RocketyMan

Alright guys...So I can't seem to get my carb to tune right AT ALL! I'm super frustrated and have been working on this for two whole days!

I don't know why but I think I have a vacuum leak SOMEWHERE and I have absolutely NO idea where it could possibly be. I have the idle screw all the way down and it still just idles at around 1000 rpm to maybe 900ish. I don't know what I'm missing here.

The only other thing I think it could be is something in the throttle plate. Recently I tried rebushing my original throttle plate and it broke. So I then got another CCC carb and took that throttle plate to rebush professionally. I then rebuilt the whole carb and adjusted the float..etc. Now it starts OK (i guess) and then I verified the choke working and coming down. I feel like it's running super rich or SOMETHING...and then a vacuum leak? I don't know. The dwell seems to be working but its so difficult to say!

The first picture is when I was about to take it off again (disconnecting everything).



I need help!

RocketyMan

anybody???

RocketyMan

Can a dirty throttle plate cause the mixture to run very rich??? As in the insides where the needle adjustments are.

RocketyMan

Okay...nobody has any input. Well I'll keep posting pics and posing thoughts until I get this RESOLVED.

So I took off the carb AGAIN for the fourth time. Managed to keep the base gasket from ripping by soaking it with grease every time and not bolting down the carb too tight to the intake manifold.

I do notice that EVERY single time I have taken off the carb, the gasket seems SOAKED in gas. One time I took the carb off after the car running poorly and looking into the intake manifold it looked rather wet and hazy from vapor. Then after I held the carb over my head and noticed the primary dwell plugs looking like they've been seeping fuel down them--almost leaking drops of fuel over my head. This makes no sense because I epoxied them and they haven't leaked before.

Now keep in mind I have two E4ME q-jets that I have been using. I've been using the same throttle plate because I got the throttle shafts professionally bushed ($91-ugh.. for brass sleeves...prim and sec). So I then changed JUST the q-jet BOWL with another one that I epoxied already while still using the same air-horn. My original air-horn got messed up because I could not drill out the TPS adjustment screw plug. Instead it just drilled the screw down while not fully removing the plug (okay..my fault...really STUPID idea. I was just trying to make it adjustable and did not know how to remove the stupid plug right). So that is why I am still using the other airhorn.

Now I am still experiencing HIGH idle with both float bowl bodies and same airhorn/throttle plate. I think it not longer is a vacuum leak, but rather an over-rich mixture. I can get the dwell to hover around 50% but the engine can ONLY idle as low as 900 rpms with the idle screw ALL the way out. I know something is up because of not only that, but also because the engine shakes as it is running so roughly.

I miss my smooth running V8..even with its slightly sporadic idle with worn idle shafts..

Question:
1. Could an airhorn be worn out in some way to leak fuel around the primary dwells? (I should post a pic of the airhorn I messed up)

2. Is there a way that a throttle plate can cause fuel to leak from something around the primary dwells?


Please help.

five7kid

iTrader: (14)

The thick base gasket is all you should need.

Rough running could be a vacuum leak. Most likely from a vacuum port on a runner. Another cause could be an ignition issue.

But, 900 RPM idle with the idle speed screw all the way out suggests something is holding the throttle plates open. The wrong base gasket could do that.

Those well plugs are a pain. If they're leaking, clean off the epoxy thoroughly, rough up the surface, degrease thoroughly (I like brake cleaner for that), and redo the epoxy over them.

RocketyMan

Hey 57...

Yeah, I'm still thinking there is a vacuum leak SOMEWHERE.

I took off the throttle plate before and looked at both the primary and secondary flaps. When they close I can see a very SMALL amount of light shine through the gaps when the shafts are "closed." So on the bowl where the idle screw is, the throttle lever never touches the bowl-body with the screw all the way out. Meaning I don't think anything is hanging up on the throttle shaft.

If the EGR was sticking open slightly, this wouldn't cause an idle increase, would it? If anything, it would just make the engine run at lower rpms and very poorly.

The only other thing on the intake runners is the accessory vacuum line that goes to the vacuum tank. I still think my brake booster is good and holds without any leaks. I could try capping off all the vacuum lines off the carburetor. I.e. PCV, early fuel evap, brake booster..

RocketyMan

Alright. So I'm following up on my initial thread since I got the time to tinker with the '84 some more.

I like rebuilt the carb a million times (took it apart and back together again) and then finally put it back on the car this time. The only thing I did NOT hook up was the PCV line that runs with the EVAP canister purge.

NOW I get a smooth idle!! I can actually tune down the idle to about 550-575 rpms once fully warmed up and it is pretty stable. I get a dwell of about 55%-65% but that's with the idle airbleed turned in all the way. If I turn the idle air bleed out any number of turns my dwell goes to like 70-80% or higher. So I know I must need to adjust my idle mixture screws a little bit fatter.

SO the main issue at hand is why can't I get a stable idle with my PCV hooked up? (I checked the evap canister and purge and they both hold vacuum)
1. Do I have a bad PCV valve? - I checked the little guy and nothing is stuck open with it. It rattles..
2. Do I have bad valve cover gaskets causing excessive vacuum leak or something like that?

I really don't know why it would acting as such. But I imagine running without a PCV is bad. So I would definitely want to run with it hooked up.

RocketyMan

I decided to work on the '84 some more this weekend and I bought a new PCV valve for it. Put that in and it seemed to idle smoother but still the lowest I can get it is at 750-800 RPMs with the idle screw all the way out.

I ensured that I was getting into closed loop by varying dwells. The best I can get is about 55-65% dwell. But on the idle air bleed, I'm still at only ONE turn out and THREE turns out on the idle mixture screws. I can't get the dwell any better with the idle airbleed screw turned in all the way.

I'll try adjusting the idle mixture screws more tomorrow and probably aim for four turns out. I have a gut feeling that it isn't going to help the idle air bleed out much and getting the nice 50% dwell.

I still don't know why I'm getting a relatively high idle when I can't bring it down any farther. The car runs pretty smooth but with the throttle blades closed all the way, how is this possible? I feel like something is wrong, and it lies in the carb.

Can a warped airhorn cause high idle/act like a vacuum leak????

RocketyMan

Okay with four turns out on both the idle mixture screws, I got the idle air bleed to be turns out at 50-55% dwell reading.

I'm thinking the reason why I can't get the idle to come down any further is because of the idle discharge holes. I'm guessing the sizes of these holes might change with different models of qjets?

http://books.google.com/books?id=lTh...20port&f=false

RocketyMan

So I finally resolved this issue. In case anybody is wondering, it was the idle discharge holes. I ended up plugging them in the throttle bore. (SEE PICTURES).

This allowed me to get the idle down to 600 with 18" Hg. And it idles steady while entering closed loop.

In the first two pictures you see me pointing the screwdriver head at these "idle air bleed discharge holes." There is one for each primary venturi. These discharge holes of course bypass the throttle blades completely and draw their flow completely through the carburetor up at the top of the airhorn.

Please see the next post for further explanation with pictures.

RocketyMan

In the next two pictures you see me pointing the screwdriver head at the passageway drilled from the top. Now I carefully examined by blowing air through the top of these holes and confirmed that there are NO other passage ways that interconnect with these air bleed discharge holes.

RocketyMan

From the throttle plate on upwards to the float bowl, these discharge ports then draw their dedicated flow up towards the airhorn.

In the pictures, you see the one with the gasket of which this covers up with the throttle plate and bowl sandwiched together. I showed the one removing the gasket revealing that these passage ways (both right and left sides remember) do not interact with anything else.

RocketyMan

Next on the other side of the float bowl (right side up). You can then follow the passage ways on both sides and verify that nothing else interacts with them.

Finally, you can see how this then follows up to the airhorn and is left completely open to atmospheric pressure via a slat in the airhorn!

Now I've read one of the quadrajet books and could NOT find anything about the purpose of these air bleed discharge holes that run past the throttle blades. So since I view this as a COMPLETE vacuum leak I decided to cover them up! Now all I used was simply a .177 cal pellet and placed several (two) in each drilled hole in the throttle plate. Then I simply punched then in a little bit and verified they would not fall out by turning the throttle plate over. Even if they did manage to come loose, the pellets would be kept internally.

Now my engine can idle at the correct RPM (hot engine and in closed loop) with this vacuum leak taken care of.