2001 Mercury 150XL rough idle, hard start hot

[nowtime4fun]

Thank you for looking.
2001 VIP Bay Stealth 18.8’ with Mercury 150XL V6 carb. It had been stored for a year. It seems to run really good at partial and wide open throttle. My problem is rough idle cold and hot. Sometimes hard to start hot. It flooded on me today. I had to full throttle crank it to get it started. One time I could not get the primer bulb to get firm until I took it loose from the engine and then after a few pumps it pumped a steady stream. I put it back on and it started right up. When I got it the tank was on 1/4 so I filled it with super unleaded and put 32 oz. of Berimens in it just in case it had some condensation. I have checked the plugs. The thermal relief valve is working properly. I pumped some gas into glass jar and let it settle out, look good. I also replaced the fuel filter just in case it had not been replaced. Any help would be appreciated.

 

[hkeiner]

Re: 2001 Mercury 150XL rough idle, hard start hot

There are lots of possible causes for poor idle. I prefer testing/troubleshooting components for failure rather than randomly replacing them upon a hunch or symptom. Less frustrating and often less expensive in the long run. Replacing certain parts as part of regular maintenance is the exception.

The symptom that the primer bulb did not get firm after squeezing may indicate a fuel supply or fuel pump problem. If you want to troubleshoot the fuel supply/pump using a vacuum gauge, check out the following link.

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

The symptom that the problem only occurs during idle (motor cold or hot) may indicate that the low speed jets are not adjusted correctly, the carbs needs cleaning, or link and sync is incorrect. Other possible culprits could be bad spark plugs, bad spark plug wires, carb float misadjusted, carb float valve leaking, etc., etc., etc.

If my motor had your symptoms, I would first check the link and sync, then I would do the vacuum test on the fuel supply, and then I would clean/adjust the carbs. A compression test is always a good thing to do when a motor does not run well, but I doubt that is your problem. Others on this forum, of course, may have additional or better advice than this.

 

[andy6374]

Re: 2001 Mercury 150XL rough idle, hard start hot

Is the primer bulb not getting firm (while pumping it) when the engine is running or not running?

If it never gets hard while the engine isn't running that you might have to adjust one or more of your carb floats and if your carb floats are set too high...it will idle like crap and flood.

 

[nowtime4fun]

Re: 2001 Mercury 150XL rough idle, hard start hot

Thank you both for the help. Sometimes it starts right up. Would you expect the fuel
pump to be bad if it ran good all out? It got up to 58 mph last time out. It’s not a solid
miss like a spark plug or wire would be. One time when it didn’t want to start, the bulb
would not pump up. The bulb is hard when it is running. I just got done running it until
it warmed up then I ran it at a fast idle, around 2000 rpm for about 10 seconds, cut the
power then pulled out a plug and it was wet with fuel. It does seem to me that it is trying
to flood. I think you both are right. I need to look at the carburators. I have rebuilt auto carb (hollys, rochesters, carter) with good results in the past. Can you tell me if there is a great deal of differance with marine engines? Do the rebuild kits come with the specifications? Thanks again for the help.
Jerry

 

[JMRuth72]

Re: 2001 Mercury 150XL rough idle, hard start hot

This question is really for both of us as I am learning about boats, but am somewhat familiar with motors. Is your choke sticking? I am not sure how a choke works on a boat, but it could be a cause of flooding at idle. I had a problem like this on a 74 chevy monte carlo. Once I cleaned it up and the choke worked correctly it idled fine. Just a idea, let us know what you find.

 

[hkeiner]

Re: 2001 Mercury 150XL rough idle, hard start hot

I don't know about your specific motor but in general outboard 2-stroke motor carbs are pretty simple compared with an automobile carb. There are not many parts involved, they are easy to clean, and there are only a few adjustments to make (on your motor is it probably only the float level and low speed idle jets). Your shop manual will describe what to do.

I cleaned the carbs on my motor for the first time this summer and found it to be very easy to do and there was a very big improvement to the way my motor idled aftewards.

 

[nowtime4fun]

Re: 2001 Mercury 150XL rough idle, hard start hot

It has an electric choke. It is key accuated by holding the key in and turning it to run for 5 seconds. There is a fuel enrichener system that used a selonoid to provide extra fuel for start up. There is also a thermal vacuum switch that provides extra air until it warms up some. The system seems to be working right. If the enrichment system failed it probable wouldn't be flooding it would be starving for fuel. I have been reading up on the system and I may be using it too much and flooding it when the engine is warm. I will have to test that therory out. If that is true, it still don't explain the rough idle. The plugs are new and all of the electrodes look the same, wet with gas. There are also two low speed ignition coils that I am still not sure I understand how they functon or how to test them.
Jerry

 

[gss036]

Re: 2001 Mercury 150XL rough idle, hard start hot

Mercury Two Stroke 150-200 hp engines seem to naturally idle rough, it just the nature of the beast. If you ever figure out how to get one to run as smooth as a Yamaha, let us know, I would love to have my 200 idle smoother than it does, but it has been that way since I bought new in 1989.

 

[hkeiner]

Re: 2001 Mercury 150XL rough idle, hard start hot

Don't use the enricher at all when the motor is warm. Also, move the throttle up a little past idle when starting the motor warm (this gives it a little extra air when starting warm and reduces the chance of flooding) then bring it down to idle after the motor starts. I had to learn this technique myself when I first got my 150HP carbed motor.

Cleaning the carbs is still a good thing to do if they have not been cleaned for several years.

It has an electric choke. It is key actuated by holding the key in and turning it to run for 5 seconds.

By the way, you say you have an "electric choke." My interpretation of an "electric choke" would be a choke plate in the carb barrel that would be closed when the motor is cold and then opens as the motor warms up. If you truly have such a choke plate, then of course you would not want it closed when the motor is warm or else flooding would occur. I don't know your particular model but I would expect that it does NOT have a choke plate.

My 150hp has no such choke plate. The cold starting features on my carb are only the enricher valve (to let additional fuel flow into the two lower carbs when the ignition key is pushed in) and the thermal air valve (to restrict air flow through the idle air jets when the motor is cold), both causing a richer fuel/air mix when active.

 

[nowtime4fun]

Re: 2001 Mercury 150XL rough idle, hard start hot

You are correct. I only call it a choke because that's how my ignition switch is marked. It says "push in to choke".

 

[nowtime4fun]

Re: 2001 Mercury 150XL rough idle, hard start hot

Lieutenant
Thank you. I have not been able to find anything wrong so your post has brought me some releif. I have come to the conclusion that my hot startup procedure was wrong also.
I also want to thank everyone else for the help.
Jerry