new to forum. have issues with rebuild on new motor

[soe1]

Hello everyone on the forum. I have enjoyed reading the very educational posts on this site as I dig into first attempt at a qjet rebuild and setup.  I bought cliffs book and read through it a few times now. I am in the middle of tuning,re-tuning, etc. my setup is as follows.  sbc 406. 11.2:1 comp. lunati voodoo cam 60103(227/233 at .05, .489/.505 lift. 110 lobe seperation, but ground 4 degrees advanced). I should have went with a different cam. qjet (17085230)dual capacity pump. single main air bleed setup as follows.I AM AT 5000 FT  idle tubes-.039, idle down tubes-.062, upper idle-.07,lower idle bleed-.07,mixture holes-.103, idle bypass-.112,  primary jet- .071/ needle 50m. light power piston spring. stock secondaries. float set at 1/4".

any help would be appreciated.  soe 

[Cliff Ruggles]

So what is the problem?

[soe1]

Cliff:  opps. I forgot to mention my issues. My issues are.  my idle air/fuel screws do nothing, which my have to do with the fact that no matter how lean I go with the main jet(71) with a 50m needle, it still seems to be too rich. I have done the rich/lean tests and all point to being too rich. My current jet/needle setup seems like it should be lean for the motor. I am starting to think that I have a fuel leak that causes this rich condition. Well plugs on the primary or secondary side??  The car runs way better than it did when I had 75/50m primary set, but it still loads up, my spark plugs show a somewhat rich burn.  any suggestions would be greatly appreciated.  soe

   

[77cruiser]

How is the timing set up?

[Cliff Ruggles]

First thing to do is to make sure the idle mixture screws are actually seating and have control of the idle fuel.  I've seen a number of later Chevy truck carburetors where the threads weren't deep enough to allow the mixture screws to seat when you drill the holes that big.

Also take a look at the transfer slots.  Many later truck carburetors have a LOT of idle transfer slot exposed provided quite a big of fuel to the engine at idle speed.

Look for nozzle drip at idle to make sure all the idle fuel is coming from the idle system.....Cliff

[soe1]

My timing is setup at 18 initial. Although the motor seems to like 22 degrees the best. distributor vac is on port vacuum. I have stiff springs in the mechanical advance and it still hits 38 degrees total before 3k.  I will check the mixture screw threads(what size tap is that).  This carb does seem to have large transfer slots as well. What can I do about that? I no longer have nozzle drip since I drilled out the idle bypass to .112.   Thanks again  soe

[Cliff Ruggles]

Do you have any control with the mixtures screws?

The idle system feeds the main system at low throttle openings thru the mixture screw holes and the transfer slots.  If you get too much fuel coming in it will make it pretty "fat" despite small jets and larger metering rods, especially at 5000'.

Hopefully you used our parts for the rebuild, good parts make for a better end result with these things.

Even the jets being sold by most places are NOT for the Quadrajet and will throw the calibration off simply because they do not have the same internal specifications.

I'm also NOT a fan of big cams on tight LSA for street engines.  I've been in this hobby for nearly 50 years and the biggest complaints we get and problems we see are from folks using tight LSA and too much duration for the CID and compression ratio.

Matter of fact, with the engines we've built, dyno'd and drag strip tested here over the years, the wider we go with LSA the more we are rewarded with smooth idle, strong power off idle, more average power, stronger upper mid-range and top end power, and better track numbers.

Big cams on tight LSA's in contrast delivery crappy idle quality, stinky exhaust, narrow power curves and poor efficiency in the "normal" driving range.

Those statements apply to real street/strip cars, not full race stuff......FWIW.....Cliff

[soe1]

Cliff:  I do not have any control with the mixture screws. From your previous suggestion, I would like to tap the holes further into the baseplate. Do you happen to know the tap size? I agree with your comment on the cam choice. Although, I never have had an idle problem. I get about 12" vac. and the motor seems like it wants to pull real hard from 2k-5k once the fuel clears out and stops loading up. I think you are right about the idle system fattening up the low throttle. so, if I tap the mixture holes and get the screws to seat shut with this slow down the transfer slots feeding fuel?  soe

[77cruiser]

You can try to mark the needles with a marker & screw them in all the way & see if they seat. Try it with the spring off too. 85 year is probably metric threads, real fine.

[soe1]

Thanks Jim: I will try the marker trick and see if the screws are seating. If not I am going to tap the holes until I do get a full seat. I think the screws are m4x.5 pitch.
                                                                                     thanks again soe

[Frank400]

  Your carb definitely has very fine metric threads (they started in '79).  With those, when enlarging the idle discharge, I have had to shorten the spring quite a few times for the screws to seat. 

   I'm guessing that at .103, you shoul get by just by cutting a coil from the idle mixture screw.
   
    Frank.