The Stovebolt Site Forums The Shop Area Engine Shop carb question

I have a single barrel Rochester on a 235, After the truck sits for a couple of days,it leaks the fuel out of the carb, and back into the tank consequently hard to start. Would this be a needle and seat issue in the carb? If you start it daily, she fires right up. Any suggestions would be appreciated.

Thanks

Kevin

very usual thing, doesn't drain back to the tank [can't], it leaks and evaporates - faster starts if you pull the choke on full before you touch the starter, and if it hasn't completely dried up, a couple quick full pumps on the pedal can fire off the bit of gas left which will quickly pull enough from the tank to keep'er runnin .... of course you could just start it daily, they were designed to be used

Bill

the fuel pump should stop the fuel from returning to the tank the carb does not have anyway to prevent fuel flow out just the float closes the needle to stop over filling .


Pete

The needle and seat is higher than the fuel in th float chamber so I don't think there is any way for the fuel to go backwards.

If the fuel pump does not hold the pressure it will let air in not drain the bowl , because the line to the tank is higher than the tank at the carb .


Pete

How do you know it leakes back to the tank maybe the pump dosen't keep enought fuel to the carb to restart after a day or so to restart with out the choke. Pull the choke crank and wait for it to hit. Even with the bowel dry the fuel pump should re fill the bowel withon a couple revs to start the engine.

This used to happen to me all the time. I usually steped on the starter a couple of times before I turned on the ignition switch. This pumped some gas up into the carb. Then pump the gas a couple times, pull the choke and start her up.

This is a common situation when they sit too long between driving. The sure cure is to drive it more often.

George

if you install an AC glass bowl fuel filter just before the carb, it will act like a small fuel resevoir. Should provide quicker starts.

Thanks for the responses guys. I thought I recalled a long time ago someone saying the different types of needles in carb kits will cause this. The needles with the neopreme end, or the steel ends would not seat properly. I must have been dreaming again.

There is a check valve ,spring , in the fuel pump which does two things .
1- when the bowl is full it allows the fuel to return to the tank .
2- when You shut the engine down it holds the gas pressure to the carb
It works on the fuel pressure that the carb is rated for if it goes bad the fuel goes back to the tank and air will get into the fuel line and when it gets realy bad the engine will not run right , loss of power ,etc.


Pete

I think yer talkin about some entirely different setup Pete, there's no return line on these ol trucks, nor is there any 'pressure' in the carb, the "check valve" [needle and seat] is controlled by the float and prevents the bowl from over filling - and if there's a properly functioning fuel pump and gas in the tank, there won't be any air in the line when running

the problem with Rochesters is simply that they're leakers from new, and the bowl is vented to the atmosphere, allowing evaporation

Bill

the check valve is in the fuel pump not the carb. the pump sucks gas from the tank and than pushes it to the carb it needs a check valve in it to give it a direction in one side out the other ,otherwise it would just suck and push in both directions and go nowhere and when the carb is full it lets the gas out the inlet side of the pump so it does not develope to much pressure in the pump.


Pete

There is a check valve to allow the gas coming in to the fuel pump to go one way. However when the needle closes in the carburetor, the pump is not able to push any more through. The pump works by charging a spring and the force of the spring determines the fuel pressure.

What I thought I recalled was, that there were 2 different type of needles, the one with the neopreme end, or the other that was all steel or brass that goes into the seat. And that the weight was different so that the float let the needle rise after pressure was off for awhile and fuel drained from the bowl. Like I said before the truck fires up immediatly if you start it daily, but wait a couple of days and it will require cranking to get fuel back to the carb. After a day or so, there is no fuel in the carb. Anyway thanks for the responses.

I just read about the fuel of today compared to way back when. Todays fuel evaporate a lot quicker then the old gas and carburetors will dry out faster then they used to. Add a leaking bowl in to this, and I could see a dry carb in a few days.

Joe

add a Rochester B name to the carb and you could see a dry one overnight

mo2 - the 'pressure' is on the needle, when the engine is off there's no longer pressure - the float cannot "let the needle move", it controls it's position, as the gas in the bowl evaporates, the float sinks and will open the needle inlet - but no fuel will exit .... going dry over time is very common with that carb

Bill

Thanks Bill!

Many collectors use the inline electric pump to overcome this problem. You run the pump for a few seconds and you are good to go.

Try this article:

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstartcold

Jon.

Thank You for the info.

Kevin