Backfire

[V8 BJC]

Hi All,
I have a couple of questions regarding a backfire (on the nearside only) that I am experiencing when I lift off the throttle at high revs. The car also seems to be drinking a lot of fuel at the moment.

The engine is a 383ci Chevy, with ally Edelbrock RPM Performer heads, Dax exhaust & headers.

I have recently fitted new Felpro manifold gaskets with new header bolts and hoped that this would fix it but it has not. Today, I tightened up the header bolts again after running the car a couple of times and their was a small improvement only.

I have check the exhaust manafold and collecters for leaks by feeling for air. Is there a better way to check this? I could not feel any air leaks.

Could it be that the intake bolts need re-torqing? Is so, would torque should be used? If this was an issue, would I not get the backfire on both sides?

I have also recently changed by air filter to the Edelbrock Elite one to match my rocker covers. Since that time, the car feels a bit hesitant at high revs. Could this be connected to the backfire issue?

Any help here will be greatly appreciated as I want to take a look to morrow to see if I can get top the bottom of this.

Thanks in advance for your help.

[dave]

Hi Brian.
The backfire could be caused by a leaking exhaust gasket but I think (With your other prob you mention) that you may have a fueling problem.
Remove your air filter and when the engine is warm and idling look into the top of the carb and see if fuel is dripping into the engine. At idle it should not be dripping.
If it is this could mean (If the floats have not recently been messed around with) that debris is preventing the floats from stopping over fueling. And then carb would then need cleaning.

[tarmacscratcher]

I'd swop the plugs round also, see if the backfire changes sides. Always do the cheap and easy things first

[Purple AK]

Brian. I did notice that you had a small header gasket type leak when you drove into the hall on Sunday morning (A ticking/shuffing noise) If you still had a leak after you have retightened the header bolts you would hear it though.

[V8 BJC]

Thanks Guys.

I will take a look at the points mentioned.

Chris - Whats the best way to find the leak. If it is the manifold, would I be able to feel the leak on tickover? I have felt around all of the ports but cant feel anything. The ticking nose seems to be coming from the engine itself and not the manifolds.

[h8jse]

Brian

To check if you still have a leak in the exh manifold/exhaust system hold a big piece of rag in your hand and cover/bung the tailpipe for a few seconds whilst the engine is idling and get someone to stick there head near the manifold, you will be able to hear for sure if you have a leak as the gases will be forced through the smallest gap.

[DiggleBBC]

I used to have a back-fire that sounded like a howitzer.
That was caused by the very early over-fuelling of the engine (black smoke a tell-tale) getting the plugs all sooted up.
Changed the fuelling, replaced the plugs, fewer people in Saddleworth think we're being invaded every time the sun comes out at the weekend!

[Miket]

Brian

I was running with a header gasket gone for weeks and didn't experience any of your symtems, but in the first year of my engines life I did have popping from the right hand pipe and the ticking/shunting noise as Chris puts it and I'm afraid to say that my problem was a rounded exhaust lobe on the camshaft, might be worth taking off the rocker covers and make sure you are getting full lift on all the valves.

[V8 BJC]

I have had the tools out today and tightened everything up. The header bolts were OK but the inlet manifold bolts all had a couple of turns to tighten.

Checked the carb with engine warm on idle. No fuel dripping so seems OK.

Blocked exhaust with rag but I could not detect any leaking ports. Sounds to me like the noise is comng from under the rocker cover. It is only there on idle. Goes as soon as rev over 1000 rpm.

Not changed the plus as yet as seems to be logical to sort the noise first and see if that fixes the backfire too.

More spanner action for me this weekend

[chocice]

Brian,
I seem to have the same sort of problem as you,I had a misfire come cough and splutter at high revs,I sorted this by having the timing reset as it was a long way out, but at the same time I noticed a ticking chuffing noise from the offside rocker cover.
I took it to my local garage who have some experience with american engines and they diagnosed a slight exhaust leak from where the sidepipes connect to the manifold pipes.They tightened the headers but got very little adjustment and sealed the leak saying they were 100% certain this was the cause of the noise.......got it home and checked for the noise and guess what ? it is still there.
The noise is more noticable when the engine is cold and at idle, once warm and the revs picked up it is much less noticable but does not go away.........the car seems to be running fine so I'm trying not to worry to much.

please let me know if you solve the problem,and I will likewise.


thanks David. chevy 350ci