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DonziDan16
07-13-2013, 10:30 AM
So close to having my boat ready for the season (finally)! Among other things, I rebuilt the carb this year. 2bbl Rochester on a 4.3l. It runs great at speed but when I come off plane, it loads up with fuel, chokes itself out, and won't restart. This was happening before the rebuild too. I've checked and rechecked the float settings (height:17/32, drop:1 3/4). Double checked the needle valve. What else could be the culprit?

Sidney073
07-14-2013, 06:27 AM
If the float settings are from the rebuild kit instructions they could be too high, automotive applications don't need to consider the angles that marine applications do. When coming off of plane the carb could be at such an angle that the fuel in the float bowl is flooding the engine via the vent/overflow tube. One way you could check this would be to place a long enough piece of tubing over the vent tube with the flame arrestor off to run into a catch bottle, and see if this both solves the problem and results in fuel in the bottle. Be sure everything is secured safely so it doesn't spill onto the exhaust or anything that could cause a fire.
Some of the more experienced people on here may have the Donzi or marine carb specs. On my Classic with a Holley I set the float level at the normal level, just a trickle out of the sight hole, and don't have a problem.
Hope this helps,
Sid

joseph m. hahnl
07-14-2013, 09:02 AM
Fuel pump diaphragm rupture. Pop of the spark arrestor and look to see where the over flow tube goes from the fuel pump to the carb. If it is ruptured fuel will pour out the tube into the carb. "Stop running it, if it is" replace the fuel pump and change the oil Immediately :eek: . There is a threaded hole in the front of the engine that goes through to the fuel pump rod, if you neck down the tip of a 2" long *** "3/8-16 bolt" about an 1/2 inch down removing all the threads. you'll finger tighten it in the hole to hold the fuel pump push rod in place while you replace the fuel pump. "do not use a wrench to tighten it", as the rod is a bearing surface and you don't want to be marring it .

The trick is not to let the rod slide down with the bolt. If it does, a strong small magnet with a finger chain will help slide it up while you stick your finger under to push it back up.


PS:*** the bolt 3/8 -16 :crossfing: some people don't relieve the tip but you only have one shot at it, and then it becomes a can of worms :redface:

MOP
07-14-2013, 09:49 AM
I go along with the float level issue or possibility of a choke issue, if the diaphragm was ruptured it would pour fuel all the time.

joseph m. hahnl
07-14-2013, 05:21 PM
I go along with the float level issue or possibility of a choke issue, if the diaphragm was ruptured it would pour fuel all the time. A rupture will clean out at top end and flood foul at mid and low rpm. just a guess though:D

wwahl
07-14-2013, 06:13 PM
I had this exact same problem. I installed a new fuel pump that was mis-manufactured. Replacing it with yet another new fuel pump resolved the issue. It sure fouled out the spark plugs.

biggiefl
07-14-2013, 08:53 PM
Vapor lock?

DonziDan16
07-14-2013, 09:15 PM
Float settings were good...finally found them after getting my hands on a copy of the service manual

I made a slight carb adjustment today and took the boat out with high hopes... Same problem. I managed to get it started again after it flooded out and it continued to dump gas as if it was a fuel pump diaphram problem (not sure if it was coming from the overflow tube or not). I eventually shut it off because it wouldn't stop dumping.
The only thing that doesn't make sense to me is if it is a fuel pump problem, why can I idle around perfectly fine on a cold start up? It's only after getting up on plane and trying to come back off again that I start having issues.

wwahl- Did you experience flooding upon cold start up idle? Or did you also only experience flooding after cruising?

DonziDan16
07-14-2013, 09:19 PM
Vapor lock?

I think vapor lock would cause the opposite...fuel not getting to the carb

dsparis
07-14-2013, 09:46 PM
Water logged/fuel saturated float ?

DonziDan16
07-14-2013, 10:31 PM
Water logged/fuel saturated float ?

Float is new

CHACHI
07-15-2013, 07:01 AM
Change your oil.

Ken

dsparis
07-15-2013, 10:07 AM
Fuel pressure too high pushing fuel past needle and seat ?

DonziDan16
07-15-2013, 12:52 PM
Change your oil.

Ken

Oil was recently changed....but I'm curious- how would needing to change my oil be related to the problem I'm having?

CHACHI
07-15-2013, 03:29 PM
The extra fuel you are dumping into the engine goes past the rings and dilutes the oil.

It doesn't help this problem, it prevents future ones.

Ken

MOP
07-15-2013, 04:29 PM
If you idle OK then it is not dumping fuel all the time, next time out and it dies pull the breather and see if the choke is full open.

joseph m. hahnl
07-15-2013, 08:55 PM
Float settings were good...finally found them after getting my hands on a copy of the service manual

I made a slight carb adjustment today and took the boat out with high hopes... Same problem. I managed to get it started again after it flooded out and it continued to dump gas as if it was a fuel pump diaphram problem (not sure if it was coming from the overflow tube or not). I eventually shut it off because it wouldn't stop dumping.
The only thing that doesn't make sense to me is if it is a fuel pump problem, why can I idle around perfectly fine on a cold start up? It's only after getting up on plane and trying to come back off again that I start having issues.

wwahl- Did you experience flooding upon cold start up idle? Or did you also only experience flooding after cruising? it Could just have a small hole and takes a little bit to get up there. Easy Diagnosis, find the tube disconnect from carb see if gas comes out when it's running. Probably should use something to catch the gas:tooth:

Oil change is crucial after a rupture smell the dip stick for gas:boggled:

wwahl
07-15-2013, 09:35 PM
it Could just have a small hole and takes a little bit to get up there. Easy Diagnosis, find the tube disconnect from carb see if gas comes out when it's running. Probably should use something to catch the gas:tooth:

Oil change is crucial after a rupture smell the dip stick for gas:boggled:

Won't it evaporate?

CHACHI
07-16-2013, 06:54 AM
Yes the fuel will evaporate, it will even evaporate faster when you run the engine and get some heat into the oil, but why
take the risk. When the fuel washes down your cylinders and you go to start it, it will be a "dry" start and once you are up and running with thinned out oil, the oil cannot offer the film strength and your rings fall thru the oil film, and the diluted oil cannot offer the cushion of oil on the bearings etc, etc,etc..

Short answer, you do not want a solvent in with your engine oil, expensive things can happen.

Ken

DonziDan16
07-16-2013, 05:01 PM
Thanks for all the suggestions guys! Next time out I will check the choke, check the overflow tube, I'll also put a pressure gauge on the fuel line so I can monitor any changes there. Won't have any time to work on things until next week, but I'll update the thread with my results.

Ken, good to know about the oil. I'd hate to have a BIG problem on my hands!

CHACHI
07-17-2013, 06:57 AM
Dan, no problem. we are all here to help.

Ken

wwahl
07-17-2013, 06:31 PM
Yes the fuel will evaporate, it will even evaporate faster when you run the engine and get some heat into the oil, but why
take the risk. When the fuel washes down your cylinders and you go to start it, it will be a "dry" start and once you are up and running with thinned out oil, the oil cannot offer the film strength and your rings fall thru the oil film, and the diluted oil cannot offer the cushion of oil on the bearings etc, etc,etc..

Short answer, you do not want a solvent in with your engine oil, expensive things can happen.

Ken

My setup has a pre-start pressurized oiling system. I guess it was meant to handle the straight 40 weight titanium oil the engine requires. I think it took care of the problem you have described. In my case the gasoline flooding was really short and the oil brand new.

CHACHI
07-18-2013, 06:52 AM
My setup has a pre-start pressurized oiling system. I guess it was meant to handle the straight 40 weight titanium oil the engine requires. I think it took care of the problem you have described. In my case the gasoline flooding was really short and the oil brand new.

Titanium oil?

Ken

GeneD
08-12-2013, 06:24 PM
If you have one idle mixture screw, you have a MerCarb. This 2 bbl carb is the scourge of mechanics nationwide.
The problem you are experiencing is very common with these carburetors.
The power valve gets stuck in the open position, and dumps fuel into manifold. You need to talk to a carb shop and somehow get them to do something with that valve. If you're not afraid to remove the air horn (top of carb), do so and you'll see the valve. It rides in the carb body up and down. I haven't taken one apart in a while, so I'm a little rusty on what it looks like inside. Engine vacuum pulls the power valve down at idle, and it stays there until you open the throttle and then it rises to allow more fuel through the main jet(s).
I had one on my engine for a bit (before I got rid of the engine), and it flooded constantly. Always when I turned motor off, and tried to restart. I had to remove the air horn and free the damn valve up. Then it would restart and work good until the next time I turned motor off and had to do the whole thing all over again.
This happened so many times to one client, and the carb went back and forth to the rebuilders numerous times. Finally he got rid of the carb and bought a refurbished one. No problems after that.
I guarantee this is your issue.

DonziDan16
09-15-2013, 01:05 AM
Between starting up school again full time and last minute trips, it has been a while since I've had any time to spend on my boat...which kills me since Fall is coming fast. BUT I'm happy to report I spent all day boating...on my boat! :kingme:
I checked the fuel pressure last week...seemed a little high but nothing out of range. Took a second look at where the gas was dripping after shutoff. and it was not from the overflow tube, but from the carb itself.
Gene, I took your advice. Ordered a remanufactured carb and she's running beautifully:worthy:I always thought the power valve was suspect, but couldn't figure out what would make it stick open, and therefore dismissed it. Glad you chimed in!
A big thank you to everyone else for their input for helping me track down the problem. After so many issues and being out of the water for 3 years, I'm a pretty happy camper :biggrin.:

joseph m. hahnl
09-15-2013, 07:10 AM
:propeller:Those Dang Power valves:tongue: . They are a great thought:confused:, But just something else to fail:doh:. Nice call:yes:!