Hard Starting....Possibly getting to much back preasure?

[rollenrock33]

Ok,

This just blows my mind. The boat is an 87 Sunsport with supertraps. The boat starts fine when out of the water with a hose hooked to it. Does not matter if the motor is hot or cold. Starts very easy. I get the boat in the lake, and I have to crank the heck out of it and have to leave the throttle at 3/4 open.

Can the water preasure in the exhaust tubes from the boat being in the water cause the motor to start hard??? I can not think of anything else that would change from the boat being in the gerage with the water hose hooked to it compared to the boat being in the lake. One other thing that makes me come to this conclusion is if the boat is running in the lake, I shut off the motor, and start the motor right back up, before the tubes fill up with water?, it fires right up. ???????

I was also thinking that maybe the boat sits at a different angle in the water than on the trailer. Could this cause the carb to flood the motor after a while sitting in the water? The motor does have a crane cam and a edelbrock carb and intake. Motor runs great once it is running, no issues at idle, mid range, or wide open. Could this be why I have to open it up to 3/4 throttle before the boat starts in the water?

Any ideas???? Are the supertraps supposed to have an internal flapper of one way valve set up so the water does not go back up the tubes??? Any suggestions would be great. Thanks for your help.

[wotan2525]

I'm positively stumped... when you're running on the hose are you also plugged into some kind of battery maintainer/charger? Do you have the engine cover off in both scenarios?

[Salty87]

sounds like bad battery cable connections. check and clean all of the terminals and cables, especially the ground on the engine block. you might inspect your cables too. if they're old and brittle, it's time for new ones.

[rollenrock33]

No, not using a charger or anything when the boat is on the trailer so I don't see how it could be the cables or the battery terminals? The cover does not seem to have any bearing on it either. Do the exhaust tubes fill up on all these old supra's??? Thanks for the help guys.

[Supra-in-steamboat]

My 87 SunSport is kind of the same. It does start differently out of the lake. A normal lake start consists of a few throttle pumps- then wide open while cranking. Fires immediately and of course I back the throttle off and let the warm up happen.
I have noticed that it warms and settles to idle @75% faster on the trailer- I have taken into account water temp but they are about the same @55degrees. Just out of curiousity I have cranked it with no throttle... On the trailer it fires immediately, in the lake not so much. Can't tell you why, I have just accepted it.

[beast 496]

You mentioned you are running an Edlebrock carb, These carbs need to set level on the engine. The floats run from front to back. The Holly floats run side to side. You could definetly be flooding while in the water. If so you can buy a carb wedge for your carb mount. Al

[ngavchris]

The supertrapps do not stop water from going into the exhaust tubes. They do stop rapid movement of water when in reverse.

[rollenrock33]

thanks everybody.

beast 496, any idea where I can get one of these carb wedges? Summit maybe? Would be worth a try.

[87SunSportMikeyD]

Chris just had his motor redone including brand new carb and this problem went away for him. The carb is a likely culprit.

[rludtke]

thanks everybody.

beast 496, any idea where I can get one of these carb wedges? Summit maybe? Would be worth a try.

Her is a link to the source where I purchased my carburator shim...
https://www.boatdesigns.com/Tilt-Shims/products/106/

[saltare inverts]

I had same problem on a boat with a PCM 351.. The carb shim fixed it for me.