Rochester Quadrajet Rebuild gone wrong? Spitting flames from carb '79 C10 350

[brody287]

So this week I decided to rebuild my Rochester Quadrajet because of some issues I've been having, and I figured she had never been rebuilt before (off a '79 Chevy C10 w/ a 350 small block). Clearly once I opened the carburetor somebody had been in there. The big giveaway was the silicone or some sort of epoxy on the well plugs. The silicone was cracked so I removed it and reapplied JB-Weld to about the same depth. Anyway, I went ahead with the rebuild and today installed it on the vehicle again. This was my first rebuild, but I took my time and watched tons of rebuilds and I'm reasonably confident everything went in where it was supposed to. There were no obvious issues to me and I had no parts left over, so I thought I was in the clear!

But my problem now is that the truck won't idle and when it starts it spits flames from the carburetor. Anything I search about flames coming through the carb is about timing issues, but obviously I haven't even touched the timing so I'm at a bit of a loss. Are there any carb-related issues that could cause the flames that I should be checking? It seems to me like the carb is getting too much gas.

I'm loathe to take it off again and open it up without a clear idea of what I should be looking at. Any ideas? Thanks

Edit: I should also say, I haven't adjusted any of the tuning except for setting the choke when I put it back on.

Another edit: I don't know why I overlooked putting this into my post, but I need to replace the choke pull-off valve, because it slowly releases vacuum if you test it by pushing it in and sticking your finger over the port. Could that be causing my issue? I've also seen online that vacuum leaks can cause this kind of problem. Weird it didn't manifest itself before, but weirder things have happened.

[bd]

Is there plenty of fresh fuel in the tank (>5 gallons)?  What "issues" prompted you to overhaul the carburetor?  What float level setting did you use and how did you check it?  How did you set the idle mixture screws (number of turns out from seated)?  Did you change the idle speed adjustment on the bench as part of the overhaul?  Did you carefully compare the gaskets in the kit with those removed from the carburetor before installing them?  Is the fuel bowl completely seated down onto the throttle plate or is there a gap between them?  Is the choke plate closing?  Is it possible that you installed the fuel filter backward?  Can you start the engine and keep it running by fogging the carb throats with starter fluid/carb spray?  If you can get the engine running, spray around the base of the carburetor with some aerosol carb cleaner.  Check for severe vacuum leaks.  Look for disconnected vacuum hoses.  If you removed any spark plug wires, check and verify the firing order.  What color is the ignition spark (don't check the spark if any flammable liquids are puddled on top of the engine)?

[brody287]

Is there plenty of fresh fuel in the tank (>5 gallons)?  What "issues" prompted you to overhaul the carburetor?  What float level setting did you use and how did you check it?  How did you set the idle mixture screws (number of turns out from seated)?  Did you change the idle speed adjustment on the bench as part of the overhaul?  Did you carefully compare the gaskets in the kit with those removed from the carburetor before installing them?  Is the fuel bowl completely seated down onto the throttle plate or is there a gap between them?  Is the choke plate closing?  Is it possible that you installed the fuel filter backward?  Can you start the engine and keep it running by fogging the carb throats with starter fluid/carb spray?  If you can get the engine running, spray around the base of the carburetor with some aerosol carb cleaner.  Check for severe vacuum leaks.  Look for disconnected vacuum hoses.  If you removed any spark plug wires, check and verify the firing order.  What color is the ignition spark (don't check the spark if any flammable liquids are puddled on top of the engine)?

Thanks for your response, this has given me something to go on at least. I was having issues with getting it to start and then run steady. Granted I am new to carbureted engines but when trying my best to tune it wasn't getting me results I decided to rebuild the carb. I'd seen advice that said any carb should be rebuilt if it hasn't been in the last 10 years, and to my knowledge this one had never been rebuilt (though that turned out false of course).

Anyway, to work through your suggestions there is plenty of fuel in the tank. The float was set to 7/16" which I checked with the supplied ruler from the kit. That's what the sheet I got with the rebuild kit said and the float was in good condition (It looked good and it floated easily) so I left it. Also difficult to source a float where I am and I was anxious to get the carb back on the truck. I didn't touch the idle mixture screws but I will set them to a bench setting (I've heard either 3 turns out from seated or 3.5 turns. I'll do 3.5 and see what happens). I didn't change the idle speed adjustment on the bench. The gaskets I laid over the old ones to check and they were the exact same. The fuel bowl is fully seated on the throttle plate. The choke plate does close just as you might expect. When the engine is cold and you tap the throttle it shuts. I'll check the fuel filter orientation. In my understanding, the rubber side faces away from the carburetor. I don't have any starter fluid or carb spray on hand but I'll pick some up and spray around the base. I'm assuming that's looking for leaks? I didn't remove any spark plug wires. And all vacuum hoses are connected. The EGR valve hose was disconnected when I got the truck, as well as the small hose which runs to the neck of the stock air cleaner. Both are plugged. I haven't checked the ignition spark but will do.

From that list of things then I will first double check the fuel filter orientation, then the choke, and then set my mixture screws to 3.5 turns out as I didn't actually touch them during the rebuild. I thought I could keep it set where it was that way. Then if that doesn't work I will begin checking for leaks. The engine will run but it will spit and then die unless I give it some gas. I think if I kept trying it might warm up and idle and then I can spray around the base.

[bd]

Before making changes, count the number of turns to seat the idle mixture screws from where they currently are and record the results to establish a recovery point.  The open end of the filter (which may contain a check valve) points toward the fuel inlet nut and line.  To check a closed cell nitrophyl float, give it a gentle squeeze or press a fingernail into any visible blisters.  If it oozes fuel, the float is saturating and should be replaced.  To check or set float level, follow the steps in the attached image according to the carburetor number.

How new are the spark plugs?

[75gmck25]

First - what is the number of the Quadrajet you have?  In that timeframe its probably a 7xxxxxx (older carburetors) not a 17xxxxxx (newer carburetors) number.  Did the rebuild kit say it was for that carburetor number?

Since you did not move the idle mixture screws, it sounds like you only replaced gaskets and checked a few things.  What new parts did the rebuild kit include?  The reason I ask is because there are some common problems you are trying to fix with a rebuild.
- Gaskets leaking.  As mentioned, make sure the new gasket matches the old and it has holes in all the right place.
- Float/needle not sealing properly, or float set to the wrong level.  The kit should have included a new needle and seat, and a more complete kit would have a new float
- Accelerator pump check ball not sealing in the well, or the seal around the pump deteriorated and not sealing to the bore. Should have a complete new pump with an ethanol resistant seal, and a new check ball for the pump well.
- Idle mixture passages plugged.  The mixture screws should be completely removed.  Then use solvent and compressed air to clean the passages.
- Sediment or dirt in the idle down tubes, jets or other passages.  Solvent and compressed air again to clean.  Also make sure the tubes are fully seated, because sometimes they fall out and down into the carburetor.
- Primary rods bent, or incorrect.  When you put the top back on you have to work these down into the jets, and sometimes the tips get mangled.  If you know the number on the carburetor you can look at the rods and  jets and verify they are the original size.
- Secondary flap tension spring set too loose.  A loose spring lets the secondary flap open too soon and creates a really significant bog.
- Secondary cam broken (little plastic piece in the middle that makes the secondary hangar rise). 

I've had my Quadrajet apart quite a few times for tuning, and even now I still forget and leave a part out or disconnected, and then have to take it apart again to do it right.   Just be patient and keep checking.  Also make sure you installed it right. For example, have you checked the vacuum lines for the brake booster, PCV and distributor to make sure they are connected properly and nothing broke when you disconnected and reconnected the lines.  Any vacuum leak from those lines can really screw up the idle mixture.

Bruce

[brody287]

Thanks for the tips everyone. 75gmck25, my carb is a 17059205 (didn't know it was a "Newer" carburetor). I have the truck running now where I am satisfied, as it starts and runs perfectly.

My problem now is that the choke doesn't appear to be opening at all, even when the truck has been given plenty of time to get warm and it's registering on the temperature gauge. I did order a new choke pull-off valve, because the old one didn't seem to hold vacuum (I was told to check it by pushing the valve in, and then putting my finger over the port. If it stays it holds vacuum, if not it needs to be replaced. Mine very slowly let out). That will be here this Wednesday, though I was wondering, if the choke spring is installed backwards would that be my problem?

[bd]

Some choke pulls have a small bleed orifice that bleeds off applied vacuum.  Check the new one before you install it and compare it to the old one. 

That carburetor should have a hot air choke.  The t-stat spring is integral with the choke plastic cover and cannot be installed backward.  However, if the choke cover is not keyed with an indexing tang the choke t-stat can be misadjusted.  Is there a steel tube plumbed between the choke thermostat housing and the manifold stove?  A 1-1/4" long orange silicone sleeve should connect the heat stove tube to the choke housing.  A second steel tube should run between the stove and a vacuum nipple on the rearward side of the carburetor air horn.  Does the choke housing get too hot to touch after the engine runs for a few minutes?

[JohnnyPopper]

For your entertainment care of Stewart Griffin 

https://www.youtube.com/watch?v=_BTEdWt2V3s&t=103s