I set the valves....

Posted here a couple days ago about my grandpas B backfiring and not running, I've set the valves and still only pops over once in a while, but will not run on any combination of throttle/choke. Gas seems to be good. Tried messing with adjustments on carb, but not such luck. Where do I look next?? Spark plugs look fine. Could my carb need rebuilt? I'm totally lost on this one guys, any advice would be great. Thanks

Is this the one that backfires through the carb?

I worked on an old B many years ago that would backfire through the carb, removed the valve cover, adjusted valves, started and it ran well. Reassembled everything, then turned the flywheel and it sounded like a shotgun through the carb. Puzzled me for a while, then I found the valves had been lapped so many times, the rocker arm was interfering with the stamped steel valve cover. I used a ball peen hammer to put a small dent in the valve cover and solved the problem.

Backfiring is caused by the following:
Combustion fire leaking out of the cylinder into the intake manifold. Caused by intake valve/s not seating (leaking), or not being adjusted even close to correctly.
An exhaust valve not opening causing combustion issues including fire to sporadically be introduced into the intake because it was not expelled through the exhaust.
Spark incorrectly getting to a spark plug when that cylinder is on the intake stroke. This results in combustion of intake mixture in the manifold and carb. Common reasons are plug wires in incorrect distributor location/s (cross wired). Cracks and carbon tracks in the distributor cap, causing spark to go where it is not intended. Also can be from a bad wire that forces radical high voltage, which then forces voltage to jump where it degrades the material of the cap. Wires leading to plugs being too close together and of poor insulation value allowing cross sparking.
Excess fuel in the exhaust system (rich mixtures, failure to ignite a mixture in the cylinder then pushing it into the exhaust, and decelerating the engine allowing high vacuum to pull fuel into the cylinder too thin to burn, but still able to concentrate enough to explode in the exhaust as a spark from carbon or still burning fuel from a opening exhaust valve ignites it) The last one in parenthesis is pretty normal and common in vehicles with carburetors without electronic fuel shutoff on deceleration.
A blown head gasket between two adjacent cylinders can also present flame to a fuel filled cylinder with the intake valve open.
The above is the best thinking I have on this.
Jim

Timing 180 off ???

That too (kind of having the wires wrong) Jim

Have you checked the spark quality? Should be able to jump 1/4" at the plug end of the plug wire. Take a good look at the cap and rotor, set and clean the points, look the coil over for cracks.

Some simple tests. Take the hood and valve cover off. Crank the engine over and watch the valve train for proper mechanical operation. If that looks right hold your hand over the air intake while somebody else cranks the motor. You should feel healthy pulses of suck. If you don't then valves are not properly set and there is no vacuum to pull the fuel through the carburetor. If this checks confirm proper timing and spark on #1 cylinder. Hold the spark plug grounding the nut of it to the engine and watch for spark when timing mark comes around tdc. If all this checks out shoot some wd40 in each cylinder and see it it pops off momentarily. If that is successful shoot some wd40 into the air intake on the carburetor while somebody cranks the engine. If it tries to run you are not getting fuel through the carb.

Simple way to tell if it is the carb. Take it loose at air filter end and put some gas in squirt bottle and squirt some in while rolling it over. Lean mixture not only backfires but also is hard to start. If it starts up and runs until the fuel starves again then you have plugged carb somewhereor supply lines. You never did answer my question a while back as to just WHEN it backfires. Is it while trying to start it or when it tries to run or when, and in muffler or back through carb?? I assume this thing has a magneto correct? You know they fire on the exhaust stroke also, right? So any thing that lets raw fuel get into the exhaust may very well get lit and bang. I assume you put new plugs in it. Is it hand start or elect?

I do not think a 2 cylinder JD fires 180 out, so it would not run at all with mag in backwards. I will be corrected if wrong.

The two cylinders fire 90° from each other and then 540° before firing again equaling 720°. By the 180 out they mean the drive lugs on the back of the mag need turned 180 and re-installed or swap the two plug wires coming out of cap to serve same purpose.

I don't remember your original post, but did you drain the carb/ let fuel run out the drain plug for a bit to expel water (if any) that may have settled in the carb. Tried to get my grandpa's Oliver Super 77 out so my brother could take it to the Mackinac bridge crossing, about 3 years after my grandpa had passed, and the gas must have separated from the ethanol or something, but we drained probably 5 gallons of water out of the carb and gas tank before any gas came out. It was stored inside our old hip roof barn, and had been put away with a full tank of gas. Drained the whole tank before refilling it with fresh. Just a thought... Ross

Five GALLONS of water? More than condensation was going on there.

Sounds like it had ethanol in it that took on enough moisture to separate the alcohol from the gasoline.

Yup, that is what I am thinking, the mag could be in 180 out and still be showing TDC on the crank during exhaust stroke of #1. Reversing plug wires at that point would do nothing, like it would on a even fire.

? Dunno, it was water, My grandpa filled it with
gas when he was done brushogging then drove
it the 75' into the barn. Then he passed away
shortly after, and there it sat for the next 3+
years. Guess it could have came from his gas
barrel, as it had no filter/water trap on it. Ross

The first thing I would do is drain out the gasoline and try some fresh gas. Be sure to drain the carb too. I've had that problem with mine and that was the cause.