Seem to have a bad fuel pump
09-17-2014, 01:06 AM
#1
Instructor
Thread Starter
Seem to have a bad fuel pump
If my 78 sits over night I must prime the carb or crank it for several seconds to get it to start. It seems that the gas is draining out of the carb back into the tank. I thought I might just replace the mechanical pump with an electric but I found that I have a fuel return line and I would not know how to deal with that.
Is gas draing back into the tank a common problem with the C3 vetts? Is there something needed besides a new pump?
Is gas draing back into the tank a common problem with the C3 vetts? Is there something needed besides a new pump?
09-17-2014, 05:25 AM
#2
Le Mans Master
That is a common problem on the Rochester Quadrajet carburetors. I don't think that your problem is related to the fuel pump. Contact the resident carb expert Lars here on the forum at V8fastcars@msn.com.
09-17-2014, 11:29 AM
#3
Race Director
If my 78 sits over night I must prime the carb or crank it for several seconds to get it to start. It seems that the gas is draining out of the carb back into the tank. I thought I might just replace the mechanical pump with an electric but I found that I have a fuel return line and I would not know how to deal with that.
Is gas draing back into the tank a common problem with the C3 vetts? Is there something needed besides a new pump?
Is gas draing back into the tank a common problem with the C3 vetts? Is there something needed besides a new pump?
Another option is well plug leaks; not as common on the later casting but can be fixed.
I know of two tests for it off the top of my head, both involve removing the carburetor:
1. Put a small amount of soapy water in the float bowl and shoot around the four plugs(bottom of main casting) with an air compressor blow gun. If it bubbles up, you have a leak.
2. Set the carburetor with some liquid in it on top of a piece of paper and let it sit overnight. Check for wetness.
09-18-2014, 10:12 PM
#4
Instructor
Thread Starter
That is a common problem on the Rochester Quadrajet carburetors. I don't think that your problem is related to the fuel pump. Contact the resident carb expert Lars here on the forum at V8fastcars@msn.com.
I'm going to do a search on Rochester Quadrajet here on the forum.
Edited 30 mins later
I just looked up Lars Grimsrud in Google.....the guy is a celebrity! I don't think he answers emails.
Edited again 5 mins later
He just responded to my email............(red face)...
Last edited by Rich123; 09-18-2014 at 10:42 PM.
09-18-2014, 10:14 PM
#5
Instructor
Thread Starter
What kind of fuel filter are you running? I've heard argument that if it doesn't have the checkvalve, this can allow the fuel to drain back into the frame from the floatbowl.
Another option is well plug leaks; not as common on the later casting but can be fixed.
I know of two tests for it off the top of my head, both involve removing the carburetor:
1. Put a small amount of soapy water in the float bowl and shoot around the four plugs(bottom of main casting) with an air compressor blow gun. If it bubbles up, you have a leak.
2. Set the carburetor with some liquid in it on top of a piece of paper and let it sit overnight. Check for wetness.
Another option is well plug leaks; not as common on the later casting but can be fixed.
I know of two tests for it off the top of my head, both involve removing the carburetor:
1. Put a small amount of soapy water in the float bowl and shoot around the four plugs(bottom of main casting) with an air compressor blow gun. If it bubbles up, you have a leak.
2. Set the carburetor with some liquid in it on top of a piece of paper and let it sit overnight. Check for wetness.
09-19-2014, 01:37 PM
#7
Tech Contributor
Member Since: Aug 1999
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23051 for the short filter (pre-1975) and 23052 for the long one (1975-1981).
Lars
Lars
10-13-2014, 04:18 PM
#8
Instructor
Thread Starter
Lars, thank you for the email you sent with suggestions on how to correct this.
I first replaced the old filter with a new one. This seemed to slow down the bowl drain but it did not fix it. Next I pulled the clip from the needle so it would settle into the seat when I turned off the engine. This completely eliminated the drain back problem, BUT, I opened a nest of hornets.
It seems these Q'jet carbs are not as simple as the old Hollys I have worked on several years ago. It took me forever to get the top section back down onto the carb. Once I finally got the top section down I spent the next half hour trying to get the two rods that mount to the secondaries back into their respective holes. And I can't get the choke links to hook up any more.
Anyhow I was able get it to run to see that it doesn't drain back anymore.
While it was open I saw a BUNCH of dirt in the bottom of the bowl. So I assume the whole carb is probably in need of a rebuild. I'm going to try to find someone local who is VERY experienced to do it for me.
I looked at the numbers on the carb and it appears to be the original. So even though I hope to go fuel injection at a later date, I better keep this carb in a bag for the next owner.
I first replaced the old filter with a new one. This seemed to slow down the bowl drain but it did not fix it. Next I pulled the clip from the needle so it would settle into the seat when I turned off the engine. This completely eliminated the drain back problem, BUT, I opened a nest of hornets.
It seems these Q'jet carbs are not as simple as the old Hollys I have worked on several years ago. It took me forever to get the top section back down onto the carb. Once I finally got the top section down I spent the next half hour trying to get the two rods that mount to the secondaries back into their respective holes. And I can't get the choke links to hook up any more.
Anyhow I was able get it to run to see that it doesn't drain back anymore.
While it was open I saw a BUNCH of dirt in the bottom of the bowl. So I assume the whole carb is probably in need of a rebuild. I'm going to try to find someone local who is VERY experienced to do it for me.
I looked at the numbers on the carb and it appears to be the original. So even though I hope to go fuel injection at a later date, I better keep this carb in a bag for the next owner.
10-13-2014, 04:55 PM
#9
Melting Slicks
Lars, thank you for the email you sent with suggestions on how to correct this.
I first replaced the old filter with a new one. This seemed to slow down the bowl drain but it did not fix it. Next I pulled the clip from the needle so it would settle into the seat when I turned off the engine. This completely eliminated the drain back problem, BUT, I opened a nest of hornets.
It seems these Q'jet carbs are not as simple as the old Hollys I have worked on several years ago. It took me forever to get the top section back down onto the carb. Once I finally got the top section down I spent the next half hour trying to get the two rods that mount to the secondaries back into their respective holes. And I can't get the choke links to hook up any more.
Anyhow I was able get it to run to see that it doesn't drain back anymore.
While it was open I saw a BUNCH of dirt in the bottom of the bowl. So I assume the whole carb is probably in need of a rebuild. I'm going to try to find someone local who is VERY experienced to do it for me.
I looked at the numbers on the carb and it appears to be the original. So even though I hope to go fuel injection at a later date, I better keep this carb in a bag for the next owner.
I first replaced the old filter with a new one. This seemed to slow down the bowl drain but it did not fix it. Next I pulled the clip from the needle so it would settle into the seat when I turned off the engine. This completely eliminated the drain back problem, BUT, I opened a nest of hornets.
It seems these Q'jet carbs are not as simple as the old Hollys I have worked on several years ago. It took me forever to get the top section back down onto the carb. Once I finally got the top section down I spent the next half hour trying to get the two rods that mount to the secondaries back into their respective holes. And I can't get the choke links to hook up any more.
Anyhow I was able get it to run to see that it doesn't drain back anymore.
While it was open I saw a BUNCH of dirt in the bottom of the bowl. So I assume the whole carb is probably in need of a rebuild. I'm going to try to find someone local who is VERY experienced to do it for me.
I looked at the numbers on the carb and it appears to be the original. So even though I hope to go fuel injection at a later date, I better keep this carb in a bag for the next owner.
10-13-2014, 04:58 PM
#10
Instructor
Thread Starter
I did not know he did this. I'll contact him. It runs now and I need to do a few other things while it's running but that sounds good.