84 K20 350 w/vortec heads: hesitation/bog just off idle

[muddpuppy01]

tighten up the tv cable on the carb it will firm up the shift and increase the shift points

[akoz]

ok, so 0.77 jets seems to have set me back some, meaning that now it doesn't take a
full "stomp" on the gas to bog/hesitate so I seem to have take a step back. I only have
another set of smaller jets and I am not convinced that going higher (over 0.79) will help.
The last time I did the jet change I got the plugs off the idle mixture screws (actually,
they are not screws) and did not touch them but at least I can now. I don't have any
idle problems and right now at 750 rpm in park, engine warmed up, it's very steady.

There is definitely a problem in the transition from idle to the primary.

I tried moving the accelerator pump linkage to the outside hole and it still hesitates
and now it pops (backfires?) a little depending on how quickly I put my foot in it. I am
not talking about jamming my foot to the floor, but something more than feathering
the gas, so closer to normal driving. I also noticed that this raises my idle to 850 rpm.
I did this test right after the rebuild with the original jets (0.073) and it did about the
same thing, maybe a little worse on the hesitation. The current setup is 0.077 jets.

My secondaries are definitely not opening.

I'm resisting the urge to start changing more things (jets, idle mixture, accel pump)
until I have a better idea of which way I should be going with this. Any other ideas
would be appreciate (oh, and thanks for that advice on the tv cable adjustment).

[akoz]

sorry, 2 big typos in my post...0.77 and 0.79 should be 0.077 and 0.079.

[akoz]

It turns out that my secondary air valve is not opening up and I can't figure out why.
I thought for sure that when I removed the primary and secondary vacumm breaks
that this was the problem, but all I can see that they do is prevent the choke from
closing, pull back on the secondary lock-out and hold back the secondary air valve
from opening. Someone told me that the secondary air valve opens by manifold
vacuum (not linkage), so I can't figure out why they don't open. I am definitely
running out of gas when I hit the gas pedal in any kind of agressive way and it
seems to be due to the secondary air valve not opening. I picked up a Rochester
carb book by Doug Roe and the problem is that the M4ME carb that they show
doesn't exactly match my setup. I have the dual vaccum break setup, but the
primary has no linkage to the seconday air valve, but this is what shows up in the
exploded parts view and in the parts view that came in my carb rebuild kit.

Looks like I'll be replacing the carb with an aftermarket one unless there is a
Qjet expert out that that understands my situation.

[Captkaos]

You physically opened it wide open and the secondaries won't open at all?
http://73-87.com/7387garage/drivetrain/damon.htm
http://73-87.com/7387garage/drivetrain/damon2.htm

[akoz]

Thanks, but I read this article before and the key is that the primary vacuum break (the one in the front) that they keep talking about is NOT connected to the secondary air valve in my case. Also, the "finger opening test" works fine and my air valve opens very wide and has no restrictions. I'll try and attach a picture of my setup so this will be a little more clear. Either way, Doug Roe's book says that the secondary air valve is opened by the force of vacuum pulling on it, so this difference in linkage doesn't seem to be the issue.

[akoz]

quick update: it is a secondary fuel metering problem...took another carb and swapping the secondary hanger/rods to figure it out, but that seems to be it. I'll do a final post and try and give people the right combination of rods/jets/hangers, but of course, every build is going to be different.

[zieg85]

Good news you found the issue, now you have some great experience with Rochester Qjet.