Old boat motor only runs if I spray starting fluid in it. Cleaned carb and new gas and plugs. Any ideas?

Do a compression test. A two stroke motor has two different compressions. One you take at the spark plug and the other is a crank case pressure test which will take special tools. On a two stroke fuel/oil is pulled into the crank case first then to a port in the piston cylinder then into the combustion chamber. If the standard spark plug test is low for the model of motor OR if the compression is a lot different from cylinder to cylinder you have found the problem and will need a rebuild.

There can be a few other causes but usually on old motors the compression factor is the main problem.

old boat motor only runs if i spray starting fluid in it. cleaned carb and new gas and plugs. any ideas?
Can you give us some info about the motor?

old boat motor only runs if i spray starting fluid in it. cleaned carb and new gas and plugs. any ideas?
My dads old 3hp johnson, I'm trying to fix for him. Don't know how old it is, but he said probably made in 50's? All I know is there is no trans/ neutral. Pull and go! Info is as follows: Johnson 3hp, model# JW22C, Serial# E2751108

. Test for a good, solid spark. Go over the entire electrical system, checking points, point gap, magneto, rust on flywheel affecting magneto, rust on magneto pickup, spark plug, and spark plug wire. Access to points will require flywheel removal. Learn how to properly "pop" the flywheel, without using a puller. Check condition of the key. Wobble in the flywheel and key affects proper timing.

. Test compression. Check for carbon buildup in the exhaust port, which can greatly affect carburetion and performance. If necessary, carefully dig carbon out. Remove any carbon from cylinder head and top of piston (replace gasket).

. Check fuel. Ensure the oil-to-fuel ratio is correct. People often mix too much oil with the fuel on two-cycle engines. I use synthetic two-cycle oil and run 100:1 in my equipment--they smoke less, don't carbon up, perform better, easier on the environment, plugs last for years, and engine life is greatly extended. Ensure there's no rust in the tank and the screen is clear. Check the condition of any fuel hoses, replacing with Tygon F-4040A Fuel & Oil tubing, if necessary. For outboards, use a BIA Certified oil, such as TC-W3, not just an API TC (air cooled) rated oil. If it's dually rated, that's fine.

If it is from the 50's it probably uses a 25 to 1 ration of oil to gas. The older motors needed a lot of oil mixed with the gas. Since it is old and all crapped up with dyno oil inside I do not recommend using synthetic oil since it will start cleaning and knocking all the old carbon loose. This will eventually get under the piston rings and not allow them to collapse in the cylinder bore and get into the needle bearings on the connecting rods. Ifthis happens you can use the motor for a boat anchor because it will be toast.

old boat motor only runs if i spray starting fluid in it. cleaned carb and new gas and plugs. any ideas?
I'm not a OB motor person but don't all engines have a fuel pump of some type? My lawn mower did this and so did my chain saw and both times it was the fuel pump.

It is a vacuum fuel pump off the crankcase