7029202 Q-jet Issues

[Z10Mike]

Just got my q-jet returned after being restored.  Looks great.  Installed the carb and can't get a stable idle, it dies when I get the rpm down to about 700, when the throttle is stabbed the rpm's jump up and won't drop back down and the exhaust is so rich it burns your eyes.  Tried to adjust the idle screws to the same turns out that they were before and also the same as the backup q-jet and it still doesn't run worth a darn. The backup q-jet would start and idle perfectly so I know the rest of the fuel delivery system is good. Any ideas what could be the issue?  I checked the base gasket again to make sure my late night flog didn't result in it being installed backward but it is on correctly.  Sure wish they put Holley's on these things.  Any help is appreciated.

[Kelley W King]

I think I would send it back to the restorer.American Carb tests the ones they on a real engine before sending back. Ask your guy if he did?

[KevinW]

Sounds like you secondaries are binding.  I had that issue recently after a quick rebuild.  Cleaned the shafts and assembled the base to the body with the butterflys open to make sure nothing was binding.

[69Z28-RS]

I assume the restorer drilled and installed bushings on the throttle shaft?   Generally the restorers price bushing the throttle shaft separately from restoring color and rebuilding. (extra charge).  That's one of the primary wear out issues with the Qjet...  otherwise you get a lot of air leakage around the throttle shaft.

[Z10Mike]

Thanks to all for the feedback.  I was busy with yardwork for a couple days and didn't get back to the car until last night.  Throttle shaft bores are tight and the secondaries have full rotation and return to their stop position without any restrictions. I will play around with it some more and if it doesn't straighten up back she goes.  If anyone has other ideas get on here and let me know.  Thanks again...

[KevinW]

OK, secondaries are closed, still rich, correct? Float issue?  Take a small pin or screwdriver in the vent hole.  You should feel the float. When you push on it slightly, some gas will come out the jets.  If the float is stuck to bottom of bowl (happened to me!), the fuel will be in the vent and spill out.  If the float is all the ways at the top, it will feel like it is hitting the gasket.  Proper float level is slightly below the gasket level (which you can also feel).

The other idea is a leaking jet well(also happened to me!). Need to replace the JB weld, but I think discussing that with the rebuilder would be a good discussion. Let us know

[Mike S]

 I wold definitely look at the power valve hanging in the bore thereby leaving the metering rods hung upward. The power valve should be closed at idle (vacuum pulls it down against a spring)and keeps the meeting rods down within the main metering jets at idle. You can try to "feel" the power valve by inserting a small rod or light weight screwdriver down the vent and feel for a faint spring loaded up/down motion of the valve with the motor off. Sometimes the valve will hang up in the bore.
 I found this picture on the web that shows it.

Mike

[KevinW]

Good suggestion Mike!  I had that happen as well. The way the power valve (PV) works is: under high vacuum (idle), the PV gets pulled down, the stepped metering rods would have the thickest part in the jet, which reduces fuel flow.  Under low vacuum (acceleration), the PV raises allowing the thinnest part of the rods to be in the jets, this increases fuel flow. 

What happened to me is a little ring of gunk (evaporated gas residue) to be in the jet.  This prevented the rods from going into the jets to their lowest point. This meant too much fuel was getting in at idle.

If the float is good, you need to open up the carb and inspect the bowl area and jet wells for any issues. Luck!

[Z10Mike]

I checked the power valve vertical displacement & spring action with the engine off.  No spring action at all.  Feels solid with no vertical movement.  Seeing as the carb has just been gone through it's likely that the power valve/primary rods are hung up.  If I recall correctly the gasket between the throttle body and top plate if not positioned correctly can cause the hang up.  I have family obligations today so I'll try to check out my spare carbs tomorrow and look at their power valve spring action.  My bets are on them being free to move vs the "new" carb.  Thanks to all for your input.  Collective knowledge on this site is vast indeed.

[z28z11]

Any update ?

I've been struggling with a number of 7029202 issues for the last couple of weeks - what I deserve for relying on someone else's rebuild (read as mangle).

Your power valve may not have been positioned well during the "top drop". Tough to keep it from popping up out of the bore unless you are very careful, or use a new split bushing which will help keep the thing positioned correctly until the top casting is set in place. It only takes four or five hands to do it, as you probably know. There is also a small spreader spring that should be in place on the upper needle mount area, helps keep them aligned and not touching the float arms. Gasket will position the hanger correctly if the power valve/needle assembly is installed in the gasket correctly -

Secondary well plugs can be replaced with new o-ringed plugs. I'm doing that on mine next weekend, will share some pics on procedure if you'd like them.

My worst problem is a heli-coiled inlet. Someone butchered the gasket sealing surface around the inlet fitting at the same time - my worst headache now. Hopefully I can get it sealed.

I still think they are great carbs, despite some drawbacks in design (like the front bolts), they flow well and last a long time in use with minimal care. A lot of parts are available still, so good luck with your 202 -

Regards,
Steve

[jeff68]

My worst problem is a heli-coiled inlet. Someone butchered the gasket sealing surface around the inlet fitting at the same time - my worst headache now. Hopefully I can get it sealed.

I had a very small leak at my inlet due to a tiny 'ding' on the sealing surface.  I ended up using one of the thicker type nylon gaskets to fix it ( IIRC it was a Holley part).  I cleaned everything really well, then used a little grease between the gasket and the inlet fitting.  This allowed the gasket to stay in place relative to the carb body, and push down into the ding.  I marked the gasket to make sure it didn't turn, and continued to re-tighten the inlet fitting every few days as the nylon gasket conformed to the carb body.