Holley 4160 600cfm Carb flooding / drips gas - Mercruiser 4.3

[jm999]

Hi all. More boating, more problems :faint2:

I have a 1989 Mercruiser 4.3 that was rebuilt with a Holley carb (the carb is about 2 years old). This past weekend it started running super rich. Black smoke, stalling out, strong smell of gas in the exhaust, and when I looked at the carb it was dripping gas from the bottom of the secondary diaphragm that hangs out from the carb (sorry, very much a carb newb). There was also some smoke jetting out of an outlet on the left. Took it home and removed and inspected the mixture screws and they're good. Reset them to the standard 1.5 turns out from lightly seated and tweaked them from there while the engine was warmed up. Ran fine for a bit. Once back on the water I began having the same issue after I had opened the throttle up quite a bit. It didn't seem to mind idling around below 2000rpms.

I read around and found that you can clean the needle and valve seat and that can take care of flooding if you're lucky. I'd like to do that but I don't see where the needle/valve seat are accessible. My carb looks just like

this one, minus any choke.

Do I need to remove the secondary float bowl to do this? I'd really prefer not to if possible. Guessing if I did, I'd have to get new gaskets, etc... The carb is only 2 years old. Would hate to tear it open. Thanks for any advice.

 

[Bondo]

The carb is only 2 years old. Would hate to tear it open.

Ayuh,.... It's about Quality of fuel, not time passed by a calendar,.....

If there's junk in the fuel, 'n it gets to the carb, ya gotta tear it down, 'n rebuild it,....

Merc don't run Holley carbs,....

Quadra-jets way back, 'n Weber AFBs later,...

There'll be a Holley guy or 2 along I'm sure,....
Volvo has run Holley's,...

 

[jm999]

Ayuh,.... It's about Quality of fuel, not time passed by a calendar,.....

If there's junk in the fuel, 'n it gets to the carb, ya gotta tear it down, 'n rebuild it,....

Thanks, definitely some common sense there. I guess I'm just hoping there is something simpler I can try before ripping it apart in the 1 year I've owned the boat it has run great and I've only fueled it with ethanol-free gas. But I can't vouch for the previous owner. I'm guessing there is probably some crud

 

[Scott Danforth]

A Holley is as complicated as a toilet. Two floats, 2 mix screws, 4 jets, a power valve (vacuum operated enrichening valve) and an accelerator pump with a few small fuel circuits that are easily fouled by dirt and crud.

If your bowl gaskets are blue, they are even reusable.

Bondo is correct, Mercruisers didn't come with holleys. Your motor was moded.

Before you go pulling the carb, make sure the clear hose from the fuel pump to the spark arrestor doesn't have fuel in it

 

[alldodge]

I would suggest first, pull the filter and dump the contents into something you can see if anything is in there besides fuel.

Next remove the fuel line and rinse it real good. Clean and rise the filter housing. Pine the filter with some clean (make sure its clean) gas and install ne filter.

Now remove the main fuel bowl by removing the 4 bolts. Have some rags to sop up the gas. With the bowl off remove the float and needle valve and inspect real close. My guess is you got a spec of dirt in there and it got caught in the valve and seat.

If the needle valve and seat look real clean and not deformed, reinstall and put the bowl back on. I have removed and replaced the bowl a few times while replacing jets, and they can be reused if your careful taking them off.

Tighten the bolts down just a good snug, don't over do it. I like using a nut driver, not a ratchet.

Fire it up and see if it stops dripping, if not, its rebuild time

 

[jm999]

Thanks for the advice everyone. I'll give these things a shot and see how she goes.

 

[jimmbo]

Hi all. More boating, more problems :faint2:

I have a 1989 Mercruiser 4.3 that was rebuilt with a Holley carb (the carb is about 2 years old). This past weekend it started running super rich. Black smoke, stalling out, strong smell of gas in the exhaust, and when I looked at the carb it was dripping gas from the bottom of the secondary diaphragm that hangs out from the carb (sorry, very much a carb newb). There was also some smoke jetting out of an outlet on the left. Took it home and removed and inspected the mixture screws and they're good. Reset them to the standard 1.5 turns out from lightly seated and tweaked them from there while the engine was warmed up. Ran fine for a bit. Once back on the water I began having the same issue after I had opened the throttle up quite a bit. It didn't seem to mind idling around below 2000rpms.

I read around and found that you can clean the needle and valve seat and that can take care of flooding if you're lucky. I'd like to do that but I don't see where the needle/valve seat are accessible. My carb looks just like this one, minus any choke.

Do I need to remove the secondary float bowl to do this? I'd really prefer not to if possible. Guessing if I did, I'd have to get new gaskets, etc... The carb is only 2 years old. Would hate to tear it open. Thanks for any advice.

Dripping from the secondary diaphragm? Not possible. Maybe the secondary side is flooding and fuel is leaking out from the throttle shaft? If so, is this even a marine carb? Do the bowl vents look like the ones in the picture?
The needle and seat are accessible once the fuel bowls come off.
On second thought. When you say secondary diaphragm, you are referring to the big roundish shape at the top of the picture? Or by chance there is a second accelerator pump on the bottom of the secondary fuel bowl?

 

[jm999]

Dripping from the secondary diaphragm? Not possible. Maybe the secondary side is flooding and fuel is leaking out from the throttle shaft? If so, is this even a marine carb? Do the bowl vents look like the ones in the picture?
The needle and seat are accessible once the fuel bowls come off.
On second thought. When you say secondary diaphragm, you are referring to the big roundish shape at the top of the picture? Or by chance there is a second accelerator pump on the bottom of the secondary fuel bowl?

Hey jimmbo, yes, referring to the roundish housing next to the secondary float bowl. The leak drips from the very bottom of that contraption. Not a ton, but enough that it forms a little puddle on the top of the engine and scares the sh!t out of me. I called it the secondary diaphragm because I looked up a blown up view of the carb and thats what it was labeled as.

Here are some photos of the carb: https://goo.gl/photos/cAeyJxYexqNQUNTZ8

 

[jimmbo]

Ok, you said you weren't carb savvy. You say your carb doesn't a choke? are the parts just missing or was the whole air horn milled off? I am trying to determine if you have a marine carb or an auto carb. I suggested in my past post that the fuel may be running out of the carb via the secondary throttle shaft. it could look like it is coming off of the diaphragm linkage. Marine carbs aren't supposed to allow that type of leakage. Hence I suspect it might be an auto carb.

Any chance of you posting a pic of the carb?

 

[jm999]

Sorry, I edited my last post. Here are pics: https://goo.gl/photos/cAeyJxYexqNQUNTZ8

I've rebuilt the carbs on a 70s motorcycle, but had very clear instructions on how to do it. I don't have enough experience to really pinpoint problems with carbs. I guess theres no better time to learn

 

[jimmbo]

The smoke is coming out of the hole that went to the missing choke housing. It is now a manifold vacuum leak

I think the fuel dripping is coming from the secondary throttle shaft. Remove the Secondary fuel bowl... Check the float setting, check for dirt in needle/seat.

 

[Scott Danforth]

Your motor was a 2barrel that someone converted to 4 barrel

 

[jimmbo]

I wonder why the choke was removed. It certainly would make the engine a pain to start. I wonder if anything else inside the carb was modified? Normally, there is no way for fuel to ever get into the diaphragm housing or the linkage. Is there a chance the secondary fuel bowl is leaking and the fuel is making its way along the throttle body. I still recommend pulling the secondary fuel bowl, checking the needle and seat, checking float and float level. Also check to see that the secondary metering plate is securely fastened to the carb body. Use a new gaskets for the fuel bowl and the fuel bowl screws

 

[jm999]

I'm not sure why the choke was removed. It has always fired right up though. I give it a little shot of gas initially when its cold, and it fires right up (at least it used to...). Then once warm, just a flick of the key gets it going. When everything is set right, it runs amazing and has great throttle response.

 

[mainejack]

Yours is a marine carb. As I recall I've never had a Holley put out gas like yours does unless there was a needle/seat issue. You had been running good previously so that makes it even more likely, as opposed to a high float setting, which racers often use. On a 4150/4160 Holley you're above a portion of the gasket surface no matter where the fuel and float is, but you're not seeing a float bowl leak.

Ethanol fuel is not our friend. Since ethanol fuel came out I've had to rebuild summer use only carbs more often, but using Marine grade Sta-Bil helps, by at least 50% IMO. Using 1 ounce to 10 gallons costs about 8-10 cents a gallon depending on the deal you get when you buy it. It won't fix dirt issues of course.

Whoever took the choke off your carb was most likely a hot rodder or racer, it's fairly common among that crowd. The choke plate and shaft cause a small amount of restriction to air flow at WOT. I never bothered to do that for the undetectable amount of improvement it makes on the street, I prefer electric chokes, but summertime starting without a choke isn't usually an issue, just as you've found out.

The air mixture screws start at 1.5 turns out from lightly seated, but for final adjustment I use a vacuum gauge and tap directly into the manifold or other source of un-ported vacuum. Adjust to maximum vacuum at correct idle RPM. The last time I did this best vacuum happened to be at 7/8 turn out from lightly seated, but it'll vary. Both screws should have identical amounts of adjustment. I've done this adjustment by ear but I do better with the gauge.

I can't think of anything that you pointed out around the screw holes on the side of the carb that could cause a vacuum leak.

I treat all carb gaskets with silicone, even the blue ones, although they don't absorb much. It makes a big difference with the plain ones. "Reusable" is another way of saying "non-stick". Someone mentioned not over tightening screws and that's good advice.

There is an almost limitless amount of online information on Holley's, including the Holley website and You Tube. Good luck!

 

[jm999]

mainejack Thanks for the reply. I removed the secondary float bowl and gave everything a really good cleaning and put it back together exactly as it was. All gaskets are in good shape with no visible wear or cracks. Needle and seat looked good, and free of any dirt, but I know it doesn't take much to keep the needle from seating so I gave it a good cleaning anyway. Reassembled and ran in the driveway for a bit with no leaks. I ordered a vacuum gauge to tune it properly.

I also changed out my fuel/water separator and checked the gas in the old one. It had no visible debris/dirt whatsoever. I'll continue to use the non-ethanol gas down the street from me until they stop selling it (hopefully never happens).

One thing I noticed was my fuel pump seems like its surging. It seems a little louder to me than it did when I bought the boat. It doesn't have a smooth buzzing noise to it. Its uneven and when the motor is running it will sound like its 'revving' up at times. I wonder if my pump is crapping out. But generally when a fuel pump is dying, it would pump LESS fuel, correct? I may replace it anyway. Doesn't sound very good to me, but I have an untrained ear.

 

[mainejack]

jm999. It doesn't surprise me that you didn't see whatever caused the needle not to seat.

You may have a point with the pump. Your new vacuum gauge may also measure fuel pressure, they often have that feature, mine does. At least you've made some progress.