97 4.3 Mercruiser runs well, starts not so well

[newt5005]

My 4.3l Merc runs excellent,and finally have the run-on issue mostly under control (2 barrel motor). When used every weekend, starting is never an issue, and daily,on the water it preforms flawlessly.The issue is when we go 2 or more weekends without using the boat, it is extremly difficult to start. Cranking is never a problem, but the engine 'hitting' is.
It's been to the Mercury Shop 3 times for this (and the run-on issue) and the starting problem cannot be duplicated, as we eventually get the thing started on the water, and the repair shop doesn't want to park the boat for 2 weeks before working on it, for the POSSIBILITY of the issue coming up at that time.
We have tried all possible cranking / throttle stroking combinations with no consistaint success. When the motor is eventually flooded (we can smell fuel at this point) the only thing to do is wait for 30-40 minutes and it starts although still with great difficulty.
Am I doing something wrong here? We have had this boat for 4 seasons and would like to put this problem to bed.

 

[Haut Medoc]

Re: 97 4.3 Mercruiser runs well, starts not so well

Describe, exactly, in detail, what you do to start the engine after the aforementioned time period.....
It sounds like a possible choke problem, though.....JK
Oh, & take the flame arrester off & pump twice....
Is the choke plate open or closed?
Do you get a small stream of fuel spurting when the throttle is pumped?
When it is flooded, put the throttle all the way open & crank till it starts, be ready to back it down though.....

 

[Don S]

Re: 97 4.3 Mercruiser runs well, starts not so well

Sounds like you may be trying to start it like one would an EFI engine. After a CARBED engine has set for a while, it's necessary to give it a one or two pumps of the throttle to get some gas to the engine to start it.
Even after it starts a little extra throttle (Shifter in throttle only position) to keep the RPM's up may be in order until the engine warms up for.

You don't mention "when" you have this run-on problem, but if it's after a run, you need to let the engine idle for a minute or two to burn off the excess fuel from slowing down, and to cool the engine a bit. Again, this is different than EFI engines which you may not be used to operating.

Here is a Merc service bulletin you may find useful.

http://www.boatfix.com/merc/Bullet/97/97_17.pdf

 

[newt5005]

Re: 97 4.3 Mercruiser runs well, starts not so well

Thanks for the responses Will try to address both at the same time.
I put the run-on issue in because I though they might be related.It was a struggle, but now is pretty much a dead issue.
After 30 minute wait, use throttle-only, at idle or just off idle, no stroking, and turn motor over. If no-start occurs, then inch throttle foreward (very little) and turn over again. Usually starts at this point. Minor amount of black smoke, but clears up almost instantly.After waiting this long, am very hesitaint to stroke throttle, as I believe the thing has been flooded with fuel.
Going back a little, when I have felt that the engine was flooded, I had tried on 2 seperate occaisions to start it with the throttle in full open, after smelling gasoline.
I am not shy with the starter. This is where the 30 minute wait was discovered. This is how long it took to go from the dock to the parts house and come back with a fresh battery. Took the used up battery out, put the fresh on in, and the silly thing fired right up. The old battery was anything but old. I had just burned it down.
I have never checked the choke plate or the accelerator pump output visually. I can and will do that, but does it behave like an auto? Pump twice an the plate closes until heat from the riser opens it back up?Should it close when the ambient temp is in the 60's and 70's? This is the normal temp (maybe the high 50's) on the morning here in the summertime.

 

[pjrogers]

Re: 97 4.3 Mercruiser runs well, starts not so well

Newt: I have a '96 Merc 4.3 w/ 2 bbl carb. After sitting for a week or two, my engine will start on the first or second crank if I do this, and only this: Before turning the key I use the throttle's button to disengage the shift link and push the throttle lever all the way forward, right to the stops. Then I back the throttle off to neutral, and forward again until I fell a tiny bit of resistance to movement, indicating, I think, that the throttle is now giving a teeny bit of fuel to the carb. Then I turn the key, and vroom. Usually I say something like "Mercruiser Marine" in a laudatory fashion, as if to encourage continued good behavior. I have found that pumping the throttle to the stops twice will surely flood the carb, as will pushing the throttle lever much past the first hint of resistance after pumping once.
All this may be known to you, and of no assistance, but if not, it may help.

 

[newt5005]

Re: 97 4.3 Mercruiser runs well, starts not so well

Thank you for taking the time to respond. Yes, I have used your throtttle system, as well as a host of others,but with a slight modification.I have switched from the encouragement type behavior modification, past the tough-love stage right into the 'Scared Straight" type of attitude. Unfortunatly niether of these personalities have been benificial.
What it seems like is there is no fuel to be had, and the motor 'wants' a certain amount of fuel. Not too much and not too little. When ot gets just the right amount, I happen to be NOT turning the motor over, then just as it receives that 1/4 of a drop too much, BAM!!!!!!! We're now flooded and dead at the dock. Maybe this is just my ranting and guessing while my blood pressire is going back down, during the wait it out time. Will still check the choke plate and the accelerator pump output though....................
One other scenario I have encountered............... With 2 weeks between boat trips (this has happened a few times)
No throttle movement at all.( Well. I LOOKED at it, never touched it) Hit the key, it started, (right away ) stumbled, and when I s l o w l y eased the throttle foreweard, the motor died, the would NOT start, and behaved exactly as it did when I believed that it was flooded. Could smell gas, long wait,etc. Maybe this helps , maybe not.

 

[newt5005]

Re: 97 4.3 Mercruiser runs well, starts not so well

I guess it's true, all things come to tose who wait. The issue is, sometimes we do not always have the patience to completly weather the storm.
Took the boat to yet another shop. Had to be EXTREMLY specific about the problem, issues, history, bla, bla, bla. Actually, the first service writer told me that he had no clue and I should come back when the senior mechanic/ service writer was available. (not the same day)
To make this whole thing less painful to read, the boat shop acknowledged that I had a problem and they would keep the boat as long as it took to take care of (keeping me in the loop, financially).
Bottom line, I had a semi-defective fuel pump. Had voltage to it correctly, but only pumped when it felt like it. Once running, it would continue to work correctly, prohibiting a diagnosis that the fuel pump was bad.
To completly understand my frustration, see the origional post date for this thread, then add a couple of YEARS.
Maybe this could help someone. I hope so.
Mike.