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  #1  
Old 07-04-2018, 11:13 AM
GDBST1 GDBST1 is offline
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Location: Melbourne
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Back firing (can't figure it out :( )

Hi all,

Hoping someone can point me in the right direction on this one.

The car has just all of a sudden started running like a dog. Back firing under any sort of load.

I've put octane booster in, checked the carby jets for blockage. The leads are only 1000kms old and the plugs were only cleaned 1000kms ago or so, also checked under the distributor cap and all seems normal.

Anyone got any ideas??

Thanks

Rob
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  #2  
Old 07-04-2018, 12:42 PM
qik66 qik66 is offline
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Name: Neil
Rob basic things to check would be the timing with a timing light, make sure you are getting advance, check the cap for cracks and the leads for damage and resistance. Just because there a 1000km old doesn't mean one has not failed.Check for vacuum leaks around the manifold. run a spanner over the bolts to make sure they are tight. Also check for split or cracked vacuum lines. Check the accelerator pump is squirting properly as well. you really just need to check all the basics and go from there. the other question is what did you do just before you started having problems? If you had just filled the tank you may have got some bad fuel, if you washed the car and engine you may have got water in something?
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  #3  
Old 07-04-2018, 07:49 PM
Geoff 4 Geoff 4 is offline
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Tell us more about the engine & components. Has idle quality changed? More info needed.
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Old 07-04-2018, 07:53 PM
GDBST1 GDBST1 is offline
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It's a 383 stroker with a 750 Holley, alloy heads, 238/242 cam. Seems to start ok and idle ok. All seems to have happened after my last fill up at a servo that I've never been to before. It was a 7/11 mobil so thought it would have been ok.

Check the accelerator pump and it's pumping fuel ok. Also tried spraying water to see if there's any vacuum leaks around the carby and manifold and all seems ok. Just tried siphoning the fuel and noticed an anti siphoning spring. Also bought a timing light which I'll check next.
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Old 08-04-2018, 11:27 AM
Intruder Intruder is offline
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After all the other checks I would suggest pumping a litre of fuel into a container check for water and if so run a bottle of metho in the tank to help disperse water if you are unable to drain and refill.
Let us know how you go.
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  #6  
Old 08-04-2018, 05:24 PM
GDBST1 GDBST1 is offline
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Thanks all for your help.

Managed to get around 15l out of it by jacking the car up.

Took the car for a good run today and not a single back fire. Must have been a bad batch of fuel. The octane booster and that top up of good fuel must have mixed in and done the trick.

What are your thoughts on going with one of those Holley efi systems?
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Old 08-04-2018, 07:42 PM
Geoff 4 Geoff 4 is offline
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If your car starts, idles & runs well with a Holley carb [ a bonus ], then an EFI throttle body that bolts to the manifold will do little except lighten your wallet. Because all the flow/distribution vagaries of the manifold remain...
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Old 09-04-2018, 07:16 PM
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Nev68 Nev68 is offline
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Quote:
Originally Posted by Geoff 4 View Post
If your car starts, idles & runs well with a Holley carb [ a bonus ], then an EFI throttle body that bolts to the manifold will do little except lighten your wallet. Because all the flow/distribution vagaries of the manifold remain...
You don't think EFI is the go?
Surely an EFI system that can correct itself with varying conditions will give you a better driving experience.
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  #9  
Old 09-04-2018, 07:52 PM
Geoff 4 Geoff 4 is offline
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The term EFI is a very broad brush.

As I said in qualifying my earlier post, if you are going to fit/adapt EFI to a 4bbl manifold, I don't think there would be much performance improvement, maybe just easier starting & a better idle. However, if the current carb is doing all those things well, what is there to be gained?
A carb is a very efficient device for mixing fuel & air.
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