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Cannot get the tune right. What next?

UKPlymouth

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5:51 PM
Joined
Nov 11, 2012
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Location
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Hi guys,
I'm having a heck of a problem simply getting my car to idle correctly.
Its a fresh built 340 motor and I have replaced all of the following;
New Edelbrock 600 V/S
new spark leads
new distributor cap and rotar arm
rebuilt distributor checking vacuum advance is correct
new coil
new spark control box

Symptoms
car alway start and once warmed up has a lumpy idle and as soon as I put the car into gear it drops onto its face and stalls. At best i can get a just about surviving idle in gear.
Playing with the timing and carb mixture makes little real difference. Ive been struggling for 3 weeks now and on the verge of giving up. Never had this problem with my 3 previous Mopars. Any ideas?
 
Sounds an awful lot like the problem I just had with my 318 and that was the distributor bushing. Really easy repair. Got it off Ebay for 10 bucks or so. only took about 30 minutes to fix.
 
TC? Convertor is stock, not high stall so I ruled that out.
Could be the distributor, are there any obvious symptoms to look for?
Im going to swap in the distributor from my 318 truck tomorrow to try and asses that angle.
 
i had the same problem and i changed torque converters and it fixed the problem,, my converter had a broken sprag
 
if the convertor was screwed, wouldn't there be other symptoms?
Timing is 16 degrees intitial
I've tried setting carb with vacuum and however mixture is set the I problem prevails.
Ive built two 360 motors from scratch and never had such a problem.
 
Well, i wouldnt give up. At what rpm does it idle in park? If you work the throttle can you keep it running?
 
the symptoms i had was it idled at 1200 in park and dropped to 700 in gear and ran erractially... i changed converters and it idles at 700 in park and 600 in gear,, no joke.. this is with dual quads too.. i tried timing and air mixtures everywhere i could to no avail. worth a shot to see if its ur problem also
 
Need to rule out the carb first. Sounds like you don't have your baseline set. When you turn the mixture screws all the way in does the motor die?
 
Thanks guys, I have checked all vacuum connections and can find no leaks. the booster is 'dead' so I have temporarily blanked off the port from the manifold.
If I turn the idle screws in the car will stall.
I tried tuning with a vacuum gauge and could only pull 10" at best with the car idling in Park which seems too low.
I haven't had the car running clean once, something is out. I've built two 360 motors with cams in them and never encountered this problem.
As for the convertor, it drives like a stock one, ie no drag like a higher stall one does.
 
Just to check, the Edelbrock carb has 3 vac ports, 2 at the front and a large (currently plugged) one at the rear?
 

3X a few quick shots of starting fluid will locate the problem if it is a vacuum leak. with the car running, shoot a couple quick shots of fluid along the intake manifold flanges at the heads and the perimeter of the carb base. if the idle picks up you have a leak. good luck with your tune.
 
Whats the camshaft profile? May be too much for your factory converter. My car idles at around 1,300 RPM. Would need a 5,000 stall in an automatic.

Another idea,
Why not ask a buddy and borrow a carburetor? Had a relatives 283 hardly running at idle, turned out to be a gasket leak on the carburetor adapter plate where it wasn't sealing properly; was nearly going to pull the engine because it was un-noticeable until you pulled the plate off or flipped over the intake manifold. Can you take off the breather, put your hand over the carburetor to block airflow? If the car keeps running, then obviously you have a major leak somewhere. A carburetor won't fix this, but it would be the next step if your car dies off. Would be simple to change and you could rule out your carburetor. He was running a 600 edelbrock, and we placed a 750 DP Holley on top. Car runs even better than before, though most would say this is overkill :headbang:

Last idea,
Just had some major issues with my car, turned out to be that my 8mm wires were shot and were arcing nearly everywhere and jumping. Car would run, but just didn't seem 100% there and would fall on its face. Turned out to be one completely dead cylinder, 3 other wires jumping, and two crossing spark back and forth. This was after a header swap, when the plug boots had something to jump fire to. Simple thing to check at night.

Just throwing some other ideas out their. Edelbrocks are usually bolt-on-and-go. The carburetor shouldn't be causing all these problems unless you have an aggressive camshaft.
 
thanks for the ideas, all. I will remove the carb and check everything at gasket level.Pretty sure that earlier today when I put my hands over the top of the carb to starve it the idle dropped but didnt kill the motor.
Ive even run the car in the dark to see if any of the leads are cross firing or shorting, but nothing to see.
Cam shaft is originals 340 auto version so nothing dramatic in terms of spec.
As I mentioned earlier, I can only get 10" vacuum and that seems too low.
 
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