Assuming the fuel pressure is normal...
Sounds like the carb has some trash stuck in the needle & seats. If they're externally adjustable needle & seats (big screw & a 5/8" nut on the top of each float bowl), the fix is pretty easy. If they're internal, the carb will have to come apart.
With the engine off (obviously)---
External:
Put a shop rag around the needle & seat adjustment screw & nut on the top of the float bowl. Use a large screwdriver to break loose the lockscrew just slightly, then turn the screw & nut counter-clockwise to remove the assembly. You may have to use a 5/8" wrench, but it should thread out by hand.
Take a can of carb cleaner and give the needle & seat a good blast, paying attention to the little tip on the needle and its seat. Give it a good blast of compressed air afterwards to make sure the debris is cleared. Make sure the needle travels freely up & down. Look for any cuts or other damage on the tip of the needle. If you see any damage, it's time for a new needle & seat. Also look to see if the rubber "O"-ring is torn or damaged. If not, you can re-install it.
Place a light smear of grease on the rubber "0"-ring and reinstall it in the carb. Using just the adjuster nut, thread it down until there's maybe 2-3 threads on the needle & seat showing above the float bowl. If your original gaskets (1 under the nut and 1 under the screw) survived, you can re-use them.
Thread the lock screw back in place and hold the nut with a 5/8" wrench and tighten the screw securely. Don't get carried away, just snug it securely.
Repeat for the other float bowl.
(Before you do anything else, find out where the trash came from. Do you have an inline fuel filter?)
Start the engine, and if you still see gas spraying from the vent tubes, it's time for new needles & seats. If not, then you can re-set the float levels after the engine has finished break-in. Just make sure the engine does NOT go lean or overheat during break-in. (breaking in new engines is hard enough w/o having to deal with a finicky carb in the process
)
Once you can let the engine idle, remove the sight plug on the side of the float bowl. Again, wrap a shop rag around the needle & seat and with the engine idling, BARELY crack the lock screw loose. Use a 5/8" wrench to raise or lower the float level (clockwise lowers the float level, counter-clockwise raises it) until you just see fuel start to dribble from the bottom of the sight plug hole. (If the fuel level is high to begin with, you'll need to let the engine run for a few moments to run off some of the fuel in the bowl.) Once you see it dribble fuel, hold the ajduster nut securely and tighten the lock screw back down. Repeat for the other float bowl.
If the carb has internal needles & seats, the float bowls will have to come off to fix it. Let me know if this is the case and I'll try to walk you through it.
Eric
