Merc 5.7L Hot start issue

[MTribe08]

Hello..1995 5.7L 235hp Carter Style 4 bbl carb.

Boat runs fantastic in every aspect accept for hot starts. Was suggested this could be a timing issue. Manual says 8 degrees at idle, which I will doublecheck. Any other ideas as to the hot start issue. I've got a Carter style 4 barrel carb. Runs smooth in all RPM conditions, idles fine, have not experienced any detonation, backfires, ect. Run's cool, normally stays around 150 or so.

I have friends with very similar setups and its normally just a turn of the key and it fires..with mine, I have pump the throttle, or hold it down as it sputters to life. Once it gets going its fine.

Thanks.

 

[OldNBold51]

Re: Merc 5.7L Hot start issue

My 1st thought would be the choke is not working properly. If it will only start after pumping the throttle, then the engine is requiring the accelerator pumps fuel shot to richen the mixture. However: a warm engine shouldn't need a richer mixture.

How long is the interval between shut down and re-start? Does the cold motor (1st start of the day) require you to pump the throttle or does it start w/o pumping? Once it starts (hot), how does the exhaust gas smell...normal or very rich?

 

[180shabah]

Re: Merc 5.7L Hot start issue

He has the weber carb - know issue, but doesn't effect all of them - no confirmed cure.

Heat soak can cause the fuel to boil in the carb - pressure forces it past the vlave and it gets dumped into the intake. Basically mildly floods the engine. Most people still pump the throttle a time or two on a warm engine adding more raw gas and making the issue worse.

Just open the throttle a little, without pumping, and turn the key. This lets more air in while cranking and it should fire right up.

 

[MTribe08]

Re: Merc 5.7L Hot start issue

How long is the interval between shut down and re-start? Does the cold motor (1st start of the day) require you to pump the throttle or does it start w/o pumping? Once it starts (hot), how does the exhaust gas smell...normal or very rich?

Well, the first start after a lengthy layup, requires me to pump the throttle a bit. Once it gets going and runs for a few minutes on the muffs, its a turn of the key to get it going again. However..when running on the muffs, I normally have the doghouse open.

On the water, if I run the boat for 10 min or so across the lake, and shut er down for 5-10 min, I'll have the issue. The exhaust smells normal, I've never seen any black smoke or carbon build up anywhere.

I've wondered about the choke, but obviously thats not needed once the engine is hot, and thats where the problem occurs.

 

[MTribe08]

Re: Merc 5.7L Hot start issue

Just open the throttle a little, without pumping, and turn the key. This lets more air in while cranking and it should fire right up.

Thank you..I will do this and report back next time we are out.

 

[PitchFork]

Re: Merc 5.7L Hot start issue

I have a Rochester QJ 4bbl and have disconnected my choke entirely and zip tied the butterflies completely open. I have no problem starting cold just pump the throttle twice and leave throttle half and start and warm up engine to 140? at 2K RPM for a minute and then to idle and back off trailer.

I too had a engine that would start when warm by just hitting the key but at that time it would stall if I went to idle if the engine did not completely warm-up. I can do that about half the time now but the other half I have to give it some throttle to start it when warm.

 

[180shabah]

Re: Merc 5.7L Hot start issue

disconnected my choke entirely and zip tied the butterflies completely open.

Why?

I have no problem starting cold just pump the throttle twice and leave throttle half and start

Normal procedure for a carb - choke has nothing to do with getting it started

and warm up engine to 140? at 2K RPM for a minute and then to idle and back off trailer.

This is where a functional choke comes in - enrichens the fuel mixture so you don't have to get to opperating temp for the engine to run on its own. Mine will be stable enough to back off the trailer after only 10-15 seconds at ~ 1800 rpm fast idle.

 

[cr2k]

Re: Merc 5.7L Hot start issue

I sure wouldn't want to be waiting for the ramp with you there warming up your boat. pitch fork.

The choke is there for start ability and drive ability. It does have a purpose.

 

[PitchFork]

Re: Merc 5.7L Hot start issue

Why?


Normal procedure for a carb - choke has nothing to do with getting it started


This is where a functional choke comes in - enrichens the fuel mixture so you don't have to get to opperating temp for the engine to run on its own. Mine will be stable enough to back off the trailer after only 10-15 seconds at ~ 1800 rpm fast idle.

I have tried both ways with the choke working correctly and choke open completely. When using the choke and I back off the trailer and if it stalls it is almost impossible to restart. So I found that letting it warm up for a minute or two it works perfectly. We have over 150 ramps on the lake and they are rarely backed up except during a drought.

Anyways I am about to get out and work on the boat so I will work on the choke and set it to specs per manual and see if works tomorrow.

 

[180shabah]

Re: Merc 5.7L Hot start issue

Spec is a good starting point, but probably going to be a little too rich if it is a merc.
VP and OMC - I don't know about thier specs.

 

[MTribe08]

Re: Merc 5.7L Hot start issue

I've had my boat for about a year now..taken it out on the water about a dozen times and I can't recall a single time where the boat "stalled". When its running, it runs. When I fire it up on the trailer for the first time when I hit the water, I could put it in gear within 5-10 seconds with no problem at all. It just doesn't like to run across the lake, sit for a while, and then start back up easy.

Gonna try 180's method next time.

 

[180shabah]

Re: Merc 5.7L Hot start issue

2003 GMC Yukon 5.4l 3.73 gears

You didn't put a ford engine in that gm did you
sure it ain't a 5.3?

 

[MTribe08]

Re: Merc 5.7L Hot start issue

You didn't put a ford engine in that gm did you
sure it ain't a 5.3?

ohh no, missprint.

 

[Cptkid570]

Re: Merc 5.7L Hot start issue

A couple of questions:

1. What is the engine doing when you shut if off? If you shut it off while you are still moving, then you can potentially suck water up into the engine when your wake comes back and hits you in the transom.

2. Is the starter dragging or is the engine turning freely when trying to start it? If the starter is dragging, I'd 1st check the timing. Oh, and when checking the timing, it makes it much easier if you take some white out and paint the line on your harmonic balancer.

 

[MTribe08]

Re: Merc 5.7L Hot start issue

A couple of questions:

1. What is the engine doing when you shut if off? If you shut it off while you are still moving, then you can potentially suck water up into the engine when your wake comes back and hits you in the transom.

No I don't do that, and never have. I always let the boat settle off plane, and let the wake subside before turning it off.

2. Is the starter dragging or is the engine turning freely when trying to start it? If the starter is dragging, I'd 1st check the timing. Oh, and when checking the timing, it makes it much easier if you take some white out and paint the line on your harmonic balancer.

Its turns freely.

 

[PitchFork]

Re: Merc 5.7L Hot start issue

This is where a functional choke comes in - enrichens the fuel mixture so you don't have to get to opperating temp for the engine to run on its own. Mine will be stable enough to back off the trailer after only 10-15 seconds at ~ 1800 rpm fast idle.

Worked on it and got the choke dialed in and now I can back off the trailer within 30 secs of starting. Like the OP I also have a hot start issue and would like to solve it, but in the mean time I usually advanced the throttle slowly to half and hit the key and usually it starts within 4 seconds. If I stop and turn it off it will fire right back up within the first minute any longer is a problem.

I have seen a lot of post of fellow boaters having the same problem and yet to see someone completely solve it. At one time I thought I had it solved.

 

[MTribe08]

Re: Merc 5.7L Hot start issue

Just open the throttle a little, without pumping, and turn the key. This lets more air in while cranking and it should fire right up.

Just wanted to report back, that this process worked out just fine. If turn the boat off, and then back on within a short amount of time(a minute or two). It will fire over without any help.

After that, I just cracked the throttle a bit and didn't touch it. It cranked 3-4 times and fired over. In the past, I made the problem worse by pumping the throttle. Thanks.

 

[180shabah]

Re: Merc 5.7L Hot start issue

Glad to hear it.