Machine Gun Full Throttle?

[ol'George]

Fire out the exhaust can be caused by a number of things.
Exhaust valve not seating, thus allowing leakage of the power stroke.
A sticking EX valve is not uncommon and will show up after some running/heating/usage
Especially an old worn engine or one that has sat, not being used.
carbon builds up around/in the guide.

A Lean mixture, I understand you have tried 2 carbs and you say you have good flow from the fuel line at the carb fitting, yes????
Also check that you don't have an obstruction at the fitting into the carb as well as under the needle valve seat,especially from new or old fuel lines allowing particles to obstruct the flow, seen it many times.
Also foreign objects ( shit) likes to float in the tank plugging flow at random times.

The proper coil, along with the proper MFD capacity condenser will insure a good combo also.
a bad condenser will allow an engine to idle all day long but will pop, fart, machine gun, etc when opening the throttle.
Do check the condenser wire's integrity where it enters the body of it, and that it has a good ground on the mounting surface it is attached to.
also check that the point wire is not rubbing the point cover where it enters it
The condenser lead attaches to the negative side of the coil with the wire to the points, if you are aware of all these mentioned things,
I, and others mean no disrespect as we know nothing of your abilities
Do make sure when you set the valves it was on TDC on the compression stroke.not on the exhaust stroke.
Procedures are described in the service manual, avail free on here on OCC.

[finsruskw]

I say again,
More to it than setting the points by eye.
Static time the engine w/a VOM or test light.
If you don't know how, search this site for the info.
Works every time assuming all other items are correct.
What's all this valve adjusting business?
Do it once, do it correctly.
Good luck

[crash-harris]

I could try the old condenser instead of the new "heavy duty" automotive one. It's just large enough that I couldn't mount it on the coil bracket, so I moved it to the next machine screw forward on the engine shroud and added another ground wire to the frame. The wire isolating grommet is intact and in place on the points cover. I've even gone as far as rerouting the points wire around the front of the engine with large stand-offs so there's no chance of it rubbing through on the edge of a shroud.

How are you guys seeing and marking/highlighting the timing marks on the flywheel without removing the rear shroud?
I have paint pens, but I've never been able to see in there very well.

All the valve adjusting was done because I didn't know about the ACR the first time and the specs I found were incorrect. First time I set them, I set them at about .018"/.024"~ for intake/exhaust (ran well, by the way). When I learned about the correct specs and ACR, I adjusted them again to .008"/.017" and watched for the ACR action. The last time was a check when I replaced the broken cover gasket and had to loosen them to get back to that .008"/.017" intake/exhaust spec.

Both carbs have free moving floats, clean seats and flow normally.

[crash-harris]

Missed one,

Yes, 12V positive is connected to the positive side of the coil and condenser and points are connected to the negative side.

When I was using the last standard automotive oil filled coil, the resister was on the positive side of the coil.