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What causes it? My 712 has decided it wants to start backfiring now if I'm going down hill and using compression as a break. It does it when I'm in 5th at highway speeds and the limit changes and I take my foot off the gas. Some of the backfires like going down a hill in a low gear are fairly muted, but others like the ones a highway speed sound like a gunshot.

The only thing that has changed is I put in the Champion sparkplugs Jim warned about on the yahoo site. That's all NAPA had.

The weird thing is that the engine still has "normal" power. Loss of power is what caused me to change the plugs. And strange as it seems, the gas mileage has gone up from 11 mpg (old normal) to about 14 to 15 mpg.

Something isn't right here, but I don't know enough to begin to have a clue.

What could it be and what can be done to eliminate the back firing.

Thanks,

Andy

First check for air leaks in the exhaust system and i have used champion spark plugs for years in my 712.

Thanks Tony, I'll get under it this weekend. I have a brake light to replace too. Hopefully it won't be 108 degrees like it was today.

Andy

Mine was doing exactly what you describe. I replaced the muffler and added a longer tail-pipe and it went away.

It was pretty exciting coming back from Yellowstone at night with that bright flash and "boom". I thought for sure the Rangers would be all over me. "That old army truck is shooting at the buffalo!"

It’s most likely an exhaust leak. It’s very common. Mine has the same problem. I have just been too lazy to fix it.

My gunshot-sounding-engine-breaking-backfiring-problem was an exhaust leak. After fixing the leak (with a flexpipe upgrade) it has never backfired again.

Thanks guys. Man, I don't wanna lay on the ground when it is 108 outside, but I guess I will have to Sunday. I hope that's all it is.

Yeah, yeah, do it early before it gets that hot. Problem is I need all the light I can get. Burned my knee, through the jeans, today kneeling while I was putting some pipe in around a pump on a ranch. At least there was a breeze.

Thanks again.

Andy

think how "not 40 below zero" it is.

Good day Andy

Might be a good thing to check those studs at the cylinder head and the exhaust manifold. Those become loose quite often and I had mine doing just like yours and it was the place the leak was from...


Have a good one while doing it and think of us here where the weather hasn't been over 70 for the past mounth.

Denis

I'll be sure to look from the engine back. If the muffler isn't messed up already I'm sure the backfires aren't doing it any good.

I'm not really complaining about the heat, because I know in December there will be days when I would give just about anything for 30 minutes of it. Just like I do now about the cold.

Thank you

Andy

Andy wrote: Man, I don't wanna lay on the ground when it is 108 outside

Andy

Easy - wait until it is 120 F!!!

-Evan

Evan, I've experienced that only once or twice, back in the day, when I worked in Presidio, Texas. That's a young people temp. If it hits 120 here I will be very slow moving if I go outside at all these days. We've hit 116 here a few years back and I would imagine the way I felt was sorta the way a potato feels in the oven as it bakes. But, that iced down beer sure goes down easy when a day like that is done.

Andy