383 trouble continues..

[pmike]

As some may already know, I have a '73 with an older 383 big block installed. I have got the car for few months, and am still having some trouble getting it running correctly;

- when I acquired it, it was running idle pretty nicely when warm, but stumbled and fired in exhaust when given more throttle. Black smoke on exhaust too, so I thought it was getting too much gas.

- I changed the plugs, which were quite black, and it ran better, but still stumbled/fired in exhaust

- it has a demon carburetor, I tried to tune it leaner by lowering bowl fuel level, but that did not seem to have much effect

- I also took the vacuum secondary bowl apart and put it back together, I think it was not working properly before, but now it should

-  I  swapped a new Edelbrock round aircleaner, in place of similar Moroso cleaner, that did not have any effect other than around same time the engine started giving a small noise which I assumed could have been a different intake air sound from the new filter. I do not know how to describe sound in english but lets try with "zzah, zzah, zzah"

- We checked the ignition advance, and it was at near 0 degrees initial, we did set it to approx 15 degrees initial and it sounds more healthy, but still fires/stumbles

- I lowered the carb bowl fuel level even more, and set the acceleration pump to a bit "less", and the engine was stumbling with throttle still, and firing in the exhaust. We located the exhaust fire to be happening on the passenger side, and infrared thermometer showed the cylinder number eight to be cooler than others, and closer inspection revealed that the spark plug wire had been burned/firing through, so I swapped new plug wires and a new Mopar orange ecu box

- now we are at today, and when tried with the new plug wires/ecu the engine still fires on exhaust, stumbles and makes the zzah zzah sound which seems to be more pronounced now with the new electrics. However when the engine is running and plug wire is pulled from the cylinder no. 8 the sound stops and the engine does not fire on exhaust anymore, at least not nearly as much.

We then thought that it must be that the exhaust valve is leaking, and thus making the sound and firing to the pipes. And the new electrics may give more correct spark to it, thus resulting to more sound. We pulled the valve covers, but it did not reveal anything. It does seem to have this type of rockers;

http://www.jegs.com/i/Mopar-Performance/312/P4529477/10002/-1  

so it probably does have hydraulic lifters, solid pushrods without adjustment possibility? Therefore for valve to stay open the problem has to be on valve itself, not lifters as hydraulics could not be jammed in the way that the valves would stay open?

I'd hate to pull the heads if not sure the cause is the valves, so I thought to ask for any advice what else could we still check?  Could it have solid/adjustable lifters or adjustable pushrods with those rockers? the pushrods seemed just plain sticks from the valve cover side, without any adjustments.

I do have a compression meter but it does return all the way to zero, so I do not know if it gives correct readings, I previously tried it on cyl 2 and got 190 psi, now from cyl 8 it gives 180 so if it works it does not seem to leak much? I have to borrow a working meter from somebody and check and compare other cylinders.

I am thinking that if the problem would be the carb, it would just stumble/boo, not fire in the pipes so much. It could be electrics, but with new spark wires and ecu box that should be ruled out, the distributor looks fine. And then there is that sound, which disappears when the spark is taken off from cylinder no. 8..

The firing order we have triple checked. I hope this explanation does make sense, my english could be better.. So any ideas? 

[XH29N0G]

See what other's say.  Someone here should be able to help.  I had one thought related to the mixture.  I did not think the fuel level changed the mixture - I thought it would require a swap in the jets, which I assume are in the metering block.  Also, when you set the accelerator pump a bit less, did you change the accelerator pump cam, the nozzle, or did you just adjust the screw on the pump arm.  If it is accelerator pump-related, I think you will need to deal with the pump cam and nozzle and adjust the screw so it does not bottom out.  If it is mixture related, I would look at the jets.   

This does not relate to the sound you are hearing.  The compression numbers look high for a 383, but this could be that I have only worked on old, worn 383s with compression around the 150 - 130 range.  The compression at 180 sounds like is not a problem to me. 

[c00nhunterjoe]

That carb will want the fuel level set half way up the sight glasses. Set the idle mixture screws all the way in, then backed out  1 1/4 turns to start. It sounds like you have messed with the accel pump linkage. The lever should be just touching the spring with no slop so that as soon as the throttle is touched, the squirters fire fuel. A 31 squirter would be a good start on a mild 383 and you probably have pink cams on the accel pump.

Now, onto this popping. Does it do it all the time or just when you snap the throttle? If you rev it slowly will it take fuel and behave?  Does it spit back through the carb at all or just the exhaust?
  If it is isolated to only the #8 cylinder you may have a mechanical problem and not a tuning problem. The only other simple things to check at that point is a vaccum leak at the carbor intake and an exhaust leak at the manifold.

[pmike]

I too did not at first think that the fuel bowl level should affect mixture, but so it seems from the various guides I have read from, apparently it kind of sets the "reference point" for the metering block/jets and should affect the mixture through all ranges. Now it is set on the primary side at the bottom of the sight glass. Adjusting it did not however have effect on the stumbling/popping trouble. I can try to return it to the middle of the glass.

The accelerator pump squirted a lot of fuel as soon as the throttle was pressed, and it had a nylon looking cam that had three holes to change it's position and we changed it to the "last" position so it would squirt later. That did not do much if anything to the functioning of the engine.

It has been giving black smoke and gas smell from the beginning, so I have assumed it running pretty rich, however it could have some effect if it has not been firing as it should thus resulting in unburned fuel to the pipes.

It does idle really nice, and when I got it first, it did not have any strange noises on idle either. When I pull off from driveway it can stumble and pop a bit, but not necessarily if given only little throttle. When accelerating, more pedal I give, more it stumbles and pops, but when it has been accelerated it usually runs just fine when pedal is not moved. Even in highway speeds. It can behave if pedal if pressed very slowly, but as soon it is moved faster it starts to stumble and pop.  It does not have to be pressed so fast that I'd think the acceleration pump is the issue, though.

Maybe it could be an intake leak, which would occur when it takes more vacuum?

I forgot to mention that I had to fix the exhaust during the weekend too, a pipe had popped off from a flange on passenger side just after the collector, probably because of the popping. Now that I think of it, maybe the sound could be that an exhaust gasket leak on 8. cyl if it would have popped it too! I have understood that an exhaust leak can result in firing in the exhaust, as it gets oxygen to aid with burn in the pipes, but should it then be stumbling so much or just bang in pipes?

It did also make a buzzing sound inside from the a/c/vent system vacuum hoses, and I plugged them off from the engine side to be sure that they are not leaking and causing anything, as they are connected to the intake manifold. I also plugged the driver side valve cover hose from the manifold side where it was connected and put the valve cover side of the hose in a coke can. That did not do anything to the stumbling and popping though.

I do not know, if it was leaking from the intake side, would it pop in exhaust so much? Carburetor is quite black too though, so it is or has been popping there too.  It is an old carb,  old photo of it attached, and I do not even now how big is it. I have not taken it apart so I do not know what jets it has. I have swapped a new fuel line on it after the photo, banjo bolts and rubber hose.

I will have to get a dependable compression meter and compare the cylinders, if there does not seem to be leaks I'd probably better to get a new carb and check the intake manifold while swapping it.. It is getting quite cold on the driveway though, it was 25 degrees F this morning so I'll have to find a warm garage if I will continue wrenching it much before spring..

More thoughts based on this?

[BSB67]

- We checked the ignition advance, and it was at near 0 degrees initial, we did set it to approx 15 degrees initial and it sounds more healthy, but still fires/stumbles

That carb is a mess.    Get it rebuilt.  It looks like this because of back fires, ie past and/or present ignition problems.  

I don't know how you checked your timing, but do this if you have not, just for a test.  Disconnect the full manifold vacuum line that may be connected to the distributor.  Plug the carb opening vacuum port.  Set initial timing at 20°.  Leave the vacuum line disconnected.  Start the car and give it a test run to see if it eliminates the off idle issues.  Make it a short test as you don't want to drive around with too much total timing.  Report back.

Check and replace your spark plugs often until you solve the problem.

[XH29N0G]

I'll add to c00nhunterjoe's and BSB67's points.  

I think you need to make sure you set up the float levels and idle mixture first (with the idle screws), then with your accelerator pump it is important that it sends a squirt of gas in as soon as the linkage moves (this squirt compensates for the rush of air that goes past the butterflies).  If there is not enough gas it can backfire back through the carburetor (which is the black color you have).  I suggest going back to the original setting on the pump cam and dealing with that after you get the idle (and if needed, jets) set.  

I would start first to make sure the ignition is correct (timing as BSB67 suggests and if you have points - dwell and points).  It will also be difficult with the colder temperatures you are working with since backfires are more common when cold.  Cold will need a richer mixture, and your car needs to be fully warmed up to do these adjustments.  

Do you know if the car ran with this carburetor at some time (in other words if it was set up properly).  This would tell you that many of the initial settings are OK and things like jets, pump cam, etc... are OK.  It might be that your car was set up for warmer temperatures and has an issue with idle, being cold, and ignition.  I had this exact issue happen with mine when I first set it up (and this was also with an out of the box carburetor that was a little lean on the jets).

Good luck  

[pmike]

We checked the ignition with the lamp, (there is a thread about me locating the correct tdc point vs. the timing tab that was hidden under the water pump inlet) by disconnecting and plugging the vacuum advance, I marked 10 degrees on the damper wheel and we ended in setting it to approx 15 degrees on idle.

I have adjusted the idle screws after messing with bowl level, at first the idle screws did not have any effect and I then learned to lower the idle speed, after which the idle screws do function and I have set them at the recommended setting and tuned a little from there and the idle does sound good now, and has infact been quite good all the time.

I think that the car worked better when it was warmer outside, but I find it hard to believe that it would be running lean based on the gas smell and black smoke it is giving. Could of course be that some of the jets are clogged from the carbon buildup of the carb, resulting in lean mix in some range.

It has not worked when it has been in Finland, and probably not before that either as the carb is so black.

The carb must be pretty old as nearly every Demon carb picture that I have found from the web has fuel inlets that are in a downward angle, and mine has them straight, so that air cleaner needs a spacer to clear them.

I have the valve cover loose right now, I will see when I will have time  to get it together to test with vacuum unplugged. Or if I'd just take the carb and intake manifold off to see if there seems to be leaks.  After thinking about it today, I am leaning towards suspecting an intake leak, and swapping a brand new carb while at there to not to have to worry what it has inside. I suppose a 670 Holley Street Avenger would be pretty sure choice?

It will badly eat my seat cover budget, but I guess it will be no good having a nice interior in a stumbling vehicle..

[XH29N0G]

I put a 670 street avenger on my 383 and had a lot of backfiring out through the carburetor at the start.  As it turned out, a significant part of my problem was the ignition (points), but some was the carburetor.  The carburetor came with 65 primary/68 secondary.  I upped the jets to 68 primary/70 secondary and it ran a little better.  I also worked on the accelerator pump nozzle and accelerator pump cams.  (I have recently started using a wideband air fuel gauge that I log into my computer, and that has given me much more useful information about the mixture.)  

I do not know what would be the right choice for your 383.  See what others say.  I have a manual transmission and was thinking a 750 DP might have been a better choice for me, but I was very happy with the 670.

But I would also wait a bit because maybe someone here will have the right advice to get your set up working well.

[BSB67]

Please describe exactly where you placed the mark on the balancer relative to the TDC mark, and which way you turned the distributer when you advanced it.

[c00nhunterjoe]

good lord, was that thing on fire? that picture is screaming timing. time for a rebuild\ replacement carb. im personally not a demon fan. the method used to set the timing sounds questionable. i would get ahold of a dialback light for your application or get a roll of timing tape to accuratly mark the balancer.

[pmike]

The setting of timing did make the engine run a bit better, when not backfiring/popping but did not do anything for the popping problem. The distributor looks nice and I have replaced the wiring from distributor to ecu box and back to coil. That did not have any effect. Coil itself I have not swapped, maybe I should do that before other things.

We did set the timing like this; at first I had hard time to find the timing tab, and thought I have to find and mark the correct TDC. However, with a little bit of help from my DC.com friends, the tab was found, but I still quickly checked to see if the TDC marka was correct by finding out approximate piston TDC and comparing it to the marks on tab and damper wheel, and the marks aligned.

I calculated the radial length (if that explains it in english) of 10 degrees on damper wheel, from the instructions in the internet, and cut a piece of tape of approximately that length (16mm or .63 inches).  Then fastened the tape on the side of the original damper mark, so that it was on the side of the rotation  which reaches the timing tab mark earlier, and marked that with a knife on the damper. If I remember correctly it was the "drivers side" of the rotation but I might remember wrong. The I took the tape off leaving the knife mark on damper at 10 degrees.

Then I disconnected the vacuum advance hose from distributor, plugged it, started the car, used the light, and on idle the timing tab mark was pretty much on the original damper mark, so approx 0 degrees.

We then rotated the distributor so that the light showed timing tab mark on my 10 degrees mark, and then a little more until the car feeled to run best at idle. The timing tab mark was now at approx half distance more from my 10 degrees mark, thus approx 15 degrees.  The timing tab is so hidden under the water hose in/outlet that the degrees on the tab cannot be read.

So I would not think that the timing advance should result in popping (perhaps someone has had the popping problem and tried to retard the advance as it was at near zero when we started). And this setting of timing did not do anything to popping/backfire problem.

Relating the ignition I have so far replaced ecu box with an orange mopar box that does not need a ballast resistor (old one was 5 wire, new is 4), plug wires, distributor to coil wire, wires from distributor to ecu and ecu to coil. It does not have a coil ballast resistor currently. So I'd better probably swap the coil next. I will try to find time to do that and fasten the valve cover back, and borrow a compression meter.

[Pete in NH]

Hi,

All Orange Box ECU's require a ballast resistor. You need a one ohm two pin resistor. The older Mopar five pin ECU's used a four pin two section ballast resistor. You still need a ballast resistor or you risk damaging the coil and the Orange Box ECU.

[pmike]

I did get a new coil today, which has a ballast resistor on the side, and it measures 1.4 ohms primary without ballast and 3 ohms total with ballast, I will swap that in place.

I also borrowed a compression meter from a friend, and bad news is that my meter was shot and the engine does not have as much psi as I got with it, but good could be that the 8. cyl might not be leaking. I did get around 130 psi from the 8. and 2. cylinder which I had time to quickly check.

I guess I will next fasten back the valve cover, replace coil with new one and try disconnecting the vacuum from the distributor to see if that is faulty. I'll try to find a new carb too.