Mercruiser 5.7 carbureted hard start

[bterrell]

First things first I have a mercruiser 5.7 2bbl mercarb. I just rebuilt my carb and I think it's very close to being adjusted correctly. It runs great throttles with no hesitation and for my first time I think it has the hp it says it has. During the rebuild I also pumped dry the fuel tank, installed new anti siphon valve ran new fuel line and replaced the fuel/water separator. My issue lies in "starting" the engine. When starting it takes about 10-12 seconds to fire up after it has sat longer than a few minutes. If I cut it off then immediatly try to fire it back up it starts almost immediately. Any ideas what to look for or do to remedy this issue? Thanks in advance.

 

[Another retired guy]

Re: Mercruiser 5.7 carbureted hard start

Hi. Carb rebuilds are always the first suspect you say it has to crank 10/12 seconds to restart. While its cranking, do you pump the throttle or have it wide open? It's possible you have a flooding issue with raw fuel dribbling into the carb while the engine is stopped. Look into the carb after a few minutes for signs of fuel leaking.

 

[bterrell]

Re: Mercruiser 5.7 carbureted hard start

I have tried both. Wot, pumping once, pumping twice to just hitting the key. All the same reaction. It had this same problem before I rebuilt the carb which is what I was hoping helped to cure this problem. The main reason I rebuilt the carb was because it would not idle at all. After winter storage I figured it had residue from the good old ethanol fuel.

 

[tank1949]

Re: Mercruiser 5.7 carbureted hard start

May have bad power valve or crap somehow in jets or it is loosing prime. If not prime, here is a suggestion that you are not going to like or at least be wondering what the heck I am talking about. BUT, it works!!! Get it running at dock or with muffs on and disconnect linkage and breather. Have fire ext. near by. manually rev. up motor while putting your hand over carb throat. Do this a couple of times, raising and lowering RPMs. This action will suck any small particles through it and may scare the crap out of you as the sucking SHOULD be powerful. Yet, I have never had my hand sucked inside the carb. You should be able to see down in throats to manually advance throttel and see if power valve is working. If no stream of fuel, then no fuel in bowl. :Loosing prime somewhere!!!!

 

[Another retired guy]

Re: Mercruiser 5.7 carbureted hard start

Ok. Is this a TKS carb?? If so, the TKS module controls starting and it could be bad.

 

[bterrell]

Re: Mercruiser 5.7 carbureted hard start

No another retired guy it is not a tks carb.

 

[bterrell]

Re: Mercruiser 5.7 carbureted hard start

Tank: this is not a running problem it is a starting problem. The prime should not have any bearing on the starting of engine as the idle circuit only uses fuel from bowl to start the engine. I will try that as I have done it before though and see if it helps any

 

[Another retired guy]

Re: Mercruiser 5.7 carbureted hard start

Now we are back to basics! A starting problem is usually a result of incorrect fuel/air mixture for a particular ambient temperature. Range varies from too lean a mixture when cold, to too rich a mixture when hot. In your case it starts fine when hot, but goes wrong as temperature starts to fall. Have you checked out the choke function? Is it manifold heat operated or electric? Is the choke plate fully open when hot, and STILL open after a few minutes?? And, of course, fully closed when cold.

 

[bterrell]

Re: Mercruiser 5.7 carbureted hard start

It actually does it hot or cold. But only after being off for more than several minutes. The only time it fires up quickly is when it was turned off then restarted within the minute or less. Thinking about it now I have a feeling the seat that the check ball in the carb sits in my be worn or not true any more causing a leaking carb. It's the only thing I could think of that would cause a low fuel to start issue. I don't believe it's the choke because I checked it for operation as it does work properly or so I think.

 

[tank1949]

Re: Mercruiser 5.7 carbureted hard start

It actually does it hot or cold. But only after being off for more than several minutes. The only time it fires up quickly is when it was turned off then restarted within the minute or less. Thinking about it now I have a feeling the seat that the check ball in the carb sits in my be worn or not true any more causing a leaking carb. It's the only thing I could think of that would cause a low fuel to start issue. I don't believe it's the choke because I checked it for operation as it does work properly or so I think.

Is this electric fuel pump or manual????????? If gas is leaking internally, as you are implying, there will be no spray via power pump after waiting a few minutes. Because bowl will have to be refilled. Sould like that is what is happening???? The automatic choke shoud stay open for several minutes after being complete warmed up. Mine stays open for hours. It is easy to examine. I removed one of mine. Here in Florida, they are not really necessary in summer months. If electric fuel pump, you have more nighmares. I do!!!!!!!

 

[bterrell]

Re: Mercruiser 5.7 carbureted hard start

No this is a manual fuel pump. I've somewhat narrowed it down to a lack of fuel. I'm going to put a block inline with the fuel supply and install a fuel pressure gauge. See if that tells me if pressure is dropping and on what side it is dropping. If its fuel pump it should drop if its carb side the needle should keep pressure up if the carb isn't leaking

 

[Bayliner 2455]

Hi bterrall I have the exact same engine with same problem
did you end up finding what the problem was

 

[GA_Boater]

Hi bterrall I have the exact same engine with same problem
did you end up finding what the problem was

bterrell; Last Activity: October 18, 2013 5:19 PM

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