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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: ChevySepticGuy on July 03, 2006, 11:28:00 am

Title: Backfiring!
Post by: ChevySepticGuy on July 03, 2006, 11:28:00 am

Hey guys,

My 350 is backfiring a lot (and scaring the wits out of everyone when i stop to get gas!..lol  ) it just backfires when i shut her off.

I had the timing set ahead a little bit. So i set it back a bit, but it still backfires when i shut the truck off.

Because i'm in the septic pumping business i have to have her timing set ahead just a bit higher than perfect so she will pump, and be able to haul the heavier load.

All the backfiring has been hard on my exhaust. I keep blowing the little rubber donut gasket off where the header meets the pipe.

Any ideas why she's back firing?

Thanks

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton)

Title: Re: Backfiring!
Post by: DnStClr on July 03, 2006, 10:35:00 am

More than likely it's unburned fuel in the exhaust. Advancing the timing may have done it. I wonder if hotter spark plugs would help.

Don St.Clair
Culleoka Tn

Title: Re: Backfiring!
Post by: ChevySepticGuy on July 03, 2006, 10:41:00 am

I put a brand new set of basic Ac delcos on her about a month ago.

The funny thing is that my number 1 plug (I believe...The first one from the drivers side closest to the headlight) it got so hot last week that the white insulator basically melted out of the housing!! I couldn't believe it!

She seems to run real hot. Coolant levels and stuff are all good though.

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton)

Title: Re: Backfiring!
Post by: DnStClr on July 03, 2006, 11:51:00 am

That's hot for sure. That's the number 1 cylinder.Do you know what temp thrmostat you're running? Oem was 180 degrees. If  you're running much over 200, you have to worry about the oil breaking down. Actually, I think a hotter running engine should use colder plugs- so if the plugs are Delco 45, they should be switched to 44 or 43. Hopefully someone else will add to this. Specially to explain why one cylinder is getting so hot-          

Don St.Clair
Culleoka Tn

Title: Re: Backfiring!
Post by: ChevySepticGuy on July 04, 2006, 01:33:00 pm

Not sure what temp my thermostat is...Haven't really looked at it.

The delcos are 43's.

I was almost thinking of adding an extra electric cooling fan or something because the heat from the engine compartment is wicked sometimes.

Thanks.

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton) 350.

Title: Re: Backfiring!
Post by: Lt.Del on July 04, 2006, 07:02:00 pm

My two cents, you may have a coolant artery blocked off in the engine, perhaps in the cylinder head.  YOur #1 Should not be that hot and if it is, it is igniting without the need of the distributor spark due to it being so hot.    

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

Title: Re: Backfiring!
Post by: ChevySepticGuy on July 05, 2006, 03:34:00 pm

To tell ya the truth I don't think my thermostat is working properlly. I would say it's stuck closed.

When i squeeze the upper rad hose it gurgles in the resevoir, but i don't think there is any noises or anything coming from the thermostat...should there be? (this is when she is hot).

The heater in the cab is great though...throws lots of heat.


Thanks.

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton) 350.

Title: Re: Backfiring!
Post by: roundedline on July 05, 2006, 04:30:00 pm

What does the temperature guage say when it is hot?

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Title: Re: Backfiring!
Post by: DnStClr on July 06, 2006, 12:34:00 am

Instead of setting your timing ahead, wouldn't it be better to take the timing back down to where it belongs and just increase the engine idle speed to help your pump run better?
By adjusting the timing, you can easily create backfire by  the piston getting rammed down at the wrong time. The engine will be too lean and the unburned fuel goes into the exhaust, and bang- there's the backfire. Every time it backfires, there's a backpressure too, and  the valves don't really like that. All this stuff going on can cause heat. Another thing that causes backfire is additional air getting into the exhaust pipes because of bad gaskets or holes in  the pipes.Or blown out donuts..  

Don St.Clair
Culleoka Tn