QJet Rebuild problems - Team Camaro Tech
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post #1 of 11 (permalink) Old Nov 11th, 02, 05:28 AM Thread Starter
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Paul
 
Join Date: Sep 2001
Location: Queen Creek AZ
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I have a 7028213 carb that I rebuilt. It has 46 primary metering rods, 71 primary jets and AN secondary rods. I took the carb apart, soaked it and cleaned all of the passages with carb cleaner and compressed air and epoxied the plugs. I bought a rebuild kit from Napa which included the accelerator pump, check ball, needle and seat, float, vacuum break and gaskets. I put everything together and set the float. I bolted it onto my 350 and pumped the throttle lever. It shoots a nice even stream on both sides. The carb idles kind of rough....The engine roams while idling around 900 RPM, which is different than my 7029202(42 rods, 67 jets, AN secondary rods) carb which idles smoothly at 700RPM. I pulled the plug from my manifold vacuum source and the engine died. With my 7029202 carb the RPMs would increase if I pulled the plug. While idling the vacuum gauge roams(with the idle) between 13 and 15 inches. With the 7029202 carb it is a steady 15 inches. While adjusting the air fuel mixture at idle the passenger side screw changes the characteristics of the engine, but the drivers side can be screwed all the way in with no impact. I took it for a test drive.....Everything seems OK until I get into the secondaries....it bogs. I figured that was because of the bigger jets?

Given the roaming/rough idle and the symptoms given above anyone have any suggestions to fix the 7028213 carb?

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post #2 of 11 (permalink) Old Nov 11th, 02, 06:26 AM
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Vacuum leak or the idle passage on the drivers side is still plugged.

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post #3 of 11 (permalink) Old Nov 11th, 02, 06:28 AM Thread Starter
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Paul
 
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Yes....that's what I was thinking....Maybe the "pickup tube" on the one side is plugged so that no fuel is getting to the one side at idle???

I hate vacuum leaks, so I hope that's not it.

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post #4 of 11 (permalink) Old Nov 12th, 02, 07:03 AM Thread Starter
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Paul
 
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I took the carb back apart and made sure none of the bleeds/tubes were clogged and bolted it back on. I am having the same problem.....I put my hand over the top of the carb and the RPM increased. That means vacuum leak or lean condition right? What are common placed for a QJet to have a vacuum leak? I sprayed carb cleaner around the base and around the throttle body/base plate gasket and couldn't find a leak. The throttle shaft has been rebushed, so no leak there either....Can there be a vacuum leak at the air horn/throttle body gasket?

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post #5 of 11 (permalink) Old Nov 12th, 02, 11:54 AM
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Matt Jones
 
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I would too check for a vacuum leak, by placing a straightedge along the baseplate.

I would also wonder if the engine is getting enough fuel at idle. This can be accomplished by drilling out the idle restrictor ports (I believe that's the name, but it's the holes where the idle mix screw pokes out of in the primary bore). There is some good info on the web about this, or if you have Mr. Roe's book.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
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post #6 of 11 (permalink) Old Nov 12th, 02, 12:02 PM Thread Starter
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Paul
 
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I am going to put on a thicker gasket tonight to try to "make up" for any warpage. I am also going to put on another airhorn gasket and rejet the carb(not that it will help but It needs it anyway).

The 7029202 carb works just fine at idle, so I'm assuming that I don't have to modify the 7028213 carb to get it to idle. I'm sure this problem was caused by me doing something STUPID again! Everytime I change anything on my car I do something dumb and have to redo it. I try to be careful and thorough, but it never seems to work out.

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post #7 of 11 (permalink) Old Nov 14th, 02, 04:16 AM Thread Starter
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Paul
 
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I took the carb back apart(again) and made sure all of the passages were clear. I put on a thicker intake gasket and added another airhorn gasket....no change. I did find that I was getting a leak from the vacuum break hose, so I changed it. It improved slightly, when I remove the intake vacuum plug the engine doesn't die, but it doesn't speed up either. I sprayed carb cleaner all over the outside of the carb and the idle didn't change at all. Actually I had the vacuum gauge hooked up and I watched for a change on that as sometimes it's hard to hear slight RPM changes.

I have no idea where else to check for a vacuum leak. I put the 7029202 carb on and everything is great, put the 7028213 carb on and vacuum leak. Can they have an internal leak somewhere?

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<A HREF="http://www.stratagaz.com/69LM1/1969LM1Convertible.htm" TARGET=_blank>My 69 LM1 Convertible
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post #8 of 11 (permalink) Old Nov 14th, 02, 05:34 AM
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Matt Jones
 
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Just to square things up, the idle discharge ports on different Qjet can be different. Some are larger, some are smaller. An engine that gets the right amount of fuel on one Qjet might not get enough at idle, causing all sorts of weird problems.

You can also get a vacuum leak around the intake gaskets too, remember. But I don't know how that would have happend.

But I am willing to bet you have worn out throttle bushings. They can cause vacuum leaks, high idle, and other weird stuff. I've got a Qjet that also needs the bushings replaced, and it did something similar to what yours is doing. There's a shop around here (www.carbs.net) that does it for $45 or so if you send them the baseplate.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #9 of 11 (permalink) Old Nov 14th, 02, 05:53 AM Thread Starter
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Paul
 
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The throttle has been rebushed and if I had a leak anywhere besides the carb, the 7029202 carb would show the same signs as well but it works fine.

With the 7028213 carb when I put my hand over the top of the carb the RPM increases so that is a vacuum leak/lean condition. I was assuming that any old quadrajet from 67-69 in good working order should be able to make the car idle smoothly.

Are you saying that the discharge ports on the 7028213 carb may be different than the 7029202 discharge ports? If so I would think that by adjusting the mixture screws that this could be compensated for.

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<A HREF="http://www.stratagaz.com/69LM1/1969LM1Convertible.htm" TARGET=_blank>My 69 LM1 Convertible
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post #10 of 11 (permalink) Old Nov 15th, 02, 05:37 PM Thread Starter
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Paul
 
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I took it apart again and cleaned all the passages....especially the two bleeds next to the primaries...also ran a fine piece of wire through them. I added a second airhorn gasket and reassembled. Everything seems to be fine now, it pulls a steady 15" at idle. I think my engine likes the new 73 jets/43 rods! Originally it had 67 jets/42 rods. The metering area changed from about 2.1 to 2.8....It seems to pull alot harder at WOT now!

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<A HREF="http://www.stratagaz.com/69LM1/1969LM1Convertible.htm" TARGET=_blank>My 69 LM1 Convertible
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post #11 of 11 (permalink) Old Nov 15th, 02, 10:14 PM
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Glad it worked out
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