302 won't idle after warm up

[djs69stang 10]

Please read the entire description and think beyond the box before suggestions start flying. I have been at this issue for 3 days and have tried just about everything.

302 with Edelbrock 600 cfm, electric choke, edelbrock mech. fuel pump, edelbrock 289 Performer IM. It was running just fine before this abrupt change in behavior.

Motor starts fine, after it warms up and the idle drops the motor starts running rough, intermittent and eventually quits. Wait 5 seconds, motor starts fine, then runs rough, intermittent and quits.

Here is everything I have done (in no particular order) to figure out why.

Removed the carb, cleaned every needle, seat, float, bowl. Adjusted the floats. Did everything the Edelbrock tech and the Edelbrock website said to do.

Drained the fuel line from the carb to the pump to the fender wall, cleaned out Edelbrock fuel filter and installed another one between the pump and the tank.

Checked every vacuum line for cracks, holes, tears. In fact, I unplugged every vacuum hose from the carb and covered the ports on the carb, unplugged every vacuum hose from the intake manifold and covered those ports.

Disconnected the power to the electric choke.

Closed the air mixture screws, opened them 2 turns (as the tech and manual says) and opened and closed them to no effect.

I loosened the distributor and moved it around to effect the timing and it still quit.

I ran the normal idle screw in and out.

With the motor running I sprayed Carb cleaner around the carb, around the IM, around ports on the IM, no effect (which should mean those items are sealed correctly and there is no vacuum leaks there)

If it is warm and I put both hands over the carb to limit air flow, no effect.

There may have been some more things I did but that is all I can think of for now.

To review, when the motor is cold, it runs fine at high idle and quits after warm up.

Aight, think deep.:helpsmilie:

[Angel 24]

Sounds like it just needs water. Na jk. Wow dude its sounds like you've already gone through the most common stuff. Sit tight. I'm sure some of the vets will be able to help you out. Does sound like an induction problem though.

[LoneWolf2U 136]

Closed the air mixture screws, opened them 2 turns (as the tech and manual says) and opened and closed them to no effect.

 

 

You have isolated your problem right there. Plugged idle passages or air bleeds.

[foothilltom 33]

Please read the entire description and think beyond the box before suggestions start flying.

 

Hmmm...I was mildly put off by this admonishment. I find the advice here to be almost always spot-on and I wouldn't discourage folks from chipping in.

 

Anywho, my suggestion would be to think on any changes since your car idled perfectly. What has changed? The passage of time only? It's crucial to start there, IMHO.

 

Your engine idles well when it's cold, under choke, which is a rich mixture. As your electronic choke opens the butterfly, the mixture leans out and it begins to run poorly. So that's a big hint: you are running too lean.

 

Mach1 already told you this, but the fact that your idle-mixture screws have no effect is also a tell-tale sign. Your idle circuit is not working as it should which could imply clogged idle fuel passages.

 

You didn't mention this, but does your engine run well after it is warm (outside of the poor idle obviously)? Can you adjust the idle screw to a high RPM and keep it running? Can you open the throttle and keep it running? Can you rev it under load? These are distinct fuel delivery circuits in your carb so it's important to know if your problem is limited to bad idle.

 

You mention a scrupulously detailed inspection of vacuum hoses and whatnot but are you actually using a vacuum gauge? If not, you're just messing around. A vacuum gauge will shed much light on your problem. Get one, hook it up and see what it says as your car warms up.

 

Finally, you talk about messing with the timing but are you using a timing light? I understand the desire to leave no stone unturned but if you're not using proper equipment, you're just winging it and could wind up chasing your tail.

 

More detailed info from you will increase the value of the responses!

Good luck,

Tom

[djs69stang 10]

Hmmm...I was mildly put off by this admonishment. No admonishment intended . . just frustrated. Freaking Spring here, perfect weather for drop top and I have yet to get her out. Missed a great car show on Saturday also. I find the advice here to be almost always spot-on and I wouldn't discourage folks from chipping in.

 

Anywho, my suggestion would be to think on any changes since your car idled perfectly. What has changed? The passage of time only? Only factor involved is time. During the winter the motor gets run every now and then or a quick spin. I live in STL so taking a convertible out in the winter is a moot point. It's crucial to start there, IMHO.

 

Your engine idles well when it's cold, under choke, which is a rich mixture. As your electronic choke opens the butterfly, the mixture leans out and it begins to run poorly. So that's a big hint: you are running too lean.I would agree.

 

Mach1 already told you this, but the fact that your idle-mixture screws have no effect is also a tell-tale sign. Your idle circuit is not working as it should which could imply clogged idle fuel passages. I removed the carb, disassembled the entire body and cleaned out every port, opening, nook, with cleaner and air. Regarding those mixture screws, I closed them and them turned them out 2 full turns per Edelbrock tech. I will try again on the in and out.

 

You didn't mention this, but does your engine run well after it is warm (outside of the poor idle obviously)? No, it doesn't run, it starts to sound like it has a monster cam in it then gets worse and eventually quits. Can you adjust the idle screw to a high RPM and keep it running? Maybe, I just had my partner keep his foot on the pedal and keep the rpm's up. Can you open the throttle and keep it running? If the rpm's drop below 1000, there is no saving it, it quits. Can you rev it under load? Only if done so before the rpm's drop. These are distinct fuel delivery circuits in your carb so it's important to know if your problem is limited to bad idle.

 

You mention a scrupulously detailed inspection of vacuum hoses and whatnot but are you actually using a vacuum gauge? Have not used a gauge yet as I was just trying to determine direction.If not, you're just messing around. A vacuum gauge will shed much light on your problem. Get one, hook it up and see what it says as your car warms up. Will do but it will be hard to do as the motor won't stay running on its own.

 

Finally, you talk about messing with the timing but are you using a timing light? Tried but the idle is so bad it jumps between 10 and 20. I only moved the dist. just to see its effects. I understand the desire to leave no stone unturned but if you're not using proper equipment, you're just winging it and could wind up chasing your tail.

 

More detailed info from you will increase the value of the responses!

Good luck,

Tom THX for your input. To try and determine if it is vacuum leak or fuel delivery problem I was going to do the following: 1st-unplug the hoses from the carb and plug those ports. Also plug the lines that went from the carb to the IM and wherever else. With the motor running and the choke open, cover the top of the carb. If it quits, then the carb is OK and the leak is elsewhere. There are 4 vacuum lines on the IM, work my way thru them and see if there is an effect. If none of those 4 hoses/ports have an effect, there must be a leak in either the IM, brake booster or pollution canister. What do you think? Also, I will get the vacuum gauge hooked up.:001_smile:

[foothilltom 33]

DJ, it sounds like you're taking a very good approach to this. I should have realized that it's difficult to do some of these tests if you can't keep it running. A couple of thoughts:

 

If you can, adjust the idle screw until your throttle is open enough to keep her running. You may need to shim it somehow to get the throttle to open far enough. Checking timing at 2000 (or more) RPMs is just fine. In other words, whatever you can do to keep it running is a good idea so you can work through your various tests.

 

Perhaps you could disengage your electric choke and keep her choked so you can keep it idling?

 

I'm still leaning toward a clogged idle circuit, but it's nice to rule out other suspects if you can (vacuum). A simple test is to leave everything connected and spray some starting fluid (or something appropriately combustible) near and around suspect leak areas (stay away from the mouth of the carb). If you can hear a change in RPMs, you may have found a leak. Focus on the IM vacuum ports as the ports connected to the carb draw a tiny amount of vacuum in comparison to the IM.

 

I know this may not be feasible, but if you have a known, good carb laying around (or can borrow one), it might be simpler to just throw that carb on there and see if your idle problems vanish. A carb is an incredibly complex gizmo with passages that are super-tiny. I know you've cleaned it up, but I am still betting this is a idle-circuit problem based on everything you've said so far. Soaking the entire carb for 24 hours would probably be a cheap experiment.

 

I feel your frustration, but take heart. We've all been here and you will solve it. The dudes here are smart (present company excluded).

 

Best,

Tom

[panteramatt 1]

Had the same problem. One of my idle mixture screws would do anything when I messed with it and I couldnt even get it in gear. Sprayed carb cleaner in the port and blew it out with th ecleaner off and that worked fo rme. Give it a try.

[djs69stang 10]

It sounds like you're taking a very good approach to this. I should have realized that it's difficult to do some of these tests if you can't keep it running. A couple of thoughts:

 

If you can, adjust the idle screw until your throttle is open enough to keep her running. You may need to shim it somehow to get the throttle to open far enough. Checking timing at 2000 (or more) RPMs is just fine. Will do. In other words, whatever you can do to keep it running is a good idea so you can work through your various tests.

 

Perhaps you could disengage your electric choke and keep her choked so you can keep it idling?

 

I'm still leaning toward a clogged idle circuit, but it's nice to rule out other suspects if you can (vacuum). A simple test is to leave everything connected and spray some starting fluid (or something appropriately combustible) near and around suspect leak areas (stay away from the mouth of the carb). I did this and nothing changed. But I will try again. If you can hear a change in RPMs, you may have found a leak. Focus on the IM vacuum ports as the ports connected to the carb draw a tiny amount of vacuum in comparison to the IM.

 

I know this may not be feasible, but if you have a known, good carb laying around (or can borrow one), it might be simpler to just throw that carb on there and see if your idle problems vanish. That is something I hadn't thought of. Funny thing is I changed to the Edelbrock last summer because my 20 yr Holley was nickel and diming me and when the base plate cracked I decided to change. I know 2 other gear heads who just may have another carb to try. A carb is an incredibly complex gizmo with passages that are super-tiny. I know you've cleaned it up, but I am still betting this is a idle-circuit problem based on everything you've said so far. Soaking the entire carb for 24 hours would probably be a cheap experiment. I can remove those mixture screws right? I didn't do that. Can I remove them now with the carb intact on the motor and gas in the carb?

 

I feel your frustration, but take heart. We've all been here and you will solve it. The dudes here are smart (present company excluded).

 

Best,

Tom

Edited May 10, 2010 by djs69stang

[djs69stang 10]

Had the same problem. One of my idle mixture screws would do anything when I messed with it and I couldnt even get it in gear. Sprayed carb cleaner in the port and blew it out with th ecleaner off and that worked fo rme. Give it a try. Can I remove those screws now with the carb intact on the motor and gas in the bowls? I didn't think to do that trick.

[1952 10]

First things first You need to Diagnose the problem Not throw parts at it

 

Install a temp fuel pressure guage and what the fuel pressure intently

 

start there...let us know

[panteramatt 1]

Had the same problem. One of my idle mixture screws would do anything when I messed with it and I couldnt even get it in gear. Sprayed carb cleaner in the port and blew it out with th ecleaner off and that worked fo rme. Give it a try. Can I remove those screws now with the carb intact on the motor and gas in the bowls? I didn't think to do that trick.

 

 

Yes. Just remove them both, spray the hell outta them, let it site for a few seconds, then with your breather off blast some air in there and then see if that clears it up.

[djs69stang 10]

Here is the testing for the day and the results.

Removed all the vacuum hoses from the carb and plugged all 4 ports.

Removed all 4 vacuum hoses from the tree on the back of the intake manifold and covered those ports.

Removed idle mixture screws and sprayed out ports, inserted screws to close and turned them out 2 full rotations.

Turned regular idle screw in so when motor warms up, it will stay at higher rpm.

Started engine (no problem), let it warm up and watched choke plate open. Set rpm to 1800. If it goes below 1600 it will quit.

Put cloth and hands over the top of the carb and it quit running.

Restarted motor, no problem.

Checked vacuum at main carb port, front center, 20 hg.

Checked vacuum at IM, 20 hg.

Hooked brake booster to IM, vacuum stayed at 20 hg.

Vacuum stayed at 20 hg as I hooked each hose back onto the IM.

To me, no vacuum problems.

Then I inserted the fuel pressure gauge into the line between the carb and the fuel pump. At 1800 it is reading just over 6 to 6.5, needle kind of bounces. Edelbrock manual says 5.5 to 6. REALLY NOW, THAT SMALL OF DIFFERENCE CAN CAUSE THE MOTOR TO "FLOOD" AT IDLE, THEN SHUT OFF? If this is the problem does that mean I have to insert a regulator?

Next test is to remove the carb and try another one.

Edited May 13, 2010 by djs69stang

[djs69stang 10]

Oh my, it is finally over!!!!!!! The agony, the disappointment, the guessing. The last tests to do before I turned the car over to some one else was to (1) run the motorand when it started to die spray some carb cleaner in the throat, if the motor kept running then we knew it was a fuel delivery issue. That did not work. (2) So, I was at my favorite repair shop as they did the inspections on my van, 2 of the guys there are Ford guys, we were talking and the one guy had an Edelbrock 600 cfm carb right there that he gave to me to test by replacing mine. That did not work. So, we pulled the distributor and the points were fried! Burnt. The felt runner that goes against the distributor was toast. So, I went and looked at MSD's website and found that their MSD Blaster coil has only .7 ohms resistance. And there on their site they clearly say that if you are using factory stock points or an Electronic ignition like the Pertronix Ignitor you need to ADD a BALLAST RESISTOR of .8 ohms are more!! WHAT?! Are you serious, that's all? (By the way, that info is not in their coil package) So I got one from Advance AP and the combination now lends to just over 2 ohms and you know what? IT'S ALIVE!!!!!! WAHOO!!!

 

Now let the summer begin!!

 

Only question is .. why hadn't the Pertronix failed before this?

[brianrupp78 10]

You need a ballast resistor.... lol

 

oh darn you already posted about it. I was going to come one here and act like i knew what the problem was. So its probably from when you put in the painless because the stock resistor wire got deleted.

[foothilltom 33]

Anywho, my suggestion would be to think on any changes since your car idled perfectly. What has changed? The passage of time only? Only factor involved is time. During the winter the motor gets run every now and then or a quick spin. I live in STL so taking a convertible out in the winter is a moot point. It's crucial to start there, IMHO.

 

Wise words...who said them? Oh, right, I did! Silly me. :)

 

To be fair, it sounds like it took some time for your points to fry and you wouldn't have necessarily equated that with a coil change.

 

But most importantly, great job and congrats!

Edited May 15, 2010 by foothilltom
cuz i still can't spell to save my life

[djs69stang 10]

THX, but I can't take all the credit. My Pop has been helping out with different tasks and he suggested we pop the top on the distributor to check some things and boom, saw those points. Tell you what though, that is one clean carb after going through it twice! :yes:

[foothilltom 33]

Old guys rule.

[djs69stang 10]

Got any pics of your ride?