302 timing
 

302/348 with E303 camshaft (44IDF webers)
Anyone have idea as to timing advance, Now set at about 12TDC, experiancing some backfiring up through carbs intermittentlly.

Your cam is not overly big for Webers, should be quite nice for the street.

You need a distributor recurve.

Run about 15 at idle.

Your sneezing is lean.

Please list your carb specs.

Gary

Ford 302 timing
 

My motor from Ford Racing said 12 degrees BTDC at idle and not to exceed 36 degrees all in. The motor has a E303 cam as well. Please check your firing order for a HO engine. Should be 13726548 and NOT 15426378. I was told the E303 is a HO cam and it does not matter what block or carb you may use.

Gary is right in that Webers require different timing than a 4 barrel carb. They like a lot of advance and they like it early. I would pay attention to what he asks and says, I have followed his posts and the advice is typically good.

It won't be firing order, since the OP says the backfiring is intermittent.

It is either crossfiring, or more than likely lean.

Gary

302/347 timing
 

Thanks for the advice from everyone, I'm going to increase timing from 12 to 15 btdc and see if it helps, Also will increase idle setting on offending Weber carb and see what happens.

This Club Cobra forum has been the best for advice that I have found, and I'v tried a lot.

A little confession, Althou I love the Cobras, I don't have one, This engine is in a 1930 ford 5 window coup.

Thanks to everyone. Joe

I would say that Webers don't "require" different timing than other carbs, but rather that other carbs can't handle the timing that Webers work well with.

What I mean is this. With typical setups of 4-barrel carb and manifold, it's not unusual (we might even say quite common) to have different cylinders getting different amounts of air and different mixtures. Some cylinders could be running rich, (11:1 AFR) and some could be running lean (17:1 AFR) at the same time, but even a modern sensor in the exhaust is only going to read the combined result of all this and give you whatever number in the middle it figures it's seeing. This also results in emissions that really are dirtier than necessary. Because of this mixture disparity, too much timing is going to cause detonation problems really easily, so you can't throw too much timing at it. With your typical Weber setup, you can more reliably get every cylinder to have the same airflow and same mixture under any and all conditions. It's a more ideal situation that the engine is seeing and it will respond well with a lot more timing thrown at it. If you want to, once the carb jetting is pretty close, you could go to a dyno shop and tweak and tune everything, including seeing just how much timing the engine is willing to take.

To the OP: a lot of people do well with 34 to as much as 36 degrees of timing all-in. But as stated elsewhere in this thread, once your timing is at a safe ballpark setting, let's chase down your mixture situation. Buckle up.

I stand corrected. Nice job explaining the difference between a Weber carb and a standard four barrel.

Here's a shot of the guys on Engine Masters measuring the mixture on every cylinder simultaneously. One cylinder goes wayy lean into the deep 16s of AFR, but even without that, the various cylinders' readings aren't close to each other. And that comes down to the intake manifold not distributing the air and the fuel that well and that efficiently. Maybe fuel isn't turning a corner and making it into a particular runner, and/or elsewhere you have air rushing past one runner to go into the one next to it or something. This leaves a lot of power, a lot of torque, a lot of smooth running, a lot of throttle response, a lot of fuel efficiency, a lot of idle quality, all on the table. This limits how much timing you can run. Take away those wild swings and you can run a few more degrees of timing, and pick up performance both from the timing increase and from correct mixture. An independent runner setup that is tuned well can do this a lot better, whether it's Webers or injection.

And that's just one reason why we love them.

Hello Boatbroke,

Have similar occasional back fire through intake on a 302 HO, 303 cam, GT 40 upper & lower intake, 65 mm throttle body, GT 40 heads(GT 40 EFI Option Package). Timing at 12-13 degrees. I've heard the same complaint from others with this set up. It is inherent without better distribution of fuel air mix. Independent runners make all the difference. Nick

With EFI, you won't be having a mixture distribution issue like single carburettor engines can have.

So you need to look at lean areas of your fuel map.

Gary

Hi Gary,

Your right on regarding lean air map. With EFI it usually a result of air fuel algos when using a non stock cam with a stock EEC. Nick