4.3L Mercruiser - Hot Start Issues / Flooding

[apexsearay]

This appears to be a very common issue (given the number of forum post's on the
topic), and from reading them I have learned allot. But I still have some questions
and I'm hoping that the experts can help me eliminate some subsystem's. This could be a long posting unfortunately.

1990 Searay 180 Bowrider, 4.3L, Alpha 1
2 Barrel Mercarb 3304-9565 rebuilt with:
Sierra 18-7098-1 carb kit, float kit 18-7202, spring needle valve

My engine starts great when its cold and runs well
(I know that "well" is a relative term) on the first run of the day. But after it's
hot, particularly after pulling a tube or skiing, it will stall when I pull the throttle
back into neutral. I can cruise at a low RPM while hot and it runs well, but once I cross the threshold into neutral, it will stall and if I don't re-start it immediately, I'll have to wait for hours. Inspected the carb and gasoline was dripping from the venturies at a steady rate - so I assumed it was flooding. I rebuilt the carb with a Sierra kit (spring needle valve) and new float kit as well. After re-installing, dripping continued so I changed to the solid needle, no change. Went back to the spring
needle and took extra care to adjust the floats correctly (14mm). I soaked the carb
in Gunk Carb Cleaner but not overnight as has been suggested (the instructions
recommended against extended soaking so I stayed conservative) and then blew it out with compressed air. The result of the rebuild: slight drip remains and once it has
hot stalled, even opening the throttle plates full (WOT) does not help. In general, I'm
not convinced that flooding is the whole problem, because WOT should help, so I'm hoping to eliminate some variables.

1) Does this sound like a flooding issue? I've read that not every carb can be rebuilt so I may need to order a rebuilt carb rather than rebuild myself
2) Does setting the float lower than instructed (to reduce the level of gas in the bowl) have any benefit? I can't see how that would be helpful but I'm open to idea's.
3) I made sure the pin holes in the ventury cluster were blown out and clear, so I
tried to eliminate siphoning from the bowl as a root cause.
4) When idling, should any gas at all be dripping from the venturies? I'm not sure how
the idle circuit works, but mine has slight drip at all times (when hot).
5) Should I target the mechanical fuel pump to ensure it is not exceeding 6 psi?
I don't have a pressure gage but if it's a likely problem, I will get one.
6) Given that holding the throttle wide open does not help, could it be a lack of fuel?
7) Should I target the ignition coil by jumping directly from the battery to the positive side of the coil? Not sure that the coil is heat sensitive.
7) Should I target the solenoid or the starter? Also, not sure they are sensitive to high heat.

I know this is long, but I've read too much and I'm getting wrapped around the axle. I think that eliminating sub-systems is my only choice now. The card was low hanging fruit but I'm not really made any progress.

Thanks so much

 

[apexsearay]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

After reading my post, see that I failed to mention that the choke is operating correctly. It opens slowly as the engine heats up and remains open at all times while running.

 

[hbmtr]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

well you definitly have a flooding issue,which long been a problem with the mercarb.if you have fuel coming out of the venturis at idle your float level is probaly to high.the idle curquitsits below the the throtttle plate/valve.
make sure your engine compartment has good venting as this will lower under hood temps.
one of the issues you are probaly experiencing is the fuel percolating/boiling in the bowl defitnely when hot or after shutting down after a hard run.make sure you are not over propped.you can cool the carb down by opening up engine hatch after a run and see if this helps.what are your out side temps?

 

[apexsearay]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

Thanks for the response hbmtr! Temperatures here in North Carolina are pretty toasty, usually in the 90's when we are out on the water. And this really seems linked to the heat because I can run the engine with muffs in the driveway for extended periods with no starting problems. Based on your response, I should see NO gas in the carb barrels when idling, so the first thing I will try is to lower the float - will lower it 3mm (1/8" to start). How likely do you think it is that I just need to replace the carb? I read a post where it was estimated that its a 50/50 shot that I can rebuild vs having it done by a pro. I also forgot to mention earlier that the throttle plates are in great shape and adjusted well. No play in the bushings and they are flat.

 

[hbmtr]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

if you can afford it buy a new carb. todays fuel is reeking havoc with a lot of older product.your temps in the 90"s are not helping though.buy a marine replacement not a car carb!
you can try to lower float level just make sure to lower a little at a time as this will have a big effect at wot. glad i could help
regard hbmtr

 

[apexsearay]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

What I don't understand is how it can still be flooding after the rebuild. There is only 1 way for gasoline to enter the carburetor (through the needle valve) and that is a new assembly. So that leads me to believe that I may have higher that 6 PSI fuel pressure and blowing by the needle. But I just can't see how a mechanical fuel pump can create higher pressure over time, so I did not target it as a reasonable solution. Also, if I am flooding, why doesn't opening up the throttle plates (WOT) clear that condition and allow the engine to start I wonder? Am I over thinking this? I have a tendency to do that..........thanks

 

[hbmtr]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

how long are you cranking engine for at wot ? some time it can take as long as a 20 seconds to start if you have original fuel pump im sure it is not over pressuring carb.net time you are out on the water pull the flame arrestor off after a run with engine off and inspect the venturis ck with a flash light if its flooding you will see it.
hope this helps hbmtr

 

[apexsearay]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

I have a tendency to crank the engine TOO long while at WOT and have run my brand new battery down twice so far. I gathered some more information from some other postings and have a plan for today: 1) charge battery to full 2) lower the float about 3mm to see if I can prevent the flooding 3) clean the battery cables back to ground and back to the starter to ensure full voltage getting where it needs to be 4) prepare to run a jumper with switch from the battery + to the coil + to rule out a bad solenoid, or I may just use a screwdriver to make the connection directly at the solenoid. Will post with my results. Thanks!

 

[apexsearay]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

Well, things appear to be going well - in the driveway with muffs on anyway. Yesterday I pulled the carb apart again, adjusted the float down about 3mm from the specified 14mm and after running it in the driveway there is no more dripping. And believe me, I've been watching that silly drip from the venturies all too long. We'll see what happens when I get it out on the water but so far so good. I also cleaned all of the obvious electrical connections: battery terminals, all connections on the starter, all connections on the solenoid, the main ground connection and the coil. And this was a biggie, while re-installing the + wires on the coil, the brass terminal broke off - which forced me to replace it - which I kinda wanted to do anyway but did not want to just start replacing things for no reason. Whether it was a bad terminal or just an old coil, or some of the other electrical connections as the culprit, it fires up now every time. And when I turn it over, its allot stronger turning and you can hear it firing early and often. In the past, when it was hot, there was no hint of it wanting to fire, just lots of cranking.

So, out on the water today it goes and I'm optimistic that we solved this problem. I think I still need to dial in the idle mixture too, but with it firing up strong, that should be a piece of cake. Thanks for your feedback hbmtr, I'll check back once I've got more news.

 

[chewwy45]

Re: 4.3L Mercruiser - Hot Start Issues / Flooding

I had the same problem over the past three days. I have a 4.3L Mercruiser motor and the carburetor was flooding excessively. I rebuilt the carb to no avail. Today I raised the float from 14mm to 11mm and re-installed the carb. It fired up after 10 seconds of cranking. Aside from adusting the idle screw the motor runs like a top!!!! To all of you who are having issues with flooding please try this first. Unless there are serious issues with you carburetor this will remedy the flooding problem and.......on the water you'll be!!!!!!!!!!!!