318 Stalling Problems HELP!

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blevins2005

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Hi All,

I've been working to get a brand new long block running. I have gotten everything together and have set initial timing. The engine idles like a dream. It revs hard like a dream. The problem is if I slowly bring it up through the RPM's when in neutral, consistently at 2,000 RPM's its stumbles and stalls. If I immediately let of and let the RPM's fall it almost always stumbles but does not die. If i stay in it it always dies.

I'm at a loss and am looking to you experts here. Any help is much appreciated.
 
Its the transition from the idle to enrichment circuit of the carb, happens at about 2000 RPM...coincidence? Check your high speed (inboard) air bleeds on a Holley. shoot some carb cleaner in there, or even a thin wire if you got one. Also on a vacuum secondary, check your vacuum diaphragm system. It relies on intake air passing a port in the venturi to create a vacuum on top of the vacuum pot to slowly open the secondaries. If the spring is too soft, it will open early and cause a bog. If its too strong, the secondaries wont open properly and will cause a flat spot in acceleration. This passage is sealed by a small cork O-ring that can go unnoticed in a rebuild.
 
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What carb, OP?

Could possibly be the fuel supply: filters, tank, lines, pump. Is the revving (when it does not stumble) done in neutral also?
 
New fuel pump / filter. Its a holley 2 barrel 2280 carb.

It idles fine and if I stab the throttle there is no hesitation. I can see the two jets spraying fuel. If I slowly press the throttle it does not appear to spray any fuel from the jets.

I looked for the air bleeds and I don't see anything that looks like what is in the video.
 
OK, forget what I said. check accelerator pump. a worn piston would not work at slow speed while it would work on a fast shot.
 
Pull vac advance hose and see what happens too.
As vacuum changes the pickup plate moves. A break in the wire could cause spark to drop out.
Check air gap too. If its tight,the pickup hittibg reluctor will knock it senseless.

Pull inlet off fuel pump and connect to another fuel source.
 
Ok. Just pulled the carb off and disassembled. Here is what I found. Bolts holding carb to intake were fairly loose (just over finger tight). The vacuum hose from carb to choke diaphragm was cracked.

I checked the accelerator pump. The accelerator pump cup seems fine (clean and pliable with no cracks). However there seems to be a lot of play sided to side with the accelerator pump stem. Is this normal?

Could a vacuum leak cause these symptoms?
 
I forgot to put a gasket under my carb once, but dont recall the symptoms.
 
So I found the new pump cup in the parts bag from when I rebuilt the carb. Apparently I didn't change it out... doh. Put the new one on and just manually moving it up and down it will pump air (since the bowl is dry) which it never did before. Fingers crossed pishta hit it on the head. We'll see. I have to run and get some vacuum hose and then reinstall and try.
 
blevins2005 said:
Well i got everything back together. Same issue. Exactly at 2000 rpms it cuts out.
Click to expand...

This may sound weird, but as you bring the throttle up partially block the air going into the carb with your hand (maybe half the air) and see if the problem gets better.
It sure acts like it's not getting the fuel it needs, and this test will prove that.

And, absolutely a vacuum leak can cause this, but it would have to be fairly substantial like a brake booster or PCV line off.
 
Guess a timing light, to check if spark drops out. Have to narrow it down somehow.
 
Thanks guys I'll check those things tomorrow when its not so late. Neighbors might hate me for reving this late at night.

I've been reading to and came across a comment in a forum and they mentioned the 2280 carb can be finicky and doesn't like emissions stuff disconnected. Think this holds any weight. Reason I ask is i recently removed the egr... I'll try putting that back on too.
 
blevins2005 said:
Thanks guys I'll check those things tomorrow when its not so late. Neighbors might hate me for reving this late at night.

I've been reading to and came across a comment in a forum and they mentioned the 2280 carb can be finicky and doesn't like emissions stuff disconnected. Think this holds any weight. Reason I ask is i recently removed the egr... I'll try putting that back on too.
Click to expand...

That's possible, but I don't think I ever remember a carb that couldn't be worked with though.

Just as a note of interest, when I first got my Dart with the 318 two barrel on it I had all kinds of little issue's with it.
Idled rough and way too high, and the idle mixtures had near zero effect.
It wasn't until I pulled it that I found two 1/8 holes drilled through the throttle plate base on the back side of the carb just below the plates that were wide open to unfiltered air. WTH?:D
If you can't make it idle right, make it idle faster I guess.
 
Sorry I did not comment but you will not typically be able to see the accelerator pump shot when you slowly open the throttles; it is too gradual.

I see you have a new pump; that is sadly no guarantee that it is good. Tooljunkie had the same thought and it is this: the pump, or a blockage, is just allowing a dribble of fuel into the carb. Under idle conditions, it will have barely enough to run, and if you blip the throttle to rev it, there is enough in the bowl to supply that short burst of fuel. But when you go to the 2000 RPM throttle conditions, then the slightly higher flow requirement exceeds the tiny flow from the pump or supply. A fuel pressure gauge on the pump outlet will tell you if this is the problem (unless it is a bit of crud in the carb inlet that has been missed). Also, there have been cases of the pump arm being inserted on the wrong side of the eccentric; not sure if you can do this on the SBM, but it will cause similar symptoms; the pump is not being operated correctly.

Just to check a few other things... what is the battery voltage at idle, and if running at say, 1200 RPM? Just checking to see if the electrical system is operating. I'd be less inclined to think ignition with your symptoms, since it seems to rev up fine.

Also, check the plugs to see if there is any sign of carbon, indicating and over-rich condition. I doubt this is the case, but it is an easy check.
 
EGR may have something to do with this as EGR usually comes in about that time, off idle. IF the carb is set up for EGR, make sure the port that supplied the egr signal (pic 1) to the valve is blocked, or else youll be pulling in air at EGR time, but it looks to be just a non timed port. Hows your advance plate function, smooth? check with vacuum (suction) on line and observe movement. should be smooth. Is this a lean burn carb? Not really an adaptable piece if so, lots of stuff designed to work with its extremely lean conditions.
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blevins2005 said:
Hi All,

I've been working to get a brand new long block running. I have gotten everything together and have set initial timing. The engine idles like a dream. It revs hard like a dream. The problem is if I slowly bring it up through the RPM's when in neutral, consistently at 2,000 RPM's its stumbles and stalls. If I immediately let of and let the RPM's fall it almost always stumbles but does not die. If i stay in it it always dies.

I'm at a loss and am looking to you experts here. Any help is much appreciated.
Click to expand...
From the description
Your carb should still be on the transfers, maybe at the top, switching to the mains.
When you whack it open in neutral you get on the mains right away with the pumpshot covering the lean hole.
At idle,the mixture screws can compensate for a poor transfer circuit.
Ima guessing this is strictly a transition problem at the top of the transfers, or the bottom of the mains.
Since these circuits are intimately controlled by engine vacuum,so yes,low vacuum that can lead to this problem. But so can a multitude of other things, most of which have already been mentioned.

But here is the stumper
If I immediately let of and let the RPM's fall, it almost always stumbles but does not die.
If it was a transition problem, or it was a shorting point-plate; as soon as you backed off, it would be business as usual.
And the clincher
If I stay in it, it always dies.
In my experience I think only two or three things can cause this;
1) insufficient fuel in the bowl, or
2) a severely restricted exhaust system.
3) a flooding condition.
#3 you wouldda seen and we wouldn't be here,lol
#2 is easy to check; get a helper
#1 leads to a fuel-pump volume output test....... with the engine idling, and the gas-cap cracked open.
If this is adequate, we're back into the carb, checking the pumps ability to keep the bowl full, the wet fuel level,and the manifold vacuum signal............And just maybe, the T-port sync., but not for the usual reason.

Good luck
 
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I want to thank everyone for the input. I have some food for thought. I checked vacuum advance as well as checked for any vacuum leaks and every thing seems to be happy. I'm going to order a rebuild kit and pull the carb and this time remove those darned tamper proof screws to do a 100% rebuild. I'll let everyone know what comes of it.
 
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