750street Hp holley Backfires cold start
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Joined: Oct 2011
Posts: 320
Likes: 6
From: Sydney Australia
Car: 1982 z/28 Right hand drive
Engine: 377 AFR195 750DP Solid cam 10.25:1
Transmission: TH/350 3200 stall spohn conversion
Axle/Gears: 10 bolt 3.42:1 Eaton Trutrac.
750street Hp holley Backfires cold start
I got a pretty healthy 377sbc running a 750dp. Fresh build.
was setup on a dyno and air fuel was perfect.
car has been sitting 12 months waiting for interior work now backfires left side of carby on a cold start, i have had a flame shoot from the carb left rear venturi on a cold start, engine warms up then runs like a dream, it revs fast and idles perfect. On a restart NO BACKFIRES when warm. I did pull the plugs and some were wet and rich, cleaned them up all good now. STILL backfires cold.
Running solid cam and big MSD pro billet and new 9mm tayler leads, EVERYTHING is brand new
i have a great engine guy but before i hassle him i will see if its a simple fix myself.
am running a sizeable cam and 34 advance. fuel is 98 mobil in Australia
was setup on a dyno and air fuel was perfect.
car has been sitting 12 months waiting for interior work now backfires left side of carby on a cold start, i have had a flame shoot from the carb left rear venturi on a cold start, engine warms up then runs like a dream, it revs fast and idles perfect. On a restart NO BACKFIRES when warm. I did pull the plugs and some were wet and rich, cleaned them up all good now. STILL backfires cold.
Running solid cam and big MSD pro billet and new 9mm tayler leads, EVERYTHING is brand new
i have a great engine guy but before i hassle him i will see if its a simple fix myself.
am running a sizeable cam and 34 advance. fuel is 98 mobil in Australia
Last edited by aussiesteve; Feb 1, 2022 at 02:08 PM.
Joined: Jul 1999
Posts: 12,096
Likes: 126
From: SALEM, NH
Car: '88 Formula
Engine: LC9
Transmission: 4L60E
Axle/Gears: 3.89 9"
Re: 750street Hp holley Backfires cold start
I got a pretty healthy 377sbc running a 750dp. Fresh build.
was setup on a dyno and air fuel was perfect.
car has been sitting 12 months waiting for interior work now backfires left side of carby on a cold start, i have had a flame shoot from the carb left rear venturi on a cold start, engine warms up then runs like a dream, it revs fast and idles perfect. On a restart NO BACKFIRES when warm. I did pull the plugs and some were wet and rich, cleaned them up all good now. STILL backfires cold.
Running solid cam and big MSD pro billet and new 9mm tayler leads, EVERYTHING is brand new
i have a great engine guy but before i hassle him i will see if its a simple fix myself.
am running a sizeable cam and 34 advance. fuel is 98 mobil in Australia
was setup on a dyno and air fuel was perfect.
car has been sitting 12 months waiting for interior work now backfires left side of carby on a cold start, i have had a flame shoot from the carb left rear venturi on a cold start, engine warms up then runs like a dream, it revs fast and idles perfect. On a restart NO BACKFIRES when warm. I did pull the plugs and some were wet and rich, cleaned them up all good now. STILL backfires cold.
Running solid cam and big MSD pro billet and new 9mm tayler leads, EVERYTHING is brand new
i have a great engine guy but before i hassle him i will see if its a simple fix myself.
am running a sizeable cam and 34 advance. fuel is 98 mobil in Australia
I assumed the carb and jetting was just too much for the low HP small block so I put a quadrajet on it.
-- Joe
Joined: Mar 2001
Posts: 10,425
Likes: 2,089
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: 750street Hp holley Backfires cold start
Engine wants different ignition timing when cylinder is cold.
Might be too lean too, causing a slow burn. Fuel pools on cold surfaces instead of atomizing in the cylinder.
Carburetors need PRESSURE DROP to fuel properly, and engines need air VELOCITY to run well. Your setup may not be doing that well enough at low speeds.
Might be too lean too, causing a slow burn. Fuel pools on cold surfaces instead of atomizing in the cylinder.
Carburetors need PRESSURE DROP to fuel properly, and engines need air VELOCITY to run well. Your setup may not be doing that well enough at low speeds.
Last edited by QwkTrip; Feb 12, 2022 at 03:17 PM.
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