Carb Problems

Hello every one posting for the first time

Got a 460 in a 1977 Jet boat

Just Purchased a Summit racing 750cfm electric Choke carb. The reason I purchased this new carb becuase last time I towed my boat to the river, I get to the lake and I go to turn it over and fuel is shooting out of the vent tube (600cfm Holly marine carb) Carb looked pretty fucked up plus luck would have it a piece of the vent tube busted off and fell into my intake, hense the new carb i purchased. Now the new carb is doing the same thing I have checked the fuel pressure on the fuel line and Replaced the Needle and seat for good measure but even with the fuel line off and the fuel bowls full of fuel still its getting pressure and blowing it out the vent tube. Talked to every one i know plus Summit tech support and were all stumped...I would have jumped to the radical conclusion of mabey the timming chain jumping teeth and now compression comming back up the intake but summit says thats not possible and it shouldnt do that threw the vent tube, now if it was comming up past the booster cluster possible.

Stock intake motor is prob 99% stock havent dove into it much.

Dirt in the Fuel system.

Thanks but not really possible with a fuel filter and a water/fuel seperator.....and how does that relate to fuel being shot of of the vent tube....so what your telling me is dirt is creating pressure to shoot out the vent tube with even the fuel line off.

Dirt can, and will, hang open the needle and seat. What kind of fuel pump? Did you properly set the float height and adjust the needle and seat after?

Like John B said, Fine Grit and stuff can and does get thru the filters and seperators, you need to clean out the tanks every now and then, epsecialy on stuff that sits alot.

The contamints can also come from degrading hoses, Tanks, Lines and the carb itself depending on the fuel and age of the components.

fattboy123456 wrote:.................................. but even with the fuel line off and the fuel bowls full of fuel still its getting pressure and blowing it out the vent tube...............

Can you explain this? If I understand it correctly you are stating that even with the fuel supply disconnected from the carb it is still blowing fuel out of the vent tube?


This sounds impossible...

Yes with the Fuel line disconected its still shooting Fuel out the the vent tube from the bowl. Trust me bad fuel is not the problem, that fuel is less than a month old plus the boat is used all the time with only fresh fuel. so please stop sugesting its fuel Yes Needle and seat are new , float levels are correct, fuel pressure is correct and its doing it with multiple carbs.....


Seriously dirt..

Standard Mech fuel pump for that year nothing special and have dialed the pressure down to as little as 3psi still does it

No fuel line = no fuel pressure, so how is the fuel shooting out the vent... If you disconnect the fuel line and you still have fuel shooting out the vent where is the fuel supply coming from. Can you post some pictures so we can see what we're working with.

What parts were changed that resulted in this happening? I'd go back to basics on it. Carb, engine and fuel only. Disconnect and cap any vacuum lines going to the engine or elsewhere. Only hook up the fuel supply and go from there...

How did you check the floats? Did you remove the sight plug and lower the fuel level until fuel just starts to trickle out of the sight plug hole? If you pull the sight plug and fuel pours out the float is adjusted too high.


And seriously yes... dirt can play hell with needle/seats. Especially when you deal with 7-9psi of fuel pressure and flow large volumes of fuel through a race engine...

Trust me I understand your confusion as am I this is a jet boat....there is no vacuume lines hooked up and yes Im as baffled as you are that with the fuel line is not hooked up and me turning the starter over fuel is STILL spraying out of the vent tube from the bowls....yes the floats are set and working correctly not sure where or how pressure is comming up or to the carb

Did this just start out of the blue? Run bad last time out before this started happening?

Will it start up and run if you ran a long hose off the vent to keep the fuel from going down the venturi and flooding the engine?

Sounds to me like the exhaust valves are not opening.

does it pop or catch on fire?

Nope worked fine 2 weeks later took it out shooting fuel out of the carb

Curt wrote:Sounds to me like the exhaust valves are not opening.

x2 on the valves not opening. compression will push back up and thru the t slot channel and or the idle circuit right into the bowls.(jump timing
Lifters not pumped up,collapsed etc)I had an oil pressure problem cause same deal not very long ago on a small block.

I'd check the timing then... Sheared the cam dowel pin?

Well it was a fun ride I figured out what was wrong the fucking ass hat at the autoparts store was supost to sell me a reverse rotation starter and he just sold me a standard one......
Boat is working perfectly now

jbozzelle wrote:No fuel line = no fuel pressure, so how is the fuel shooting out the vent... If you disconnect the fuel line and you still have fuel shooting out the vent where is the fuel supply coming from. Can you post some pictures so we can see what we're working with.

What parts were changed that resulted in this happening? I'd go back to basics on it. Carb, engine and fuel only. Disconnect and cap any vacuum lines going to the engine or elsewhere. Only hook up the fuel supply and go from there...

How did you check the floats? Did you remove the sight plug and lower the fuel level until fuel just starts to trickle out of the sight plug hole? If you pull the sight plug and fuel pours out the float is adjusted too high.


And seriously yes... dirt can play hell with needle/seats. Especially when you deal with 7-9psi of fuel pressure and flow large volumes of fuel through a race engine...

Lol.

What does "reverse rotation" mean?

crittersf1 wrote: What does "reverse rotation" mean?

it meas instead of turning your engine clock wise it will turn it counter clock wise, anotherwards backwards

Just work in reverse of your own symptoms ... what can cause a positive pressure in the fuel bowl or intake manifold ...?
Somewhere within that question is your answer.
Turning the engine backwards from the way it is supposed to run is one of those.

By the way ... you never mentioned anything to us about also changing the starter just before this started happening ... you might have received the correct answer if you were forthright in the first place.

the Coug wrote:

crittersf1 wrote: What does "reverse rotation" mean?

it meas instead of turning your engine clock wise it will turn it counter clock wise, anotherwards backwards

Just being sarcastic!

Right the reason being that my starter was located in the back of the bell housing not in the standard location under the exhaust ports

Reading this is sounds like the engine was running in reverse rotation? Can you really do that?

yep