Engine dies when the choke is open.
This could be 1 of 2 problems
1. There is a vacuum leak somewhere. Are there any loud sharp noises coming from the carburetor? A vacuum leaks will sometimes cause a loud noise. Spray carb cleaner around the base of the carburetor & intake manifold. Check all vacuum hoses for cracks.
2. Not enough fuel. Here are some possibilities not in any order.
- Test your fuel pump. 4.5 - 5 lbs would be about right.
- Sticking fuel valve, or needle. Clean the viton tip with mineral spirits. Is there a clip from the needle to the float. The clip helps pull the needle out.
- Check the float level. Also check the float drop. If the float isn't dropping then fuel entering will be restricted.
- If the engine sits a lot, or has been sitting then it is very likely the carburetor is coated with turned gas, or ethanol residue restricting small passages. Clean the carburetor using carburetor dip, rinse with hot water, blow out all passages. Running thin wire down passages is sometimes necessary.
- Make sure there are not kinks or restrictions in the fuel line.
Doesn't die, but runs bad on cruise, or power
White plugs is a sign of too lean for sure. Now whether it's caused by lack of fuel, or too much air (vacuum leak) is hard to say. You just have to start checking.I'm thinking that the 2150 should be plenty for your engine and the jet size is about correct.I think I would look at other things before increasing the jet size again. Just doesn't seem like the engine would require that much more fuel.
Make sure the fuel pump is putting out 4.5 - 5 lbs. It may be weak, which would show up off-idle.Check the float level. It may be off and not filling up the bowl enough.Look at the power valve - There should be numbers stamped on the face. Look for a 7 5, or 8 5. Anything else might be a problem unless you are pulling low vacuum because of a cam, or something. Here is some information about the power valve. https://www.carburetor-parts.com/2150-Power-Valve_ep_1974.html
Look down the carburetor (engine off), pump the throttle. There should be 2 strong squirts coming out of the main discharge.
If the bucking is when accelerating then look at the accelerator pump circuit. If it does it when cruising, then it's in the power circuit, or main circuit.The idle circuit uses a different path for air/fuel than the cruise and power. If there was a vacuum leak, then most likely the engine wouldn't idle very well. So in your case it's most likely nott the idle circuit.