Hypermiling with a carburetor - Fuelly Forums

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Old 10-17-2010, 10:03 AM   #1
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Question Hypermiling with a carburetor

Any carburetor-specific hypermiling thoughts for my Quadrajet-equipped 1980 Buick?

I'm used to hypermiling with a high-tech wideband controlled fuel injection system, where you always slam the go-pedal to the floor and shift as low as possible. That worked ridiculously well in my 2008 VW. Now a good shove to the accelerator will squirt from the accelerator pump, which might waste more than allowing some pumping loss.

Obviously there's no DFCO so I'll avoid engine braking when it's unnecessary.

What else would differ?
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Old 10-17-2010, 11:14 AM   #2
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Re: Hypermiling with a carburetor

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Originally Posted by theholycow View Post
Any carburetor-specific hypermiling thoughts for my Quadrajet-equipped 1980 Buick?

I'm used to hypermiling with a high-tech wideband controlled fuel injection system, where you always slam the go-pedal to the floor and shift as low as possible. That worked ridiculously well in my 2008 VW. Now a good shove to the accelerator will squirt from the accelerator pump, which might waste more than allowing some pumping loss.

Obviously there's no DFCO so I'll avoid engine braking when it's unnecessary.

What else would differ?
Also you will have to work with the power piston which is activated by low vacuum signal. Make sure you establish the maximum vacuum at idle also. Other wise it will think the cars is accelerating and it will be enabled at idle.

Also most carburetors when the power enrichment system is activated will dump more fuel then the engine really needs due to the limit of the mechanical mechanisms that make up the carburetor. So under power enrichment you will be around 13.5 to 13.0 A/F and just wasting fuel. The manufacture did this because they knew that as the time goes by the emulsion tubes would start to plug up and the carbs would loose the ability to atomize the fuel correctly.
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Old 10-17-2010, 11:29 AM   #3
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Re: Hypermiling with a carburetor

i believe you'll need a fuel lube more than an FI vehicle...would affect your FE long term.
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Old 10-17-2010, 12:39 PM   #4
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Re: Hypermiling with a carburetor

Adjust your auto choke so it comes off as soon as possible (or switch to a manual choke).

Adjust your accelerator pump linkage so that it only squirts when the pedal is pressed at least halfway (be prepared for a little hesitation though)

You could check in to finding some smaller jets to lean it out.

Make sure the hot air intake on the air cleaner is working correctly.
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Old 10-17-2010, 01:54 PM   #5
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Re: Hypermiling with a carburetor

As long as the engine is warm when the engine is shut off, the auto choke would not be an issue with that carb. Also, the choke on that vehicle requires it to be "set" by punching the accelerator to the floor once before starting. In restarting I don't think the pedal would need to be pushed at all provided the system was at operating temperature to begin with.
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Old 10-17-2010, 02:37 PM   #6
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Re: Hypermiling with a carburetor

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Originally Posted by pgfpro View Post
Also you will have to work with the power piston which is activated by low vacuum signal. Make sure you establish the maximum vacuum at idle also. Other wise it will think the cars is accelerating and it will be enabled at idle.
Even after googling, I'm not sure I understand what the power piston does. Does it move a jet in and out of the air stream depending on vacuum?

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Originally Posted by bowtieguy View Post
i believe you'll need a fuel lube more than an FI vehicle...would affect your FE long term.
Good point!

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Originally Posted by Erik View Post
Adjust your auto choke so it comes off as soon as possible (or switch to a manual choke).
The Quadrajet has a choke unloader that operates if I stomp the accelerator to the floor. It also has a (brand new) choke pull-off that still doesn't seem to work; it never comes out of fast idle until I unload it with the accelerator.

It's annoying.

Quote:
Adjust your accelerator pump linkage so that it only squirts when the pedal is pressed at least halfway (be prepared for a little hesitation though)

You could check in to finding some smaller jets to lean it out.
Interesting ideas, but power is a little anemic, I don't think I want to further reduce driveability.


Quote:
Make sure the hot air intake on the air cleaner is working correctly.
I think I figured out a way to check this last year, but how would I check it?

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In restarting I don't think the pedal would need to be pushed at all provided the system was at operating temperature to begin with.
Warm starts are a cakewalk, no choke required (if it managed to turn off at all during the previous drive).

I sure do dislike carburetors. Choke? Yuck. High vacuum (aka pumping loss) required for good FE? Yuck. Vacuum-operated power enrichment? Yuck. Etc...it's all Rube Goldberg stuff. Still, I'm going to give it a chance.
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Old 10-17-2010, 03:07 PM   #7
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Re: Hypermiling with a carburetor

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Originally Posted by theholycow View Post
it never comes out of fast idle until I unload it with the accelerator.

It's annoying.

That's the way they all operated, even when they were new.

My 1980 Bonneville, 81 Regal, and 86 C-10 all operated like this.
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Old 10-17-2010, 03:16 PM   #8
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Re: Hypermiling with a carburetor

To test the hot air intake, pull the long flexible tube off the air cleaner so you can look down the metal part with a flashlight. The little vacuum operated mixing door should be closed when the car is first started (all air is coming from around the exhaust manifold) and should be slightly open when the car has been driven a few miles on a warm day.
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Old 10-17-2010, 03:42 PM   #9
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Re: Hypermiling with a carburetor

Under actual operating conditions the power piston meters additional fuel by raising and lowering metering rods in and out of the primary jets. The motive force for this movement is engine vacuum and the resisting force is the tension of the spring located underneath the piston. If vacuum is too low for the spring tension then the power piston will be pushed upwards, which raises the rods out of the jets and richens the fuel mixture. This is normally what happens at mid to heavy load with low vacuum.
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Old 10-18-2010, 06:50 AM   #10
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Re: Hypermiling with a carburetor

Feeling adventurous? You can give this a try.
http://journeytoforever.org/biofuel_...earth/me3.html
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