Hard Start All The Time

[JM3820]

I have a 4.3L Mercruiser with a 2bbl carb (807764A1). It has a hard start hot or cold. No matter what I do it takes a while of turning over to eventually fire up. Once warmed up it idles great at 650-700rpm. It has a mechanical fuel pump that is new. The electric choke is set and when cold, the choke plates are closed and when warms up is completely open. The air/fuel adjust screw is 3/4 backed out for the best hot idle. I just put new spark plugs in when I put in new exhaust flappers and hard the risers off.

I rebuilt the carb 2 seasons ago to spec and am going to do it again in the next week or so. Do you have recommendations of what to look for?

1. Do i need to replace the distrubutor or rotor?
2. Could it be a dirty carb?
3. Would a fuel logged float cause flooding and a hard start?

 

[kenny nunez]

You need to check if the by pass circuit is the problem. Get a volt meter and check that there is at least 12 volts going to the coil while the engine is in cranking mode.
On the starter solenoid there are 2 small terminals on either side of the battery cable. One side has a #10 ga. Yellow/red and the other should be purple/yellow. The purple/yellow should have full battery voltage in cranking mode. Quite often the contacts in the solenoid are corroded and there is no voltage. This makes the engine hard to start.
If your starter solenoid only has the yellow/red then the boost solenoid on top of the engine will have the purple/yellow wire. I might be wrong about color of the stripe on the purple wire.

 

[nola mike]

You need to check if the by pass circuit is the problem. Get a volt meter and check that there is at least 12 volts going to the coil while the engine is in cranking mode.
On the starter solenoid there are 2 small terminals on either side of the battery cable. One side has a #10 ga. Yellow/red and the other should be purple/yellow. The purple/yellow should have full battery voltage in cranking mode. Quite often the contacts in the solenoid are corroded and there is no voltage. This makes the engine hard to start.
If your starter solenoid only has the yellow/red then the boost solenoid on top of the engine will have the purple/yellow wire. I might be wrong about color of the stripe on the purple wire.

Which 4.3s have a bypass circuit?

 

[Scott Danforth]

yes it could be a dirty carb

what is your staring proceedure exactly? please specify in detail

did you just set the idle specs to 3/4 turns out and not verify that is where your motor wanted it? Never ever had a motor that ran best at a generic setting. every one required validating correct idle mix with an un-lit propane cylinder.
do you get a squirt of fuel every time you advance the throttle?

 

[tank1949]

I have a 4.3L Mercruiser with a 2bbl carb (807764A1). It has a hard start hot or cold. No matter what I do it takes a while of turning over to eventually fire up. Once warmed up it idles great at 650-700rpm. It has a mechanical fuel pump that is new. The electric choke is set and when cold, the choke plates are closed and when warms up is completely open. The air/fuel adjust screw is 3/4 backed out for the best hot idle. I just put new spark plugs in when I put in new exhaust flappers and hard the risers off.

I rebuilt the carb 2 seasons ago to spec and am going to do it again in the next week or so. Do you have recommendations of what to look for?

1. Do i need to replace the distrubutor or rotor?
2. Could it be a dirty carb?
3. Would a fuel logged float cause flooding and a hard start?

anyone moved distributor?

 

[JM3820]

anyone moved distributor?

I haven't move the distributor. But need to check it and the rotor for any corrosion after I rebuild the carb.

 

[JM3820]

yes it could be a dirty carb

what is your staring proceedure exactly? please specify in detail

did you just set the idle specs to 3/4 turns out and not verify that is where your motor wanted it? Never ever had a motor that ran best at a generic setting. every one required validating correct idle mix with an un-lit propane cylinder.
do you get a squirt of fuel every time you advance the throttle?

Starting procedure is to give it 1/4 to 1/3 throttle to start hot or cold and back off when started. When running there is a heavy smell of fuel out the exhaust. I set the air/fuel mixture screw at 3/4 backed out because it ran the smoothest like that. I'm going to put a new float in when I rebuild the carb. I wonder if the float is slightly heavier due to fuel absorption.

 

[Bondo]

Starting procedure is to give it 1/4 to 1/3 throttle to start hot or cold and back off when started. When running there is a heavy smell of fuel out the exhaust. I set the air/fuel mixture screw at 3/4 backed out because it ran the smoothest like that. I'm going to put a new float in when I rebuild the carb. I wonder if the float is slightly heavier due to fuel absorption.

Ayuh,..... On a cold start, you should go to Wot, once, to set the choke, then do as you do,....

You'll have to weigh the float to answer that question,....

 

[dubs283]

1. Do i need to replace the distrubutor or rotor?
2. Could it be a dirty carb?
3. Would a fuel logged float cause flooding and a hard start?

1. Distributor no, cap/rotor yes as part of a standard tune up including plugs, wires (if 10+ years old) and fuel filters. Check/set idle timing to spec and adjust carb for spec/desired speed and smooth running. If thunderbolt ignition it's recommended to replace the ignition sensor in the distributor if it isn't the latest style, three wire fully potted

2. Yes

3. Yes