Why does my holley carb backfire

There's a lenghtly post on this very subject. The ported vacuum doesn't come in until your throttle plates open - Therefore it adds to your total timing while accelerating. It sounds like your PV is a little low - I'd try running a 6. Are we talking about going from a dead stop, or a kickdown? Exactly when does it pop and backfire, and at what rpm? Sure there is - it's getting it's vacuum from the same source as the vacuum secondaries..

My previous engine would pop under wide open throttle and backfire like a shotgun. The problem was the valve springs on 2 of the cylinders. I would check the valve lash. Everybody I know that bolts avengers on don't have to change PV. Plus if you were going to change the PV you should have just bought the block PV. If you add a 1" spacer it make improve a little giving air and gas more room to mix better!

Probably not enough for most vac cans. The vacuum secondaries operate off of incoming air flow, not any vacuum line. As opposed to mechanical secondaries that are operated by mechanical linkage. RaGG- exactly when does the problem occur? I've also ordered new gaskets for the intake just incase. Timing I doubt, as nothing had changed. The timing was the same and the distributor hadnt moved. I've ordered a new coil, rotor and cap to try but doubt it would be these as they are new with the engine and appear fine on the surface.

Will I still be able to notice a difference in idle if I spray onto a leak? Last edited: Apr 19, Apr 19, 4.

Messages: 3, Likes Received: 3. Using carb cleaner or some other flammable agent will cause the idle to increase if a vacuum leak draws it into the combustion chambers. If you use a propane torch unlit of course , the method will work in a similar manner, you just won't have the mess of carb cleaner on your intake to deal with. The problem sounds to me like either a vacuum leak or something with the timing. I would assume that the number of times you have adjusted and readjusted the carb would have fixed the problem if it was carb related.

What is the initial timing? Good luck. It also fas a tad bit of hesitation off idle. Any suggestions? Thanks is advance. Bugman , Mar 27, Joined: Feb 13, Posts: Profile Page. I just went through that same thing on my small block. I eliminated the hesitation by increasing the accelerator pump squirt by changing the plastic cam that bolts on the throttle. I also advanced the timing a few degree's more and it's been running fine ever since. Joes50 , Mar 27, Joined: Mar 3, Posts: 1, Profile Page.

Joined: Mar 3, Posts: 16, Profile Page. I couldn't agree more with Joe's If that accelerator pump lever isn't tight against the plastic cam, it'll do the same thing. Look down the carby to see if you're getting a fuel shot as soon as the throttle blades start opening. Adjust as needed. Also, is the engine warmed up jet? If its' dead cold, you may need just a scosh of choke until you build a little heat in the engine to stop the backfire..

Rocky , Mar 27, Joined: Mar 21, Posts: 1, Profile Page. Glen , Mar 27, Hard starting. How do you adjust the air fuel mixture in a carb? When it's at running temperature, find the 2 screws on your carburetor that adjust the air and fuel mixture. To adjust your idle speed, find the idle mixture screw that limits the flow of fuel at idle. Marua Fraca Explainer. What causes popping through carb? There's only two common things that can cause a backfire thru the carburetor and that's excessively early ignition timing and an exhaust valve not opening.

Actually, the most common cause of backfire through the carb is a lean condition caused by a failed accelerator pump.

Aldara Maties Explainer. Can a spark plug cause backfire? Yered Sardelis Pundit. Why does my Chevy backfire through the exhaust? First, check that the mixture screw s on the carburetor are adjusted properly. Afzal Blankennagel Pundit. Is backfiring lean or rich?

A " lean " mixture is one that doesn't have enough fuel, and too much air. Lenna Amaondo Pundit. What causes popping during deceleration? Popping on deceleration is due to unburnt fuel being ignited in the exhaust.

The reason you do not hear this on a bike with a stock exhaust is due to the baffling of the stock exhaust.