426 Backfiring

My freinds 426 started backfiring after he had a hard fall on it. The second he leaves off the throttle it does it and flames come out of the muffler. Does it in netral also. Anyone know what the problem could be?

Make sure he did knock the header loose. You may want to re-seat the header pipe.

I think Shawn makes a good point of where to start. Also, while you are at it, check to make the sure the air box wasn't pulled away from the carb and check that the entire intake tract didn't suffer a small separation. A good way to check this is to run down to Wal Mart and buy one of those little oxygen bottles(if you don't have an acetylene rig) with the little vavle assembly. Take this bottle and crack open the valve so that just a little oxygen escapes and wave the valve outlet around the intake tract with the engine set at a steady idle. If there is an intake leak, the oxygen will be sucked in and cause the engine to speed up. Be safe and do this in your driveway and have an extingisher handy.


I am sorry but No way SA

Never pump pure oxygen near a possible flame , if that thing back vented or back fire that oxygen would ignite a inferno.


Shawn is right and Boit had a good thing going until the oxugen bit. Do a Visual take things apart first. You can use a good carb spray instead to find air leaks and it is alot safe. I do not remember the name of the stuff, but If you go down to a local HotRod shop you should be able to get the stuff. iT is specificly designed to detect air leaks as Boit stated for the Oxygen

But never use Pur Oxygen near an open flame or potential flame.

He did get the fire ext right

Sorry Boit


I've seen butane and propane used but never O2. Sounds like it would work. O2 in a bottle doesn't burn until it comes out of the bottle. With a small setting, I can't imagine enough buildup to change the flamability of the boot or plastic parts. Other than gasoline, what else is to burn.


p.s., I know that in lots of O2, magnesium burns but you were just talking about a very low flow that would get sucked into the air stream if there was an intake leak, right?

Yep, it's pretty safe if you just have a tiny bit of oxygen escaping. Besides, if you do it in your driveway, the oxygen would not have a chance of concentrating. This whole procedure shouldn't take more than about 1 minute.

Ego. Just how is a backfire going to get to this oxygen? The bottle won't be near the air box opening. And it certainly won't be near the exhaust tip. It's safe if common sense is used.

I mention Back Vent, (My term for Carb Back Fart)

Hey with all the Flames that Rat racer Got regarding cutting out the steel mesh on the Airbox Gaurd.

(BTW Did anyone catch or happen to see the AirFilter Gaurds for the CR450f. Hummmm No Screens Makes ya think Rat Racer may have a point Ehhhhhhhhh)

Anyway it only takes a spark with Pur Ox, Look at apollo 1 (Bad Example)

Ok here is one

Rihrad Prior :)

Oh ya he was free basing Never Mind

[ April 14, 2002: Message edited by: EgoAhole ]

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