Carburetors, what can go wrong?

[david craft]

1. The throttle blade shaft can wear in the bore. This allows air to leak past at idle causing poor atomization. Need to replace base or put a bushing the bore.

2. Idle screws can be over tightened and destroy the lands where they seat. You'll never get a good adjustment.

3. Quadrajets can leak fuel at the bottom center of the main body at the plugs. Old hot rodders use to sand this area and epoxy.

4. The base can be bolted down so tight that the throttle blades wont close.

5. Choke coils can burn out, choke kickdown linkage bent, a whole host of other stuff.

Be sure to check rebuilts out of the box, I've seen sloppy shafts that never should be on the shelf. Folks use too much return spring because of throttle linkage friction or bad geometry. Ideally the spting should be 180 degrees from the linkage and just enough to return to idle.

A random simplified carb adjustment procedure;

Bring engine up to temp. Change oil if dirty. Make sure choke unloader had functioned and choke is off. Plug vacuum line to distributor and set timing. Be sure that RPM is below 1000. Reconnect vacuum line. Kill engine. Count how many turns (full and partial) to lightly seat idle mixture screws and return to initial setting. Record data. Fire engine. Adjust engine idle to factory setting. Slowly adjust screw inward till rpm just begins to drop and record. Open back up to full rpm and add a quater turn. Adust idle down to specs again if it has increased and repeat process. Do both sides. There should be at least a turn or so between lean drop and rich stumble, otherwise the screw seats may be compromised. This thread is open to comments, questions, and fine tuning...lol

[Jim Stoltz]

Yeah he was weird on the phone but a lot more descriptive in person. Fingers crossed!

[Rich Thomas]

Got my fingers crossed for you Jim, My old palace has a q-jet that seams to be in good order but if it goes tits up I may have to have a conversation with that guy. Good luck

[Jim Stoltz]

Installed the rebuilt rebuilt carb today.

The choke actually works! It pulls off too fast, but I can adjust that. Fast idle kicks down like it should. 

It runs much better. Previously it sounded like it had a big, lopey cam. The snow was black by the exhaust pipes. We got some fresh snow last night and no blackness by the tailpipes (unscientific, I know). It idles much smoother now. It doesn't run on after I shut it off, either.

Still a raw fuel smell for a while after I shut it off, but I think that's because of the open element air cleaner. The stock air cleaner is sealed up much tighter and has a horn with a hose on it that points out the front. This would greatly minimize the smell. I'm going to try to use it if I can.

[Russell E Johnson]

Glad to hear the carb worked out so well.  My son, who is a mechanic, is going to adjust my carb as the choke keep setting at warm and flooding the engine.  He wants me to spend the money for fuel injection, $1500 worth and he would put it in.  I don't know if I will go that way or not, these engines ran a long time on just a carb, and I want to save up the money so when this motor does die we will have the funds to go with a Cummins 5.9 and an Allison 6 gear tranny.

[Jim Stoltz]

Thanks. There is a night-and-day difference in the way it idles (and the way the exhaust smells at idle). I'm hoping it will get through emissions inspection now. And having a working choke is the icing on the cake. 

With all due respect to your son, I've done a lot of research on the fuel injection thing myself. It all points to a waste of money for our purposes. The Quadrajet on the 454 is a tried and true combination (to your point) and can be reliable. The problem is finding someone that knows how to tune them properly since that combination hasn't been manufactured for decades.

The Allison 6-speed will bolt up to the 454 no problem. You need to manufacture a custom crossmember and shorten the driveshaft, but it will work. Need an electronic controller too. It's an expensive modification but will work with the stock engine. I met a guy at the Pocono Raceway that had an Airstream motorhome with a stock 454 and carb with an Allison 6-speed behind it.

[Jim Stoltz]

I adjusted the choke yesterday. It's taking a few minutes to fully open at idle now, which I think is fine given the fact it was in the high-teens (F) outside. I'm not used to the choke actually working so I pumped the pedal out of habit and flooded it.Other than that, it's running great. I can't wait for all this snow to melt so I can get it re-inspected (and so I can get under it to install the scissor jacks - a different topic altogether).

[Rich Thomas]

Man am I glad to hear your happy with your carb rebuild. I know its almost an art to tune these things and I'm happy there's still someone out there that can do it. 

[Jim Stoltz]

As soon as it fired up I could hear the difference. Plus watching the choke operate like it should was pure magic. 

What I didn't hear when I fired it up was the air compressor for the suspension. It's not running on its own anymore. It's either the relay or the pressure switch. I bypassed all that and it ran fine and leveled itself. Something else to fix before Spring....

[Jimco_W001]

Jim,that's great news.Let us know how the e-check goes.

[david craft]

awesome news Jim. I know that here in cali, I always ask the smog tech to do a manual check first rather than risk a "gross polluter" designation by hooking up to DMV recording results right off, saving a lot expense later...

[Jim Stoltz]

In NJ you can fail as much as you want, but risk getting a ticket for the REJECTED sticker on the windshield. They don't mess with motorhomes though. I've been driving around with that sticker since last June. It would be good to have a good sticker on there, though.

The real issue is going to be that when I run it back through I'm supposed to produce a receipt from the "certified emissions repair facility" that did the repairs or produce receipts for the repairs that I made myself. I don't have either. The carb shop isn't a "certified emissions repair facility" and I paid him cash. I'm going to tell them I adjusted the carb and see if that flies.