Fuel dumping in 5.0 cobra 1994 mechanical pump, not electric.

[saddle816]

First time here, hoping to have a future at this site. I have a 5.0 cobra 1994 dumping fuel, no start this year. Was running fine least 3 years. I have taken carb needle and seat apart inspection of float shutoff height seems good. I blow thru tube move float and it stops. Everything is very clean inside, bowl. While cranking fuel fills bowl then pours out of vent into carb. Way too much fuel to start. My question is…can a mechanical fuel pump cause this ? Also where does the fuel get re routed to when needle closes off seat ? Is there a valve somewhere that might be not working ?

 

[Scott Danforth]

Check your fuel pressure to rule out high pressure issues

If your float isn't set right, or your carbs needle and seat are leaking it will also flood

 

[alldodge]

My question is…can a mechanical fuel pump cause this ? Also where does the fuel get re routed to when needle closes off seat ? Is there a valve somewhere that might be not working ?

Yes, but since this is the same pump that's been fine I wouldn't think so

Fuel isn't rerouted, the needle just stops all fuel from coming in

No other the the float needle. Could be the float is heavier (depends what kind of float) from soaking up some fuel, or small hole which allows fuel to leak in

 

[flashback]

There's a small hose coming from the pump to the air horn on the carb. If that's the vent you speak of then the pump is failing..

 

[saddle816]

Yes, but since this is the same pump that's been fine I wouldn't think so

Fuel isn't rerouted, the needle just stops all fuel from coming in

No other the the float needle. Could be the float is heavier (depends what kind of float) from soaking up some fuel, or small hole which allows fuel to leak in

So I think you’re saying that the needle and seat work when blowing thru the inlet port. But when fuel goes in then the float might be staying to the bottom thus allowing fuel to keep poring in ? The carb is 1 year old. Was purchased last summer and was working great until this summer. I will ck the float closer. So the mechanical fuel pump, fuel just bypasses when the needle is seated and fuel stops flowing. the pump keeps pumping xtra fuel has to go somewhere I’m thinking but you saying no ? The needle and seat stops flow from pump?

 

[saddle816]

There's a small hose coming from the pump to the air horn on the carb. If that's the vent you speak of then the pump is failing..

Not sure, will look closer. But it seems to be when the float bowl is filled it then spills out the carb vent into the throat. I’ll disconnect that hose and see if it comes from that port as you suggest While I’m cranking. something for me to try and look at closer.

 

[alldodge]

The needle and seat stops flow from pump?

Yes, fuel pumps keep pumping but no fuel moves until valve opens (float drops and needle valve open)

Think of your water faucet at home. The city water pumps keep pumping water but nothing comes out your faucet until valve is opened

 

[saddle816]

Yes, fuel pumps keep pumping but no fuel moves until valve opens (float drops and needle valve open)

Think of your water faucet at home. The city water pumps keep pumping water but nothing comes out your faucet until valve is opened

Sounds good, so the needle and seat are not stopping the flow. period. Or the pump has failed internally and is pumping too much mechanical pressure. I have some things to ck out. Thanks for info. I’m going to replace the 6 year old pump first then go from there. I will get a fuel pressure tester if I need to after I get a new pump. Does anyone know what a new pump should pump ? I’m guessing maybe 5 to 10 lbs very low pressure.

 

[alldodge]

My guess is the pump is fine, need to adjust float level so it shuts fuel off a tad lower in the bowl

 

[saddle816]

My guess is the pump is fine, need to adjust float level so it shuts fuel off a tad lower in the bowl

Well, I did take it off and blow through the inlet and it seemed like the float completely closed off when it was level I could adjust it slightly lower, but it does completely shut off when I’m blowing through it. It’s just not shutting off the fuel pressure. Apparently the pump is like I say six years old and I run up and down Lake Powell a lot with this boat so new pump is definitely in my future but of course when I replace the pump, I will have the same exact problem then I will buy a needle and seat kit and adjust that float slightly lower since that’s my only two options at this point. At least now I’ve got an understanding of how the system works. Thanks for all that input.

 

[Scott Danforth]

Check fuel pressure..... Only after you have that information can you move on to the next step in troubleshooting

 

[dubs283]

There's a small hose coming from the pump to the air horn on the carb. If that's the vent you speak of then the pump is failing..

I'm thinking the excess is exactly this. Overflow/spill tube from fuel pump is dumping excess fuel from a ruptured diaphragm into the carb

OP has mistaken the air horn inlet/tygon hose for the bowl vent?

 

[saddle816]

There's a small hose coming from the pump to the air horn on the carb. If that's the vent you speak of then the pump is failing..

Definitely not coming from the hose from pump to carb top. This is disconnected and fuel is just poring into carb. I replaced fuel pump but that didn't fix issue. Guess I’ll just replace needle and seat to see if that might do something. Like I said I blow thru inlet and then move float until it stops Air flow. Seems to be ok but obviously it’s still poring fuel when cranking.

 

[saddle816]

I'm thinking the excess is exactly this. Overflow/spill tube from fuel pump is dumping excess fuel from a ruptured diaphragm into the carb

OP has mistaken the air horn inlet/tygon hose for the bowl vent?

Nope hose has been disconnected to make sure, it’s definitely not being shut off by float needle and seat I’m guessing. I’ll try new needle and seat next. Pump has just been replaced, took me forever to get the right one. All the ones on Amazon are not direct fit.

 

[Scott Danforth]

Nope hose has been disconnected to make sure, it’s definitely not being shut off by float needle and seat I’m guessing. I’ll try new needle and seat next. Pump has just been replaced, took me forever to get the right one. All the ones on Amazon are not direct fit.

all the amazon ones are chinese junk

original mechanical pumps are Carter. under $50 from Summit Racing

test the fuel pressure. more than 7psi and you run the risk of pushing the needle and seat open.

 

[saddle816]

all the amazon ones are chinese junk

original mechanical pumps are Carter. under $50 from Summit Racing

test the fuel pressure. more than 7psi and you run the risk of pushing the needle and seat open.

Tried the carter ones from eBay but none of them are a direct fit for my boat. Marine application ones are around 100 or more depending on brand From what I can find. My particular one was a perfect fit and it was 213.00 to get a cheaper automotive application then yes 50 bucks. I would have to fabricate new fuel lines and I didn’t want to do that unless I had to. Have no fuel pump pressure tester, guess I’ll have to get one. It just act like the needle and seat isn’t working with fuel but when I blow thru it it works fine. Needle and seat is my next choice I guess. Lol this is fun.

 

[flashback]

Lol this is fun.

Yes it is, to some folks!

 

[Scott06]

Tried the carter ones from eBay but none of them are a direct fit for my boat. Marine application ones are around 100 or more depending on brand From what I can find. My particular one was a perfect fit and it was 213.00 to get a cheaper automotive application then yes 50 bucks. I would have to fabricate new fuel lines and I didn’t want to do that unless I had to. Have no fuel pump pressure tester, guess I’ll have to get one. It just act like the needle and seat isn’t working with fuel but when I blow thru it it works fine. Needle and seat is my next choice I guess. Lol this is fun.

You can get a fuel pump gauge at auto store or amazon very cheap some autoparts stores will loan or rent them. Some replacement fuel pumps are also too high in output pressure. I have seen this myself.

You likely need to replace float and needle and seat with good quality parts

Mikes carb parts has good kits and parts for reasonable prices

 

[saddle816]

Yes it is, to some folks!

Definitely fun for me. Learning new stuff. Wish I had fuel injection. So much easier to deal with for me. carbs and boats are new to me.

 

[saddle816]

You can get a fuel pump gauge at auto store or amazon very cheap some autoparts stores will loan or rent them. Some replacement fuel pumps are also too high in output pressure. I have seen this myself.

You likely need to replace float and needle and seat with good quality parts

Mikes carb parts has good kits and parts for reasonable prices

Mikes carb parts .com I’m assuming