Quadrajet help

[steveimpala]

I have an issue with my 1969 Chevrolet C20. It has the 350 V8 with the automatic transmission, the carb is the Rochester Quadrajet. The truck starts up fine, comes to a idle after a few minutes. The problem that is occurring is that after driving for 15 mins or so, you come to a stop and the truck wants to die. The truck has 88,000 miles and I'm guessing that the carb is original. Any thoughts....adjustments or rebuild ?

Thanks!

[rjs53]

Is it running out of fuel? I think those had a filter at the inlet, might check it. Quadrajets are good.....when they work

[dmjlambert]

Sounds similar to the problem I had
http://67-72chevytrucks.com/vboard/s...d.php?t=760430

[steveimpala]

Yes, gas filter was replaced.

[geezer#99]

Check for a vacuum leak.

Is this a recent occurrence or has it been ongoing?

[steveimpala]

It just started... just had some work done to the truck - new exhaust, hoses, belts and brake lines.

[68Gold/white]

www.cliffshighperformance.com

You need a rebuild. Cliff can sell you a kit and all the parts to calibrate your carb for todays gas, and his parts are ethanol resistant. His stuff isn't cheap, but it IS the best!!!
Get his book ,also!

[geezer#99]

Yes you might need a rebuild but find the source first. You might be chasing it after a rebuild too.

When you say it comes to an idle after a few minutes, is that from you kicking the high idle off?
And when it does that is the choke completely off?

[steveimpala]

Yes, after a few minutes, I'll tap / kick the accelerator to bring the engine to an idle....I'll have to look later today regarding the choke...

Thanks!

[geezer#99]

Originally Posted by steveimpala

Yes, after a few minutes, I'll tap / kick the accelerator to bring the engine to an idle....I'll have to look later today regarding the choke...

Thanks!

Easiest visual check is look at the tang on the secondary lockout. If it’s dropped off the pin on the end of the secondary shaft then the choke is completely off.

Here’s a pic on a link.

https://www.google.com/search?tbm=is...d5PpmhDXHRHTM:

[Coley]

It does sound like something in the choke circuit (passenger side of carb) is off somehow.
When they did the work on the truck, did they touch the timing?
I'll take a page from Geezer's book and say check that first to make sure you have (at least) 8°..personally I would recommend 10-12° to start.

Regardless, make sure the choke equipment is working properly....check all carb hoses as well...or simply replace them (they are cheap).
These include the main hose up to the power brake booster, the PCV valve, the short air cleaner connection, the vacuum advance hose, and even the little short one between the choke pull off and the carb.
Also check the transmission vacuum hose which comes down from the upper manifold to the trans.

When the truck is idling...is it smooth? or does it sound a little rough?
...if it not a smooth idle, all cylinders hitting...then you probably have a vacuum leak.

Do you have any pics of your set up?


Coley

[steveimpala]

Nothing was touch regarding the engine... the truck runs smooth on all cylinders...here are some pic:

[geezer#99]

Nice pics!
I can see your choke plate wide open but the lockout tang is still hooked on the secondary pin.
Could just be some crud on the tang.
I’d spray it and clean the whole choke area with some carb/choke cleaner first. Then if that doesn’t help we can help you with a couple more possible things to check.

[steveimpala]

Thanks again.... will give it a try

[steveimpala]

Just an update, I did clean up the carburetor and gave the truck a run later that day...... so far so good...

Will keep you all posted

Thanks !

[steveimpala]

I thought I was all set with the idling issue, but it's back. Took it out over the weekend, about 10 mins into the drive while at a stop light, it felt like it was going to stall out, so I place it in neutral until the light change. Not sure on what to check next...

Any suggestions....Thx !

[Steeveedee]

Spray carb cleaner around the primary throttle shaft on the driver's side and see if the idle speed changes. You likely have a worn bore where the throttle shaft goes through the base plate. If there is a vacuum leak there, it will be covered up by the richer mixture when it is on the choke.

[geezer#99]

Originally Posted by steveimpala

I thought I was all set with the idling issue, but it's back. Took it out over the weekend, about 10 mins into the drive while at a stop light, it felt like it was going to stall out, so I place it in neutral until the light change. Not sure on what to check next...

Any suggestions....Thx !

Check your timing.
What’s your initial timing set at?

[geezer#99]

No wonder it dies!
Bump your initial up to 12.
You’ll see a world of difference.

[steveimpala]

Thanks for your input geezer ! I'll post results tomorrow.


Steve

[steveimpala]

Set timing at 12.....went for a drive.... no issues !

Thanks again !

[geezer#99]

Good deal!

[steveimpala]

Just an update... last month while driving to work, had the idling issue come back again.... I was going up a hill, accelerated to get up over the hill, came to a intersection and the truck wanted to stall out. Talked with my mechanic about it and he mention that it could be the accelerator pump - so at that point, decided to go ahead and rebuild the carburetor ( the truck has 88000 miles and the carb appear to be untouched) . The carb is back on the truck, no vacuum leaks, timing is around 12. The truck starts up and runs great for the first 10 to 15 mins into the drive, then I noticed the idle has come down again....not sure to look at next.... it does have a HEI that was installed by the previous owner - could this be an issue ? Very frustrating... like I mention, she runs great at the start, but something is happening once the engine get's hot.

Thanks guys.... I appreciate any input !

Steve

[dmjlambert]

You are supposed to do the tuning such as setting the idle speed when the engine is fully warmed up. So go ahead and get it warmed up, make sure the choke is fully open, and then adjust your idle speed and mixture screws if necessary, for smooth idle. Idle should be about 600 to 700 while in drive with parking brake set and wheels chocked and you standing to the side making the adjustment. Then see how it does the next day. When the engine is cold and choke is active it should idle faster, there is a fast idle adjustment screw tied to the choke.

[steveimpala]

Ok.... we'll give it a try.....

Thanks