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

[david craft]

i see the conundrum. what if you mistook the ruptured diaphram for a vapor lock and pumped the engine full of fuel anyway? good hoses from the tank forward and the stock line placement should do ok. you could always run the electric rear mounted and go a fuel pump blockoff plate. i always liked the idea of those fuel pressure regs that return fuel to the tank..overkill i know but a cool idea..can hardly wait to see how the rebuild goes.

[Jim Stoltz]

To make a long story longer, I have the GM motorhome supplement from 1984. At that time, they invited all the manufacturers to their Arizona proving ground to try to get to the cause of the vapor lock issues. They found poorly insulated lines, too small lines and low pressure due to the length of the run. Their recommendation was to install 1/2" steel line from front to back and an electric fuel pump in conjunction with the stock pump. Someone did that on mine. The manual made no mention of concerns over blowing past the diaphragm on the stock pump.

The manual did recommend a couple of different brand pumps, including a Holley that required no regulator. None are manufactured anymore. They provided a diagram of how to set up the pump with a regulator, return-line and anti-drainback valve.

I spoke to the manufacturer of the aftermarket pump I bought. They said it will support the WOT GPH requirements of the 454 and that no regulator was required. He, too, suggested a block-off plate and to use the electric pump exclusively. I may do that, but I want to beef up the wiring. Whoever installed it used very small gauge wire for the 30+ foot run. I installed a constant hot, 4-gauge wire for the air suspension compressor which is near where the fuel pump will go. I'll probably tap into that circuit and control the pump with a relay.

I can't wait to get my carb back, either. It hasn't run right since I installed that engine. The emissions testing and my nose tells me that it's very, very rich but the oil isn't watered down with fuel nor are the plugs fouling so that's good.

Also, in talking to the carb guy he said that you should be able to see fuel when you look down inside it. It's a vent for the float bowl. I assume that's why I get such a strong fuel smell inside when I shut the engine down. I have an open-element air cleaner - maybe I should find a way to make the factory "snorkel" air cleaner to work (there's stuff in the way - even longer story). My dog house isn't sealed either - I never properly reinstalled it after the engine swap (another long story related to why the stock air cleaner won't work).

[david craft]

there is that butterfly valve in the exhaust manifold that diverts exhaust gas through the intake base to warm up the carb. if that thing sticks shut it will boil gas out of the float bowl on shut down. 

[Jim Stoltz]

I took mine out when I put the new engine in. They always seize up, leak, rattle or otherwise become a pain in the butt. It takes a little longer to warm up but its fine without it.

[Jim Stoltz]

So the carb guy called today. Conversation went like this:

Him: "Yeah that's all done"

Me: "Did you fix it?"

Him: "I hope so!"

Me: "Was there anything obvious wrong with it?"

Him: "No. But they're like women, sometimes you have to slap them around to get them to do what you want, and they'll still take all your money."

Me: "How much do I owe you?"

Him: "$300"

So the carb was $300 "new" from the eBay seller. I should have just sent it back, but I didn't so here we are another $300 in. $600 so far. Could've gotten a nice Holley spread bore double pumper for around $500 (rebuilt, too, though). 

I really like the idea of the correct carb, so I'm just going to keep telling myself that. I'm going to pick it up tomorrow and pop it in over the weekend. It better work!!! I need a choke and to get through emissions.

[david craft]

seems like he would have checked clearances and settings going in per your conversation, looking for something amiss.  especially with all the cleaning etc... he saved with the carb in the present condition.  hope it works bro...been nice to get some confidence with the carb!

[Russell E Johnson]

Ditto on the repair of the carb, hopefully this guy knew what he was doing and the end result is worth the money.  I am having problems with my Quadrajet and am threatening to ditch the stupid thing and get an Edelbrock.

[Jim Stoltz]

I was there, and threatened to go the Edelbrock route. Then I read the issues with adapters that go between the square bore carb and spread bore intake. Yeah you can put an Edelbrock square bore intake on, but that's more time and money.

People say that when the Quadrajets work they're the best. I haven't found one that works yet, though. Every car I had that came with one I replaced with a Holley. As a result, there are lots of Quadrajets on the shelf in my dad' garage. 

[Russell E Johnson]

ROFL

[Rich Thomas]

Hope the rebuild works well for you Jim. This guy reminds me of my deceased brother in law. He could take a bucket of nothing but parts and pieces and turn it into a well tuned running carburetor quicker than most shops could put a new one on and tune it. Point is I'm hoping for you that he's as good as Tom was and you won't be disappointed. 

[Jim Stoltz]

Thanks. I picked the carb up today. Had to drive an hour to get it, drive another hour to get to my brother's house to load some furniture in my truck (where there's a 50-yard un-shoveled trek to the driveway), then drive to my brother's new place to unload said furniture, and now I'm finally home. It's snowing hard with 4-8" projected. So....I'm not really feeling like going out there to install this carb though I might if the propane for the furnace holds out. It's warming up now.

The guy opened up his shop today so I could pick the carb up. He was working on a Dodge Power Wagon carb and intake combo (2, 2 BBL carbs) for a customer in Alaska. I brought my 11-year-old daughter with me to show her what a carb is (she asked, so I figured I'd show her all the shapes and sizes).

The $300 smarts but this guy clearly knows what he's doing. He replaced everything - complete rebuild. He said the float on my "rebuilt carb" was old and maybe not floating. Replaced some dry-rotted lines and all needle seats, vacuum pots, pull-off linkages, etc. Obviously all new gaskets, too. He said the choke wasn't working because the secondary lock-out linkage was FUBAR'd. He replaced that, too.

So, fingers-crossed. Hopefully a working choke and able to get through emissions. If it ever stops snowing I'll run it through emissions inspection again soon.

[david craft]

Now thats the kind of conversation I was hoping you would have had with the guy...hard to get a laugh with the dry humor attempted in previous discourse. Obviously there were problems found and you DO have a reasonable expectation of success!