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Backfire Through Carb Hif44


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#1 R1cbm

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Posted 22 July 2020 - 05:09 PM

Hello,

 

Got a weird issue where my new setup has the odd backfire through the carb usually under load at lower revs... can't consistently replicate.

 

1380 MG Metro unit, built by RobWalker, refurbished Hif44, MG Metro manifold, RC40 exhaust, piper cam, DISTRIBUTOR WITH VAC A PLUS YELLOW TYPE.

 

Engine has been setup properly, timing set by a friend of mine (engine builder), 2 weeks ago a rolling road tune up got 112bhp which was sweet.

 

Everything is essentially new.... followed the best practices everywhere.... can't seem to work it out?

 



#2 cal844

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Posted 22 July 2020 - 05:33 PM

It's either timing or mixture

#3 slidehammer

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Posted 22 July 2020 - 06:27 PM

Could it be fuel stand off from the carb? If you have a wide overlap cam fitted, which at that bhp figure I would imagine you have you are probably off cam at lower revs. Try putting the accelerator down more slowly until is is well on cam.



#4 cal844

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Posted 22 July 2020 - 07:22 PM

Could it be fuel stand off from the carb? If you have a wide overlap cam fitted, which at that bhp figure I would imagine you have you are probably off cam at lower revs. Try putting the accelerator down more slowly until is is well on cam.


I agree, the car should be set up so that it will come on cam with no backfiring, I know that mixture vs timing can be a compromise

#5 R1cbm

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Posted 22 July 2020 - 08:13 PM

Makes sense usually lower revs under pressure not in the cam




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