I have a mildly built 355 with a Holley 750 double pumper. Starts perfectly in the driveway. Hot or cold. Engages perfectly as well and doesn’t stall shifting into or out of gear.

Normally, on the water she starts perfectly when cold but is hard to start when warm. I could still start it every time when warm but there was only one way that worked… give it a little throttle, start the engine, gradually give it more throttle until it’s about 2/3 open (she fires then), then quickly shift back into neutral because it’s revving too high.I figured it was heat soak/flooding.

I started keeping the throttle wide open anytime I shut off the engine and also installed a spacer between the carb and intake. It didn’t cure the hard start when hot completely but it seemed to help a little.

It’s a trailered boat and toward the end of last season I slipped it in the water and started it at the dock like normal (just turn the ignition, don’t even need to give it gas in or out of the water when it’s cold). I shifted into reverse to back out which went fine but when I shifted into forward it stalled. I couldn’t get it started any way I tried. The gas gauge is a little erratic. I thought I had enough (still do) but at the time I figured it was out of gas because I’ve never, ever had a cold start problem. I fueled up and finally got it to start but it took a while. The rest of the day it was fine. Hard to start when warm still but that’s been the norm.

At the end of last season I was approaching a landing after being on the water most of the day, shifted into neutral, and she stalled. She would not start no matter what I did. Figured it was flooded. Long story (yeah, even longer than this one), but we went back the next day and she fired right up. I purposely putted back to the dock to keep from bouncing around too much. When I got back to the dock the engine was hot. She shifted into and out of gear without stalling. Started and stopped multiple times perfectly.

I’m probably way off on this but is it possible that the sloshing around from trailering and/or riding around at cruising speed is somehow causing this? Maybe the floats are set too high? Or, is it something else?

I know the shift cable is usually the cause of stalling when shifting into and out of gear but I don’t think that it. It’s not consistent and I replaced it about three seasons ago.

Sorry for the long post. Just trying to give all the info I have to help diagnose this.

Ayuh,..... Sounds like a carb problem,......

A 750 cfm is Huge for a SBC,.....

check your float levels in the water. Sounds to me like your boat sits at a different angle in the water vs on the trailer

Not saying it is your issue,but could be a good place to start.

Choke working correctly ?

OP, do you know how to clean out/service a Holley carb ? do you know how to tune them ? Especially, at this time, idle with the idle mixture screws?
Was this carb new or used ?

Not really, lots of 350's with 750's. I'm not sure how mild his engine is. 375hp and up a 750 would be a good choice. Also, remember, with a dual plane intake, each cylinder see's only 1/2 the carburetor.

With a strong light, take a look down the throat of the carb immediately after shutdown on the water. Chances are you going to see fuel dripping into the intake (flooding). Like mentioned prev, check float levels on the water.

Installing a fuel press gauge can help to troubleshoot this. If you see the fuel press drop down quickly after shutdown, something is wrong with the needle/seat assy or float level. Mine will hold press for hours.

Unless its turning 6000 rpms, its not getting close to use 750 cfm with 355 cubes, but no expert with volume, just using the auto calculator

Do agree, float level could be the issue, its flooding

No doubt, all true, But,.....
The vacuum signal, 'n general response is better from a 600/ 650 cfm carb on a 350 SBC,.....