backfire

indybob · Mar 15, 2013

Iam restoring a JD 720 gas. The tractor has an intermittent backfire through the intake.
New rings,valve job, new points,coil dist cap,carb rebuilt,new wiring harness.
Compression 100lbs on both cyls.Any suggestion is apperciated.

Janicholson · Mar 15, 2013

Two Most likely opinion a crossfire in the distributor cap. or a sticking intake. If the cap and rotor look good, the intake valve hanging up on occasion seems reasonable to me. Jim

Texasmark1 · Mar 15, 2013

I've seen them but never had one. With the popper electrically staged as it is, isn't it pretty hard for one plug to talk to another via the cap or the wiring, unlike a V8 distributor? Light it off at night and look for an arc.

+1 on the valve. So if you had the valves done, why would one be sticking? Who did the work and what all did he do?

My 2c,
Mark

Switchflicker · Mar 15, 2013

My 2c,
Mark[/quote]

Hey Mark

Do you still have pennies in the USA? In Canada they stopped making them and although you can spend them if you have, the merchants will not give pennies as change anymore. The round up or down to the nickel.

Yea I know this is off topic, but your 2c note caught my eye. I would say two fifths of a nickel!!

Sw

John B. · Mar 15, 2013

I agree with Janicholson.

One other thing I can add from experience is the gas. It can put a film on the sparkplugs and make the back fire. Even if the plugs are new and run a short time. I have sand blasted sparkplugs before then blew them out real good with air then reused them and it takes care of the backfire for a short time. But the best cure in this case is 104+ Octane boost used as directed cures the backfire that I'm speaking of. I pick the octane boost up at Walmart.

MrJDMan80 · Mar 15, 2013

The simplest explanation for an intake "pop" is a lean situation. What is your carb set at? Does your tractor have alluminum piston? That can also make a difference.

Traditional Farmer · Mar 16, 2013

Loosen the intake valves up a couple thousands

Texasmark1 · Mar 16, 2013

I am wondering what lobby is pushing for their continuance. I read
the other day that they are zinc filled and just copper plated like
other coins (plated) to save the cost of copper, but why fool with
them anyway. They're not worth 2c. Grin.

Mark

backfire

indybob

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Janicholson

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Texasmark1

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Switchflicker

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John B.

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MrJDMan80

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Traditional Farmer

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Texasmark1

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