318 Engine stumble

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glhx

glhx

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Around 15-1700 rpm.....huge stumble
When I get pst it the power is there


In neutral
Slowly raising gas......stumble occurs like a surge. Starting about 15-1700
And doesn't go away

Vac at idle is 19
Timing 8°

318 1976 stock and original everything
Holley 600 vac sec

1968 points distributor
 
A couple thoughts, secondaries coming in too soon. Vacuum advance overworking or underworking-vacuum leak.
Float level too high-to low.
Now I have a headache---------------------:)
 
This might be a fun one for us to figure out from our computer keyboards but at least you can make it act up in the driveway in neutral. I would check out the ignition side first with a tach/dwell meter and a timing light. Make sure everything is set to specs with the distributor, point dwell, advance at rpm. etc.
 
toolmanmike said:
This might be a fun one for us to figure out from our computer keyboards but at least you can make it act up in the driveway in neutral. I would check out the ignition side first with a tach/dwell meter and a timing light. Make sure everything is set to specs with the distributor, point dwell, advance at rpm. etc.
Click to expand...
I agree, good start. It can only be fuel or fire. Eliminate the fire and move on to the fuel.
 
Sounds good.....will check
Total timing
Gap
Dwell
At leaks in advance

I really need to put that electronic distributor in there
 
This may sound weird but I've seen it before. Pull the plugs and make sure the side electrode hasn't closed or any of the plugs are grounding out some other way (like fouling).
 
glhx said:
Sounds good.....will check
Total timing
Gap
Dwell
At leaks in advance

I really need to put that electronic distributor in there
Click to expand...
Agreed. Check out the basics. Never overlook the obvious. The old point distributors really work well. Depending on how many miles you drive, it may be all you need. The electronic systems are pretty maintenance free and do provide a hotter spark. I have used the stock distributor and installed a simple Pertronics in one of mine. It works great and is simple. My 66 still has the original dual point stuffed with points and it works well also.
 
The plugs are champion. I didn't know the part number.
I remember gapping them to 35

I took them out and sanded the tips not too long ago and cleaned them up. They are not new. 7 years old with less than 100 miles on them.

I'm going to pull the plugs and regap them.
Also check the part number on them to make sure they are right.

Might be a few days but I'll get to it eventually
 
bottom line.... use stock plugs. Anything more advanced will be too hot. It will cause detonation throughout the driving range of the 318. You may not feel it at idle. Do you ever have a problem with dieseling? (running on after shutting off the ignition)
 
No it never diesels.

The idle is pretty smooth as well. The plugs are basic plugs. No platinum or anything special. I don't hear any valve chatter or pinging either.

I rev it up slowly and it starts shaking......surging.
 
Ok, lets do this intelligently. Is this something it just started? Has it been running well and then started messing up? Or has it always run this way? If not, when did it start? Think about it. After getting gas somewhere? After a rainstorm? Lets not change anything yet until you give a little more info.
 
RustyRatRod said:
Ok, lets do this intelligently. Is this something it just started? Has it been running well and then started messing up? Or has it always run this way? If not, when did it start? Think about it. After getting gas somewhere? After a rainstorm? Lets not change anything yet until you give a little more info.
Click to expand...

I've never much run it. Let it sit for a really long time.
Came back and replaced the gas tank
Put a Holley 600 vacuum secondary....on a streetmaster intake with a 1" spacer as the streetmaster is so low.
The floats were checked but I will check again.
Points distributor

On the carburetor.....the butterfly's were open due to a screw under the carb base plate......I adjusted them closed. Not too tight. However...was unsure of the formal procedure on what to do with them....so I guessed.

Replaced all vac hoses

It's almost like lack of gas but that's a guess

Checked the plugs and set the timing to 8° after not finding an obvious vac leak.

Once the vac leak was fixed I adjusted the carb mix to 19" vacuum. Used a vacuum gauge to set the mixture.
Then set timing to 8° and then the idle speed to 750rpm

The car now idles fine.....

So I changed the carb basically....how it ran before that I have no idea.

It does it all the time. The gas comes from the same place but it's at least clean and not bad gas. It is 87 octane

Plugs are gapped to 35

At idle....the timing mark stays steady.

All other parts are original to the engine. I have no idea what shape anything is in.
 
Vacuum leak at the manifold that opens at a certain value, but past a certain throttle level it mixes fine? Maybe? AKA a sympathetic leak.

I've seen stranger...
 
The carburetor secondary butterflies should be adjusted so that the transition slots are perfectly square. If you have any questions about that, there are many videos on youtube to show how.

Also, it sounds like you could use more initial timing. Try it on 12. If it does not spark knock on acceleration, try 14, then 16........keep going up as long as it does not spark knock. If you find where it spark knocks, back off till it quits and lock er down.
 
I had a similar issue, 74 Duster, mild built 318, stock electronic distributor, Pertronix flamethrower HEI modue and Pertronix flamethrower coil. Bought motor carb to pan from a 3rd party who took the intake off to photograph the motor to sell it showing assembly lube on the cam etc. Turns out they never re sealed the front and back of the intake with new RTV, just tightened the bolts.
the motor fell on its face about 1500 to 1700 then smoothed out. I had a leaky brake booster so the motor sucked air thru the vacuum port. Fixed that then had 18" vacuum, but a wicked oil leak then showed up with motor running. Took the manifold off and discovered bolts were super loose and RTV was not sealing. Got new fel-pro caskets and re sealed water jackets and corners and 2 small beads on top and bottom of front and back cork gaskets. Going to put it back together and I hope I have no leaks and it runs as it should. I look forward to hearing what happens with this poster...
 
Haven't been back in the shop yet.

What I'm going to do is check the distributor for play and/or
install the electronic one I have for the 76 which I just checked for play and found it to be tight. Put in a new guide for the shaft.

Regap the plugs

Reset the timing as said above starting at 12° from the 8° it's set at now. Get total timing as well.

Maybe shut down the back two barrels? See if that changes anything.

So far when I was timing it. The mark was not jumping around. I know the motor is older and probably has that plastic coated chain on it 1976 engine out of a charger. I bought a double true roller to put on it.

Also bought a high volume melling pump with a hardened shaft and a gasket kit. Can I run this pump with a stock pan?

If I can't find the problem there I'll check the transfer slots. When I got the carb. The butterfly's were open 1/8" and I didn't know the setting for the right adjustment so I guessed.


Electronic distributor. What is the advance like on this thing? Is there any improvement thst can be done to it?


Other than that I'm considering putting a performer intake on it instead of the streetmaster. The performer has a/c holes I've heard.....Porting the heads quite a bit. And running between a 250-270 cam. Leaning on 270° with stock compression. And putting 235lbs springs....edelbrock sure seat

Adding the short headman headers with 2.5 exhaust.

Changing out the gears from 2.76 to 3.55 with locks......same stall?

I don't want to get crazy with this thing. 300hp or close is fine with me. Adding factory a/c

All the added stuff might take a while

I'm ready for this thing to run well. The heater won't come on unfortunately. Might be a bad switch
 
So I checked the transfer slots

It shows that the secondary transfer slot should be a square

The primary also

My secondary was closed off.
And my primary is not a square
It’s more rectangular
And the idle speed screw was backed out all the way


When I adjusted the secondary to look like a square

The idle shot way up.
The mix screws would not back it down

Are the secondaries supposed to be closed

D0A57CC2-C019-47C5-8F3E-BBE8C8F56A67.jpeg


7DE9DBA7-8EA8-4049-9176-D089DC2BE01A.jpeg
 
This is where it’s at right now with the idle way up in speed

The secondaries are slightly open
 
If the photos are after adjustment, they look like rectangles.slots look long.
 
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