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Old 10-17-2010, 10:17 PM   #1
John 65
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Default Cold start problems with rochester quadrajet. Fuel draining out of carb ?

Carb is in a 68 402 motor. It has the corect inline filter with the return line to the gastank. The 1st start of the day takes lots of cranking for a good stream of fuel to be sprayed out into the carb and finally fire up the engine. Then all day long it will start fine. Today prior to starting, I removed the air cleaner, upon working the throttle hardly any fuel comes out. No stream, just a little dribble. Its like the carb is draining itself down. A float problem ? accelerator pump ? The car runs fantastic, but gets starved for fuel when it sits overnight. Thanks in advance.
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Old 10-17-2010, 10:39 PM   #2
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Sounds like the well plugs in the main body are allowing the float bowl to drain when sitting. Common problem on a Q-jet and back in the day the well plugs would be epoxyed in place to stop the leaking. Not having been around a Q-jet in a long while there may be better fixes available.
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Old 10-17-2010, 10:54 PM   #3
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No carb guy here but I would like to try a repair on it, not real sure what the well plugs are or where they may be located, but I am guessing on the bottom of the carb if gravity has something to do with it. Are these plugs pressed in, do they have to be removed and sealed with a type of adhesive ? Thanks
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Old 10-17-2010, 11:35 PM   #4
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Quote:
Originally Posted by John 65 View Post
No carb guy here but I would like to try a repair on it, not real sure what the well plugs are or where they may be located, but I am guessing on the bottom of the carb if gravity has something to do with it. Are these plugs pressed in, do they have to be removed and sealed with a type of adhesive ? Thanks
Thinks Lars makes some mention of these plugs in his write up. I know I saw mention of the somewhere.
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Old 10-18-2010, 01:05 AM   #5
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Default Well plugs

The well plugs are a possible problem, you can check them by removing the carb and pouring an oz of fuel in the vent tube and then see if it leaks out the bottom.
Click the image to open in full size.

You might want to make sure the choke is set and working properly first.
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Old 10-18-2010, 02:14 AM   #6
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I have the same issue with mine.

Lars did a rebuild on it so I don't think it's the well plugs.

I believe I've read something about the fuel pumps can allow gas to be siphoned back if they don't have the proper check valve in them. I haven't "checked" mine, the way I figure if it's been sitting for a week or two the cranking pushes some oil into the bearings before start up.

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Old 10-18-2010, 04:01 AM   #7
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True or false: Run your Vette for 10 miles and park it. Wait 10 minutes and open the line to carb connection. If fuel comes out under pressure than the check valve is good?

You might want to request LARS papers on "Q-Jet hard starting and fuel drainback" and his how "To adjust a divorced choke".
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Old 10-18-2010, 05:04 AM   #8
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A place in CA, H-O Racing Specialties used to carry these well seal kit's, but not sure if they're even around any more. If you want, PM me an e-mail address and I'll send you a scan of the instruction's, as look's like you can easily duplicate the part's needed from the local hardware store. Mark
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Old 10-18-2010, 08:50 AM   #9
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Quote:
Originally Posted by Poppa Bud View Post
I have the same issue with mine.

Lars did a rebuild on it so I don't think it's the well plugs.

I believe I've read something about the fuel pumps can allow gas to be siphoned back if they don't have the proper check valve in them. I haven't "checked" mine, the way I figure if it's been sitting for a week or two the cranking pushes some oil into the bearings before start up.

Try clamping the rubber fuel line at the frame the next time you turn the car off , this will block the fuel from returning to the tank.
If the car starts its probably the check valve and not the well plugs.
You can also check by removing the carb , sit it on the bench , if fuel drains out on the bench its the well plugs.
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Old 10-18-2010, 02:23 PM   #10
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Quote:
Originally Posted by petes74ttop View Post
True or false: Run your Vette for 10 miles and park it. Wait 10 minutes and open the line to carb connection. If fuel comes out under pressure than the check valve is good?

You might want to request LARS papers on "Q-Jet hard starting and fuel drainback" and his how "To adjust a divorced choke".
Thank you all for your help. I just ran the car for 10 mins or so, waited a lil bit and cracked the line at the carb and it was dry. No pressure...no fuel. Starting to wonder now if it is the pump. Maybe I should just pick up another pump. Its just that the car runs fantastic. Can I assume that even if it is this check valve in the pump, that this valve does not have anything to do with performance, its mainly just for startup and keeping the pressure up till restarting. The choke works fine also. Going to remove the carb anyway and have a look. Maybe I can see fuel weeping from that wellplug area. Thx again.

Last edited by John 65; 10-18-2010 at 02:27 PM.
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Old 10-18-2010, 03:33 PM   #11
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If you're thinking of a new pump, you might consider going electric, as this will fill up the carb bowl before actually cranking. I usually run one with a power switch to stall out on an empty bowl, when parking.
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Old 10-18-2010, 07:01 PM   #12
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My '75 with a Q-Jet does the same thing. Swapped fuel pumps. Same issue.

Mine takes about 10 sec to start so I am living with it for now.
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Old 10-18-2010, 10:07 PM   #13
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Ya sounds like its pretty common. I removed the carb after it ran and noticed the inside of the intake was wet with fuel. Going to take it apart tomorrow and have a look. Thanks.
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Old 10-18-2010, 10:13 PM   #14
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I don't know if all c3s are like the 1978, but mine did something similar. I tore the carb apart-no fix. Replaced pump to carb line- no fix, then i puller the 6 inch rubber hose on top of the fuel tank off and replaced it. The car starts after sitting for months now. You can get to that hose by taking off the fuel cap and the rubber around it.
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Old 10-19-2010, 07:25 PM   #15
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Well I took the carb apart and to my surprise somebody beat me to it. They have been sealed already. At this point I hope they are leaking. I filled the bowl up and placed some cardboard under it. Now just waiting to see what happens.
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Old 10-19-2010, 07:38 PM   #16
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Did you check the rubber hose? I would never have known anything but my uncle told me to. Mine was so rotted it was crazy. Mine basically did the same exact thing. I started it with starting fluid. You could start it all day and for the next even. It kept getting worse down to under a day and it wouldnt start. Now I had it sitting over last winter and it started no problem after.
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Old 10-19-2010, 08:14 PM   #17
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My '77 QJET does the same thing. IIRC some have removed the needle seats needle clip. This prevents float raising needle and draining bowl when some fuel evaporates as car sits. Pump pressure will raise it as needed. Also there are some needle seats without slots that also prevent draining bowl completely. I have an old one from a past rebuild but have not seen any new ones. mike...
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Old 10-19-2010, 09:03 PM   #18
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Quote:
Originally Posted by shank0668 View Post
Did you check the rubber hose? I would never have known anything but my uncle told me to. Mine was so rotted it was crazy. Mine basically did the same exact thing. I started it with starting fluid. You could start it all day and for the next even. It kept getting worse down to under a day and it wouldnt start. Now I had it sitting over last winter and it started no problem after.
Thanks but no hose. Just the 1 that gets returned to the tank from the inline filter. I remember the hose you are mentioning now from when I had my 80. Glad that worked for you.
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Old 10-19-2010, 09:10 PM   #19
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Quote:
Originally Posted by ...Roger... View Post
Try clamping the rubber fuel line at the frame the next time you turn the car off , this will block the fuel from returning to the tank.
If the car starts its probably the check valve and not the well plugs.
You can also check by removing the carb , sit it on the bench , if fuel drains out on the bench its the well plugs.
Thanks, Sadly I didnt, but I certaintly will if there arent any leaks. That needle and seat, the one thats attached to the float, it seats in the front area by the paper filter, I placed a weight (socket) on it to keep it shut while the bowl had fluid in it. If this does not seal properly, is it possible it could drain the bowl down ?
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Old 10-20-2010, 01:12 PM   #20
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I put a friends carb on my car last night and brought it up to normal temps. This morning I opened the top, worked the linkage and there was a normal stream of fuel spraying out of his carb, and the car started as it should. So I would like to think the problem lies in my carb and not anything before it in the fuel system. Did a little research and my carb is from a 73 corvette 454 275 hp motor. I see that this carb takes a paper filter with some form of an insert in the center of its tube. The one I removed from mine didnt have this, you could see straight through it. Not sure if that means anything, needs a new filter anyway. The bowl still had fluid in it this morning so it dosent look like much of it was lost. Cleaned the parts, its back togther now, and going to try again after sitting all night. Will know in the morning.
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Old 10-20-2010, 01:12 PM
 
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1982, back, bowl, car, carb, draining, drains, fuel, hard, jet, plug, qjet, quadra, quadrajet, sitting, start


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