Quadrajet about to be tossed.

[bonehead]

I noticed in your pics that you are using windshield washer hose for the vacuum hoses. That is too flimsy and will suck shut and mess up your timing. change all vacuum hoses for the proper hose and you might be in business??

[Coley]

...don't forget to plug that open vacuum port/tube (shown) on the passenger side of the carb....poking right out in the middle of the choke assembly.
Normally this is connected to the air cleaner so I will assume that in the pics without the air cleaner it is simply not shown.
Regardless if your air cleaner is an aftermarket that doesn't use that vacuum then make sure you put a cap on that port.
Also a very good idea to check each and every vacuum leak line or port or fitting on the carb before proceeding.
Check and/or tighten the following: power brake fitting to rear carb port (unless manifold vacuum runs the p.brakes), check-correctly tighten (4) carb hold down bolts (new gasket? good gasket?), pcv hose and fittings, choke pull-off (functioning correctly? new? holds vacuum?)....usually the reasons for carb issues are not always major but there are enough small details involved to easily miss one or two then you end up fighting the carb.
Also...super double ditto on getting a vacuum gauge for tuning....really eye opening info comes from those things and well worth the minimal investment.
Quick story:
I had one guy come over to the house once and he couldn't figure why his truck was running so poorly...especially given the fact that a 'mechanic friend' helped him install the motor and tune it up. Turns out...the back vacuum port on the carb for the power brake was completely open....they had piped the vacuum on that truck into the manifold and somehow/someone had not put a plug in the back port...lol. Anywhoo.....I put a spare fitting in it for him....super simple 'hero' moment...lol.


All Good
Coley

[TCONNELLY]

I think I found the culprit. The PCV valve seemed to be making a lot of noise. I had replaced it a few weeks ago. Today, I decided to also change out the PCV hose. It seemed tight fitting , but it also seemed like the rubber was a bit hardened. It's running much better. The idle is a steady 600 rpm in drive and vacuum is 20 inches. I first adjusted the idle mixture in park , then put it in drive and found that I needed to richen the mixture a quarter turn each side, to smooth out the idle at get the vacuum back up. The weather is on the cool side today, but I did have it running for almost an hour. I'll take to work to give it a proper test, stop and go traffic.

Thanks everyone for all the great suggestions. It's what make this such a great forum, people who are passionate about these trucks and generous with their willingness to help others with their trucks.


Posted via Mobile Device

[Coley]

Originally Posted by TCONNELLY

I think I found the culprit. The PCV valve seemed to be making a lot of noise. I had replaced it a few weeks ago. Today, I decided to also change out the PCV hose. It seemed tight fitting , but it also seemed like the rubber was a bit hardened. It's running much better. The idle is a steady 600 rpm in drive and vacuum is 20 inches. I first adjusted the idle mixture in park , then put it in drive and found that I needed to richen the mixture a quarter turn each side, to smooth out the idle at get the vacuum back up. The weather is on the cool side today, but I did have it running for almost an hour. I'll take to work to give it a proper test, stop and go traffic.

Thanks everyone for all the great suggestions. It's what make this such a great forum, people who are passionate about these trucks and generous with their willingness to help others with their trucks.


Posted via Mobile Device

Good to hear, keep us posted...but...take Geezer's advice on definitely checking and setting your timing...this should be done before ANY carb adjustments.

Again...keep us posted on how it tunes out.
all Good
Coley

[TCONNELLY]

I've been able to drive it a to work this week and it is running so much better. I've been able to drop the idle rpm a bit more to 550 rpm in drive, to the point where I can hear some mechanical noises that I couldn't here before. Nothing abnormal, just little things that I couldn't hear when the idle was higher and the engine was louder. The acceleration is also smoother and crisper. I really enjoy driving it more. The idle quality is, I would estimate, at least 90% there. I'll need to do a bit more fine tuning. Although, I'm a bit afraid of to change anything, for fear of upsetting the apple cart. Since, it seems very close, I'll stick with very small adjustments and test drives. That way I can reverse what I did, if it seems to be going in the wrong direction. I don't know if it's reasonable to expect much better from this old motor. I don't know how many miles it has or if it's ever been rebuilt. It shows 18,000 on the odometer, which I think represents 118,000.

I was really believing all the complaints about the quadrajets, but now see that they really can be great running carbs.

[Coley]

That's a nice looking truck...in exactly the right color combo....blue on white!
72? 3/4 ton?...Post up some more pics of it if you get the chance...we are all about the pics around here...lol.
All good
Coley

[TCONNELLY]

Originally Posted by Coley

That's a nice looking truck...in exactly the right color combo....blue on white!
72? 3/4 ton?...Post up some more pics of it if you get the chance...we are all about the pics around here...lol.
All good
Coley

As requested, a couple pics. It's a '72 C20. My wife thinks this is her truck. She doesn't care if we sell any other vehicle. This one she wants to keep forever.