it not do anything? What about the ignition, have you checked that at idle the engines getting enough spark? If there's a voltage problem it can lead to low voltage to the coils resulting in weak sparks at idle speeds. Hope it works out.
if u have 15-18" of vacuum sometimes at 1000 the cam is not too big. do a cranking compression test on all 8 cylinders when warm and with the carb open. with solid lifters the cam can be measured at the spring retainer, with hydraulic lifters they can blead down some and give less than true numbers. a 600 is not too small to idle, maybe too small to make max top end power. a vacuum leak usually makes for a higher idle. take the top of the carb off and clean inside.
Cleaning the idle air jets did not seem to do anything. In the middle of testing it stopped starting. So I stopped working to avoid the urge to shoot the car. Tomorrow I will be at it again. It looks like I may have fried the ignition control module. I may have left it energized too long without it running. I would just let the thing idle high, but it makes a heck of a jolt when you put it in gear. Perhaps I need a higher stall torque converter.
Well compression test was good. The lowest cylinder was 142 PSIG, and the highest was 150 PSIG. I disconnected everything, but my vacuum gage. I was able to idle in neutral steady at 850-960 rpm. The vacuum was 16". The air fuel ratio was 13-14. All was good, until I put it in gear then moments later it died. How much of a vacuum leak would cause this. Everything gets steadily worse the more vacuum attachments I hook up. The pcv valve caused a noticeable increase in rpm and leaning of the air fuel mixture. Hooking up the vacuum advance made the idle go up vacuum get very erratic (12-19"), and air fuel get very lean. Tomorrow I will continue trouble shooting.
with the PCV valve installed....hook up your vacuum gauge.. back off on the idle speed screw to slow the idle down.. while watching the vacuum gauge.. back the idle mixture screws out one at a time to get to the highest vacuum.. then turn it in slowly till it starts to drop.. stop and back it slightly out to reach the point where it started to drop..do the other idle mixture screw... backed out to reach the highest vacuum. then turn it in till it just starts to drop... then.. reset the idle speed again.. then the idle mixture screws.. if the idle speed is not proper.. go through this one more time..last adjustment is to turn the idle mixture screws in to drop the idle vacuum 1/2" overall.. this is lean best idle mixture.. the screws may not be matched exactly.. but they should be close.. you are adjusting flow.. without a PCV.. there is too much throttle opening for the car to idle properly on the idle circuit..it is NOT designed to idle on the idle transition slots.. it will load up and stall if its idling on idle transition slots as its WAY too much fuel for idle..how about a carb number... did you see this... you might want to read page 5 and 6.. perhaps 7 a few times... its still not really clear how it operates... http://www.mymopar.com/downloads/carterafbtuning.pdf
i found some more stuff... you will want to copy and print to go over a few times.. this was for another brand of carb.. no not a holley.. well kinda.. TUNING BE SURE TO FOLLOW THE NEXT INSTRUCTIONS IN THE PROPER SEQUENCE, DEVIATION WILL CAUSE THE CARBURETOR TO NOT FUNCTION TO ITS IDEAL SPECIFICATIONS AND MAY NOT PROVIDE THE PERFORMANCE AND FUEL ECONOMY AS DESIGNED.Start the engine, the engine will run very slowly more like a tractor. As long as the engine stays running idle speed is not important at this point.The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). The engine should pick up speed and begin to smooth out. Back out ½ turn more, or until the screw does nothing or runs worse then turn back to the point where it ran its best.Use your ear, not a scope or tuning instruments at this point. You want to tune the engine by sound. Adjust to best, fastest and smoothest running point.Now that the mixture screw is at its best running location, you can adjust the Idle speed the screw. The screw will be sensitive and should only take ¼ to ½ turns to achieve the idle speed you like.Check and set idle to your driving preference. Put the car in gear and apply slight load, (AC on) and set the Idle as you like it. Don’t set it too high, as this will cause causes excessive clutch and brake wear. The Idle only needs to be 7 to 900 RPM with light load or AC on.Recheck timing and vacuum hook ups. Recheck mixture screw to lean best idle again. If all is still best and smoothest idle then confirm and note the final settings.To confirm settings with the engine running. Start by screwing in the mixture screw and count the number of turns it takes to bottom out and note if the engine dies. If Idle Mixture screws are with in ½ turn of base line setting then all is well and have fun. Also check the speed screw and note how many total turns from initial contact. You may have opened (turned in) the speed screw. Your final setting should be under 2 full turns. Reset the screws (back in) to the best final settings (Per your notes) and go on a test drive and have fun. If the settings are other than described then you may want to recalibrate the Idle circuit (low speed circuit) to your engines needs. This is done by following the rule of thumb BELOW. Simple Rules for low speed calibrationIf the mixture screw is more than 2 1/2 turns out turns then the Idle jet is too lean (too Small). When the mixture screw is less than 11/2 then the Idle jet is too rich (too large). These assumptions are based on the fact that the speed screw setting is not opened more than 11/2 turns. If the speed screw has to be opened 2 or more turns then this is also an indication of a lean condition usually requiring greater change. At times it may appear to be showing signs of richness or flooding it is really a lean condition. See pictures and notes in the tech 2 article supplied in the kit instructions, view and please understand the need to keep throttle plate as near to closed as possible so as not to prematurely expose the transition holes. This is what causes the visible rich condition, and confirms the need to increase the jet size. JET KITS are available if needed.EXAMPLE With the speed screw set at no more than (1 1/2) turns in after contact with the stop lever; and the best idle occurring with the mixture screw set at 3 turns from bottom, indicates the need for a larger Idle jet. Achieving the best idle at under 2 turns indicates the need for a smaller idle jet.wayne says.. DON"T WORRY about the idle jet sizing but the theory is correct..
I will be trying this tomorrow. I had to work on something else for a while or dynamite may have gotten used to solve the problem.
Well tried that adjustment method. I am still a little worried about the drivers side idle jet. I even checked the fuel pressure at idle. 5-7.5 psig all the way down to 500 ish rpm. So I had the wife get in and put it in drive while I was watching parameters went down into the 500s for idle rpm. 5-10" vacuum. and 6-7 psig fuel pressure at the inlet to the carburetor. This was with all vacuum hoses disconnected and plugged with the exception of the pcv valve. Tomorrow I will look at all this with my air fuel ratio meter hooked up.
fuel pressure is good. a lil more ignition advance-hook up the vacuum advance-sounds like it maybe bad cuz hooked up it was erratic and lean. replace the vacuum advance unit, or leave it off and try more advance by rotating the distrib on the smallblock counterclockwise