Car dropped 250 RPM and is now stuttering

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Can anyone advise me on where I should start in order to track down this issue that just popped up.
I was driving around today and things were going great. I stopped for gas and when I started the car back up I noticed that the idle revs we sitting at 500-450 instead of the 750 they are normally at. On the drive home I was experiencing some stutter (like surging but opposite, I was losing power not gaining it) under light load, specifically noticeable between 1500-2000 light throttle.
I'm not quite sure where to start. I'm letting it cool down now but it seems like all the plugs are connected still, which was my first thought.
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That is a pretty radical rpm change.And it seems to be in the lowspeed circuit. And it came on like a switch, immediately on start-up, not a minute and a half later.
There are really only three things that can cause such a huge jump;
1) a jumped timing chain.
2) a change (uncontrolled) in timing
3) A fluctuating vacuum leak.

The cam chain tension is easiest to test. Then the Timing. And last is fuel.
Of these, and in conjunction with the 250 drop in idle speed,yet it runs at 500rpm; I would like to rule out a vacuum,or even a fuel, problem.Another reason, to look elsewhere, is because it was like a switch.
I am kindof leaning towards the timing, but first;

I do not think this problem has anything to do with the voltage supply. I have seen MSDs run just fine at 10.5 volts. But never the less, put a timing lite on it and see what the strobe says as the rpm is slowly varied. If the timing is not jumping around. Then check the chain tension.
Timing
>52* at 2200 is usually too much timing. My guess is one or both of your springs is/are not working correctly. 42* would be a better number. So, IMO, I would slow the mechanical advance down to; all-in no earlier than 2800.And I would check out the springs and the entire advance mechanism, for binding or sticking.I might also consider slowing the vcan down some, but the engine would tell me yes or no on that, after the mechanical has been slowed down a tad.
If your engine is getting 52* at 2200, imagine what it is getting at 1500 to 1700; my guess is waaay too much, And it's current behavior is it's way of protesting.
>And finally it could be a combination of the timing changing AND the engine flooding.
This with an automatic only;
if the boosters are dribbling, then the engine will go rich, and the rpm will drop. With the rpm drop, the vacuum will drop. If it so happens that the vcan is overly sensitive, then the timing will drop out.And the rpm will further drop. Then if the boosters stop dribbling at the new lower rpm. the AFR cleans up, the rpm begins to climb, the Vcan maxes out, and the rpm rises. This can go on forever, as the TC sucks it all up.
The timing check is easier, so I listed it first.

A wildcard is if your metering rods are not staying down. You cannot run the engine with the covers removed, but you can loosen the cover screws and rotate them far enough to see the pistons and then lock the screws down again. Now you can run the engine up and watch them.This is a highly unlikely situation.
Another wildcard is a problem in the brake booster. Or the PCV. These are easy checks, just pinch the hoses closed.
And one more, an intake leak in the valley. But this is usually accompanied by blue smoke. This is another easy test, just seal the engine, remove the pcv from the port, and check there for a vacuum. With the pcv out, there should NOT be any vacuum there,lol.
And another; the PCV hose should be connected to the carb at the port that the manufacturer has designated for it, usually at the front.And the Vcan hose should be connected to the spark-port.And the booster; to the vacuum port on the manifold.

BTW,
your flyweight springs are not retracting the timing cam properly; you should never have to return the rotor back to the base timing by hand. While I don't think this is your problem,I do think this needs to be fixed.

Kindof another wildcard but, If you have been using secondary cracking as an idle air bypass, and if the adjustment has gone away, that could explain the idle dump. but this will have no effect anywhere else except at idle.
 
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Let me be the voice of reason for a moment. Think about the variables related to your engine suddenly running rough, the ONLY thing that changed was you added fuel! I've had a car that jumped timing, it didn't do any of the things your engine is doing, it just went down on power and tanked. I had a Chevy that had a vacuum leak and it developed a cam surge like a fuel car, but it was constant. I've had bad gas foul plugs and cause surging like yours is doing, but anew tank of gas cleaned everything up. I am not a MOPAR engine expert, but I think you are overthinking the problem. So let me ask you again, what changed?

I went back and read your 1st post. Lets assume it is not the gas, the chain did not suddenly jump and your distributor is good. This has already be asked but how about your MSD box. I've never had a bad one but from what I've read they go bad.
 
So while all the recent ideas were coming in I was rebuilding the eddy 1406. I took it apart, didn't find any blockages. I cleaned it good, took the jets and stuff out, cleaned those. All of this is superficial cleaning. I blew the passages out, nothing came out of them except air and gas/carb cleaner.

The main thing I did was change the gasket between the top and bottom part of the carb.

Hooked it back up. Hooked my cap and wires back up.

Fired it up, bam, runs just like it had no issues in the first place.

I'm happy but still miffed because I have no idea what the issue was. Maybe here was a vacuum leak on the gasket I changed? I sprayed it down looking for one earlier and didn't find anything.

I am still going to check out the timing and vacuum again now that it's back.

Although, I sort of feel like I'm jinxing myself by writing this post.
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Well
The only critical function that gasket serves is to seal the float bowl from the throttle bores, and to seal the accelerator pump circuit. Remember I talked about the boosters dribbling? Same thing if the gas was being sucked out of the pump circuit.
So check the gasket in that area. It could have been loose screws too.

Congrats
 
WSUTARD said:
So while all the recent ideas were coming in I was rebuilding the eddy 1406. I took it apart, didn't find any blockages. I cleaned it good, took the jets and stuff out, cleaned those. All of this is superficial cleaning. I blew the passages out, nothing came out of them except air and gas/carb cleaner.

The main thing I did was change the gasket between the top and bottom part of the carb.

Hooked it back up. Hooked my cap and wires back up.

Fired it up, bam, runs just like it had no issues in the first place.

I'm happy but still miffed because I have no idea what the issue was. Maybe here was a vacuum leak on the gasket I changed? I sprayed it down looking for one earlier and didn't find anything.

I am still going to check out the timing and vacuum again now that it's back.

Although, I sort of feel like I'm jinxing myself by writing this post.
View attachment 1715050278

View attachment 1715050277
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Nothing came out that you saw! Glad to hear it's back to normal.
 
You jinxed yourself when yo decided to have a performance engine .... like all of the rest of us LOL. Good work.
 
Glad to hear you got it figured out!

Safe to say it was a vacuum leak at the carb gasket?
 
It might have been a vacuum leak at the carb but when I sprayed for a leak nothing happened.

I just confirmed my timing readings again:

700 RPM 12 advance
2200 RPM 32 advance
2200 RPM w/vacuum advance 51 advance.

I am still concerned about my vacuum readings. Prior to this I was getting about 10.5-11 for vacuum at 650-700 rpm. The readings are back up there but jumping around a lot more than previous. Im wondering if this is due to the PCV valve that I have added since my last vacuum reading.
 
AJ/FormS said:
Yes it may be, the mixture screws will have to be adjusted in compensation. And 650/700 for that cam is kindof a stretch.
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Good point about the mixture screws. Forgot that I had moved those out messing around. I will see if I can get the gauge to steady up.

Regarding your comment on 650/700 is a stretch for the cam. What do you mean by this?

seabee said:
Which pcv did you get?
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Equivalent of a Fram FV191. Supposedly this one works with lower vacuums around 11.
 
Well as to the idle, that cam sounds like about a 268*/110
If the cranking compression is not at least 160 then it will want more idle timing than 12, and the 32* at 2200 IMO is too much, especially with iron heads.
So taking the picture as a whole, 650/700 is gonna be hard , unless this is 650/700 in gear.Hard as in, somewhat unstable.The 268 has only 52* of overlap, but it is enough to play havoc in the intake at low rpm.
Finally cruising in second gear at 2200 with 51* of timing, in my experience will cause missfires. But cruising with only 32*@2200 in second, is not enough either. But if you can make it work than you are a pretty sharp tuner.

Now on the off chance that you are in fact having other issues, I will give you my opinion, and you can kick it to the curb if you like.
Try 14/16* of idle timing and limit the all-in to 34*@3600 for iron heads, and 32*@3200 for aluminum. Then make sure the T-port is synced up, and the mixture screws are in the middle of their adjustment range which is about 3/4 turn for Holley types and 1.75 for most others. Set the idle speed with Idle-Air-Bypass, and a bit of timing either way from the 14/16 base. With closed chamber heads and tight Q, and under 160psi, you may be able to run cheap gas with this tune.
You may experience a slight torque loss from 2200 to 3200 with this tune, but it is safe. I got that torque back with a one-long-loop advance spring, from a 318 dizzy . I reset the rate of advance until I got 28* at 2800 on the light spring, and then let the long-looper take it to 32*@3400(aluminum heads). In this way the torque came back, the cruise got cleaned up, and the power timing was fine, and I am able to run 87E10 under all conditions.
The increased timing at idle and the T-port sync, allows an idle down to 550, but I don't run it there; I kindof like to see some oil-pressure on the gauge lol.

Now if your cam is bigger than a 268*, then the same principles still apply,a synced up Transfer port, more idle timing, and power timing limited to what the engine wants when she wants it; and not some number you have read others may be using. Don't force-feed her timing, thinking more is better. It's only better until it detonates, then it is suddenly waaaay worse. And you may not always hear detonation. It is better to be 3 degrees short of optimum than just 1 degree too much. Your butt dyno will not feel the difference of 3 degrees too little power-timing.
 
AJ/FormS said:
Well as to the idle, that cam sounds like about a 268*/110
If the cranking compression is not at least 160 then it will want more idle timing than 12, and the 32* at 2200 IMO is too much, especially with iron heads.
So taking the picture as a whole, 650/700 is gonna be hard , unless this is 650/700 in gear.Hard as in, somewhat unstable.The 268 has only 52* of overlap, but it is enough to play havoc in the intake at low rpm.
Finally cruising in second gear at 2200 with 51* of timing, in my experience will cause missfires. But cruising with only 32*@2200 in second, is not enough either. But if you can make it work than you are a pretty sharp tuner.

Now on the off chance that you are in fact having other issues, I will give you my opinion, and you can kick it to the curb if you like.
Try 14/16* of idle timing and limit the all-in to 34*@3600 for iron heads, and 32*@3200 for aluminum. Then make sure the T-port is synced up, and the mixture screws are in the middle of their adjustment range which is about 3/4 turn for Holley types and 1.75 for most others. Set the idle speed with Idle-Air-Bypass, and a bit of timing either way from the 14/16 base. With closed chamber heads and tight Q, and under 160psi, you may be able to run cheap gas with this tune.
You may experience a slight torque loss from 2200 to 3200 with this tune, but it is safe. I got that torque back with a one-long-loop advance spring, from a 318 dizzy . I reset the rate of advance until I got 28* at 2800 on the light spring, and then let the long-looper take it to 32*@3400(aluminum heads). In this way the torque came back, the cruise got cleaned up, and the power timing was fine, and I am able to run 87E10 under all conditions.
The increased timing at idle and the T-port sync, allows an idle down to 550, but I don't run it there; I kindof like to see some oil-pressure on the gauge lol.

Now if your cam is bigger than a 268*, then the same principles still apply,a synced up Transfer port, more idle timing, and power timing limited to what the engine wants when she wants it; and not some number you have read others may be using. Don't force-feed her timing, thinking more is better. It's only better until it detonates, then it is suddenly waaaay worse. And you may not always hear detonation. It is better to be 3 degrees short of optimum than just 1 degree too much. Your butt dyno will not feel the difference of 3 degrees too little power-timing.
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Awesome write up you are correct about the cam and the rough idle.

I am the dullest of the dull when it comes to tuning but I'm willing to at least try.

I'm going to try to parse out what you just wrote down and see if I can make some positive changes.
 
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AJ/FormS said:
OK, then, good hunting
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your t-port sync write-up is confusing. What kind of carb are your instructions referring to? I can't find anything online about an edelbrock carb having a transfer port adjustment.

Also, you state that 32 at 2200 RPM is too much. Im assuming that the only way I can change this is with new springs in the distributor? Supposedly my FBO limiting plate is set for 36.

Regarding the vacuum total, I have read that cruising at 50+ isnt a big deal and there is no way to adjust it anyway. Thus, I was going to forget about it for right now.
 
One thing that is weird that the car was doing prior to my issue and is still doing now is a curb idle fluctuation. What I mean by this is the warm idle end up being different than the "driving idle". If I set the warm idle to 600 my car will idle at 900 when I come to stops. If I tap the gas then sometimes the idle will drop down to 600, sometimes it wont.
 
Comments inside the quotes;click to expand
your t-port sync write-up is confusing. What kind of carb are your instructions referring to? I can't find anything online about an edelbrock carb having a transfer port adjustment.All automotive carbs that I know of have transfer slots.You can see them right beside the idle discharge ports. They are the vertical slots there, about 3/16 "tall.If you are unfamiliar with these, you cannot see the idle discharge ports from the topside. But to set the sync, the carb will have to come off anyway.
Also, you state that 32 at 2200 RPM is too much. Im assuming that the only way I can change this is with new springs in the distributor? No; the springs set the rate of advance, the flyweight-stops set the total mechanical advance available. You set the all-in power-timing and the idle-timing is then power-timing less available timing.Supposedly my FBO limiting plate is set for 36.You set the plate for how much available timing you want;EG if you want to run 34 power and you want to run 14 idle then you set the plate to 34 less 14=20*. NOT 36*!

Regarding the vacuum total, I have read that cruising at 50+ isnt a big deal and there is no way to adjust it anyway.Yes there is! Thus, I was going to forget about it for right now.You can ignore it while you get the power-timing/idle-timing T-port sync sorted out.
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WSUTARD said:
One thing that is weird that the car was doing prior to my issue and is still doing now is a curb idle fluctuation. What I mean by this is the warm idle end up being different than the "driving idle". If I set the warm idle to 600 my car will idle at 900 when I come to stops. If I tap the gas then sometimes the idle will drop down to 600, )sometimes it wont.This is a symptom of one of four things, 1) a sticking primary throttle plate, or 2) a misadjusted T-port sync. or 3) the return spring is not anchored correctly,or 4) Distributor timing cam not returning properly to base timing.
5)I suppose the kick-down system could be involved too.
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Ok so the number one thing is to get the T-port synced, and the idle timing will sort itself out during the sync procedure. Then you will know exactly what to set the idle-timing to; it could be 12 or 16 or 20, I cannot say. The cam will figure it out for you. While you have the carb off, make sure the secondary stop is correctly adjusted, so they are fully closed but not sticking.
The number two thing is to get the FABO plate set right. You cannot chose an exact number for this until the idle timing has been determined by the sync.
The number three thing to do is to set the rate of advance, using various combinations of springs.
And the fourth thing is to address the "weird issue". By this time, the primary throttle blades will be nowhere near closed, so sticking is not likely. Therefore go straight to making sure the KD system operates freely and no wiring and such is touching it. Then make sure the linkage on your carb is for a Mopar, and that the spring is engaging it right at where the cable is anchored on it.And finally put a timing lite on it and check for a sticking timing cam. You will see it when the timing does not return to base timing every single time. Do not snap the throttle, rather open the throttle gently until the timing starts to advance, then gently close it.
And you better be using the 4bbl throttle cable bracket!
For help with the T-port sync, click on the little blue M below in my sig
 
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AJ/FormS said:
Comments inside the quotes;click to expand



Ok so the number one thing is to get the T-port synced, and the idle timing will sort itself out during the sync procedure. Then you will know exactly what to set the idle-timing to; it could be 12 or 16 or 20, I cannot say. The cam will figure it out for you. While you have the carb off, make sure the secondary stop is correctly adjusted, so they are fully closed but not sticking.
The number two thing is to get the FABO plate set right. You cannot chose an exact number for this until the idle timing has been determined by the sync.
The number three thing to do is to set the rate of advance, using various combinations of springs.
And the fourth thing is to address the "weird issue". By this time, the primary throttle blades will be nowhere near closed, so sticking is not likely. Therefore go straight to making sure the KD system operates freely and no wiring and such is touching it. Then make sure the linkage on your carb is for a Mopar, and that the spring is engaging it right at where the cable is anchored on it.And finally put a timing lite on it and check for a sticking timing cam. You will see it when the timing does not return to base timing every single time. Do not snap the throttle, rather open the throttle gently until the timing starts to advance, then gently close it.
And you better be using the 4bbl throttle cable bracket!
For help with the T-port sync, click on the little blue M below in my sig
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If I am understanding your Transfer Port Sync post correctly, I use the curb idle screw to adjust as I normally would, but instead of adjusting the actual idle to my chosen RPM I look at the transfer port area and adjust the curb idle screw till the exposure of the t port is .025/.03 "high". Then, instead of setting the RPM with the curb idle screw I now set the RPM with timing advance adjustments, but ensuring that I'm not setting it too high so I don't detonate.

Sorry if this seems like a total repeat of your writeup but I had to read it about 10 times before it clicked...assuming what I said above is correct.
 
WSUTARD said:
I'm happy but still miffed because I have no idea what the issue was. Maybe there was a vacuum leak on the gasket I changed?
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I bet so. It seems like you said earlier in the thread that when you covered the carb it didn't stall.

It seems odd though, that it happened when you filled up.
 
Bad Sport said:
I bet so. It seems like you said earlier in the thread that when you covered the carb it didn't stall.

It seems odd though, that it happened when you filled up.
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It would stall, it just didnt "suck anything out". Which was the going theory at the time.
 
WSUTARD said:
If I am understanding your Transfer Port Sync post correctly, I use the curb idle screw to adjust as I normally would, but instead of adjusting the actual idle to my chosen RPM I look at the transfer port area and adjust the curb idle screw till the exposure of the t port is .025/.03 "high". Then, instead of setting the RPM with the curb idle screw I now set the RPM with timing advance adjustments, but ensuring that I'm not setting it too high so I don't detonate.

Sorry if this seems like a total repeat of your writeup but I had to read it about 10 times before it clicked...assuming what I said above is correct.
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You got it! But you may have to add bypass air to control the idle quality and speed as well. The bigger the cam, the more bypass it wants.
I have had a 270/110 cam and it didn't want much bypass. I have a manual trans tho, and so I do not have to compensate for the TC dragging the idle down, when put into gear.
In post #9 you gave us a video of the idle jumping up and down some 200 rpm. This is usually called surging. It is very often the result of a fault in the power-valve system. For your Eddy this means, in all likelihood the metering rods were not staying down. The springs were too strong for the amount of vacuum the pistons were seeing. The most logical conclusion I came to was a large vacuum leak.
 
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AJ/FormS said:
You got it! But you may have to add bypass air to control the idle quality and speed as well. The bigger the cam, the more bypass it wants.
I have had a 270/110 cam and it didn't want much bypass. I have a manual trans tho, and so I do not have to compensate for the TC dragging the idle down, when put into gear.
In post #9 you gave us a video of the idle jumping up and down some 200 rpm. This is usually called surging. It is very often the result of a fault in the power-valve system. For your Eddy this means, in all likelihood the metering rods were not staying down. The springs were too strong for the amount of vacuum the pistons were seeing. The most logical conclusion I came to was a large vacuum leak.
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Yeah that #9 post has been "solved" by the carb rebuild. Now, we are talking about something that is a tad different, at least I think.
I will see what I get motivated to do today on the carb.
 
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