Engine stall coming off idle speed

Good Grief

Good Grief

New Member
Mar 26, 2008
314
Lusby, MD
Boat Info
290 Sundancer 1998
Engines
4.3L V-6's w/ Alpha 1 Gen 2 drives
My port motor is a little hard to keep running when started from cold. It will fire right up but then taper off and stall. If i attempt to give it gas during this time, it stalls instantly unless I pump the throttle a few times. When the engine is warm, it will idle fine but when I attempt to give it gas, I get the same results as above. Once I get past that point, everything is fine again. It appears to be happening whenever leaving idle speed. Plugs/wires/cap inspected, everything appears OK. Any suggestions?
 
Ignition parts are 18 months old. How do I check the choke/accelerator pump operation?
 
The choke is the flapper/butterfly that closes on the top of the carburetor when the engine is cold. It should start to open after the engine starts and as the engine warms it should fully open. The accelerator pump is inside the carburetor but you can check it's operation by pumping the throttle while looking down the throat of the carburetor. You should see fuel squirting down into the throat. If you don't have a helper to pump the throttle for you while you look, you can disconnect the cable on the side of the carb, and pump the throttle right there at the carb.
 
Do you have fuel injection? If so, sounds like a classic case of a bad IAC.

Carbs? Then I would go with the accelerator pump....
 
Thanks. No EFI, 2bbl carbs...

Can you recommend a good resource for replacing the pump?
 
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duplicate, couldn't figure out how to delete...
 
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Does your configuration have electric fuel pumps? On mine, they are located between the fuel filter and the carb. They run for a short time (5 secs or so) when the key is first turn on and then unless they see oil pressure they turn off. I had a similar problem and it was the oil pressure switch not showing pressure and shutting the pump down. It didn't happen every time and the problem seemed to go away when the engine was at operating temperature.
 
I'm embarrassed to admit that I do not know that much about it. There is a device, which I thought was a solenoid, immediately after the filter that could be a fuel pump, I never gave it that much thought until now. Which motor/configuration do you have?
 
tdappleman said:
Does your configuration have electric fuel pumps? On mine, they are located between the fuel filter and the carb. They run for a short time (5 secs or so) when the key is first turn on and then unless they see oil pressure they turn off. I had a similar problem and it was the oil pressure switch not showing pressure and shutting the pump down. It didn't happen every time and the problem seemed to go away when the engine was at operating temperature.
Click to expand...

Where is this switch? My boat is a 1998 310DA w/ the 260HP 5.7s and V-drives. I have the electric inline fuel pump, rochester-style 2 barrel carbs.

I've had nothing but troubles with my carbs and idle for 3 seasons now. I'm literally on my 8th carb between the two engines. I've had the originals rebuilt, tried exchange carbs, rebuilt the exchanges, tried several different rebuilders, etc. Some of the rebuilds were clearly wrong - done by an idiot even though the places were highly recommended. The boat will run fine for a few months - then the problem repeats. Fuel is good, water separator looks good, filters are clean, plugs, wires, caps, ignition, all look good. I keep telling these guys that it can't still be the carbs and they need to look into some other problem.

I want to check this switch!

Next proect - I'm ditching these carbs and putting on Edelbrock 4-Barrels.

Thanks!
 
After all the money you've spent maybe a fuel injector conversion is in order.
 
I'm going to stroke the engines to 383 eventually. My compression is still OK - but I have 450 hrs on the engines. The boat is under-powered w/ the 260hp and V-Drives. With the torque of a stroker motor I can spin larger props at lower RPM. Should make the boat much nicer. The incremental cost to stroke the engines is minimal. Fuel injection conversion has been considered but it is a big project and I don't want a custom system that requires an expert to fix. I can't even get simple stuff fixed around here and I'm sick of spending my free time in the bilge.

Just trying to decide if I should do the carbs now - depending what happens w/ the current idle problem. Hoping it is the oil pressure switch - just need to know where it is.
 
Still looking for help on the location of the switch/sensor that shuts off the fuel pump if the oil pressure drops.

I thought it might be one of the sensors on the top of the manifold screwed into the thermostat housing - but neither will cutoff the fuel pump. One is for the oil pressure gauge. The other I think might be for the o'sh*t warning. I've disconnected, bridged, grounded, etc on both engines - no change on either engine (port won't idle, starboard is fine).

This sensor must be elsewhere. Any ideas?

Thanks
 
The sensor is located roughly were the fuel filter would be on a SBC installed in a car. Cost was about $25 each. BUT - I have an issue. The thread is different on the new part vs. the old. Mercruiser pulled up my serial #s and swear the part is correct. I bought the boat from the original owner where it was dealer maintained. I have all the paperwork. Pretty darn sure the old sensors are original. Waiting to hear back if this is a known issue w/ a resolution. A buddy is checking to see if he has the right die to re-thread the sensors by comparing old vs. new. What a PITA.....

I'll try to post pictures of the sensors and location when I have a resolution.
 
Scott,

Check your choke! Already mentioned but you seemed to be leaning towards the accelerator pump. Which is fine, but the choke can be checked by visual inspection without costing a thing. I assume to start your engine, you move the throttle to full, then back to idle. This should set the choke. If you go back and look at the carb, you should see that the choke is now closing off the inlet to the carb, more or less completely. As soon as you start your engine, the choke should slowly open until it's straight up and down, parallel to the flow of air.

Electric chokes go bad frequently. My guess is it's not being set to begin with, which makes for hard cold starting.

Tom
 
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