Hesitation - '67 Camaro 396CI - Team Camaro Tech
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post #1 of 5 (permalink) Old May 28th, 19, 12:47 PM Thread Starter
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Hesitation - '67 Camaro 396CI

Over the winter and through the spring I have performed some suspension and performance upgrades to this '67 Camaro convertible. It has an unknown year 396 with Quadrajet 4-barrel (carb is from a 1975 Chevy truck) with a new 4L60 transmission and a new 3.55 geared 12-bolt rear.

A couple of months ago during acceleration the engine would stall like it was starving for fuel. I had noted earlier when installing a new fuel tank and fuel sending unit the fuel filter on the old sending unit had disintegrated with some strands remaining. This car had an inline fuel filter before the mechanical pump so I figured it was probably full of residue from the old pickup unit filter.

I replaced the fuel pump, removed the inline fuel filter and installed a fuel filter in the carburetor. My recent driving did not display any hesitation tendencies. I felt the hesitation problem was solved.

Today the brother of the car's owner came by to check things out. The owner lives out of town and due to distance he cannot visit. He drove the car for about 10 miles, sometimes aggressively, with no hesitation. We then we stopped to fill up with gas. During the fill up the car sat in the sun.

After re-fueling he began experiencing hesitation during spirited driving. Not super aggressive driving but feeling the pull of the engine.

It is 95 degrees today with no clouds and the humidity is low Really too hot for a convertible with top down but it was fun nonetheless. Could this car be experiencing vapor lock? Another thing I noted as I replaced the fuel pump this car has 5/16" fuel line from the fuel tank to the fuel pump. Should a 396 have 3/8" line? This 396 seems pretty stock with no thumpy cam and as stated the Quadrajet 4-barrel on a cast iron intake. Pretty basic for a big block, but for all I know it might be a 454 engine. There are no stampings on top by #2 piston, they may have been cut off when decking the block. I didn't concern myself with the 5/16" line because this is not a high performance engine. Are there some casting numbers somewhere on the block that might identify it?

Please school me on Quadrajets and how I might rectify this concern. If it were a Holly I would be checking float levels and maybe changing out the jets. I know very little about the workings of a Quadrajet.

I may drive the car again in cooler morning climate to see if I can repeat the hesitation. What do you Camaro experts think? If it is vapor lock how do I rectify it?

I am sorry for this wall of text but hope I clearly represented the concern.
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Last edited by Andrew69; May 28th, 19 at 01:09 PM.
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post #2 of 5 (permalink) Old May 28th, 19, 01:04 PM
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Re: Hesitation - '67 Camaro 396CI

It's possible the accelerator pump on the carb needs to be replaced. It's fairly common
on quadrajets and not difficult to do. The carb could probably use a rebuild if it hasn't
been done for a while. I actually prefer quadrajets over just about anything else on these
old car engines.

Al

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post #3 of 5 (permalink) Old May 29th, 19, 04:04 AM
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Re: Hesitation - '67 Camaro 396CI

As QAl suggests, remove air cleaner and check accelerator pump is pumping fuel.
Another item you could do is give it full time vacuum on vacuum advance and adjust dist for best running at idle.
Usually, advancing timing lessens hestiations. You should be able to go from idle to wide-open throttle, 5K rpms, in about 5 microseconds.
If it pings, decrease by 2 until gone.
Adjust carb with vacuum gauge. Speaking if vacuum gauge, a stock cammed engine should give 18-22 inches od vacuum at idle.
Any value less means aggressive camshaft.
Again, look at engine pad determining engine size & originality.
There is an air valve adjustment on pass side of airhorn for air valve opening rate, spring adjustment, and usually, one complete turn tensioning the spring gives smooth acceleration.

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post #4 of 5 (permalink) Old May 29th, 19, 09:17 AM Thread Starter
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Re: Hesitation - '67 Camaro 396CI

The accelerator pump on the carb is squirting when the pedal is pushed. It seems okay, but I haven't disassembled it.

This morning I took the car for a drive. On a country road I stopped and accelerated repeatedly and couldn't get the hesitation to kick in. The car ran great. Instead of returning home I stopped to visit a friend. After the car sat for about 15 minutes after leaving his driveway it again displayed the symptoms of vapor lock. Then everything returned to normal.

I think I can move the fuel line leading to the fuel pump further away from the header tubes and will wrap it with heat shield tubing. The hard line between the pump and the carb lays against the lower radiator hose and near the engine block and head. I'll try to bend it to allow more air gap. I'll let you all know the results.

Thanks for the input thus far.

Skunk Works
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post #5 of 5 (permalink) Old May 30th, 19, 02:35 AM
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Re: Hesitation - '67 Camaro 396CI

Quote:
Originally Posted by Andrew69 View Post
...I think I can move the fuel line leading to the fuel pump further away from the header tubes and will wrap it with heat shield tubing. The hard line between the pump and the carb lays against the lower radiator hose and near the engine block and head...
That fuel line IMO would be a huge potential for inducing vapor lock, as it is getting some hefty heat from the lower radiator hose.

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