Q-jet starting issue
 

I have a Q-jet on my '71 Corvette Stocker (454/365). Whenever it sits for an extended period of time, the carb will not squirt any fuel. It doesn't matter wether or not the fuel pump is running. So I remove and disassemble the carb, find nothing, reassemble and reinstall the carb and it works fine. This has happened the last 3 times I've let it sit for an extended period. Any ideas? Remedies? Common problem?
Ben Kallies C/S 3869

Re: Q-jet starting issue
 

More times than not when you have this problem on a Q Jet the "main well plugs" in the bottom of the carb are leaking letting all of the fuel seap out of the carb and into the intake where it evaorates. To solve this pull the carb flip it over and take the baseplate off (dont forget to pull the back top long screws out first as they hold the rear of the baseplate) where you will find the plugs,(5 total but the 2 rear/bigger ones leak the most) clean them good with carb cleaner and a tooth brush. Take some JB weld or JB quick and seal them back up. I leave them upside down overnight to let it dry before I put fuel back in it. Hope this helps, Mike

Re: Q-jet starting issue
 

Thank you Mike. I'll try that. If this is occuring, does it make sense that it still doesn't squirt once the fuel pump has pumped fuel back into the carb? Is it possible that the needle is sticking in the seat due to being dry? - Ben

Re: Q-jet starting issue
 

Yes, it is possible that it is sticking. In the other thread, I asked if you had tried pushing the float down. I usually use the plastic straw from a can of carb cleaner, and push on the float through the bowl vent tube. Push down lightly, and release, the float SHOULD push the straw back up. If it does not, turn on the fuel pump, push down again, count to 3 fairly quick, and release. See if it pushes the straw back up.

When dealing with the well plugs, I take a small hammer and tap the plugs to fold the lead edges over. I use JB Weld, it's an old habit from when I used to work at a carb shop, I do all of my Q-Jets that way.

Are you using a nitrophyl float? If not, get one, and set it at 5/16".

Re: Q-jet starting issue
 

One last thought, I wonder if the accl. pump check ball is sticking after the car sits? This could happen if the float bowl is dry from the main well plugs leaking also.
Give it a look the next time you have the top off. Hope this gets you going, Mike

Re: Q-jet starting issue
 

Thank you both Mike and Alan. I appreciate you taking the time to respond. That gives me a few areas to work with. If I find something, I'll let you know. - Ben

Re: Q-jet starting issue
 

Ben,

All that is happening is your accelerator pump plunger is drying out when your car sits for a while. When you are ready to use your car fill the carb up with gas by brunning the fuel pump a day prior to starting it and this will swell up the plunger and the accelerator pump will work again. The racing gas is very dry especially C-11. When your car is sitting fill the carb regularly to stop the drying out this will solve your problem. I have the same problem on my super stocker. Dont get to race enough.

Mike

Re: Q-jet starting issue
 

Ben,

You have received very good advice so far. One question, is the rubber pump cup on your accelerator pump black? If it is, these cups usually have a short life when exposed to racing fuels. Like Mike mentioned, C-11 is the toughest to deal with because it even seems to leave a residual film inside the carb when it dries. If you have the black cup, I'd be happy to send you one of mine to see if it helps.

I would also recommend that you take a look at the check ball and the seat that it sits in to make sure they are clean. If the check ball is not sealing properly, the upstroke of the accelerator pump could be sucking this circuit dry. I can give you some pointers on how to check this if you want me to.

Keep in mind also, the bowl area of a Q-jet is very small, so if the car sits for a couple of weeks most/all of the fuel inside the carb can be lost to evaporation. If this is the case, then the carb is simply "empty". However, this leads to the situation described earlier where the pump cup will now start to dry out.

Dean Oliver
www.deanoscarbs.com

Re: Q-jet starting issue
 

Ben,

You have received very good advice so far. One question, is the rubber pump cup on your accelerator pump black? If it is, these cups usually have a short life when exposed to racing fuels. Like Mike mentioned, C-11 is the toughest to deal with because it even seems to leave a residual film inside the carb when it dries. If you have the black cup, I'd be happy to send you one of mine to see if it helps.

I would also recommend that you take a look at the check ball and the seat that it sits in to make sure they are clean. If the check ball is not sealing properly, the upstroke of the accelerator pump could be sucking this circuit dry. I can give you some pointers on how to check this if you want me to.

Keep in mind also, the bowl area of a Q-jet is very small, so if the car sits for a couple of weeks most/all of the fuel inside the carb can be lost to evaporation. If this is the case, then the carb is simply "empty". However, this leads to the situation described earlier where the pump cup will now start to dry out.

Dean Oliver
www.deanoscarbs.com

Re: Q-jet starting issue
 

Thank you Mike and Dean,
It sounds like you've both got the problem figured out. I appreciate your input. Dean, I would love to try one of your pump cups. I'll give you a call soon.

Ben Kallies C/S 3869