Engine will not idle after a good run

[robinsbd]

I am experiencing a strange issue with my engine. I took the boat out yesterday evening for a run up the river. The engine seemed to run fine. I was able to get on plane and ran for many miles without any issues.

When I came back to the marina and as I approached the harbor entrance, I of course wanted to throttle down and bring the boat to the minimum forward speed. When I backed the throttle down, the engine stuttered and wanted to die. To keep it from dying, I had to throttle up a lot. I had shift quick into reverse with a lot of throttle to slow the boat down and keep the engine running. When I approached the slip, the engine sputtered and died. I had to quick shift to neutral, start the engine, and then throttle hard in reverse. I didn't hit the dock, but it was close.

To me, this seems like a fuel delivery issue. Engine was fine out on the water, but no good in the harbor. Do you guys have any ideas what I should do next?

 

[alldodge]

I also thinking fuel issue. Start with the basics, check the fuel filter for crud by emptying into a glass jab or baggie and see what's if anything shows. Don't think its fuel pressure right now because it runs on plane ok. So if filter checks out, I would look at the inside of the carb

 

[robinsbd]

I replaced the fuel filter in November. The gas in my tank is also from November. I did put Stabil in the gas, but probably not as much as it needed. It's 87 octane gas.

I will take off the filter and inspect the gas.

The interesting part is that I could still restart the engine and throw it into reverse to slow down. So the engine still starts. Although I haven't tried it since the docking issue.

 

[FreeBeeTony]

Sounds like the idle circuit in the carb............

 

[jorgeoliva]

I have a 5.0 mercruicer had this exact problem last year every time while in throttle no problem as soon as I neutral it engine die's discover that my problem was the carburetor pulled it out had them clean and rebuild now the engine purrs like a kitten if your boat have carbs and you never had them rebuild I truly recommend you do it.

 

[robinsbd]

I went out to the boat with a new fuel filter in hand. I removed the flame arrestor and took a look at the carb. Before I remove the fuel filter, I decided to test the engine again.

Now, usually when I start it, I pump the throttle once or twice and then start it with throttle at about 1/4. I noticed something very odd this time. When I moved the throttle (throttle only) just out of neutral position to the first click, I saw the choke plate on the carb immediately close. I thought that's kinda strange because I thought the choke plate only closes when I push the throttle all the way down. This time it closed immediately and it also looks like it closes all the way with no air gap.

Please look at the attached picture of my carb and let me know what you think. Maybe this is normal. I'm not sure. On a cold engine, I didn't think the choke plate should close until the throttle is pumped and I don't think it should be closed all the way. Otherwise, where's it getting air?

I was able to start the engine, but it ran pretty rough. When i tried to increase throttle, the RPMs would barely increase and the engine sounded rough and bogged down. Definitely not normal. Also, at this same time, the volt meter was hovering under 12 volts and didn't seem to be charging at all, but I'm not certain the RPMs were good enough for the alternator to kick in yet. I have 2 identical batteries that I got new last year. They are very good Die Hard Platinum Marine. At the moment I had the battery switch on 1 battery. The last time I had the boat out this week, it was charging fine at above 13 volts and that time I had it set to use both batteries so they both were getting charged.

What do you guys think?

 

[alldodge]

I don't see an issue with the choke closing with just a slight movement of the throttle, I do see an issue with it closing all the way. Need to adjust the plate for a 1/8 gap.



So far as the voltmeter, you are probably fine, it takes a little time for the gauge to come up and normally needs rpm to increase to 1500.

 

[robinsbd]

When should the plate have an 1/8 inch gap? When it's cold?

If I push the throttle all the way down to max throttle, the plate does open slightly. I understand this behavior is for clearing flooded engines.

Here is a picture when the throttle is at max:

 

[robinsbd]

My questions about the choke plate are when the engine is cold, not running, and after the choke is set by pushing the throttle forward right before starting.

I'm starting to suspect something is not right with my electric choke.

 

[robinsbd]

Another question is does the electric choke turn on when I turn the key to "on" before starting, or does it only turn on after the engine is running?

I can verify with a volt meter next time I'm at the boat, but I just wanted to ask.

Thanks.

 

[alldodge]

I also believe your choke needs adjusting. The choke plate should have a 1/8 gap when cold and throttle at the idle position. Moving the throttle full forward should open the plate a tad more.

Loosen the screws on the electric choke pot and rotate it until you get a 1/8 gap. Give it a start and if it does well, then retighten the screws

 

[alldodge]

Another question is does the electric choke turn on when I turn the key to "on" before starting, or does it only turn on after the engine is running?

I can verify with a volt meter next time I'm at the boat, but I just wanted to ask.

Thanks.

The choke turns on as soon as the key is turn to ON. If you leave the key on long enough without starting, the choke will fully heat up and open

 

[robinsbd]

I turned the key to ON yesterday. I sat there and watched the choke, but it never moved. I could rotate the choke plate by hand with no issue. I had left my volt meter at home so I couldn't take a reading at the positive terminal.

 

[alldodge]

couldn't take a reading at the positive terminal.

The choke pot may be burned out. The meter would be the next thing

 

[robinsbd]

I did some reading on the electric choke for my engine. It appears that it is wired to the alternator so it will only receive power when the alternator is working.

 

[alldodge]

I did some reading on the electric choke for my engine. It appears that it is wired to the alternator so it will only receive power when the alternator is working.

Suggest you need to look a bit closer. The wiring diagram illustrates how wire are connected but NOT actually were they are connect at. Note in the drawing below all the Purple dots. The dots are marking were the purple wire runs to each component. When the ignition key is turned to ON, the power is supplied to all components by the purple wire. The purple wire supplies 12V to the field winding of the alternator, coil, distributer, carb choke and other areas. The only time the ALT supplies anything is once the motor is running.





To test the analysis, put a voltmeter on the purple choke wire and turn the key ON. If you do not get any voltage you have a break in the wire somewhere.

 

[robinsbd]

I was thinking that way too, but then I read the following post regarding a Mercruiser service bulletin that covers my engine serial number.

http://forums.iboats.com/forum/engi...ation-on-97-5-7-mercarb?p=3919493#post3919493

I will still do a test with my volt meter with the key ON next time I'm at the boat.

 

[alldodge]

Did some searching on the 1coolguy post in you link. Only bulletin found dealt with choke adjustment but did not mention a pur/yel wire, only to check voltage at the choke. One thing about Merc is since the early 70's they have stuck with their color codes for wiring. The Pur/Yel wire is used for ballast bypass, this is the connection between the starter and the electric fuel pump which is used when the motor is being started.

I've posted things I thought were correct and were not, I'm thinking this happened here also

 

[robinsbd]

Well, I'll give it a test with the meter. I'm still trying to get back out to my boat. We have big severe weather coming in this afternoon and evening.

 

[robinsbd]

I tested with my volt meter. On my engine, there is no power at the electric choke when the key is in the ON position. I see that the positive wire at the choke is a purple/yellow wire, and I also see a purple/yellow wire connected to a terminal on the alternator.

My next step will be to adjust the choke for an 1/8 gap. I'll post back with my results.