Footage taken from Holley Carburetor Installation & Tuning DVD Also when the engine is floored with the accelerator pedal, the engine dies unless you let up right away on the gas. He states that the engine is holding a steady 12 inches of vacuum at idle. I have a friend that has a Nova with a 383, aluminum heads, comp cam, and new Holley Avenger 670 carb. Backfiring from the carb is normally a sign of a lean mixture, but it doesn't do it unless I go hard on the pedal. Cam is hyd roller 209/216 deg @.050. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these . He also has new distributor and components. Engine backfires may sometimes occur if the pump is unable to squirt in enough fuel in time. 3. Float levels checked etc. Things I have done in the past week:-rebuild carb with Holley marine kit-new cap, rotor, plugs, wires, ignition coil and ignition module-reset timing (the timing does advance)-new fuel filter Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. Engine backfires when cold. Too small of an accelerator pump in carb(s). Usually when the engine backfires through the carburetor when starting, something is wrong in the valve and rocker arm area. It could be . It was running great the day before yesterday, today its running so bad its nearly undrivable. The backfire on hard acceleration is almost always pump shot related and there is not 1 correct answer. 334. holley carburetor trouble shooting chart. So its jetted 65 front and 72 rear. Len 1980 Capri 2.3 1983 Mustang GT. If your car or truck is equipped with a Holley four barrel carburetor and stumbles upon acceleration, more than likely the carburetor needs an adjustment to the accelerator pump assembly. I'd check that first. This is all in an S-10 pickup. Gbauer's got 32, says 31 would probably work just fine. E EXECJIM Registered Joined Jan 31, 2002 I have an edelbrock performer intake and 600 cfm performer carb. Timing was set to 10 initial. Backfire thru the carb on acceleration is generally a lean condition. Backfiring through the exhaust is a result of problems arising out of rich fuel mixture and out-of-turn sparking of spark plugs. 1 turn out on all 4 seems to give the best response. I have not run the engine much since the cam install, but I now have noticed a slight . Brand new crate motor (less than 3k miles), I got the 350 HO Deluxe - carb to pan complete. The discharge nozzle may be too small, or the accelerator is not giving you a long enough fuel squirt. This may be because the pump is plugged up or simply not working. And yeah, those backfires have probably hurt something in the carb most likely the power valve. 12/02/2009. Together with the unburned fuel in the exhaust system and an open exhaust, the sparking results in the . Dumping the Weber for a Holley 350 cfm carb, an American carb someone can actually work on. base plate and metering blocks are totally cool, too. Air/Fuel Mixture. 334. Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. I have been experiencing backfiring and what feels like a misfire. Looking at the Holley video, it looks like I have too small accelerator squirter. 1 7/8 headers 3" exhaust. bikingplumber. 2) rocker arm/s is maladjusted or worn, ditto the rest of the valve train. If your air/fuel mixture is too rich and you have unburned fuel in the exhaust system, cross firing from one spark . Backfiring happens when the ignition occurs in the intake or exhaust system rather than the combustion chamber during acceleration. I have a friend that has a Nova with a 383, aluminum heads, comp cam, and new Holley Avenger 670 carb. to the carb, with the choke plate fully open. I haven't tried heavy throttle due to fear of violent backfires. I am getting what amounts to a single backfire through the carb during heavy acceleration. I noticed that on hills I would get some backfiring and sputtering. Conversely, if off-idle acceleration does not feel crisp or clean, then the pump nozzle size may already be too large. Holley 3310 - 4160, vac secondaries New 350, vortec heads. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve. I'm not really familiar with Edelbrock carbs, but there might be a bigger squirter nozzle or a different accelerator pump cam. If your car or truck is equipped with a Holley four barrel carburetor and stumbles upon acceleration, more than likely the carburetor needs an adjustment to the accelerator pump assembly. Check the float level and make adjustments if necessary. The "pump" is actualy a circut within the front float bowl (on most Holley carbs) actuated by a diaphragm. He states that the engine is holding a steady 12 inches of vacuum at idle. Solution #1: A low float level will create fuel starvation, which will cause the engine to stumble. It will idle ok but if you stab the throttle it will backfire out the carb and tailpipes. A backfire (lean condition) on acceleration also calls for a step up in pump nozzle size. video. Can bad spark plugs cause backfire? Backfiring is typically caused by an air/fuel mixture that is too lean, meaning the mixture has too much oxygen in it. If you have anything under 3.55 gears and 17 inch or larger tires, I would not, even on a good day, expect to accelerate from 2000 rpm, in 5th gear. Checking your fuel injectors may not be that easy of a task as you may have to remove the fuel rail from your engine to check the fuel injectors if your engine. In this case a smaller size is required." . If your fuel injectors are clogged up and not sending enough fuel into the intake of your engine this can also be a cause for your engine to backfire. Upon acceleration the car will backfire through the exhaust. I can get 20" hg at idle, steady gauge with no fluctuation. mine is 25. This tends to happen under light to medium throttle. Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. Joined Feb 6, 2002 Messages 15,370 Location OC, CA. The condition as stated to me, is when accelerating under load the engine hesitates severely . I can accelerate from a dead stop just fine, doesnt seem to be a problem. Hi guys. He also has new distributor and components. I have a 1978 302 in a 1926 model T. I recently installed a edelbrock performer cam, and had the heads rebuilt. Drivetrain specs as follows: 87 truck 460. However, while "at speed" or 1/3 throttle I try and accelerate (2/3 throttle) and the . We have a persistent problem despite carb rebuild twice, new plugs, wires, fuel filter. control valve in the passage from the throttle bore provides an efficient degree of spark advance during periods of acceleration by momentarily providing a partially retarded spark. Place the carburetor on top of the flange gasket on the manifold. 5. Brandon, FL. seem to disapper under hard acceleration (maybe 3/4 thorrtle) but it. When the throttle plates are opened quickly, the pump squirts . and it was running great. It had an edelbrock on before the Holley that didn't pop like this so it's not the motor itself. Fixing these faults is often enough to solve the problem. Full weight street machine. Like DragRacingSpirit said, check your accelerator pump shot, and check for vacuum leaks. Lots of wet black soot out the tailpipes. You can get an off-idle stumble/hesitation/back-fire from both too much squirter as well as not enough. accelerate hard (3/4 throttle) I either get a carb backfire or popping in the exhaust. While the power valve can be bad, this will not effect acceleration in the way adamblitzer describes. Backfiring during acceleration occurs when ignition takes place in the intake or exhaust instead of the combustion chamber. There's no flames, just a pop and maybe a little puff of smoke. The 750 3310 square bore vac secondary is cheap and works well, 650DP also good on a stocker but more expensive but would also be punchier and better throttle response but more fuel around town. Bill Tichenor. Set your idle & timing, then adjust idle screws for highest manifold vacuum. But if your in neutral and start revving it, around 2000 rpm it starts popping out the carb. . BG Demon carb trivia: A single Demon on an RPM intake made more hp AND more low speed torque than an aftermarket race fuel injection setup. Video. Little Elm, TX. We usually refer to an exhaust backfire as a "backfire", and backfiring through the carb as "spitting" or "coughing". Backfiring during acceleration occurs when ignition takes place in the intake or exhaust instead of the combustion chamber. better than ever. (1) No start or hard starting - hot or cold (2) Rough engine idle and stalling (3) Hesitation on acceleration (4) Loss of power on acceleration and top speed (5) Engine to run uneven or surge (6) Poor fuel economy (7) Excessive emissions BEFORE PROCEEDING WITH TROUBLSHOOTING THE CARBURETOR, CHECK THE ABOVE ITEMS FIRST! I am trying to tune out a hesitation in the off idle part throttle range. Not a backfire. Solution #2: Check your fuel pressure and adjust it to these psi ranges: 5-7 psi for Holley, Quick Fuel, AED, Willy's, or Summit Racing; or 4-5 psi for Edelbrock or Jet. Now getting a backfire through the carb (seems to always be the one over the 5/7 cylinders) on acceleration. The engine still stumbles and backfires through the carb. The backfire tends to happen while slowly accelerating when the A/F Ratio is 12.8-13.2. I have fixed a lot of these type issues and it is usually a combination of . 1.) Mechanical is working and goes all in by 3000 rpm. Got an '84 Mastercraft, PCM Ford 351, Holley 4 bbl., Prestolite electronic distributor. Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. Holley 4 barrel carburetor troubleshooting. Internal carburetor issues, poor compression, fuel tank leaks, lean engine conditions, and weak or broken valve springs can all cause backfiring during acceleration. Check Your Fuel Injectors. The problem is as follows: (1) After the engine is switched off, heat from the engine heats the fuel in the fuel line. Engine hesitates or "bogs" during initial acceleration (after engine is at operating temperature). Holley 2140 & 4000 troubleshooting. The electric choke works fine. Timing is 14 intial and 34 total. The boat can run like a dream, pull skiers up with absolutely no hesitiation on acceleration, run at top speed without a hiccup. . Comp 305H cam (.525/.525) 305 Duration (253 @.50) 110 lobe separation. Oct 14, 2005. Either increase the pump size or the nozzle size or both. Backfiring during acceleration occurs when ignition takes place in the intake or exhaust instead of the combustion chamber. I'm having a little trouble with a backfire or miss when the engine's cold. Changing the pump fixes the problem. They're awesome carbs. The car drives decently under light acceleration but when I try to. Holley truck avenger 770 (new) Hesitation in acceleration, occasional backfire through the carb. If you have a carburetor older than 1992 (or you have experi-enced an extreme backfire) and expect a blown power valve, use this simple test. . Little Elm, TX. pipes. (2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor. 66 Satellite. Most of the carburetors installed on the 350 use a single air/fuel mixture screw, while some carburetors use two. Location. What would cause Ford 390 to backfire through carb Yahoo Answers Setting Curb Idle Speed of Carburetor Video Holley Carb DVD TEST: At idle turn your idle mixture . This can happen under load when: 1) timing chain is worn. I too would suspect the accelerator pump. 5) Reconnect the vacuum advance to the Timed Spark Vacuum source at the top of the carb. (3) The check valve prevents the fuel backing up through the fuel pump. Share. I have a smooth even idle. After a few weekends of tuning my Holley carburetor I might have finally found what might be the root cause of my carb backfiring and hesitation.What I found. If you went to a Holley set up properly you would get gains all round especially by optimising the timing. takes the throttle better but still popping now and then only under acceleration. A few notes that may be important. Acceleration Enrichment can't be tuned until the Base Fuel Table is well tuned. stalling rough idle flooding hot start economy hesitation acceleration surge backfire power stalling (cold) (cold) idle adjustment y y. x. y y y. x. y y. x. y. idle needles damaged y y. x. x x x x x x x . Quote. Check this link for backfire issues:. Post. And under hard acceleration it does it even worse. I turned the mixture screws out some to richen and the pops. The billet alum. The roller rockers are 1.5 stock with a 650cfm double pumper Holley carb. roller timing set (early set, not 8 deg retarded) Hydraulic Flat Tappet cam, Duration 276/ 286, Lift .503/ .503, Duration at 050 inch Lift: 218 int./228 exh. All other areas the 0-80670 perform great. 446ci 440. Backfiring during acceleration occurs when ignition takes place in the intake or exhaust instead of the combustion chamber. Furthermore, what causes a small engine to backfire through the carburetor? Once I've been driving it for 10 minutes or so it's fine, or close to fine. It has an after market fluid balancer and Flowmaster shorty headers with 2.25 exhaust all the way out and Thrush ultra flow mufflers. Carburetor Installation and Tuning. It's more like a miss and a spit of aerosol fuel gets shot out of the top of the carb. Hi, I've got the 250 six cylinder with Holley 4BBL 390 CFM, bumped up compression, larger intake valves, and a moderate CAM. 10 min read. Backfiring caused by internal carburetor problems is a result of a defective accelerator pump. Insert the accelerator pump and push it to the bottom. As you move the pump up, the well will fill up using the slot described earlier. In general if the engine backfires through the carb one or more intake valves is open during ignition on one of the cylinders. Lots of folks lately with Holley issues. Sometimes it is a quiet muffled pop, other times it is a loud bang. posted 11-25-2003 02:44 PM. Remove the spark plug(s) from the engine.Put a clean small screwdriver into the spark plug opening so you can tell when the piston is at the top of the stroke. Try a "green" pump cam and a .031-inch discharge nozzle, available from Holley. Pin_Head. Check for restricted fuel filter or lines. 6) Installed the new Accel 0414 shorty plugs gapped to .035". Sounds like it is lean on acceleration. You are dumping a lot of fuel into the cylinders, and because of the low rpm, and the overdrive (drag) gear you are in, the excess fuels ignites and causes the backfire. Check for sufficient fuel pressure. Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. I called the carb place that rebuilt it and they said it must be an electrical or iginition problem as a backfiring problem is 99% electircal. Incorrect Timing [SIGPIC] 1966 Coupe Restomod. Actually, I'm not sure if it's a traditional backfire. Results, Runs better than it ever did before. Either the engine is not getting enough fuel, which is also called running lean, or the engine is getting too much fuel, which is also called running rich. Backfire under acceleration yesterday I was driving my 79 coupe (5.0 t5, stock 90 engine, holley 600cfm vac secondary elec choke carb f303 cam.)