Poor performance with 1971 Blazer with 350 4bbl quadrajet

Hi all,

I have a 1971 Blazer with a 350 and a quadrajet. The engine is pretty new -
about 2 years old. The carb was rebuilt with the new engine at that time.
Everything has been working great until last week. The Blazer sat for a
little over two months. It started right up but ran very badly. At idle it
runs ok, but misses here and there. However, when I open it up it
practically stalls and almost dies. At wide-open throttle, I get a second
or two of normal acceleration before it stutters, then a second or two of
acceleration.

Here's what I've done so far and the problems I've eliminated:

Replaced coil, cap, rotor, wires, plugs. Replaced fuel pump, fuel filters
(at tank and at carb) and blew-out fuel-lines. Checked the vacuum hoses -
they all seem to be sucking properly (no blockages).

Since this problem started after a long period of inactivity, I suspected
bad fuel. The tank was at 1/4 full, and I added a water remover/fuel-line
cleaner, and filled the tank with new fuel. It's been cycled through to the
carb.

I'm running out of options. I now suspect it may be the carb - perhaps bad
fuel has messed it up. I'm looking for any suggestions that might solve the
problem and any advice any of you may have.

Thank you!

Andy

"Mindspring" <[email protected]> wrote in message
news:[email protected]...
> Hi all,
>
> I have a 1971 Blazer with a 350 and a quadrajet. The engine is pretty
new -
> about 2 years old. The carb was rebuilt with the new engine at that time.
> Everything has been working great until last week. The Blazer sat for a
> little over two months. It started right up but ran very badly. At idle
it
> runs ok, but misses here and there. However, when I open it up it
> practically stalls and almost dies. At wide-open throttle, I get a second
> or two of normal acceleration before it stutters, then a second or two of
> acceleration.
>
> Here's what I've done so far and the problems I've eliminated:
>
> Replaced coil, cap, rotor, wires, plugs. Replaced fuel pump, fuel filters
> (at tank and at carb) and blew-out fuel-lines. Checked the vacuum hoses -
> they all seem to be sucking properly (no blockages).
>
> Since this problem started after a long period of inactivity, I suspected
> bad fuel. The tank was at 1/4 full, and I added a water remover/fuel-line
> cleaner, and filled the tank with new fuel. It's been cycled through to
the
> carb.
>
> I'm running out of options. I now suspect it may be the carb - perhaps
bad
> fuel has messed it up. I'm looking for any suggestions that might solve
the
> problem and any advice any of you may have.
>
> Thank you!
>
> Andy
>
>
>

Andy,

I too would suspect the carb. A vehicle that sits a while will have the gas
evaporate out of the float bowl and passages. If repeated often enough
residue from the gas will build up and cause blockage in the smallest of
passages. Since you seem to be able to get an initial shot of gas, the
accelerator pump is likely fine. But it seems that sustained high volumes of
gas like extended acceleration is causing starvation. Get yourself a can of
gumout spray( I have used Ether in a pinch.) and pull the top off the carb
and start spraying the small holes of the carb. I would prefer to pull the
whole carb from the engine and do the lower passages also. Re-check the
float height, if it's one of those cheap plastic floats, it may have soaked
up gas and will throw off the levels. Switch to brass/copper.

As a precaution, re-check the fuel filter, shake out the filter onto a piece
of white paper or cloth to see if any rust has been trapped. If the filter
is plugged, I would suspect the tank is very rusty and the pickup tube is
still getting a lot of it.

Just my $.02, but I am just a shadetree mechanic.
Brian

"bulletsnbrains" <[email protected]> wrote in message news:<[email protected]>...
> "Mindspring" <[email protected]> wrote in message
> news:[email protected]...
> > Hi all,
> >
> > I have a 1971 Blazer with a 350 and a quadrajet. The engine is pretty
> new -
> > about 2 years old. The carb was rebuilt with the new engine at that time.
> > Everything has been working great until last week. The Blazer sat for a
> > little over two months. It started right up but ran very badly. At idle
> it
> > runs ok, but misses here and there. However, when I open it up it
> > practically stalls and almost dies. At wide-open throttle, I get a second
> > or two of normal acceleration before it stutters, then a second or two of
> > acceleration.
> >
> > Here's what I've done so far and the problems I've eliminated:
> >
> > Replaced coil, cap, rotor, wires, plugs. Replaced fuel pump, fuel filters
> > (at tank and at carb) and blew-out fuel-lines. Checked the vacuum hoses -
> > they all seem to be sucking properly (no blockages).
> >
> > Since this problem started after a long period of inactivity, I suspected
> > bad fuel. The tank was at 1/4 full, and I added a water remover/fuel-line
> > cleaner, and filled the tank with new fuel. It's been cycled through to
> the
> > carb.
> >
> > I'm running out of options. I now suspect it may be the carb - perhaps
> bad
> > fuel has messed it up. I'm looking for any suggestions that might solve
> the
> > problem and any advice any of you may have.
> >
> > Thank you!
> >
> > Andy
> >
> >
> >
>
> Andy,
>
> I too would suspect the carb. A vehicle that sits a while will have the gas
> evaporate out of the float bowl and passages. If repeated often enough
> residue from the gas will build up and cause blockage in the smallest of
> passages. Since you seem to be able to get an initial shot of gas, the
> accelerator pump is likely fine. But it seems that sustained high volumes of
> gas like extended acceleration is causing starvation. Get yourself a can of
> gumout spray( I have used Ether in a pinch.) and pull the top off the carb
> and start spraying the small holes of the carb. I would prefer to pull the
> whole carb from the engine and do the lower passages also. Re-check the
> float height, if it's one of those cheap plastic floats, it may have soaked
> up gas and will throw off the levels. Switch to brass/copper.
>
> As a precaution, re-check the fuel filter, shake out the filter onto a piece
> of white paper or cloth to see if any rust has been trapped. If the filter
> is plugged, I would suspect the tank is very rusty and the pickup tube is
> still getting a lot of it.
>
> Just my $.02, but I am just a shadetree mechanic.
> Brian


I had a 86 chevy with a 350 and same carb as you. had the engine
replaced and everything re-worked exept the carb. when i got the
truck back it ran fine for awhile, then had the same problem as yours.
I rebuilt the carb (major pain for quadrajet) and it didnt help. I
found out the quadrajet has a diaphragm that has a tendancy to leak
after years of use and i could not replace it. I changed the carb to
a carter 650cfm for under $200.00. It was easy and never had the
problem again.

Thanks all for the information. I've changed the filters twice now and
still the same problem. It's ok at idle, a little rough, but dies as WOT.
I plan to try and clean the carb out.

Thanks again,

Andy

Mindspring wrote:

>Hi all,
>
>I have a 1971 Blazer with a 350 and a quadrajet. The engine is pretty new -
>about 2 years old. The carb was rebuilt with the new engine at that time.
>Everything has been working great until last week. The Blazer sat for a
>little over two months. It started right up but ran very badly. At idle it
>runs ok, but misses here and there. However, when I open it up it
>practically stalls and almost dies. At wide-open throttle, I get a second
>or two of normal acceleration before it stutters, then a second or two of
>acceleration.
>
>Here's what I've done so far and the problems I've eliminated:
>
>Replaced coil, cap, rotor, wires, plugs. Replaced fuel pump, fuel filters
>(at tank and at carb) and blew-out fuel-lines. Checked the vacuum hoses -
>they all seem to be sucking properly (no blockages).
>
>Since this problem started after a long period of inactivity, I suspected
>bad fuel. The tank was at 1/4 full, and I added a water remover/fuel-line
>cleaner, and filled the tank with new fuel. It's been cycled through to the
>carb.
>
>
>
Check power to the coil. My '66 Mustang was giving me fits last
year with similar symptoms- slightly rough idle, stalling when the revs
came up. I checked everything and could not find anything that tested
wrong. But it staill ran like crap. Very frustrating. The (by
accident) that coil voltage was low when above idle. Turned out to be
the ignition resistor - $2.50 part.


--
..boB
97 H-D FXDWG - Turbocharged!!
01 Dakota Quad Sport, 5.9/Auto/4x4
83 GMC Jimmy (beater)
66 427SC Cobra Replica - Project
66 Mustang coupe - Daily Driver



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