Hi fivepassgeorge! Welcome aboard the forum. What boat do you have? I'm a sailor myownself.
Probably doesn't matter but is it a manual choke or auto? If it's an electric start it's auto. Anyway, there is no air filter to change and I doubt that it is a fuel filter issue.
You may have a point though about the motor being from Denver as there are three different main jets for this carburetor. The link below is the carb parts blow up. If you scroll to the bottom of the page, item 22 (main jet) has three choices. The only way to know which one you have would be to disassemble the carburetor and have a look. I think you are probably headed that way in any case.
http://www.boats.net/parts/search/H...# BABJ-1600001/CARBURETOR (MANUAL)/parts.html
My guess is that you have a stuck accelerator pump piston. Item 14 is the pump assembly with push rod, piston, spring and hold down screw. These carburetors don't like it when there is a problem with the accelerator pump circuit.
Note item 11 in the blow up. If you take off the engine cover and look on the side of the carb, you will see item 11, a rubber bellows type boot seal that is meant to keep dirt out of the carb. The boot is mounted on the accelerator push rod. Locate those parts and see if you can move the push rod down with your finger. Or, operate the throttle while observing the push rod and see if it goes down and then comes back up. If not, that's most likely your problem.
These carbs are VERY sensitive to being put away with fuel still in the fuel bowl and if you don't drain them frequently and try to use fresh, water free gasoline, you will have problems. We always advise to manually drain the bowl with the drain screw as opposed to just running the engine with the fuel line disconnected until it dies. We also recommend that you use a fuel additive such as Sea-Foam to keep the fuel system clean.
It would be good to know what main jet you are running as well because, if one of the leaner jets was installed for high altitude operation, you will want to go back to the larger jet for operating on the Delta.
Sorry to be the bearer of bad news but it isn't too bad as these are GREAT engines with that carburetor being pretty much the only "finicky" thing about them. Many guys repair their own with help here on the forum so, if you go that way, don't be bashful about asking for help.