Hot start issue

S

Sean195

Member
Jun 29, 2019
59
Boat Info
1995 Sea Ray 195 Sport
Engines
4.3L
Mercruiser 4.3l 2 barrel carb. Starts fine and runs effortlessly. After short stops (30 minutes or so), the boat will either start and stall shortly after,
or not start at all. Taking the flame arrestor off shows the carb is almost dry. Fuel pump is running and confirmed it is pumping fuel to the carb. The carb is a fully refurbished carb purchased last year. Thoughts ?
 
Heat soak may be boiling the fuel out of the carb when you shut it off.

If this is the case, the fuel flows into the intake manifold and causes a rich condition, preventing the motor from starting.

look down the carb right after shutting off a hot Engine. Within a few minutes you may see the fuel pushing out of the bowl.

A phenolic spacer under the carb will help prevent this if it is indeed your problem.
 
Based on what I see, it does look like there is fuel dripping in the carb after it shuts off when it is hot. Is the spacer the only solution ? Also, where could I find one
 
eBay, Amazon, carb rebuild kit, google, something should pop up.

Look for something at least 1/2” thick.

Thicker the better.
 
It’s crazy to me to think that this is a needed modification... why would my carb be dry after cranking during hot start though ?
 
A mechanical fuel pump only supplies fuel when the engine is spinning. I would think that if you cranked long enough, there would eventually be enough fuel in the carb.
 
The fuel pump is electric. But even with the fuel pump running manually, the carb is still dry. My plan is to disassemble and clean the carb but not sure that will fix it for certain
 
Do you leave the bilge blower running while not on plane to keep the engine compartment cooler?

If you don’t, see if that makes a difference.
 
Normally don’t. Still doesn’t explain to me why the carb is bone dry
 
Doesn’t hurt. Might even be something in the owners manual about The blower cooling the bilge as well as prevent build up of vapor.
 
Yeah I follow the bilge instructions as far as letting the fan run before starting, etc, but I suppose the extra ventilation can’t hurt
 
Make sure the throttle plate is closing completely when you pull it back to neutral. This can cause leak down and run on at shutdown. It’s a throttle cable adjustment. Stock mercarb should already have the spacer.
 
Last edited:
BillK2632 said:
Make sure the throttle is closing completely when you pull it back to neutral. This can cause leak down and run on at shutdown. It’s a throttle cable adjustment. Stock mercarb should already have the spacer.
Click to expand...
All is good on this end
 
Carb shouldn't leak at all after shutdown. Pull a couple of plugs when your in the "no start" see if they're wet or dry.
 
What do you mean the carb is "bone dry"? Just looking into the throttle body, your not going to see any fuel - what happens when you pump the throttle, does fuel squirt out of the two venturi jets? Running the fuel pump manually should fill carburetor bowl and eventually shutoff, you should not see any fuel pouring into the throttle body.

I am starting to think two things since this is a newly rebuilt carburetor:

1. Assuming the initial adjustments were done (set the float, choke and initial idle adjustment)? Then the final adjustments after you got it running with the rebuilt carb?
2. Are the fuel lines all the way to the fuel tank pickup in good shape and double clamped and tight? It doesn't take much for the fuel pump to suck air and things just don't work right at all. If your fuel lines are original, it's time to replace them - they literally will deteriorate from the inside especially with ethanol fuel.
3. Vapor lock? That's what this sounds like, if the pump is running and not pumping fuel it's either sucking air from a loose fuel line fitting or it is vapor locked.
 
Vapor lock is why I alluded to engine compartment temperature and blower operation. Low speed plowing or extended idling can really heat things up.
 
Fuel lines seem fine. The carb was dry and even pumping the throttle was not putting any fuel into the carb. Maybe vapor lock is my issue then ...just hard to imagine a vapor lock issue when there is an electric fuel pump
 
Last edited:
Type of fuel pump doesn’t matter - fuel in the line heats up and vaporizes and the pump can’t punp the vapor. Next time it happens pour cold water on the fuel lines to cool them down and see if it starts. I’ve had my engine vapor lock a few times.
 
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