high idle without load, low idle under load

[mfj]

Hello again,

I was having issues with my Holly 4160 (accelerator pump, power valve, shaft leakage, poor tun-ability) so I decided since I have replaced everything on this motor except the long block it was time for a brand new carb. So I got an edelbrock performer 750 electric choke. I started the car and the problem was some what solved, throttle response improved greatly no more backfiring, and the off idle stutter was gone. Now another problem reared it's ugly head...

The Problem, in Park the idle is high at 1100ish Rpm, and in drive the idle is low at 450Rpm. when in drive the motor will chug and sporadically rev up to 800ish Rpm, and not in a predictable way. I have chased down every vacuum leak and exhaust leak, and it's making good vacuum 22ish(watch the last video)

So my roommate and I are all out of ideas, any help would be greatly appreciated. If there are any members in the Santa Cruz area that may be able to help me out I have a ridiculous amount of beer for you!!! Just PM me and we'll chat.

The things I have done so far this week to correct the problem:
New plugs, wire's, dist, electronic ignition, coil, tightened the exhaust, fixed all vacuum leaks ( two cans of ether worth), checked timing (started at 12.5 BTDC, while tuning and tweaking it's running best at 16 BTDC) checked oil and trans fluid level ( a ok)

Now I am going to attach some video's so yall can actually hear and see what the problem is. There are six video's in all and I will list them in order. check the description to see what I had changed or fixed. And once again thank you for all of your help in getting my daily driver back on the road!

http://www.youtube.com/watch?v=jowqZLFC1_w

http://www.youtube.com/watch?v=L8C1ZIvPYnY

http://www.youtube.com/watch?v=dB86XBOX4J0

http://www.youtube.com/watch?v=6WTEF_8-vKA

http://www.youtube.com/watch?v=NzXfp8CLf80

http://www.youtube.com/watch?v=qql1L7q7DN4

 

[q-ship]

There can be a number of causes, but the most common (I will guess 99%) is due to a vacuum leak.

Use a spray bottle with 91% alcohol (available from any drug store) in it and spray the mating surfaces of the manifold, carb, vacuum fittings, PCV, etc; while the car is ideling in gear.

If one or more of the areas you spray causes the engine to change RPM, you have a vacuum leak at that point, and need to fix it.

Do the tests with the vacuum advance disconnected and plugged.

 

[mfj]

There can be a number of causes, but the most common (I will guess 99%) is due to a vacuum leak.

Use a spray bottle with 91% alcohol (available from any drug store) in it and spray the mating surfaces of the manifold, carb, vacuum fittings, PCV, etc; while the car is ideling in gear.

If one or more of the areas you spray causes the engine to change RPM, you have a vacuum leak at that point, and need to fix it.

Do the tests with the vacuum advance disconnected and plugged.

I have gone to town with TWO cans of starting fluid, and did find a few vacuum leaks and fixed them. As of right now and yesterday I have no vacuum leaks. Any other ideas?

 

[mfj]

Last night after I got a ride home I ran the car for about a half of an hour and the problem is still there. Went to town with more starting fluid and am 100% sure I do not have a vacuum leak, I removed the #1 spark plug and it looks great. so not sure what to do now...

 

[Redpolara]

I have a few questions on this one.
What are the camshaft specs?
Does it have a stock converter or otherwise?
Is the vacuum advance hooked up to the full or ported vacuum port?
What's the vacuum reading when you pull it into drive?

 

[mfj]

Well I can answer three of those right now;
It has a stock 383 2bbl camshaft
the converter is also stock
I have the vacuum advance hooked up to ported vacuum
I asked my roommate this morning about the vacuum in drive and he couldn't remember, so I'll check that this evening. If you have any other question ask away.

 

[wingcarenvy]

It sounds from the video that it has a lean misfire, which gets worse under load. This is typical of a lean misfire. This can be caused by a few things, obviously vacuum leak is the top suggestion. It can be caused by too much advance in the timing. Idle mixture screws set too lean or on the edge of too lean. Does it have a stock cam? Does it drive good other than idle quality? I would definitely be looking real hard at the carb and its tune up.

 

[mfj]

It sounds from the video that it has a lean misfire, which gets worse under load. This is typical of a lean misfire. This can be caused by a few things, obviously vacuum leak is the top suggestion. It can be caused by too much advance in the timing. Idle mixture screws set too lean or on the edge of too lean. Does it have a stock cam? Does it drive good other than idle quality? I would definitely be looking real hard at the carb and its tune up.

That sounds very interesting, thinking back on my tuning process so far that is a possibility. When I first put the new carb on I tuned it to the lean side, after the idle issue was apparent I bumped up the timing thinking more fuel=more timing. When adjusting the timing it sounded best at about 16BTDC. This did not solve the issue. I then tuned the carb to the rich side. Now adjusted to the rich side it dose not like any timing below 14BTDC and can't really give it to much more than 16ish. As far as drivability with 16 deg it falls on it's face after 1/4 throttle and rich mixture, but adjusted lean and with 12.5BTDC above 1100 rpm this baby howled, but idle was horrible in gear somewhere around 450. Now this is a factory direct edelbrock carb with factory metering rods and springs. the cam is a stock 383 2bbl carb camshaft. With about three hours of running on the new spark plugs do you think it would be wise to read all of them?

 

[Redpolara]

Something else purely as a process of elimination, have you checked the vacuum unit on the dizzy? if the diaphram goes it can be the source of another vacuum leak.

 

[YY1]

...and you're running a 4 BBL on a 2 BBL cam...

 

[mfj]

Something else purely as a process of elimination, have you checked the vacuum unit on the dizzy? if the diaphram goes it can be the source of another vacuum leak.

Thank you for the helpful input, this is driving me crazy and I'm glad I don't have to do this alone... So I checked the vacuum in drive and it is at 15psi, and the dist dose not leak(it's about two months old, the last one I got was D.O.A) so I know what I was looking for. This has got me stumped, I don't hear any noise coming from the heads like a collapsed lifter or broke spring, and my timing has not jumped. Gotta be the carb...maybe?

 

[mfj]

...and you're running a 4 BBL on a 2 BBL cam...

...yup...

 

[wingcarenvy]

I think I read that you have the vacuum advance hooked to manifold vacuum? If it is, it needs to be hooked to ported vacuum. There should be no vacuum to the dizzy at idle. Do you have a known good carb from another car that runs perfect? If so you might want to try it. I feel for ya man, I just went through a nightmare running issues with my roadrunner. The process of elimination will get you there. If you had a mechanical valvetrain issue it would make noise. I would go back to basics and do a compression test then leak down. I would inspect the distributor for shaft play and point condition. I would then check the timing at idle and at max advance. Then comes dwell. I would then take the valve covers off and look at the valvetrain and valvesprings. I would even check to make sure you have consistent lift. After all that I would seek out a smog station thats willing to sniff the car at idle to see where your idle mixture is. One thing I forgot is that I would look down the carb while its idling and make sure it isn't dripping. And one more thing while my thoughts are scattered. I would check the timing in and out of gear. I had a distributor once drop 10 degrees of timing when I put it in gear, I locked out the advance and set the timing to 36 degrees and it ran perfect.

 

[mfj]

I think I read that you have the vacuum advance hooked to manifold vacuum? If it is, it needs to be hooked to ported vacuum. There should be no vacuum to the dizzy at idle. Do you have a known good carb from another car that runs perfect? If so you might want to try it. I feel for ya man, I just went through a nightmare running issues with my roadrunner. The process of elimination will get you there. If you had a mechanical valvetrain issue it would make noise. I would go back to basics and do a compression test then leak down. I would inspect the distributor for shaft play and point condition. I would then check the timing at idle and at max advance. Then comes dwell. I would then take the valve covers off and look at the valvetrain and valvesprings. I would even check to make sure you have consistent lift. After all that I would seek out a smog station thats willing to sniff the car at idle to see where your idle mixture is. One thing I forgot is that I would look down the carb while its idling and make sure it isn't dripping. And one more thing while my thoughts are scattered. I would check the timing in and out of gear. I had a distributor once drop 10 degrees of timing when I put it in gear, I locked out the advance and set the timing to 36 degrees and it ran perfect.

I have many questions regarding this post but I'm at work and have to go to school tonight so I will keep it short(for now) I have thrown a vacuum gauge at both the manifold vacuum and ported vacuum, both pull vacuum at idle. The ported pulls 7-10psi and the manifold vacuum pulls 22psi at idle, could that be an issue? we'll get to the other tonight or tomorrow... thanks for the input I need it, and it is greatly appreciated!!!!

 

[scotts74birds]

Just a quick basic, did you tune the idle mixture to ear [speed], or to highest vacuum [recommended]. I just want to knock one thing out. An old wrench once told me that most, [not all], carb problems are in the distributor.

 

[mfj]

Just a quick basic, did you tune the idle mixture to ear [speed], or to highest vacuum [recommended]. I just want to knock one thing out. An old wrench once told me that most, [not all], carb problems are in the distributor.

That was one wise old man!!! Last night I re-inspected my entire ignition system and found that my pertronix ignitor 2 was not adjusting the dwell as it is supposed to. I had 10 deg of dwell through out the entire rpm range, so I threw some new points and a condenser on a viola!!! Problem solved!!! HOWEVER now my starter will not disengage while in park or neutral, it grinds... OH GOD!!!! when I drop it in gear the grinding noise goes away? What? So I have a little electrical work to do, so I can drive it. I swear if it isn't one thing it's another...

Thank You to everyone that offered up good advice I really appreciate the help, this is why I own a Mopar, good cars and good people.

 

[mfj]

...and you're running a 4 BBL on a 2 BBL cam...

And she runs like a champ!!

 

[scotts74birds]

Sticky bendix, or possibly broken spring. If you are handy, you can fix it for a couple of dollars rather than replacing the whole starter.

 

[mfj]

Well in my haste to start driving again I accidentally hooked up the ignition wrong...

Re-ran one wire and my girl is on the road again!!!!!!

Thank you all so much! Really top notch!!!!

 

[wingcarenvy]

Excellent! Way to stick with it. I have one question. Whats with the Petronix ignition? I have never had a problem with them, and if you call the tech line they are really helpful. Just a thought. I hate points.