Question on setting float level for a '76 QJet

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wcsinx

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Feb 16, 2009
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So I heard Lars was here now. :D Hopefully he'll see this post.

I'm trying to get thie QJet back together. The rebuild kit says to set the float to 13/32" (.406"). So I put light pressure on the rear, slipped in the gauge, measuring the back (bracket side) of the float, and with a little bending I got it spot on 13/32. Then just as a sanity check I pumped it up with water, measured the float again and now it's a 7/32" :huh2: I tried it with both the Tomco valve that came in the rebuild kit and the stock valve with the exact same results both times. 13 with finger pressure, 7 with water. I'm being sure to keep the bracket/hanger thing seated properly.

Am I just not pushing hard enough or is this normal?
 
Ok nevermind, I think I got it sorted. It was a combination of not enough finger pressure and measuring in the wrong spot. I remeasured at the end of float opposite the hanger, and pushed just hard enough to square the hanger to the valve but not hard enough to unseat anything. Now I pump it up with water and I get 13/32", so I think I'm good.

But if I've said anything wrong, feel free to chime in. :D
 
Set pre-75 Q-Jet floats to .375". 1975+ Q-Jets set to .420".

Float level is measured at the rear edge of the float (away from the pivot point). Apply firm pressure to seat the float pivot pin while pressing down modestly on the float arm above the needle. Be sure that the needle retaining clip is not installed through the hole in the float arm - it slips over the rear edge of the float arm.

Lars
 
lars said:
Apply firm pressure to seat the float pivot pin
Click to expand...

Yeah, I think that's the part that got me. I wasn't pushing hard enough because the pin would pop out.

Lars, would you recommend the Tomco style valve that came in the rebuild kit, or should I stick with the needle valve?

Thanks!
 
I only use stock-type needle and seats - I have had nothing but problems with other designs.
Lars
 
Well crap, I guess I'll switch it back out. :bump:

And the plot thickens. I figured what was actually happening. That plastic chunk that holds the hanger down has apparently shrunk over the years, and now it's allowing that pivot pin to rise up ever so slightly. And that subtle movement after being multiplied by the lever that is the float was turning into a difference of 8/32" at the far end. So I readjusted with that in mind, and I THINK all is well now. :banghead:

Thanks again, Lars! :drink:
 
The "plastic chunk" is the float bowl filler, and it does not retain the float pin in any way. The air horn retains the float pin. If the float pin is bent "too tight" and does not have any springiness to it, it will move. You need to simply open up the pin bend a little so that the height of the pin when installed is slightly above the bowl casting. This will allow the airhorn to sandwich it down when you install the top of the carb.

This topic is covered in my "Q-Jet Problems" tech paper.

Lars
 
Ah hah! Well now that makes perfect sense, Lars. When I look at that pin, it's not even above the top surface of the float bowl filler (plastic chunk thingy). That would probably explain the fuel I saw on the air horn gasket.

Do you have a link for your qjet problems document? I have your tuning guide, but I can't remember where I got it.

Thanks!
 
wcsinx said:
Ah hah! Well now that makes perfect sense, Lars. When I look at that pin, it's not even above the top surface of the float bowl filler (plastic chunk thingy). That would probably explain the fuel I saw on the air horn gasket.

Do you have a link for your qjet problems document? I have your tuning guide, but I can't remember where I got it.

Thanks!
Click to expand...

Go to the tech tab up top...you'll find it there.

Or, click on this link:

http://vettemod.com/forum/forumdisplay.php?f=47
 
I grabbed all of them from the link SmokinBBC provided, so I'm good for now, thank you. :thumbs:

I got it all back together last night, and she's running so much better now. The stumbling is gone, the fuel smell is gone, and the off idle response is instantaneous. I do however have a lean idle condition as indicated by your test (cupping hand lightly over the primaries). The engine surges just like you said. I've dialed out the idle mixture screws about 12 turns each side. They still have adjustment left, but they don't seem to be making any difference at all. I'll try backing them out farther tonight, but if that doesn't work then I believe you said you said to increase the primary metering, correct? Sooo question ...

1. How do I tell what size primary jet I have?

I believe your tuning paper says the stock jet for a '76 is a 77 with a 48 rod. When I pulled it apart, it turned out I had 51 rods in there. I knew I was running rich (but in retrospect, that was prob. the damn float) so I went up to 52s, but I have no idea what size jet is in there. I couldn't see any stamping on it.

2. What jet/rod combination would you recommend for a completely desmogged '76 with headers/duals?

Thanks!
 
Depending on your carb number, I see 2 combinations; 77/48 and 77/51.

Too bad you can't see your jet number. All of mine are stamped on the top. Since you had a 51 rod, I'd think that your jet is a 77.

I am by no means a master at this, but now that you have your float problem fixed, I would put the carb back to stock specs as a base and see how it runs. Also, clean the plugs so you can try to get a good reading.






17056206 CHEV 76 Vette & Nova A/T 77 48 17052057 CH
17056207 CHEV 76 Vette & Nova M/T 77 48 17052057 CH

17056210 Chev 76 FEDERAL AT VETTE HIGH PERF 77 51 17052057 CH
17056211 Chev 76 FEDERAL MT VETTE HIGH PERF 77 51 17052057 CH

17056226 Chev 76 FEDERAL AT A/C VETTE HI PERF 77 51 17052057 CH

17056282 CHEV 76 NOVA, VETTE CANADA 77 48 17052057 CH

17056506 CHEV 76 Vette & Nova A/T Calif 77 48 17052057 CH
17056507 CHEV 76 Vette & Nova M/T Calif 77 48 7037851 CH
 
Oh ok, so there was a stock configuration with a 51 rod then. I think you're probably right in that my jets are 77s. (Is it odd that they're unstamped?)

The cruise circuit is actually running really damn well now better than it ever has for me at least. I backed the idle mix screws way out, and it's still idling lean but not by much. I think I might just live with it for now.

Thanks for all the help!
 
1. Without a carb number, I can't make any jetting recommendations.
2. If there is no number stamped on the jets, it is likely that they are "generic replacements" and you need to repalce them with a known good set of jets at the right jet size.
3. If you have put fatter-than-stock primary rods in the carb, it will run way too lean. Again, without a carb number, it's impossible to say.
4. Make sure your power piston APT is set to the correct height. A low APT setting is a primary cause for idle and part-throttle lean condition.

Lars
 
roger that, I'll post up carb numbers when I get a chance

Just thinking out loud here ...

stock is 77/51 - 0.00261381

As I recall, your rule of thumb is to go down 2 sizes in rods for a desmogged/real exhaust setup

soo 77/49 - 0.00277088

but I already swapped in 52 rods (one of my 51 rods is ruined btw :blush:), so if I put in a 79 jet

79/52 - 0.00277795

Edit: Nevermind ... the biggest jet that both Summit and Jegs carry for the QJet is a 77. Looks like I'll be ordering both.

close enough?

As to the piston height, I did set it the way you recommended (measuring with the jet and rod lying next to each other).
 
Last edited:
Again, can't make any recommendation on jet/rod without the carb number.

wcsinx said:
As to the piston height, I did set it the way you recommended (measuring with the jet and rod lying next to each other).
Click to expand...

That's not the way I recommend it - you are working to an old, out-dated paper. You need to set the APT to get .020-.030" height on the inner sleeve as descibed in the paper. If you set as you describe, you are too lean.

Lars
 
That's an obsolete paper that should not be posted or followed. It was cancelled 4 years ago - please tell the person posting that paper to pull it. The current and correct procedure is outlined in revision "AL" of the Q-Jet Tuning paper.

Current papers are not available via Internet postings - papers posted on various web sites are generally obsolete and outdated and should not be used. Current tech papers are available by e-mailing me a request for the current version.

Lars
 
Baby steps :)

I dialed out the piston to 0.025. It's idling better now ... still lean but better. I'm going to take it out 0.030 and see how that works. Unfortunately I forgot to pop out the plug, but I'm getting pretty good at pulling that air horn off.

Carb # is 17056211 (exactly what I'd expect)

'76, 49 state, Chevy, manual
 
That carb, in its stock format, is jetted very lean for idle and part throttle. If you can find a pair of 48K or 49K (not "M") rods for it, that would get you in the right range for a good performance application. Keep in mind that all of the Edelbrock rods sold for that carb are "M" rods, and cannot be used. The only source for rods for your carb is from other used carbs - all primary rods have been discontinued by all sources for that carb except the truck ("M") rods. If you continue to have a lean indication, bump the float level up to .400".

Lars
 
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