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'67 429 Propulsion Issue (Fuel Issue)?

Started by Snibbor, August 08, 2022, 09:21:10 AM

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Snibbor

Just started encountering an issue that occurs from a stopped position. From a stop...when I press the gas it has a sudden intermittent loss of power. When I continue with modest/consistent pressure on the gas it does it again and again then normalizes propulsion.

Based on what I have described is this something simple?

Snibbor

I will say that I have looked at the following thread but still in the dark:

Technical / Authenticity / Re: lagging and pulsing on acceleration 67 Cad with 429 rochester QJ
September 17, 2021, 07:40:14 AM by James Landi

Michael Petti

Sounds like insufficient fuel upon acceleration. Common causes are a dirty fuel filter, a worn accelerator pump, a dirty carburetor and a failing fuel pump. Disconnect fuel line from carb, run a rubber line into a jar and crank engine. See if you have good healthy flow of fuel or not and go from there.

Snibbor


Snibbor

Michael,

Can you or anyone out there provide a reputable online source for a:

> fuel filter
> accelerator pump

???

Michael Petti

NAPA is a good place to start. Other sources are Mikes Carburetor and/or the Carburetor Shop. Both are online. Your fuel pump should be putting out 5ish pounds of pressure. 4 pounds is low end acceptable. Another question to ask is does this occur all the time or only on hot days? Could be boiling fuel.

Michael Petti

I forgot to mention to discuss getting a slightly oversize accelerator pump. Todays ethanol gas is different. Get a leather pump if you can. That was original.

Snibbor

Thanx again Michael. And yes, it was quite a hot day when it first occurred.

Snibbor

Boiling fuel had to have been the culprit as it WAS a hot as hell day and things have cooled down and I have not had her out in those temps since...Had never heard of such a thing...but this is why I am here..to learn..

Thanks again Michael.

klinebau

There are a few things to look at with the Quadrajet.  Assuming that the Q-Jet is in good repair, I would check each of these items in order as the most likely candidates are on top with the least likely at the bottom of the list.

1. Make sure that you have adjusted the idle screws so that the idle mixture is rich enough.  Too lean an idle will make a flat spot when transitioning to off idle.

2. Check to make sure that the linkage on the accelerator pump is on the inner hole.  There are two holes and the inner hole will allow for a greater pump shot.  Regardless of what the manual says, the inner hole should be used for modern gas.

3. If the secondary's are opening, then you will want to make sure that the air door spring is clocked correctly.  If the air door flops open too soon, then it causes a momentary lean condition.  This would be more likely show up if your flooring it from a full stop rather then just normal acceleration.  See the manual for details on how to adjust that spring.

4.  The '67 Q-Jet does not have an adjustable part throttle setting, but raising the power piston slightly can help with this transition.  You can shim the power piston with small washers.  Check Cliff Ruggles book/ website for more details on this.
1970 Cadillac Deville Convertible
Detroit, MI

Snibbor