Truck won't start after sitting a week

[Ole Blue 71]

Hi all,

I have a 71 C10 stock 350/350 with a HEI distributor. If I let the truck sit for a week or more, I have to pour gas in the carb to get it to start. After that, it fires right up. Had the carb (Q-jet) looked at a couple weeks ago and he found a torn diaphragm on the accelerator pump. Thought we had it licked but it did it again this morning. Where should I be looking for this issue? Is it time for a new carb or am I chasing my tail. Recommendations, please!

Thank you

[Richard2112]

My C-30 does the same thing. Run it daily-no issues. Let it sit for a week-gotta prime the Q-jet. I don't know why but I think warm fuel tend to evaporate more quickly in the Q-jets. Could be wrong.

[LockDoc]

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Have the small well plugs on the bottom of the carb base been epoxied? If not it could be that the fuel is draining out of the float bowls when it sits that long. It could also be that the fuel is siphoning back into the tank, draining the fuel lines.

Here is a kit for the plugs:

https://cliffshighperformance.com/Qu...ottom-plug-kit

Some people use JB Weld but I don't know how long it lasts.

LockDoc

[3757chevy]

I like Qjets JB WELD is good for this application . standard motor products QJK2 is an option . NAPA 2-1401 works well.

[Steeveedee]

Mine does the same thing, but the well plugs don't leak. I believe that that problem was cured in the late '60s with some updates to the design. If you look at the size of the float, the size of the float bowl and the phenolic block that holds the float on the pivot, you will realize how little fuel is actually in there. It's no surprise it has evaporated in a week.

[54blackhornet]

Mine does the same thing. Combination of ****ty gas, leaking well plugs and tank pressure siphoning gas back into tank.

[rpmerf]

My 70 does the same thing if it sits longer than 2 days. I have to crank it about 10-15 seconds, pressing the gas about once every other second.

The accelerator pump in the quadrajet only works if the float bowl is full. Once the level in the bowl starts to drop, it needs to refill for the accelerator pump to work. Since it has a mechanical fuel pump, it is only filling when the engine is spinning / cranking.

There was a thread somewhat recently about using an electric pump as a 'primer' pump.

EDIT:
If you want to google around on this issue. Look for posts by a guy named Lars on corvette forums. He has written lots of good info on the quadrajets over the years.

[mikeshome]

Put a check valve in fuel line so it cant drain back.I think fuel pump has one built in.

[Ole Blue 71]

Thanks for all the suggestions so far. Sorry, I forgot to add I did put a check valve in the fuel line above the fuel pump last fall. It takes way longer than a few seconds of cranking and pumping it seems. This morning, the starter was smoking.

[mikeshome]

May have a pin hole in fuel line somewhere.

[HO455]

Originally Posted by Steeveedee

Mine does the same thing, but the well plugs don't leak. I believe that that problem was cured in the late '60s with some updates to the design. If you look at the size of the float, the size of the float bowl and the phenolic block that holds the float on the pivot, you will realize how little fuel is actually in there. It's no surprise it has evaporated in a week.

The update you are referring to did help the problem. In other words it delayed the onset of the leaking plugs past the warranty period and that helped GM. Carburetors well into the 70's can still develop leaking well plugs. The fact is that you have steel plugs peined into pot metal. The two materials have different temperature expansion rates. After hundreds heat cycles cracks and voids develop around the plugs and eventually fuel gets past. The greater the temperature extremes the carburetor was exposed to the greater the chance the plugs will leak. And lets face it the quality control in the 1970's was less than optimal. I've see a couple pretty poorly installed plugs on late 70's carbs. An issue I have yet to see on any of the earlier carbs.

[KQQL IT]

Mine sits 5-6 days every week and starts like it was parked 5 6 minutes ago. Used to be a turd then.
Rebuilt carb
New fuel pump and new rubber lines from the tank to the carb.

[HO455]

Originally Posted by Ole Blue 71

Thanks for all the suggestions so far. Sorry, I forgot to add I did put a check valve in the fuel line above the fuel pump last fall. It takes way longer than a few seconds of cranking and pumping it seems. This morning, the starter was smoking.

If it takes more then several revolutions of the engine to get the float bowl filled then your fuel pump is dying.
I would also check the accelerator pump action. When you know the float bowl is full. Pull the air cleaner and look into the primary bores and wing the throttle. You should see a good solid stream of fuel shoot into each venturi. If you don't it is likely the accelerator pump has failed. The A pretty thing these days with the fuel available to us now. There are a couple more items that could cause it not to spray fuel. But check if you have good accelerator pump action first.
If you do then it is a fuel supply problem to the float bowl.

[Steeveedee]

Originally Posted by HO455

The update you are referring to did help the problem. In other words it delayed the onset of the leaking plugs past the warranty period and that helped GM. Carburetors well into the 70's can still develop leaking well plugs. The fact is that you have steel plugs peined into pot metal. The two materials have different temperature expansion rates. After hundreds heat cycles cracks and voids develop around the plugs and eventually fuel gets past. The greater the temperature extremes the carburetor was exposed to the greater the chance the plugs will leak. And lets face it the quality control in the 1970's was less than optimal. I've see a couple pretty poorly installed plugs on late 70's carbs. An issue I have yet to see on any of the earlier carbs.

Thanks for that. It's good to keep facts in a discussion. I read elsewhere what I wrote above. I guess I'm lucky with my carb so far. It is the original.

[dz1087]

Originally Posted by KQQL IT

Mine sits 5-6 days every week and starts like it was parked 5 6 minutes ago. Used to be a turd then.
Rebuilt carb
New fuel pump and new rubber lines from the tank to the carb.

Same here. It can sit for weeks now. Give the pedal a pump or two, he fires up pretty fast.

[tdangle]

Use to have the same issue with my Quadrajet. Rebult, epoxy on the plugs didn't help. I figured the gas was evaporating. Always a slight gas oder. New engine has a new holley on it and starts super quick even when sitting for more than a few days.

[rockyrivermark]

I just solved this on my c10. One way valve didn’t help.
It’s evaproating from in the bowl.
I have mechanical fuel pump but also installed a cheap inline electric pump under the cab and wired it to a momentary switch. Basically a primer pump
Hit the switch for 10 secs and fires right up even after sitting 2 weeks. Electric pump from amazon was $22
Prob solved.

[HO455]

Originally Posted by Steeveedee

Thanks for that. It's good to keep facts in a discussion. I read elsewhere what I wrote above. I guess I'm lucky with my carb so far. It is the original.

You are lucky to still have the original carburetor. Treat it with care. I couldn't count the number carburetors I seen that were treated like a cheap hammer. Then they wonder why they won't work.

[Steeveedee]

Originally Posted by HO455

You are lucky to still have the original carburetor. Treat it with care. I couldn't count the number carburetors I seen that were treated like a cheap hammer. Then they wonder why they won't work.

Yeah, next rebuild I'd like to get the chromic acid plating kit and take it back to original looking. Maybe in about 10 years. It's been a few since I rebuilt it, and I had bushings put in the throttle plate. Good for another 50 years.

I also have an electric fuel pump to prime with, since my truck sits for weeks at a time.

[custom10nut]

I have the same issue with mine. If I start her everyday, she starts right up, but the longer she sits the longer it takes.. Though mine has the Edelbrock 1406 w/pressure regulator.
I never made the connection with the Fuel pump. Mine is about 20 years old now, so it might be time for a new one.��