Can you name the problem?

[mfj]

Hello all,

So, I have an issue with my belvedere. It runs horrible. The problem as I see it is that it putts pretty regularly, when I have the car in gear it will chug and putt so bad the car will jump forward, needless to say in traffic this is a problem. The car stutters bad upon start up and will idle pretty well until it warms up then the putting gets worse and the result is the video I have attached to this post. In the video you will see and hear the problem, notice I don't touch the gas peddle until about 1:45 into the video. Mind you the car is up to proper operating temp in the video. in fact about ten minutes before I shot the video I just about hit a prius while stopped in traffic. Yes I did want to hit it, but didn't want to have to buff my bumper again. I have replace everything but the long block on this motor, I did take out a faulty pertronix electronic ignition modular and replaced with new points and condenser which helped the idle speed but didn't have any effect on the putt. I am all out of idea's, I have ruled out a vacuum leak after hours of starting fluid and gas wasted. So please any ideas?

My car specs:
1967 383 bone stock internals, no rebuild
1971 383 4bbl dual plane manifold
edelbrock 1411 750cfm
stock 727
no ac
points style ignition
8 3/4 rear end stock
high level of badassness

http://www.youtube.com/watch?v=LKQI2cjLCrM

 

[Redpolara]

That type of exhaust spitting can be associated with badly seated/burnt valves, have you done a wet and a dry compression test?
As for jumping forward/surging, what condition is the carb in?

 

[mfj]

I have yet to do a compression test, I think I know what I am doing this weekend... As for the carb it is a brand new edelbrock 1411.

 

[q-ship]

How old is your distributor?

If it's original, I would replace it with a new electronic unit and coil.

Assuming you have really eliminated a vacuum leak, I have frequently seen worn distributors cause intermittent firing at idle, but it sure sounds like a vacuum leak due to the substantial difference in idle RPM, vs. in gear, while still sounding like a stock cam.

You should also check for bad plug wires by starting it in a totally dark garage with the hood up, and see if the wires are cross arcing.

 

[mfj]

You make some good suggestion q-ship. When this all started a few months back the first idea I had was ignition. I replaced everything but the ballast resistor (I put pertronix elec ignition which dose not use the ballast.) So with a new Distributor(came with cap and rotor), coil, elec pick up, I also changed plugs and wires. I have not run it in the dark and actively looked for cross arc, that is something I can do tonight...with a beer. Now I know it is quite common for people to say "I don't have any vacuum leaks." then only to find out it was in fact a vacuum leak. Well I have checked, re-checked, triple checked, and double checked the triple check. I was sure that was the problem because the new ignition sys didn't seem to help, I found a couple of leaks and resolution of those did not fix the issue either. I am 99.9% certain it is not a vacuum leak. My manifold vacuum is steady at 22. I'll check the wires tonight when I get home and let you know what I find. Thanks for the advice!

 

[q-ship]

With a steady 22" of vacuum, I would say it's not a vacuum leak, or bad valves.

Have you adjusted the idle mixture screws on the carb? A lean mixture can cause the surging you described, How does it run at cruise?

What do the plugs look like? what brand/heat range are they? Just as important is what is your cranking compression (compression test), as the early engines usually needed a hotter plug.

For a few bucks you can go to an emissions station and have them stick the sniffer up your exhaust (GOD that sounds kinky!), and you can see what the air/fuel mixture is at idle and cruse RPM.

If your coil and wires are new/good, with all the changes you have done, and a steady 22" of vacuum; the solution is going to be fairly simple, even if it's elusive.

 

[1970Moparmann]

The vacuum is the odd one. I was going to say could be a bad cam. I had a 68 Dart that had a bad cam, and it was doing a lot like what your seeing.

 

[mfj]

From the box edelbrock's are adjusted lean, after I fixed the leaks and re adjusted the timing I adjusted the carb full rich. I got the smell of un-burnt fuel all the way in the engine bay(mind you this is a station wagon and that has to be rich to smell it that far away.) It didn't really have much of an effect if any. So my next step was to lean it with jets and rods. Went 4% lean, ran a little smoother, so went the next step down to 8% and no change. Just for ****'s and giggle's I then went 4% richer from base calibration(out of box) and had little to no change(the idle got rougher and idled higher) I have now gone back to 4% lean as that is where it runs best. As for the plugs the old one's looked a little carbon fouled, but since I have put the new plugs they look pretty good, I'm attaching a picture of my number one plug taken a few weeks after the carb and ignition change. at this point the plug had about 40 miles on it and eight hours idling in my driveway diagnosing. My feeling about this problem is that it is something horrible simple yet not very obvious...

 

[racedodge]

i would pull the valve covers and rotate the assembly checking the overall movement of each rocker. you may see where a collapsed or failing lifter may cause your missing as it is not adequately opening an exhaust or intake valve. worse yet.. your camshaft could becoming well worn.

 

[mfj]

Well folks,

Checked for cross arcing last night and did not see any thing out of place. this weekend I'll rip into the heads and do a wet and dry compression test and see what I find. Thanks for everyone's input.

 

[mfj]

Sorry for taking so long to post the result's it's been an interesting month... So Friday I dug into the heads rotated the motor and checked for stuck valves and collapsed lifters and didn't see a thing. So I proceeded with the compression test and the results are...

cylinder #, Dry comp, Wet comp

1-123/144
2-110/134
3-124/
4-115/120
5-131
6-119/124
7-135
8-126/128.5

didn't have enough light to do the wet comp test on 3,5, and 7. So what do you think about the numbers and where do I go from here? Is it time to rebuild?

 

[Coronet 500]

Number 2+4 look close on that side making me want to do a leak down test,if you have one.If not simply pressurizing each cylinder at TDC then listening at intake and exhaust can narrow down the trouble.I'm hoping it's not a head gasket.

 

[Meep-Meep]

First of all I have to wonder why you are running plugs with a recessed tip. Get a set of Autolite 85's. Also, a 750 is way too much carb for a bone stock 383. Not that it's solely responsible for your idle condition but for the sake of properly matching up parts a 600 is more than enough. Is your firing order correct? 1-8-4-3-6-5-7-2 with #1 at the drivers front.

 

[Dennis H]

Plugs: NGK's only on my big block. Amazing difference.

 

[larj]

what is the dwell? If the dwell is wrong it will sound and run just like in your video? The dwell should be 30-32 at 1500 to 2500 rpm.

 

[Manifold]

From the box edelbrock's are adjusted lean, after I fixed the leaks and re adjusted the timing I adjusted the carb full rich. I got the smell of un-burnt fuel all the way in the engine bay(mind you this is a station wagon and that has to be rich to smell it that far away.) It didn't really have much of an effect if any. So my next step was to lean it with jets and rods. Went 4% lean, ran a little smoother, so went the next step down to 8% and no change. Just for ****'s and giggle's I then went 4% richer from base calibration(out of box) and had little to no change(the idle got rougher and idled higher) I have now gone back to 4% lean as that is where it runs best.

This is not how to tune the carb for idle. Hopefully I'm mis-reading your description on your carb tuning changes.

Always get the ignition/timing set first, then adjust the carb. I'd be going over the basics: correct plugs (already mentioned), good wires (test the resistance of each one), dwell correct (mentioned), timing set right (I'd do the basic method of 34-36 degrees when the timing is all in as a starting point), then adjust the carb with a vacuum gauge (run idle mixture screws out evenly until maximum vacuum is achieved then set idle speed).

Best of luck figuring this out!

 

[mfj]

This is not how to tune the carb for idle. Hopefully I'm mis-reading your description on your carb tuning changes.

Always get the ignition/timing set first, then adjust the carb. I'd be going over the basics: correct plugs (already mentioned), good wires (test the resistance of each one), dwell correct (mentioned), timing set right (I'd do the basic method of 34-36 degrees when the timing is all in as a starting point), then adjust the carb with a vacuum gauge (run idle mixture screws out evenly until maximum vacuum is achieved then set idle speed).

Best of luck figuring this out!

You must have mis-understood I timed the car to a total of 36BTDC before adjusting the carb, then tuned from there, I also have checked all the new parts I have put on. I am now in the process of ripping the entire motor apart, so far about 100 pieces. I have a feeling that the head gasket is shot and the rings are going. I have to cut the exhaust at the factory collector due to age but after that it's off to the races.

 

[mfj]

what is the dwell? If the dwell is wrong it will sound and run just like in your video? The dwell should be 30-32 at 1500 to 2500 rpm.

Yup 32 it is at 2000rpm.

 

[mfj]

Well Gentlemen the verdict is in, The motor is just plain wore out. I tore down the top end and the head gasket was fine. The burnt valves, worn cam, and multiple types of pistons tells me it's time to re-build. So here is a quick video of the break down, tell me what you think of the cam and piston situation. Thanks for all the great advice.

http://www.youtube.com/watch?v=lWMBlB8nr50

 

[msbaugh]

mfj I love your videos. They make the thread pretty interesting. You are pretty skilled. Nice music choice too!
Sorry to hear about your engine. Never a good sight that one