Engine runs fine. Won’t start after it gets warm.

[berry7199]

I have a 1988 boat with a 4.3L Mercruser. It will start just fine when it is cold. After it runs for a while we sometimes turn it off and it won’t immediately re-start. It will crank and turn over, it just won’t fire up. Then if we let it sit for a while, 15 minutes or so, it will start again. I am worried that some day it won’t restart and leave me stranded. The battery is fine. The starter is fine. The starter solenoid is new. I’ve only owned the boat a few months so I’m not sure about the spark plugs. It seems to be running fine when it’s running so I didn’t think it’s the spark plugs but I’m up for any suggestions. Thanks!

 

[Alumarine]

Have you tried applying some throttle while in throttle only mode?

 

[Rick Stephens]

What carburetor?

If you post engine and drive serial numbers when posting questions it is much easier to give relevant answers.

 

[berry7199]

Have you tried applying some throttle while in throttle only mode?

Yes. A little. A lot. Doesn’t seem to matter. Just cranks with no firing.

 

[berry7199]

What carburetor?

If you post engine and drive serial numbers when posting questions it is much easier to give relevant answers.

4.3 Liter Mercruser Engine S/N 0B811539 Model GM 262 V-6

Mercruser Drive unit serial # 0B798144

Mercruser Transom Assembly unit serial # 0B811539

 

[dubs283]

You may be experiencing one of or both of two issues.

One is the carburetor is flooding out upon shutdown thus flooding the engine. The other is loss of ignition spark.

To check for carburetor flooding, upon shutting off a warm engine immediately inspect the carburetor. Remove the flame arrestor and look into the carburetor throats. If you see fuel dripping/running down one or both primary throats the carburetor needs cleaning/rebuild. To start the engine in this scenario you will advance the throttle in neutral slowly before starting the engine. Do not pump the throttle, just move it to wide open and leave it there. Then turn the engine over to start. It may take a bit of cranking to clear the flood and the engine may try to catch and start but wait until it fully runs then pull the throttle back to idle.

Second scenario involving no spark will require the use of an in line spark tester between the coil tower and main input on the distributor cap. Once in place turn the engine over and look for the spark tester to verify spark/no spark. If no spark you have an ignition issue, if spark is present verify it is good, strong spark and if so look at fuel supply issues

 

[Rick Stephens]

4.3 Liter Mercruser Engine S/N 0B811539 Model GM 262 V-6

Mercruser Drive unit serial # 0B798144

Mercruser Transom Assembly unit serial # 0B811539

That engine serial number is for the transom, not the motor..

 

[berry7199]

You may be experiencing one of or both of two issues.

One is the carburetor is flooding out upon shutdown thus flooding the engine. The other is loss of ignition spark.

To check for carburetor flooding, upon shutting off a warm engine immediately inspect the carburetor. Remove the flame arrestor and look into the carburetor throats. If you see fuel dripping/running down one or both primary throats the carburetor needs cleaning/rebuild. To start the engine in this scenario you will advance the throttle in neutral slowly before starting the engine. Do not pump the throttle, just move it to wide open and leave it there. Then turn the engine over to start. It may take a bit of cranking to clear the flood and the engine may try to catch and start but wait until it fully runs then pull the throttle back to idle.

Second scenario involving no spark will require the use of an in line spark tester between the coil tower and main input on the distributor cap. Once in place turn the engine over and look for the spark tester to verify spark/no spark. If no spark you have an ignition issue, if spark is present verify it is good, strong spark and if so look at fuel supply issues

Thanks for the info! I will definitely give those a try.

 

[berry7199]

That engine serial number is for the transom, not the motor..

B779146

 

[Rick Stephens]

B779146

Looks like that has the 4 barrel Rochester carb on it. There were some possible sealing issues with pressed in plugs in the bottom of the bowl. Been a LONG time since I worked on a Roc, but there are others on this forum that can assist greatly. May very well be dumping the bowl contents down the intake causing a flood. One great way to test that is next time it does this, pull a spark plug and look at it. Is the plug wet?

 

[berry7199]

You may be experiencing one of or both of two issues.

One is the carburetor is flooding out upon shutdown thus flooding the engine. The other is loss of ignition spark.

To check for carburetor flooding, upon shutting off a warm engine immediately inspect the carburetor. Remove the flame arrestor and look into the carburetor throats. If you see fuel dripping/running down one or both primary throats the carburetor needs cleaning/rebuild. To start the engine in this scenario you will advance the throttle in neutral slowly before starting the engine. Do not pump the throttle, just move it to wide open and leave it there. Then turn the engine over to start. It may take a bit of cranking to clear the flood and the engine may try to catch and start but wait until it fully runs then pull the throttle back to idle.

Second scenario involving no spark will require the use of an in line spark tester between the coil tower and main input on the distributor cap. Once in place turn the engine over and look for the spark tester to verify spark/no spark. If no spark you have an ignition issue, if spark is present verify it is good, strong spark and if so look at fuel supply issues

 

[berry7199]

This is what the carburetor looked like after it ran for a while. Do you know if those droplets are supposed to be there? If not, is the only fix a new/rebuilt carburetor?

 

[berry7199]

Looks like that has the 4 barrel Rochester carb on it. There were some possible sealing issues with pressed in plugs in the bottom of the bowl. Been a LONG time since I worked on a Roc, but there are others on this forum that can assist greatly. May very well be dumping the bowl contents down the intake causing a flood. One great way to test that is next time it does this, pull a spark plug and look at it. Is the plug wet?

I’ll check. If it is does that mean I needs a new or rebuilt carburetor?

 

[Rick Stephens]

Almost infinitely rebuildable. Well, barring corrosion or worn out shaft holes.

A really good resource on information, parts and service about Rocs is https://cliffshighperformance.com/

 

[Rick Stephens]

Your picture looks like it might be water droplets. When was the photo taken? - during time it wouldn't restart? If so, then that s a lot of fuel on the plates and would not be because of leaky plugs but because of excessive float height , needle valve stuck open or junk in a check ball.

 

[berry7199]

Your picture looks like it might be water droplets. When was the photo taken? - during time it wouldn't restart? If so, then that s a lot of fuel on the plates and would not be because of leaky plugs but because of excessive float height , needle valve stuck open or junk in a check ball.

The photo was after it ran for about 15 minutes. We were trying to recreate the situation we are seeing on the lake. It started just fine after we turned it off. I sprayed it with carb cleaner and this is what it looked like afterwards

 

[Rick Stephens]

Ah, carb cleaner. Didn't look like fuel to me.

Spraying carb cleaner is about as useful as getting a flu shot squirted on your head. Probably needs rebuilding with a quality carb kit.

 

[achris]

When the engine 'won't start' are the instrument still working?

 

[berry7199]

When the engine 'won't start' are the instrument still working?

Yes. Everything is as it should be. It just won’t “fire up”. After it sits for 15-20 minutes it will start like normal

 

[achris]

Pull one of the spark plug leads and put an old spark plug in it and lay it on the engine. When you crank the engine, see if there's a spark.