Rough-idling 360, can't figure it out!

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Guy gave me 8 LA cams when I picked up an intake, told me take em for scrap. 4 mic'd clean and even (2 318 stockers, an SSI .440 and an Isky 'Turbo Grind'), and the others looked like roller lifters like G. Jets pencil pointers. Just lbs of iron scrap. A rhythmic loss of ignition sounds like...ignition.. or possibly carb loading up but that usually takes longer to manifest itself. I took off every hose on my carb looking for a leak. The EGR should not open on high vacuum idle (not applicable but good info).
 
Well I spent the past hour and a half messing with the truck. Checked voltage to coil at idle, 12V we're good there. Disconnected and plugged both the PCV and brake booster at the carb/intake, no change. Removed idle mixture screws, blew them out with carb cleaner then reinstalled screws and adjusted idle mixture, again no change. I also (carefully) sprayed carb cleaner around the base of the carb, nothing. One thing I've noticed is it always seems to get worse once the engine is warmed up.

I think the only thing left is the cam which if I do have to replace it isn't going to happen for at least a few months, I need this truck and don't have the time to dive into the engine yet again.

Here's a video of how it runs. I forgot to hook up a vacuum gauge but you can guess what it would be like; I've hooked one up before and it reads normal then drops 3 in-Hg or so and fluctuates quite a bit when it starts "chugging".

 
MopaR&D said:
Well I spent the past hour and a half messing with the truck. Checked voltage to coil at idle, 12V we're good there. Disconnected and plugged both the PCV and brake booster at the carb/intake, no change. Removed idle mixture screws, blew them out with carb cleaner then reinstalled screws and adjusted idle mixture, again no change. I also (carefully) sprayed carb cleaner around the base of the carb, nothing. One thing I've noticed is it always seems to get worse once the engine is warmed up.

I think the only thing left is the cam which if I do have to replace it isn't going to happen for at least a few months, I need this truck and don't have the time to dive into the engine yet again.

Here's a video of how it runs. I forgot to hook up a vacuum gauge but you can guess what it would be like; I've hooked one up before and it reads normal then drops 3 in-Hg or so and fluctuates quite a bit when it starts "chugging".

Click to expand...


OK we are taking in everything you are telling us and we can now see how it runs with the video.

Before going into the cam, I am thinking it is a fuel issue.

Looks to me like it is starving from low fuel pressure at an idle and here is what I am seeing.

Your fuel filter is at a high point of the gas line enroute to the carb. The high point is where all the air in the fuel line collects. If you have ever had a plastic see through fuel filter you will see they are only about 1/2 full of fuel even when pointing up hill.

If you swap in a plastic see through fuel filter for the metal one you have on there now you will probably see that it is air locked being in there on the horizontal.

Now for quick 2nd test, take out the plastic filter and put on a short piece of steel gas line to eliminate the fuel filter all together. I am guessing this is going to eliminate your air lock at idle and it will run better.

Here is my recommended solution, set up your fuel line and fuel filter down by the fuel pump pointing strait up the way mopar did it ftom the factory. Then go up from the fuel filter with s steel line on the front side of the fuel pump to keep it cool and then on up close to the carb, final 6" hook it up to the carb with rubber 5/16" rubber gas line. Just like the photo below. This keeps the excess air out of the fuel filter and sends the gasoline up the line.

Give this a try:

Screenshot_20200730-073349_Gallery.jpg
 
Yes here is the problem area with your fuel supply air locking at an idle,

Fuel filter needs to be down by the fuel pump, pointing straight up so the air gets out of it, and delivers clean fuel to the carb.

Screenshot_20200812-213642_Gallery.jpg
 
oldkimmer said:
U more than likely have a cracked intake manifold. Kim
Click to expand...

But I also had this same problem with the stock 2-bbl carb and intake...

George Jets said:
OK we are taking in everything you are telling us and we can now see how it runs with the video.

Before going into the cam, I am thinking it is a fuel issue.

Looks to me like it is starving from low fuel pressure at an idle and here is what I am seeing.

Your fuel filter is at a high point of the gas line enroute to the carb. The high point is where all the air in the fuel line collects. If you have ever had a plastic see through fuel filter you will see they are only about 1/2 full of fuel even when pointing up hill.

If you swap in a plastic see through fuel filter for the metal one you have on there now you will probably see that it is air locked being in there on the horizontal.

Now for quick 2nd test, take out the plastic filter and put on a short piece of steel gas line to eliminate the fuel filter all together. I am guessing this is going to eliminate your air lock at idle and it will run better.

Here is my recommended solution, set up your fuel line and fuel filter down by the fuel pump pointing strait up the way mopar did it ftom the factory. Then go up from the fuel filter with s steel line on the front side of the fuel pump to keep it cool and then on up close to the carb, final 6" hook it up to the carb with rubber 5/16" rubber gas line. Just like the photo below. This keeps the excess air out of the fuel filter and sends the gasoline up the line.

Give this a try:

View attachment 1715577197
Click to expand...

Interesting idea, it's easy enough to be worth a shot. When I first got the truck the fuel filter was close to the pump but on the suction side; after installing the 4-bbl I noticed it would starve for fuel badly especially on the freeway so I did a quick-and-dirty relocation of the filter to the pressure side. I know Edelbrocks are pretty sensitive to fuel pressure I thought of putting in a regulator for it.
 
Fuel filters are supposed to be on the pressure side after going through the fuel pump.

So stock mopar Carter fuel pumps put out 6 psi. Your used fuel pump diaphragm could be stiff and stretched out, not giving you full pressure of 6 psi. May be time for a new Carter fuel pump.

Here is the one you need 23.00 plus ship. Do not need a fuel pressure regulator with these.

Summit Racing has the Carters and Jegs too.

Screenshot_20200812-235830_Chrome.jpg
 
When it starts to chug, shut it down ASAP and then pull the top off the carb (8 screws) and check your fuel level. Probably low as that is a lean surge. Vacuum leak would do the same, lean it out.
 
Not trying to be a dick, but, heave you considered a compression test,and teeing in a fuel pressure guage? also keep in mind there is a fuel pressure and volume test. Then there is vapor lock is the fuel line tight o the frame away from the exhaust? 1/2 inch makes all the difference as in 1/2 inch further away from the heat source.

Untill you do some real diagnoistics you are guessing, and throwing parts at it. Do you have a Chilton manual? the classic 64-71 book? it should have a tune up section in it. It will cost time but you wont be buying parts you dont need.
 
Working through the "Process of Elimination" here.

Let's see if it is a fuel starved situation when it is warmed up idling in gear.

When it starts to stumble, reach up to the Choke Butterfly on the carb and slowly start to close it down by hand and see if the stumble starts to go away. This should give it a little more fuel at idle, if the fuel bowls are full of fuel.

20200813_082105.jpg


If the fuel bowls are not full of fuel, this probably won't help.

So if it is a fuel supply problem try this next test. With the engine running idling in gear (with someone with their foot on the brakes).

As the engine is stumbling give it a quick shot of Starting Fluid into the front 2 barrels at the choke, see if your stumble starts to go away. If it does, then you have a fuel supply problem.
 
So fuel pressure is a part I haven't looked into yet but obviously should have. It has a new Carter mechanical pump but it pulls from what used to be the auxiliary tank under the bed so it might not be flowing what it should especially at idle; I have no idea the condition of the pickup or "sock". I need to go buy a fuel pressure gauge but first I'll try spraying carb cleaner down the primaries when it's idling rough first. Regardless I'm also going to relocate the filter.

@Dartswinger70 I did a compression test with the old heads, one cylinder was down a bit but it had a burned/sunken exhaust valve which is now fixed. I do have a Chilton manual for the truck I'll check over the tune-up section in there.
 
I cant view the vid just yet (at work) but I will look over the weekend. Just for the hell of it, have you disconnected and plugged all ports on carb? or eliminated vacuum leaks? How are the power brakes? Power brake boosters can leak vacuum. For the sake of saving time have you swapped the carburetor just to see if it does anything dififerent? although you said it did the same thing with a two barrel corrrect? Like said isolate the carb remove hoses and plug all vacuum ports see if there is a difference. the fuel fliter,yes id set it up vertical, but I have ran them similar also with no issue.
 
Dartswinger70 said:
I cant view the vid just yet (at work) but I will look over the weekend. Just for the hell of it, have you disconnected and plugged all ports on carb? or eliminated vacuum leaks? How are the power brakes? Power brake boosters can leak vacuum. For the sake of saving time have you swapped the carburetor just to see if it does anything dififerent? although you said it did the same thing with a two barrel corrrect? Like said isolate the carb remove hoses and plug all vacuum ports see if there is a difference. the fuel fliter,yes id set it up vertical, but I have ran them similar also with no issue.
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A few posts back i mentioned I removed and plugged all the vacuum lines including power brakes and PCV and it made no difference. Last thing to check is fuel pressure and flow, pretty much. I'm praying that is the issue as opposed to flattened cam lobes. That would also explain why it gets worse once the engine is warmed up; fuel is warmer so more vapor in the filter/lines and the pump has to work harder to maintain pressure (I think?)
 
MopaR&D said:
A few posts back i mentioned I removed and plugged all the vacuum lines including power brakes and PCV and it made no difference. Last thing to check is fuel pressure and flow, pretty much. I'm praying that is the issue as opposed to flattened cam lobes. That would also explain why it gets worse once the engine is warmed up; fuel is warmer so more vapor in the filter/lines and the pump has to work harder to maintain pressure (I think?)
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Have you considered the MP electronic ignition kit? Bsically set it and forget it. Get a hot spark going and never look back. yes t in to your fuel system check the pressure, also you can do things like put your inductive timing light lead on each wire,shine it somewhere dark, see if there is a rhythm to the strobe light...a bad wire will be an erratic strobe rhythm. I don't know what you have for wires,but Beldens are junk. I guess what Im saying is if the wires are newer they can still be junk, one bad wire will cause a misfire. Three things will make an engine not run, Mechanical failure( worn cam lobes) Timing,( ignition or the timing belt/chain "jumps a tooth")
lack of of spark( distributor cap,rotor,wires,points or module) or lack of fuel( out of gas, low fuel pressure,restricted carburetor passages ,stuck float etc)
thois four things are what you are after in your elimination process, a compression check will tell you if there is a mechanical or broken engine internal part like the valves and cam lobes( it sounds like you already fixed these issues with the sunken valve) it may be safe to eliminate internal engine issues at this point and move on to the other three. Once you start thinking thios way, the stress kin dof backs off then you systematically go through your checks untill the problem rears its head. For example when ever I had a "no start" job, the first thing id do is spray carb ckeaner into the intake and crank it, if it fired i knew I had spark and it was a fuel issue. Took less that 5 minutes to do that check. But that eliminates spark as the culprit. Just pointers so the process doesn't drive you crazy.
 
Dartswinger70 said:
Have you considered the MP electronic ignition kit? Bsically set it and forget it. Get a hot spark going and never look back. yes t in to your fuel system check the pressure, also you can do things like put your inductive timing light lead on each wire,shine it somewhere dark, see if there is a rhythm to the strobe light...a bad wire will be an erratic strobe rhythm. I don't know what you have for wires,but Beldens are junk. I guess what Im saying is if the wires are newer they can still be junk, one bad wire will cause a misfire. Three things will make an engine not run, Mechanical failure( worn cam lobes) Timing,( ignition or the timing belt/chain "jumps a tooth")
lack of of spark( distributor cap,rotor,wires,points or module) or lack of fuel( out of gas, low fuel pressure,restricted carburetor passages ,stuck float etc)
thois four things are what you are after in your elimination process, a compression check will tell you if there is a mechanical or broken engine internal part like the valves and cam lobes( it sounds like you already fixed these issues with the sunken valve) it may be safe to eliminate internal engine issues at this point and move on to the other three. Once you start thinking thios way, the stress kin dof backs off then you systematically go through your checks untill the problem rears its head. For example when ever I had a "no start" job, the first thing id do is spray carb ckeaner into the intake and crank it, if it fired i knew I had spark and it was a fuel issue. Took less that 5 minutes to do that check. But that eliminates spark as the culprit. Just pointers so the process doesn't drive you crazy.
Click to expand...

I used a Pertronix Ignitor 2 setup to convert from points because I've heard the quality of the new electronic ECUs is junk and it was easier/cheaper. Plug wires are Summit brand 8mm spiral-core which IIRC I checked the resistances and they were all good.

I've pretty much gone through all the standard troubleshooting you mentioned except for fuel pressure and flow to the carb.

Something regarding ignition though... when I pulled the cap and rotor I noticed the wear was on one edge of the contacts, not the center. Could this be causing issues? Like maybe the rotor for the magnetic pickup isn't phased right with the spark rotor?
 
Try an alternate fuel source like I have here on my engine run stand.

20200715_183142.jpg


Make sure the end of the rubber gas line is submerged in gasoline, mighy have to weight it down. Then go to starting it, a good fuel pump will suck it right out of the jug and on to the carb.

Also dump out your fuel filter into a container and see what pours out of it. Rusty colored gas and grit, not good.

Very well could be your steel fuel fiter is plugged, can't see into them. Dump it out, blow it out, then try breathing through it to see if it is plugged. Then put on a brand new one anyway.
 
I think the wear on the edge is normal, as in the lower edge of the 8 contact in the dist cap. have you pulled plugs to check the color see which one look fouled etc. If oyur fuel system checks out, do some googling/rsesearch on the pertonix. I think there is some ide issue complaints out there on the web. Of course the quick verify would be to throw a points distributor in and see what you got.
 
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OK guys I'm pretty sure I've narrowed it down to an ignition issue, specifically the distributor. I tried @George Jets idea of spraying starting fluid down the carb when it was chugging; that just made it worse, almost stalled out and I didn't spray much at all.

I then thought about how yesterday I replaced the distributor rotor; "old" one was the unit that came with the Pertronix kit, "new" one was an Accel. I noticed the Accel rotor didn't fit as snugly into the magnetic wheel thingy that triggers the Pertronix module. Today I put the Pertronix rotor back in and made sure it was pressed down tight; lo and behold I started up the engine and put it in gear, it stayed smooth!!! I also have a feeling I wasn't getting the cap seated fully on the distributor body, it felt... different this last time I put it on, like I was able to slide it down a tad farther. Might have been hanging up on one of the wires from the Pertronix module.

Here's a video of it running "fixed", I guess now I need to find a replacement points distributor with good bushings...?



EDIT: The vacuum might seem low but I'm at 5000' elevation and that gauge is not accurate, I dropped it once and the diaphragm inside got bent and I just took it apart and bent it back till it was at zero again. Probably need a new one lol.

I took a video of me moving the distributor shaft around. It has roughly 1/16" play side-to-side (radially) and almost 1/8" play up-and-down (axially).

 
Sounds a whole lot better!!

Aren't those Pertronix rotors special fit? As in you have to use a replacement Pertronix rotor? I run a Pertronix Igniter II in my car and I like it. But I do carry a spare igniter and a set of points!!

Glad you got it going. If you can't find a distributor locally to you FABO member @halifaxhops usually has a good stock of them for sale.
 
Yeah it's really nice now I can start moving into my new place lol. Thanks for all the help guys!

@George Jets that D100 is gorgeous, I'm not sure if I'd want mine that pretty since I use it a lot lol but I plan to keep it for a long time. Ultimate goal is a 12-valve Cummins diesel swap with a 6-speed manual (NV5600, G56 etc.) This is the first truck I've ever had, or anyone in my family even for that matter. You don't know how useful a 3/4-ton with an 8-foot bed is until you have one!

@66fyssh thanks for the tip, there is a local shop that specializes in classic Mopar parts I found just a couple weeks ago I'm going to give them a shot. If they don't have one (I'd be really surprised if they don't) I'll hit up @halifaxhops

Regarding the dist rotor, it doesn't look like it requires a special rotor but a regular replacement piece needs to be filed down a bit in some places to seat fully in the magnet wheel. I could make that Accel one work but the Pertronix rotor is in perfect shape. The Accel one did fit it was just a tad loose and didn't sit all the way down into the magnet wheel.
 
I am sure the upper bushing is shot. The petronix unit will take any Mopar rotor one fo the beauties of it. Send me all the info on the motor I am sure I have something with the right curve and can put your petronix unit in there.
 
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