Rochester 4 barrel flooding

Check the needle & seat seal - use the Cliff Method - hand held vac pump plumbed into that 3/8" inverted flare fitting in the front of the carb.

Air expanding - possible - but from where??? have to be on the suction side or it'd be easy to smell the leak. If large enough, it won't deliver any fuel to the carb. Could use a piece of clear hose with the fuel pressure gauge hookup. Just get something that will tolerate the fuel.

Kind of curious about what changes when "up on the hill (& on the hose)" when it runs ok to when it floods - tilted?

DD - I've never seen anything other than the spring loaded outlet valve that sets the output pressure level. My old materials book indicates springs usually fatigue (k constant is reduced over time and cycling)....only way I could see the pressure increasing would be to corrosion, over time, lifting up the spring cup and compressing it.

makomark said:

Air expanding - possible - but from where??? have to be on the suction side or it'd be easy to smell the leak.

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Exactly. If it were on the pressure side, it would not suck air. It would spit fuel. On the suction side (everything before the pump, and possibly parts of the pump) it would be possible to suck air into the system and you would have no idea other than, quite possibly, the problem he is having. A small amount of air being sucked in may go unnoticed indefinitely.

I am not dismissing the needle and seat idea, but it just does not sound right based on the symptoms he is describing, IMHO. I was thinking as you are in, "what changes when it runs okay to when it floods..." and I just cannot figure anything that would cause a seal that initially holds to start leaking, then hold again after the engine has cooled, unless whatever the seal is holding has increased in pressure. I went from this to, "Now why would the pressure increase only after the engine has been running for a while?" Air expanding is the only logical thing I can think of.

My only concern with testing the needle and seat is the seal holding initially. He would almost have to run it until it floods out, then quickly test the seat while it is still in flood mode. Know what I mean? If he were to test it cold (engine running fine), it would likely test good I would think.

makomark said:

Kind of curious about what changes when "up on the hill (& on the hose)" when it runs ok to when it floods - tilted?

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That is one of the reasons I keep thinking it has to be something temperature-related; but what can be altered, or damaged from temperature, and essentially fix itself once cool? Even if temperature is not the trigger for the problem, what can basically "heal" itself every time the engine sits for a while? Definitely a strange one here.

I'm not sure its temperature related. It seems to be related to running at higher RPM for a period. Leaving the engine cover open doesn't help/hinder.

On the hill, the boat sits about the same angle as it does in the water at idle- it warms up 100% in 10 minutes - I've run it for 30 minutes at a time - no problem. I can also put the boat in the water and idle around for a long time with no problem.

Could the spring on the internal regulator of the fuel pump corrode due to water possibly pulled past the fuel/water separator (it fills quickly with the ethanol in the fuel - and the boat sitting). A corroded spring would allow the pressure to climb.

I'm also now suspicious of the sender for my FloScan. Could it be corroded and allowing air bubbles? I can plumb around this.

I'll have time to try some things Thursday ...

another quick check you can do is to use the "straw trick" to monitor the float, in the carb, to see if it is sagging.

Take a standard fast food straw and cut it ~ 3" long. insert it into the forward vent tube. Its bottom will sit on the float. Mark the UP position after the engine is running and the bowl is full. It will oscillate as the float opens and closes the needle. If it drops when the flooding starts, you'll have a bit more insight.

PS - haven't done this in a little while so I can't say how long today's "plastics of choice" survive with modern fuels.

I thought the front vent tube just gave access to the Power Piston?

It is a float problem. Either your needle and seat is leaking or your float is taking on fuel. If it's brass....replace it. Fuel can weigh just enough to keep it from floating wich will keep it from shutting off. it runs fine on the hill because the angle shuts the fuel off sooner. To test needle and seat Invert the top of carb with float in place while its apart. Blow into fuel inlet. Thers should be no air passing by.

Rvrcruiser; not a bad idea. reply 12 indicated the brass float was dry, BUT, my 15hp merc last year had this issue and it was the float. When i took the carb apart, there was only a drop or 2 of gas inside. I tried to solder it, FAIL. Anyway, at this point, I think I would replace the float too.

Gentlemen,

I will check the float again. It looks fine and was dry last time I took it out (1 week ago), but good to scratch potential problems off the list.

FYI - I haven't pulled the entire carb off since I installed it 5 years ago. Testing inverted makes senses, but will require a little more work (2 bolts and few linkages).

Can't get to it until Thursday ...

Mack:

I checked a casting on the bench early this morning. You are right, you can't measure the float via the front vent hole. You need to use the vent hole at the back of the primary bore, where the trailing edge of the choke plate is, to access the toe of the float.

Roger that. I'll "test dip" the straw in fuel to see if the ethanol eats it.

Something else to consider. When I took mine apart then put it back together it ran ok when I put it on at 1:00 pm at lunch. I went back down to the boat at 7:00 and started it up and it was flooding. I wonder if there is a pinhole leak in the float. It was dry for the 10 minutes I had it running then filled with gas over the afternoon. I guess the brass float test is to place it in hot water and look for bubbles. The hot water will cause the air to expand in the float and bubble out.

The float is fine. I can leave it it all day after running and it run fine. Just when I run it up to 1,500 RPM or so for 3-5 minute does it flood.

If I tart it and run it at idle, she'll idle (with occasional rev as well) all day.

Does the carb seem HOT when it floods? Just a wild guess that the exhaust crossover below the carb is passing too much hot gas, making the fuel boil in the carb. It seems heat is the issue, somehow making either the level to rise, or boil out. Is there a thick/insulator gasket below the carb?

My oh my, such a simple problem got so many diffrent answers!???? If the carburetor is fine, you have to change the fuel filter, that goes in top of the fuel pump!!! If this fuel filter has the return line obturated, or has no return line at all, you get a flooding carburetor!!! It is no philosophy!! Many people change this filter, which the original has two outlets, one that goes to carb and the other that return to the fuel tank, with a simple one, much easier to find and much cheapper, who has no return line!! When they do that, the flow and the pressure from the pump is just to big to be handle by the needle and you choke the engine, when you rev it up to 1500RPM!!! I have an 1968 Caddy Eldorado, with 4bbl Rochester carburetor and I tune maybe 30 or 40 carbs like this, on old US cars! If you do not install an fuel filter like this, you may change a thousand carbs, you still have this problem!! My fuel pump is mechanical and I mesured when I intended to change it with an electrical one! At 5000RPM the pressure was almost 18 PSI!! The needle can hold back more than 5psi!! So they install this filter with one inlet and two outlets, just to lower the pressure in the carb!! When the needle close, the fuel return to the fuel tank! When opens, is the same thing when you install a tee in the middle of one hose, who has the other end open!! You get water from that tee, but you could also hold it with your finger, if you want to!! Your finger is the needle!!
Try to verify this and you will see that I am wright!
Don't ever change your Rochester with any other carb, because theese are the best!!
Good luck!

Are the floats a plastic composite??? If so, test them for weight and fuel absorbsion. Try to float them in a pan filled with gasoline.

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