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Hemi keeps dying

Started by hemitodd, August 03, 2010, 03:33:52 PM

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hemitodd

Hi All

Having a little trouble and could use some help.

I haven't tweaked the carb(850 Mighty Demon) since spring and its been running great till this past friday.
It fires up and idles fine but after driving for any length of time as soon as you take you foot off the throttle it sputters and dies(every time) whether im coming to a stop or just cruising.
I can always start it back up again.
I pulled the carb apart and blew it out( the gaskets are a bit beat up), put it back together and it still has the same problem.

Float levels are fine
temps are fine
oil pressure fine
spark plugs look good
vacuum lines good(only one to the booster)
MSD 6A box
timings fine
i found an empty stretch of road and brought it up to 120mph so the engine is running strong.

Hoping someone out there has some ideas.

thanks

ChgrSteve67

Check to see if any of the vacuum plugs are cracked or fell off.


68X426

Running a PCV value? Maybe loose/broken line to the intake manifold. :popcrn:


The 12 Scariest Words in the English Language:
We are Here from The Government and
We Want to Help You.

1968 Plymouth Road Runner, Hemi and much more
2013 Dodge Challenger RT, Hemi, Plum Crazy
2014 Ram 4x4 Hemi, Deep Cherry Pearl
1968 Dodge Charger, 318, not much else
1958 Dodge Pick Up, 383, loud
1966 Dodge Van, /6, slow

hemitodd

thanks for the info

i did get some new gaskets for it and will try that.
no pvc and i didnt check the vacuum plugs for cracks but god idea, i will
i forgot to mention that its a 2 year old carter  mechanical fuel pump  with a high flow in line filter.
im  not running the best gas since i moved from the city to the country. highest i can get is 91 octane and i do find it likes to diesel a bit when turn it off. which when i fill up with  94 it doesnt.
when i had the tank out to put in a new sending unit a few years back it wasnt rusty inside.

Anymore suggestion would be helpful.

i have an 850 speed demon on my 440 plow/mudder truck i might try swapping it on just to see.

ACUDANUT


elacruze

If you changed nothing, and can't see anything that changed itself then it must be something you can't see. (obviously)

Drive it around and get it to stall. Check your float level before you restart it.
If your float level is low, try this;
Connect the carb to a secondary fuel source (boat tank with electric pump works nice with no fire hazard) then take the output of the fuel pump to a clear container of a half-gallon or so (far enough away to avoid fire hazard) and run the engine so you can watch the output of the pump. Hold the hose to the bottom of the container and watch for bubbles. You should have clear fuel with no bubbles. Bubbles indicate an air leak on the intake side of the pump somewhere, which can effect your fuel delivery; the symptoms can be varied, too, such as idle fail, high-speed fail, or good idle and HS delivery but marginal in the middle.

This is a pretty unlikely scenario, but if you're grasping at straws it's valid and common enough on diesels where the fuel system is often closed-ended.

Perhaps more likely is that your local gas has more alcohol in it, causing it to lean out and die.

Could just be some mung in the passages, too.
1968 505" EFI 4-speed
1968 D200 Camper Special, 318/2bbl/4spd/4.10
---
Torque converters are for construction equipment.

b5blue

Don at FBO loves those carbs, give him a call.   :scratchchin:

hemitodd

just an update:

cleaned the carb, new gaskets, new power valve, new gas..................didnt fix problem

changed plugs and new cpa and rotor and while measuring coil resistance, i noticed where the coil wire attaches it was very corroded. i checked the wire and the end broke off, it was in sad shape too. so i cut the wire back crimped on a new end and cleaned the conection and shes running great now.

so im not sure if at idle and low speeds there isnt enough spark energy to overcome the corrosion or it was another problem that fixed itself?

68X426

You found it. It was the intermittent spark. Hurrah!! :cheers:


The 12 Scariest Words in the English Language:
We are Here from The Government and
We Want to Help You.

1968 Plymouth Road Runner, Hemi and much more
2013 Dodge Challenger RT, Hemi, Plum Crazy
2014 Ram 4x4 Hemi, Deep Cherry Pearl
1968 Dodge Charger, 318, not much else
1958 Dodge Pick Up, 383, loud
1966 Dodge Van, /6, slow