Quadrajet Boiling

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NicolasB
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Quadrajet Boiling

Postby NicolasB » Wed Mar 31, 2021 9:28 am

When I drive my Toro when it’s cold, the car feels fine and responds immediately when I press the gas. However, when it’s up to operating temperatures for a bit the response is delayed and sometimes sounds like it’s going to stall when I press the gas. It’s worse especially in traffic where it wants to stall. When I check the carburetor all I hear/see is sizzling/vapor every time I press the throttle. In cases where it’s 80 degrees and stuck in traffic for a bit, I could hear the gas boiling in the carb. If I am correct, could I be experiencing heat soak? I heard that this issue could be because of ethanol in fuel and that it can be fixed with a heat insulator gasket (I only have one gasket between the carb and the intake manifold as of right now). Is this true? Thanks!

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Otto Skorzeny
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Re: Quadrajet Boiling

Postby Otto Skorzeny » Wed Mar 31, 2021 10:42 am

It's possible but I'd suspect that your idle mixture is too rich. Also, there are plugs in Q jets which should be epoxied over to prevent fuel leaking through. Google it up and see what to do. If you send the carb to a rebuilder, the good ones will normally seal those plugs.

They were problems when new. First Gen Toros were also prone to engine fires as a result.

NicolasB
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Re: Quadrajet Boiling

Postby NicolasB » Wed Mar 31, 2021 1:24 pm

Ah okay, I might have to check if those plugs are sealed. In my case, the car was running lean rather than rich so after I adjusted the idle mixture screws it improved a bit but not by much.

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Otto Skorzeny
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Re: Quadrajet Boiling

Postby Otto Skorzeny » Wed Mar 31, 2021 4:32 pm

Those screws only affect mixture at idle.

When it's idling, look down the throat of the carb. If you see gas dribbling from the center jets or pooling on the throttle plate, it's too rich.

NicolasB
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Re: Quadrajet Boiling

Postby NicolasB » Wed Mar 31, 2021 6:29 pm

Ah okay, I’ll check to see what mine is doing when I get back home.

NicolasB
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Re: Quadrajet Boiling

Postby NicolasB » Wed Mar 31, 2021 6:46 pm

Just a quick update, the car cooled to 180 degrees when I was at the store (from 205), but it runs like crap, keeps wanting to stall. Also doesn’t start right up, as if the gas in the bowl went away. So I’m sure it’s a carb issue.

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Otto Skorzeny
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Re: Quadrajet Boiling

Postby Otto Skorzeny » Thu Apr 01, 2021 1:31 pm

You might also be experiencing a vapor lock situation. If the gas in the fuel pump is vaporizing before it gets to the carb, your car will be starved for fuel. Sometimes you'll get no gas to the carb if the fuel between the pump and carb vaporizes.

It all sounds heat related, though.

NicolasB
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Re: Quadrajet Boiling

Postby NicolasB » Thu Apr 01, 2021 2:01 pm

The weird thing is that when I check the fuel filter it’s full of gasoline, so the fuel pump is fine. It’s when it gets sprayed into the carb that it immediately vaporizes.

bcroe
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Re: Quadrajet Boiling

Postby bcroe » Thu Apr 01, 2021 7:53 pm

Its good to have a Wide Band OX sensor. These are AMAZING, telling you exactly
what is going on with the mixture, directly responding to any adjustments. The
internal circuit is complex, but that is taken care of for you. I built my own in 2000,
still using it. Any air pump needs to be stopped to use it, or big errors result.

Here is a pretty good one from Evil Bay. It should have a moving indicator, as
any digital display will be only a blur of segments on a fast transition (just
when you need it).
303755511920 (other colors available)
APSX V2 Anti-Glare D2 Digital Wideband O2 AFR Gauge & Sensor Kit
AFR ratios in properly working fuel injection should be more or less as follows:
12.5 for WOT
13 for accelerating
14.5 for cruising
15.5 for lean cruising
13.5 for idle (it is desirable to set slighty enriched mixture for smooth operation)

Bruce Roe

NicolasB
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Re: Quadrajet Boiling

Postby NicolasB » Fri Apr 02, 2021 8:11 am

Dang I wish I could get one cause they seem really good, but it’s out of my price range. Right now I own a vacuum gauge and use it, but still have a bit of trouble figuring out where the highest vacuum is.


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