jon pickens

Hi,

I have a 1986 K5 Blazer. A new 290HP crate engine was put in about a
year and a half ago. At that time, the mechanic deemed the stock
Quadrajet to be shot, so I put on an Edelbrock.

The Edelbrock is a 600cfm carb, with electric choke and vacuum
secondaries. The specs for the metering rods and springs are "Metering
Jets - Primary .098, Secondary .095; Metering Rods - .075 x .047;
Step-Up Spring - yellow (4" Hg)."

Basically, the timing is set at a ridiculous 15 degrees BTDC at idle
just to keep it running. The manifold vacuum reads out at 12" Hg at
idle. Right now there are only 2 vacuum lines connected; the brake
booster, and the ported vacuum going to the advance on the distributor.
I have detected no leaks, and even changed out the rubber line going
to the distributor for good measure about 30 minutes ago. The manifold
vacuum on the carb is plugged, and so is the PCV port.

While I was under there I double checked the idle mix, I set it using
the vacuum gauge, opening each side to allow max vacuum...they were
already where they needed to be.

I installed a fuel pressure gauge on the gas line, post-filter,
pre-carb. It bounces like crazy at idle (I'm assuming it's the pulsing
action of the pump) but when you hit the throttle it's around 2-3 psi
right off idle, and steadily increases... but it never exceeds 5 psi.

This 290hp engine has barely more power than the stock, 16 year old 305
had (with a blown head gasket). I had to make a trip out of town
yesterday, and I determined that it's getting around 12.5mpg on the
interstate.

It's running so rich that at times it can cause a headache even while
driving with the windows up, or make you smell like you had a mishap at
the gas pump.

PLEASE HELP!

Thanks in advance,

~jp

jon r. pickens

Oh, I forgot...

You can see gas puddling up in the carb here:

http://www.absolutepickens.com/K5/gas.jpg

And there's an usual (to me at least) residue on the carb at the idle
screws, PCV port, and next to the throttle...see all that here:

http://www.absolutepickens.com/K5/dirt01.jpg
and
http://www.absolutepickens.com/K5/dirt02.jpg

Ideas?

Thanks,

~jp

shep

Just plain old Carter AFB 4bbl, ran em for years on my Maxwedge SS race car,
any way your idle vacuum is way to low, stock cam here? Make sure the
secondarys are completely closed. Find this low vac problem first. I assume
the float level and drop are set to specs?

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jon pickens

I haven't disassembled the carb to check the floats yet. After I sent
this, I realized by doing a little reading that the vacuum was low
enough to warrant first priority.

I went to the parts store and got 2 new gaskets--one for the Quadrajet
manifold-to-adapter plate, and another for the adapter-to-carb. The
stock bolts that came with the adapter plate to secure it to the
manifold are pretty cheap--they use a phillips drive. I ran to Home
Depot and got some Allen-head cap bolts and used them instead. I
torqued it down pretty tight with an Allen wrench and then replaced the
carb, also making sure it was good and tight.

After that I was measuring about 14.8" Hg of vacuum... What should the
vacuum be?

Stock cam yes, looks like ".450'' intake and .460'' exhaust lift", and
"Flat Tappet Duration @ 0.050'': 222° I, 222°"... that was taken off
the Jegs site. I ordered the motor from somewhere else, but that's the
one.

Thanks,

~jp

shep

That cam is hotter than stock but not crazy. Also check with the cam mfg.
for expected vacuum on a good running engine. It is possible the metering
rods are are up out of the mains at idle and on up. Check with Edelbrock's
tech line for possibly changing the springs, but do the other carb checks
first. Try spraying carb cleaner around the intake manifold to check for
leaks there.


I haven't disassembled the carb to check the floats yet. After I sent
this, I realized by doing a little reading that the vacuum was low
enough to warrant first priority.

I went to the parts store and got 2 new gaskets--one for the Quadrajet
manifold-to-adapter plate, and another for the adapter-to-carb. The
stock bolts that came with the adapter plate to secure it to the
manifold are pretty cheap--they use a phillips drive. I ran to Home
Depot and got some Allen-head cap bolts and used them instead. I
torqued it down pretty tight with an Allen wrench and then replaced the
carb, also making sure it was good and tight.

After that I was measuring about 14.8" Hg of vacuum... What should the
vacuum be?

Stock cam yes, looks like ".450'' intake and .460'' exhaust lift", and
"Flat Tappet Duration @ 0.050'': 222° I, 222°"... that was taken off
the Jegs site. I ordered the motor from somewhere else, but that's the
one.

Thanks,

~jp


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jon pickens

Yeah, that's right about the cam. Supposedly the 290hp motor is the
same as GM's 260hp motor, with the exception of the cam. That's what I
remember the sales-dude telling me. It did come direct from GM that
way though, in long-block form.

I did some serious thinking about the vacuum issue and then I
remembered something... When I was in the process of installing that
Edelbrock, it wouldn't clear the EGR valve--even with the adapter
plate. The EGR was shot so I decided not to use it. But I didn't have
a block-off plate, so I improvised (uh oh). I basically removed the
upper portion (diaphram) and sunk a screw into the lower body of it to
keep it in what I thought was a closed position.

So I may have just found the source of the vacuum leak. Either way, an
EGR block-off plate will be installed this week. I don't like using
"improvised" parts on my engine.

~jp

shoe salesman

Try hooking up the PCV, its a large metered vacuum leak in a since. Why
didn't you hook it up? Is this carb not supposed to use it but its on it?
That would cause a rich condition. Then, once its hooked up re-adust
everything back to normal.

shades

With gas puddling up it is because the needles aren't closing off the
fuel to the bowls. I have almost the exact same carb and had an even worse
over-gassing problem. Pull the top, set the floats a hair lower than
recommended. Follow the procedure for teardown that is in the book. I had to
add a fuel pressure regulator on an olds 350 that I ran a Performer carb
on...must have had a high pressure mech fuel pump installed before I got it
or something.

DEFINATLY get a tuning kit for your carb because with the slightly
hotter cam, the factory set 1406 will be to lean. Also, get an aftermarket
intake from Edelbrock for your engine. If you don't, you will never get the
drivability, performance, and economy out of your engine...guaranteed!

jon pickens

The PCV port is plugged... I have it disconnected because I was trying
to eliminate any leaks and was removing anything not necessary for the
engine to run.

~jp

jon pickens

What all does the tuning kit include? I was at Napa yesterday and the
guy behind the counter pulled out the Edelbrock catalog. I was going
to get the spring kit to try to experiment and lean it out. I saw the
tuning kit listed--wasn't sure what it was.

If you missed it, in a previous response to Shep, I remembered my
homemade EGR block-off plate from a year ago. It could possibly be a
source of major leak. In any event I ordered one from an eBayer that
machines them, aka custombilletworks.com....
http://www.custombilletworks.com/files/egr.htm

It's supposed to ship this morning. I'll post the results.

Thanks,

~jp