Cuda keeps dying!

Author Topic: Cuda keeps dying!  (Read 3592 times)

Offline hemitodd

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Cuda keeps dying!
« on: August 03, 2010 - 04:27:33 PM »
Hi All

I was read the "Challenger keeps dying" thread and im experiencing something similar.

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




Offline drewcrane

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Re: Cuda keeps dying!
« Reply #1 on: August 03, 2010 - 05:10:03 PM »
Im running a demon, and i do know this, the gaskets were questionable and i replaced them and it helped alot,

what kind of fuel are you running? because todays  fuel is not good for carbs or there gaskets, they get saturated with the stuff and they leak

,try some higher octane,

 also i dont know where you are from but in Colorado they have 5 different kinds of fuel for different times of the year, in the spring my car does fine , but in the hot summer it can sputter,stall,and sometimes its just the fuel and where i bought it :stirpot:

Offline TinCuda

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Re: Cuda keeps dying!
« Reply #2 on: August 03, 2010 - 10:27:42 PM »
I had a problem with rust floating in the fuel tank from prolonged storage.  The junk floating in the tank would plug up the pick up line.  The motor would stop(engine driven pump would stop) the junk would float away.  I could start and run the motor for a while then it would quit again.  I ended up replaceing the fuel tank to fix this. 
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Offline 72cudamaan

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Re: Cuda keeps dying!
« Reply #3 on: August 03, 2010 - 11:24:57 PM »
Sounds like a clogged idle circuit to me. :2cents:
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Offline hooD

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Re: Cuda keeps dying!
« Reply #4 on: August 04, 2010 - 04:48:34 AM »
just throwing my 2¢ at you....

- how's the fuel pump?
- how's the fuel filter?  Is it on correctly?
- what's the condition of the fuel line going to carb? 
- Are the carburetor vent tubes blocked or covered by the air cleaner lid?
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Offline Chryco Psycho

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Re: Cuda keeps dying!
« Reply #5 on: August 04, 2010 - 11:06:17 AM »
could be a bad power valave or needle & seat flooding it out ?

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Offline hemitodd

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Re: Cuda keeps dying!
« Reply #6 on: August 05, 2010 - 10:33:14 AM »
thanks for the info

i did get some new gaskets for it and will try that.
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.


Offline acudanut

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Re: Cuda keeps dying!
« Reply #7 on: August 08, 2010 - 10:08:20 AM »
Sounds like a clogged idle circuit to me. :2cents:
WHaaaat ???? :clueless: :dunno:  :screwy:

Offline moper

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Re: Cuda keeps dying!
« Reply #8 on: August 09, 2010 - 11:58:01 AM »
If it was me I'd pull the metering blocks adn very carefully check them. I've had three Demons apart. All had the same issues and they were years apart. The passages are drilled in the billet block, but the little shred of aluminum from the bit breaking thru gets stuck on the edge of the hole. On two, they impeded fuel flow in the idle circuit right out of the box (you can tell this when you can get it to idle better on two of the 4 screws rather than all 4 balanced) ont he 3rd, it broke lose two years later and got stuck in a passage. The klast brand new Demon I looked at (for my buddy's mustang) was full of the same machining chips as the first one I looked at 4-5 years ago. Not my favorite carbs...lol. Once they are cleaned up they are decent. So I'd say look very closely and clean clean clean...

Offline hemitodd

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Re: Cuda keeps dying!
« Reply #9 on: August 29, 2010 - 08:47:23 PM »
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?

Offline Chryco Psycho

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Re: Cuda keeps dying!
« Reply #10 on: August 29, 2010 - 11:25:03 PM »
Vacuum leak into the power brake booster , have you checked float levels etc .
 When you hit the brakes it will drop the vacuum inthe manifold & sometimes cause stalling

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Offline mopar12372

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Re: Cuda keeps dying!
« Reply #11 on: August 31, 2010 - 11:45:36 PM »
if you have a old ballast resister (REPLACE ) that is part of a tune up. fyi
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