Vaccuum Secondaries...not opening????

[Paso76GMCstepper]

Ok Guys the truck runs awesome I just dont feel that surge of power when you really get on it. Could my secondaries not be working. Its got a quadrajet carb. There are no vaccuum leaks and it runs perfect. No pinging or anything. What can I check to see if they are working correctly?? Any info or easy test would be super.

Thanks again guys.



Tony

[TwinTurbo]

Only a mech. secondary carb will give that feeling of the secondaries kciking in. The Q jet is a variable flow type of carb, meaning that the pos. of the secondaries varies with engine demand (that's why they fit so many engine applications)

[Paso76GMCstepper]

Hey Twin, Thanks for the speedy reply I just looked at it it looks like its got mechanical secondaries??

I see a rod next to the throttle linkage and when I push the throttle linkage all the way it doesnt seem to move. Haw can I check if its manual or vaccuum. It has an electronic choke. I dont think the is the original carb.



Tony

[TwinTurbo]

Is it a seperate rod (as something for a cruise control) or do you mean the pump link rod??? Kind of hard to figure out what you mean. Can you snap a pic and point out what you mean?

[Paso76GMCstepper]

I understand Here are a few pics. If you need anything else let me know. If I open the throttle all the way manually should the secondaries open??



Tony

[skillet]

Chevy High Performance March 2004 has a good article on Q-jet entitled "Special Q." It mentioned that "the air-door tension (on the back barrels) must be properly adjusted. If it's too tight, the door won't open under load and the engine will strain. If it's too loose and the door opens too quickly, it will bog. If you feel some light-to-moderate resistance when pushing the door open, the adjustment should be about right." If the front of the carb was facing north, the screw would be at the southeast corner of the carb, corner passenger side as it's mounted. On mine(1969), an allen set screw should be loosened before the other screw is adjusted. I tinkered with mine, but never really noticed much difference. Still learning.

[Grim Reaper]

Originally Posted by skillet

Chevy High Performance March 2004 has a good article on Q-jet entitled "Special Q." It mentioned that "the air-door tension (on the back barrels) must be properly adjusted. If it's too tight, the door won't open under load and the engine will strain. If it's too loose and the door opens too quickly, it will bog. If you feel some light-to-moderate resistance when pushing the door open, the adjustment should be about right." If the front of the carb was facing north, the screw would be at the southeast corner of the carb, corner passenger side as it's mounted. On mine(1969), an allen set screw should be loosened before the other screw is adjusted. I tinkered with mine, but never really noticed much difference. Still learning.

Yep and screwing up that door setting is where Quadra "BOG" moniker came from.

If your pulling steep hills with no Ping or spark knock...They are opening. Leave it hte hell alone.

[TwinTurbo]

The little rod just operates the butterflies (throttle plates) on the secondary part of the carb, the plate above them in the airhorn assembly is controlled by a valve (pressure difference between primary and sec. sections) so the secondary butterflies are mechanical of course but the plate in the airhorn is what determines the amount of flow possible through the secondary stage.

[Paso76GMCstepper]

Ok I kinda get it. What do I check to see if they are truly working or not.

[Destructo]

Originally Posted by TwinTurbo

The little rod just operates the butterflies (throttle plates) on the secondary part of the carb, the plate above them in the airhorn assembly is controlled by a valve (pressure difference between primary and sec. sections) so the secondary butterflies are mechanical of course but the plate in the airhorn is what determines the amount of flow possible through the secondary stage.

This rod that controls that goes from the secondary linkage at the top to the same vacuum pot that controls the choke right? What happens if it is missing? Mine is not there and I suspect I have a carb problem but I did rebuild it but don't think I did a good job and didn't get it totaly clean.

[NeCrOmAnCeR]

Keep in mind also that if the choke is closed (engine cold) the q-jet secondary butterflies are prevented from opening . If you look on the pasenger side of the carb when you open the throttle by hand, you can see the lever which blocks the secondaries from opening. Make sure that when the choke is fully open that that lever is held out of the way by the choke mechanism. The secondary air valve uses both spring pressure and engine vacuume (choke dashpot / pulloff) to prevent it from opening too soon. You can see this linkage running from the air-valve to the vacuume dashpot, also on the passenger side of the carb.

[Paso76GMCstepper]

Ok I am really stumped. After taking the air cleaner off and looking at it. Here are some pics. I know this is a nwebie question but I need some help. When I move the throttle linkage by hand it goes all the way back but the secondary doesnt move. I CAN move it both if I use the secondary arm then they both move. Here are some pics. Will I be able to see this sitting still or will this be one of those u gotta drive it deals.

Any and all opinions are appreciated.

Also here is the numbers off the carb 17066575 2302W

I tried decoding it it seems to be a Pontiac California Emmissions carb on it. The truck is registered federally




Tony

[NeCrOmAnCeR]

To Paso... When you operate the throttle by hand, you may open the secondaries depending on wether the choke is warmed up (see my previous post) Even if it is opening, the secondary air valve (the plates you see on the top of the carb which lift the secondary metering rods) will remain closed. In your most recent post, the second picture shows the linkage I talked about earlier (holds the secondaries closed until the engine is warm), and in this position it is keeping the secondaries closed. Warm up the engine and check to see if this linkage is swinging out of the way to allow the secondaries to open. I have attached the image with the part circled (hopefully).

[Paso76GMCstepper]

Well I had my boss look at it and there is a black piece of metel on the drivers side that when the throttle linkage goes back the black metal thing was all bent in towards the carb. We bent that straight and now the secondaries open. I got on it from a stand still and it scared the Krap out of me. Definatly working now. Thanks for all the help. What I wonder is how that metal tab got bent in the first place. The piece Im talking about gets pushed by the throttle linkage when it goes back it now hits the black metal making it possible that the secondary linkage now works.

NECROMANCER:: The thing you circuled has the black metal piece on the throttle linkage side. on the other side of the carb is what was bent so the thing you circuled didnt get out of the way. I bent it back and works like a dream

Tony

[Grim Reaper]

Originally Posted by NeCrOmAnCeR

To Paso... When you operate the throttle by hand, you may open the secondaries depending on wether the choke is warmed up (see my previous post) Even if it is opening, the secondary air valve (the plates you see on the top of the carb which lift the secondary metering rods) will remain closed. In your most recent post, the second picture shows the linkage I talked about earlier (holds the secondaries closed until the engine is warm), and in this position it is keeping the secondaries closed. Warm up the engine and check to see if this linkage is swinging out of the way to allow the secondaries to open. I have attached the image with the part circled (hopefully).

Man that is one hobbed together Q-Jet pobably from Micky mouse rebuilders( Holly). It will wor but you have at least two different model carb bolted up there.

Looking at the passenger side picture you have see that red vac plug at the top rear of the carb. That's for a hot air style choke used late 70's till about 81 when they went electric.

The choke atleast is a newer then 81 because it is indeed a electric choke bowl. If it matched the top plate it would have two Vac connections on it and you can easily change a hot air into a electric.

I dont have my book with me but the 2302 is the date code. I think thats 23week of 02=1982 so it could match the choke. THe scary part is that is about the same time mix soloniods came on. Also if you look at the passengerside at the back you can see there use to be a bracket there. Well some years the vac pot for the secondary top door lock out mounted there and the threads look used. They went with the early style because it mounted to the top cover as well.
Base plates were pretty much all the same so no biggie.


Real bastard of a carb ya got. If it works go with it.

[Paso76GMCstepper]

GRIM:

Thanks for the info. I always wondered about that. I have looked at pictures and tech stuff and the parts on my carb never seem to be right. My question is what would be the best way to deal with this problem. Would this carb be less efficient? Should I get a new one or can this one be made right?

Thanks again,

Tony

[skillet]

Are the electric choke Q-jets carbs any better/less complex, etc. than the thermostatic Q-jets?

[Grim Reaper]

Originally Posted by skillet

Are the electric choke Q-jets carbs any better/less complex, etc. than the thermostatic Q-jets?

Much more consitant with electric choke. You do have to add a oil pressure switch so that if the engine is not running if doesn't get power. That's how GM had it. If you jusnk yarding then any GM with a Quad or a Dual will have the switch if it was made between 81 and 86. It's either behind the distribuotr or above the oil filter. Get the harness as well and fuse it at 15 amps on a IG circuit.

Now pass on the Quads that have the plug on the top of the carb front. THos are a pain.

[Grim Reaper]

Originally Posted by Paso76GMCstepper

GRIM:

Thanks for the info. I always wondered about that. I have looked at pictures and tech stuff and the parts on my carb never seem to be right. My question is what would be the best way to deal with this problem. Would this carb be less efficient? Should I get a new one or can this one be made right?

Thanks again,

Tony

Sounds like it's working. Stick with it till it's not.

[NeCrOmAnCeR]

To Destructo...

If this linkage is missing it is almost certain that the secondaries are allowed to come in to soon. A tempory linkage could probibly be made out of some welding rod, bend it to look like the one shown above. With the vacuume pot fully withdrawn, the linkage needs to just hold the secondary air valve in the closed position.

[Destructo]

Originally Posted by NeCrOmAnCeR

To Destructo...

If this linkage is missing it is almost certain that the secondaries are allowed to come in to soon. A tempory linkage could probibly be made out of some welding rod, bend it to look like the one shown above. With the vacuume pot fully withdrawn, the linkage needs to just hold the secondary air valve in the closed position.

That would certainly explain the bog I have when I go from closed throttle to WOT, I figured it was supposed to have a linkage there and the air coming through would allow them to open to quickly, i'll have to see if I can fab something up or get a rod from somewhere.

[apstguy]

Do you have a PCV valve on that truck?

[Paso76GMCstepper]

Yes I do would that make a differance. I put a filter breather on the valve cover where the thermostatic air cleaner used to be hooked up

[apstguy]

Not the breather but the actual PCV vlave. You have the PCV valve line blocked off at the carb. No it probably wouldn't make a difference. The yellow cap is where my PCV valve is connected.

[Russell]

Yeah, I'd reccomend getting a proper PVC valve for that truck... You'll gum your motor up something nasty if you don't get all that stuff taken out and burnt