Problem Restarting, Idling and Acceleration when the engine is warm. Merc 140hp 3.0 Alpha 1 Gen 1.

[1985 Century Mustang]

Having an issue with my boat. I could run her for 3 hrs straight literally, and with no issues at all. The problem is, when I shut down for say 10-20 minutes and restart, the engine has major issues starting/idling and accelerating. After attempting it a few times, eventually it gets going fine, but after baby feeding the throttle.

Engine- 1985 Mercruiser 140 HP A1-G1

I suppose it could be the choke which I will inspect today.

I rebuilt the carb about 3 months ago, all fuel filters were changed, it was recently tuned up, the plugs are good, it has a new electric fuel pump which runs at 5-11 psi. The compression is 150-155-158-148. The engine runs really amazing, it's just when I turn it off thats when the shyte hits the fan.

Any Ideas or what to check,,, please elaborate. Thanks.

 

[Bondo]

Ayuh,.... Carb fuel pumps should run 4 to 6 psi,....

 

[1985 Century Mustang]

Ayuh,.... Carb fuel pumps should run 4 to 6 psi,....

I just checked the specs on my fuel pump, its 4-7 psi. Photo Enclosed below.

 

[dubs283]

Performance "automotive", nice

Is the electric fuel pump installed/wired properly?

 

[1960 Starflite]

Sounds like a flooding issue after shutdown. Could the vent to float bowl be partial blocked? Needle n seat leaking?

 

[Scott06]

Yeah most likely the fuel in bowl is dribbling into manifold after shutdown and flooding it. If the choke closes and gets set this only makes it worse. You need to open the throttle wide to clear the overly rich condition.

two safety related comments-
is the fuel pump marine rated? Marine applications need more rigorous spark and fire protection

Did you run the pump through an oil pressure switch as is required by coast guard regs? This is done to prevent the pump from running while ignition is on but engine is not running. Again for fire and explosion safety.

I'm not a big safety wennie but there are legit reasons these requirements have been arrived at over the years...

 

[1985 Century Mustang]

Sounds like a flooding issue after shutdown. Could the vent to float bowl be partial blocked? Needle n seat leaking?

No gas leak at all from carb..The carb was rebuilt, 2 months ago. All the internals, jets, gaskets and seals were changed. I'm going to try running it with blower on and engine cover off. See if it could be vapor lock.

 

[1985 Century Mustang]

Yeah most likely the fuel in bowl is dribbling into manifold after shutdown and flooding it. If the choke closes and gets set this only makes it worse. You need to open the throttle wide to clear the overly rich condition.

two safety related comments-
is the fuel pump marine rated? Marine applications need more rigorous spark and fire protection

Did you run the pump through an oil pressure switch as is required by coast guard regs? This is done to prevent the pump from running while ignition is on but engine is not running. Again for fire and explosion safety.

I'm not a big safety wennie but there are legit reasons these requirements have been arrived at over the years...

Thanks for the info, Yes the pump is wired to the oil switch.

 

[1985 Century Mustang]

Performance "automotive", nice

Is the electric fuel pump installed/wired properly?

Yes

 

[1985 Century Mustang]

I'm going to diagnose if its vapor lock or not. It sounds like a good possibility now. Everything is good with respect to fuel filters, plugs, gas, and carb, except for decent ventilation. I'm going to keep the blower on and the engine cover off when I run it for an hr or so to troubleshoot it. I'll then see if it starts and idles etc after shutdown and restart. The outside Temps were real hot here yesterday when I went out. So it's highly a possiblity. Thanks for all the responses.

 

[1985 Century Mustang]

I may consider hooking up another blower to bring fresh air into the engine. The current blower now removes air f om vacation engine area. I can also put some vents on the side of the engine cover I suppose, as I'm building a new engine cover/doghouse soon. Your thoughts?

 

[Scott06]

I may consider hooking up another blower to bring fresh air into the engine. The current blower now removes air f om vacation engine area. I can also put some vents on the side of the engine cover I suppose, as I'm building a new engine cover/doghouse soon. Your thoughts?

probably a rabbit hole.

Figure out why your hot restart issue is occurring - no spark, no fuel or too much fuel.

Do you get black exhaust momentarily when it does restart?

 

[Dubed]

I may consider hooking up another blower to bring fresh air into the engine. The current blower now removes air f om vacation engine area. I can also put some vents on the side of the engine cover I suppose, as I'm building a new engine cover/doghouse soon. Your thoughts?

No need to re-engineer the fresh air system. Fan blows engine compartment air out one side, draws fresh in from the other. When you get moving, the vents take over the same function. Works for every other boat on the water

 

[1985 Century Mustang]

probably a rabbit hole.

Figure out why your hot restart issue is occurring - no spark, no fuel or too much fuel.

Do you get black exhaust momentarily when it does restart?

It's a fuel issue, the see thru Fram inline fuel filter is low of fuel when this occurs, so I'm leaning towards vapor lock now. No black smoke. I'll know tomorrow. Thanks.

 

[boozer1966]

Make sure to check the small filter inside the fuel pick up tube inside the fuel tank. I had a similar situation on a ‘85 Merc 140 where it acted like valor lock but was actually debris from inside the fuel tank getting sucked into that small wire mesh filter. I’ll try find a picture. When the engine was running after first cold startup there was apparently enough pull from the pump to overcome the obstruction but after running for a while and turning off and sitting for a bit it would not restart. After a while I think some of the debris would fall back into the tank and it could pull enough to get pressure to start but did not really run right. I tried all sorts of venting and insulation in the doghouse to no avail. Also tried both mechanical and electric pumps. I was unable to properly diagnose it until I put a fuel pressure gauge on it. I just removed the pick up tube filter entirely and added an inline filter in the doghouse. Runs fine now. Do you have a pressure gauge attached to the fuel system or just guessing that’s what your pump is running at?

 

[boozer1966]

Here is what the filter looks like. It is inside the pickup tube. You have to unscrew the pickup tube from that junction block to find it. (Ignore the rubber hose and cap in this pic. It was from pressure testing the unit for a possible air leak.)

 

[Scott06]

It's a fuel issue, the see thru Fram inline fuel filter is low of fuel when this occurs, so I'm leaning towards vapor lock now. No black smoke. I'll know tomorrow. Thanks.

I had that on a clear filter on my 65 gto. been a few years but went away when i replaced the 30 year old mechanical fuel pump. Tank was rusty and seemed that when it would sit it took a while for fuel to get back up to the carb… replaced fuel pump and it almost immediately refills carb bowl after sitting