Low idle - dies when shifting when cold

[dougm]

I have a 2003 2452 Bayliner Classic with a 5.0 Mercruiser. The engine was dying when not fully warm when shifting gears. So next time I started it up, let it warm up to near normal engine temp in the boat house, adjusted the idle set screw a bit faster to 700 rpm. Tested it and it did not die at all when shifting. The momentary kill when shifting from in gear to neutral is working fine. Just a momentary kill.

Then we took it out and ran it at cruise for an hour or so. When I pulled it back to idle, it was idling at about 1200 rpm - way too high. Had to quickly adjust the idle set screw back down to 700 or so in neutral. Now I am afraid the next time I start it up cold - i'll have the same problem with a low idle. I carefully inspected the idle set screw and the choke cam that the idle screw sits on. I was amazed to find that there is no slope to this cam. The cold choked setting for idle is the same for hot. I am wondering why this is so.

I had another Mercriuser - a 95 Bayliner 2655 a few years ago and had the same problem - died when shifting before fully warm, but lived with it.

Can anyone advise what may be going on here and how to have an engine that doesn't die when shifting, but idles properly when fully warm. Thanks.

Doug M

 

[Haut Medoc]

Re: Low idle - dies when shifting when cold

Welcome to iboats......
I would have to say that it is the nature of the beast on a carbed engine, let it get warm before you take off & live with it......​

 

[Uraijit]

Re: Low idle - dies when shifting when cold

Yup, playing with the idle on a semi-warmed boat won't fix your problem. Set your idle and mixture the right way, and warm your boat up before you take off. My carbed motorcycle is the same way. If you must take off immediately, get fuel injection.

 

[achris]

Re: Low idle - dies when shifting when cold

.... I carefully inspected the idle set screw and the choke cam that the idle screw sits on. I was amazed to find that there is no slope to this cam. The cold choked setting for idle is the same for hot. I am wondering why this is so....

Doug,

This is so people like yourself can't take off with a cold engine running at 1000+rpm... If you did, you would kill the drive in very short order. The clutch in the drive is a dog clutch, not a nice smooth friction clutch like a car, so engaging at higher speeds than idle is a really bad thing.

Hope this helps you understand the whys and wherefores....

Chris....
(Be nice to your engine... let it warm up)

 

[dougm]

Re: Low idle - dies when shifting when cold

Thanks for your replies. However, I don't think I explained the situation fully. The boat is kept in a boat house - to let it fully warm up would probably mean carbon monoxide poisoning. The CO detector starts squawking after about 2 minutes at idle in the house. I do let it warm up for say 3 or 4 minutes, but it still dies - right when I am trying to make the critical departure from the boat house in tight quarters, usually with a breeze and current. Not the time to have the engine die. It also seems like the longer I let it warm up, the more likely it is to die, so for that reason and the CO hazard, I try to get out without a lot of waiting.

There has got to be a way to adjust things to keep it running while shifting.

Doug

Next boat will have an EFI engine!

 

[Don S]

Re: Low idle - dies when shifting when cold

It's cold in western Washington this time of year. After 3 or 4 minutes, you are probably getting carburator ice. Happens all the time in damp areas when in the mid 40's

 

[JustJason]

Re: Low idle - dies when shifting when cold

where are you located doug?

 

[newport dave]

Re: Low idle - dies when shifting when cold

One reason you may be having trouble getting the idle adjusted is that you have to do it in Base Timing Mode so the module isn't adjusting the base timing (changing the idle speed) at the same time.

 

[dougm]

Re: Low idle - dies when shifting when cold

Hmm, carburetor ice. That could be it! I live in Gig Harbor and have the boat at Day Island right now - and yes its been cold...high 30's or low 40's. Is there any way to prevent the icing, other than move south?

Also, what is this Base Timing Mode and how do i get the engine in to it?

Thanks for all your ideas!

Doug

 

[Loren Warner]

Re: Low idle - dies when shifting when cold

After starting, only idle for around three minutes between 1200 & 1500 rpm, then stop the engine. Wait 5 to 10 minutes for the heat to work its way up through the carb before starting again. While waiting, go ahead and finish getting the boat ready. Engine should start right up and idle fine.

 

[Don S]

Re: Low idle - dies when shifting when cold

Is there any way to prevent the icing, other than move south?

MPI engines don't have carbs, on your next boat, get one with MPI.
Basically, do it like Loren mentions. All it does is warms the engine up a little. If you start it and set the idle at say 1500 rpm, after a few minutes the engine will start slowing down. That is the carb ice building on the throttle plates and closing off the opening. After running for a while heat builds in the engine. When you shut it off, the heat from the engine warms the carb base and throttle plates. Then you don't have further icing.
30? to 40? is perfect for carb ice.

As far as timing, you really should get an OEM service manual for your engine if you plan on working on it. Here is from the manual.

 

[dougm]

Re: Low idle - dies when shifting when cold

Thanks Don for the information. I will give it a try.

The education continues...

Doug

 

[flystrong]

Re: Low idle - dies when shifting when cold

I have the same type of problem on my 5.7 Mercruiser. I have been told that the carb is icing but I am puzzled as it sometimes cuts out when shifting in and out of gear when approaching a mooring after a long run. Could the problem be that I am tentatively shifting into gear at such low revs that the engine is stalling when engaging the dog clutch?

 

[Haut Medoc]

Re: Low idle - dies when shifting when cold

To answer your question, possibly......
You should start your own thread with the specific model & serial # for more specific input......
One thing is for sure though, with a dog style clutch, you should shift swiftly in & out of gear in one motion.....​