Carb Rebuild Yields Extra Parts!?!

[lintcollector]

My daughter and cleaned and rebuilt a 1972 c10 Quadrajet Carburetor. Things were going well until we found two issues, one of which we will order the second is where we are stumped.

1. Our carb is missing the Power Piston Spring, I'm ordering one today.

2. We found we ended with an extra part and can't find a diagram, pic, or anything related to this bonus part: Secondary Air Valve Cam (see stock pic below).

While I know that being more efficient is important, I can't see having extra parts left over from a rebuild being a good thing. Can anyone provide a pic, or an idiot proof reference where this little guy should be located in my carburetor?

Thank you in advance.

Mike

[68Gold/white]

OK, on top of the carb, there is the area or housing where the choke flap resides...
Just to the rear of that, on top is the secondary air flap. That flap controls secondaryair into the secondaries... If you push down on the sec air flap, you will see the secondary fuel metering rods raise up, at the same time you push down on the flap. This little piece of plastic is what is raising the needles. It's on the sec flap shaft, right in the middle.

[fast/cheap/right]

Looks like the cam that goes on the secondary rod in the top plate to me.

68 beat me to it, what he said.

[lintcollector]

Originally Posted by 68Gold/white

OK, on top of the carb, there is the area or housing where the choke flap resides...
Just to the rear of that, on top is the secondary air flap. That flap controls secondaryair into the secondaries... If you push down on the sec air flap, you will see the secondary fuel metering rods raise up, at the same time you push down on the flap. This little piece of plastic is what is raising the needles. It's on the sec flap shaft, right in the middle.

Thank you so much, I do appreciate it. This was one of those parts that fell out along the way and I had no idea when/where it was located. I bet it'll work a bit better now.

[lintcollector]

Originally Posted by fast/cheap/right

Looks like the cam that goes on the secondary rod in the top plate to me.

68 beat me to it, what he said.

Thanks for your help, I appreciate it.

[Ironangel]

That is the Secondary Air Flap Cam. It locates inside the slot (between the two air flaps) on the Secondary Air Flap Shaft. Underneath the Secondary Metering Rod Holder shown as #9 in this diagram. http://www.carburetion.com/Quads/M4MC-E.htm Here's the kicker, most kits and diagrams don't show or come with that part. Although the link above does have them available, they do not show an installation procedure or diagram. They have a phone number though, call em up...

[68Gold/white]

I've never had any issues with that part being/going bad. It can be a royal pain if it's worn down a little, or a lot, performance problems...

[lintcollector]

Originally Posted by Ironangel

That is the Secondary Air Flap Cam. It locates inside the slot (between the two air flaps) on the Secondary Air Flap Shaft. Underneath the Secondary Metering Rod Holder shown as #9 in this diagram. http://www.carburetion.com/Quads/M4MC-E.htm Here's the kicker, most kits and diagrams don't show or come with that part. Although the link above does have them available, they do not show an installation procedure or diagram. They have a phone number though, call em up...

I tried calling but they are enjoying a nice loong weekend. I sent them an email to get the cam, Power piston spring that was missing, and a few fuel filters.

Thanks for your help!

[HO455]

The power piston spring Is what controls the part throttle enrichment. When at steady state cruising the engine vacuum is high pulling the piston and the metering rods down to the leanest position. When the throttle opens and vacuum drops the spring pushes the piston up and raises the rods richening the fuel mixture.
There are at least a dozen different springs that were used in Qjets and they all respond at a different vacuum level. When you call they should at the very least ask you what your manifold vacuum is at idle. If you were to know what the vacuum is at cruise that would help them get you the correct spring.
Having no spring probably means you have had poor light throttle acceleration and maybe some lean misfiring and or pinging.

[Steeveedee]

You will need to pull the secondary air valve flaps off and pull the shaft out part way to get to where you can install that metering rod cam. Use a lot of car over by the secondary air valve return spring to avoid damaging it. You need to remove it to get the shaft out. This part broke on my truck, and I don't know where the parts went. It just about died whenever I floored the throttle, because it got lots of air and no fuel. I ordered a carb kit from Cliff Ruggles and asked that that cam be included.

[lintcollector]

Originally Posted by HO455

The power piston spring Is what controls the part throttle enrichment. When at steady state cruising the engine vacuum is high pulling the piston and the metering rods down to the leanest position. When the throttle opens and vacuum drops the spring pushes the piston up and raises the rods richening the fuel mixture.
There are at least a dozen different springs that were used in Qjets and they all respond at a different vacuum level. When you call they should at the very least ask you what your manifold vacuum is at idle. If you were to know what the vacuum is at cruise that would help them get you the correct spring.
Having no spring probably means you have had poor light throttle acceleration and maybe some lean misfiring and or pinging.

Thank you for the detailed explanation on the purpose and how to know what each kind of spring will accomplish in regards to the fuel being rich or lean. I greatly appreciate it.

[lintcollector]

Originally Posted by Steeveedee

You will need to pull the secondary air valve flaps off and pull the shaft out part way to get to where you can install that metering rod cam. Use a lot of car over by the secondary air valve return spring to avoid damaging it. You need to remove it to get the shaft out. This part broke on my truck, and I don't know where the parts went. It just about died whenever I floored the throttle, because it got lots of air and no fuel. I ordered a carb kit from Cliff Ruggles and asked that that cam be included.

I had the same little issue. My daughter told me she gave it to me, but I have no idea where it took off too... Then again, it'll keep her from flooring the pedal, but her bank account will quickly encourage her not to try and bury the needle on this monster.

[Steeveedee]

Originally Posted by lintcollector

I had the same little issue. My daughter told me she gave it to me, but I have no idea where it took off too... Then again, it'll keep her from flooring the pedal, but her bank account will quickly encourage her not to try and bury the needle on this monster.

Yabut, she's not going to be able to go over about 50 MPH on level ground and hills will be a challenge. I know from personal experience.

If you can't find it, it was probably cycled through your engine like mine must have been. In order to take it off during a rebuild, you'd have to do what I said earlier, with removing the secondary air valve flaps, etc.

[lintcollector]

Originally Posted by Steeveedee

Yabut, she's not going to be able to go over about 50 MPH on level ground and hills will be a challenge. I know from personal experience.

If you can't find it, it was probably cycled through your engine like mine must have been. In order to take it off during a rebuild, you'd have to do what I said earlier, with removing the secondary air valve flaps, etc.

Ya, I took apart the carb very well to make sure it was cleaned through and through. I'm going to do an update on the truck rebuild probably tomorrow night.

Thanks for your help on this and other parts I've came across and started.

[HO455]

Originally Posted by lintcollector

Thank you for the detailed explanation on the purpose and how to know what each kind of spring will accomplish in regards to the fuel being rich or lean. I greatly appreciate it.

You are welcome sir.

[Steeveedee]

Originally Posted by lintcollector

Ya, I took apart the carb very well to make sure it was cleaned through and through. I'm going to do an update on the truck rebuild probably tomorrow night.

Thanks for your help on this and other parts I've came across and started.

¡De nada!

[lintcollector]

The parts came in and the carb now moves like I hoped it would. Thank you for your help one and all.

One item of note for any future folks who may need this, the Secondary Air Flap Cam goes with the large side facing towards the center of the carb, not with the large side resting against the piece the Secondary Metering Rod Holder connects with. It looks like it is made for the large side, but then the carb won't open when it's supposed to. We learned that little detail too!