Carbon Inside Intake Manifold

[c3po]

I was replacing some vacuum caps on my 1983 Chevrolet El Camino that has a Quadrajet carburetor and a Edelbrock 2101 Intake Manifold.

There is a housing on the passenger side for a hot air choke if the car had it, since I have an electric choke it is capped off.

I removed it and looked inside the passageway and there was some light carbon, is this normal, or do I need to clean it out.

The carburetor was bogging so I replaced all of the vacuum caps as well as the vacuum lines with new ones. I am wondering if this carbon inside the intake manifold means there is carbon on the pistons and this may or may not be the cause of the carburetor bogging.

I am going to try to take the car out for a drive either tonight or tommorow.

There was no thick buildup of carbon, just a thin dusting from what I could see.

Any advice would be appreciated.

 

[Jim 5]

It's too bad that you can't seem to buy those big cans full of carb cleaner that you could sink the whole carb into anymore. I would dip the whole thing.

When people say that the carburetor bogs, they usually mean that the engine hesitates when you step on the gas right off idle.

If that's what you're experiencing, then you probably don't have enough fuel going into the engine during the transition from the idle circuit to the main circuit under load/vacuum. The transition circuit includes the accelerator pump which gives the engine a squirt of gas off idle until the engine speeds up enough to start pulling gas through the main jets.

I'm not familiar with how quadrajets work, but every carb has an accelerator pump. This is how i'd deal with this if you were working on a holley. If this just started happening recently, I'd suspect the accelerator pump squirters. It's like the tip of the squirt gun. If this gets gummed up, it'll close the holes up and you'll let less of a shot of gas from the pump. Find out where the gas comes out of the accelerator pump and clean the squirters.

If that doesn't solve your problem, and if it's always been a problem then you need to match the squirt gun blast of your accelerator pump to your engine's needs. You do this on a holley by changing pump cups (different displacement), squirter size (different aperature), accelerator pump cams, and finally ajusting the rotation of the accelerator pump cam. Those were listed in order of drastic to fine tuning.

The accelerator pump is part of your transition circuit and your carb will have also a dedicated transition circuit that kicks in after you've pumped the accel pump shot and before the main jets kick in. Find out where those little holes/rods are and clean them too.

In short, clean all the tiny holes in the carb (pump sprayers and transition circuit jets/aperatures). Next, look for issues in your accelerator pump mechanism. These would be things like the wrong pump shot, sprayers, cam or even a torn accelerator pump cup/diaphragm.

This is a great site for understanding how carbs work:


Carb Tuning the Scientific Way

 

[Jim 5]

Also, did this all start when you changed you intake manifold?

 

[eljefino]

It might be fun to fit an o2 sensor to this truck with an in-dash AFR gauge. Great tuning aid for the carb, cheaper than you think. I assume it never had a computer? If it did there'd be an abandoned o2 already in the manifold but it's easy enough to drill a hole lower in the pipe and put one of those muffler-clamp-with-bung adaptors in. Probably could do for $50 with ebay parts and bosch universal o2.

 

[c3po]

The carburetor would BOG after it was warmed up, I checked the accelerator pump and it was fine. I still have to restart the car with the new gasket that sits on top of the carburetor.

I have had this intake manifold on there for 5 years. The funny thing is that she started running rough like this after I changed my thermostat, I had not bled the air out of the system. I then bled the air out and the car was running a little bit hotter than normal so I put a higher flowing Robertshaw thermostat on since I have an Edelbrock high flow water pump.

All of my vacuum caps had cracks in it so I replaced them, the vacuum hose for my vacuum advance on the distributor had a crack in it so I am replacing that hose.

I can still get GM Top Engine Cleaner which you pour down the carburetor and it gets rid of the carbon builup.

I plan on spraying carb cleaner around the carb gasket that mounts on the intake manifold as the carb bolts were loose, I may need a new gasket and I probably will put studs on instead of the carb bolts.

I think the other issue is that if I drive to soon after I start the car I can here popping in the exhaust system, kind of like a drum sound, I am still trying to get this choke to work right.

This car may only be driven in the warm weather after I get these issues resolved. I may have to take this carburetor to someone who really knows what they are doing. The inside of the carburetor is clean but maybe the accelerator pump is going even though I checked this to make sure it was squirting.

 

[Jim 5]

If it were me, I would save myself some hassle by going to a "pick n' pull" type junkyard and pulling one off a similar vintage car for about $15.

Then I'd bolt it on and see if your problems are solved. If not, you could take it off, give it a thorough cleaning at your leisure and then just bolt it back on without taking the car out of service.

Alternatively, if it doesn't help things, you could probably return it to the pick n' pull and get your money back. That's the pleasure of owning these older model vehicles.

 

[c3po]

Originally Posted By: Jim 5
If it were me, I would save myself some hassle by going to a "pick n' pull" type junkyard and pulling one off a similar vintage car for about $15.

Then I'd bolt it on and see if your problems are solved. If not, you could take it off, give it a thorough cleaning at your leisure and then just bolt it back on without taking the car out of service.

Alternatively, if it doesn't help things, you could probably return it to the pick n' pull and get your money back. That's the pleasure of owning these older model vehicles.


I would think that it would be less time consuming too add a can of GM Top Engine Cleaner. I have a friend coming over tommorow and I need to change his oil, so I will have to move my car out of the garage, I will let everyone know how this thing runs.

 

[JackFish]

Bogging could be caused by a ruptured accelerator pump, or perhaps it's just mis-adjusted.
I would rebuild the carb.

 

[c3po]

I checked the accelerator pump and it is fine, the place where I got the carb told me to richen it up a little bit. They want me too turn the mixture srews 2 turns counterclockwise.

 

[Rabbler]

The hot air choke (stove pipe) is in the exhaust crossover port.
The carbon won't be in the fresh air/fuel side of the manifold. It in a separate sealed chamber. Look elsewhere for a solution.

 

[c3po]

Originally Posted By: JackFish
Bogging could be caused by a ruptured accelerator pump, or perhaps it's just mis-adjusted.
I would rebuild the carb.


I went ahead and replaced all of the vacuum caps, and the vacuum hoses, it was still bogging when the car was totaly warmed up.

Sean Murphy, from Sean Murphy Induction, he sells and buids carburetors, told me to turn the 2 mixture screws, 2 TURNS to the left or we can say counterclockwise, and the BOG is no longer there. I guess richening the mixture made the bog go away, why is this, maybe I had a lean bog from not enough fuel.

The car is running much better and it feels more powerful, any thoughts or ideas would be appreciated.

 

[Jim 5]

You richened the transition circuit on your carb. Like I mentioned, there are two parts to the transition circuit, one is the accelerator pump and the other is the transition jets. Looks like you can adjust them on a quadrajet which is a nice feature.

Otherwise, you just richened your idle jets. In either case, you richened your fuel air mixture when your carb is just beginning to suck air, at low CFM values before your main jets kick in (which need higher CFM flow before they start having fuel pulled past them).

 

[johnd]

Bogging is usually spark plugs, not carburetor problems-esp. on that year of a vehicle and esp. if it occurs when warmed up.

 

[demarpaint]

Bogging could also be an incorrect air/fuel mixture. I mentioned to c3Po that the 2 turns counter clockwise is a ballpark figure, and COULD mean two turns CC from the needle valves being seated, not from where they were. Another mechanic had his hands on adjusting that carb, and who knows EXACTLY what he did.

Setting up the air fuel is a little more involved than just turning screws in or out a few turns, especially if good running and performance is a concern. JMO

 

[c3po]

I went ahead and e-mailed Sean Murphy from Sean Murphy Induction, he used to work for Jet Carburetors that rebuilt Quadrajets.

I mentioned in my e-mail too him what Demarpaint and my other buddy said about the needle valves needing to be seated and then turned out or counterclockwise. All I can say is that there is no more BOG, and that's with normal driving and a few times hitting the gas peddle hard.

I remember when I replaced my valve seals, my Dad's friend who was a mechanic adjusted the mixture screws and it ran great, but that was back in the summer, this problem started in the early winter when it got cold.

I may have to adjust it back a little in the warmer weather, but at least I have an idea as to what I am doing.

I will report back as to what Sean Murphy recommends for me to do with the mixture screws.

 

[demarpaint]

Hi Brent,

I think you're in the ballpark, and no bog is certainly a good thing. I was pointing out that there is no exact formula for adjusting a carb, by turning the screws CC wise 2 turns. Years ago we would seat the needle valves, back them out 1 1/2-2 turns and work from there with a tach, to get it to run the best it could. Very low tech but it worked, and was an easy way for the DYI'er. I'm sure Mr. Murphy will shed some light on the subject. For now no bog is great news!

 

[c3po]

Originally Posted By: demarpaint
Hi Brent,

I think you're in the ballpark, and no bog is certainly a good thing. I was pointing out that there is no exact formula for adjusting a carb, by turning the screws CC wise 2 turns. Years ago we would seat the needle valves, back them out 1 1/2-2 turns and work from there with a tach, to get it to run the best it could. Very low tech but it worked, and was an easy way for the DYI'er. I'm sure Mr. Murphy will shed some light on the subject. For now no bog is great news!


Frank, my buddy said the same thing that you said, and he was a lawn mower mechanic for 25 years, but he does have a lot of experience with carburetors, I am not going to be driving this car until I get his e-mail,meaning Sean Murphy. I don't need to start other problems like fouled plugs, NO BOG IS GREAT NEWS.

 

[c3po]

I got an e-mail back from Sean Murphy, and he said:

You acted correctly, you can now start turning them in 1/8th turn at a time until the bog returns, then go back to the previous setting that showed no bog.

 

[demarpaint]

Good to know my memory hasn't totally failed me yet. We used a tach, vs. the bog, it was a little more precise. Either way will work.

 

[artificialist]

At Carquest and NAPA, I have seen huge buckets of Chemtool that are designed so that a whole carb can be put in the bucket until the bad stuff dissolves away.

They aren't gone. I guess they get less popular once carb engines became much less common.