Carb mod for better mileage? - Fuel Economy, Hypermiling, EcoModding News and Forum

suspectnumber961 · 03-11-2010, 05:49 AM

Was trying to find the post by someone with an '82 Toyota 4x4 that had mpg issues....

"....also lower your floats to the lowest point possible without starving engine for fuel 1/4 to 3/8 of normal hight is a good start....carb manufacturers run 'just below flooding' fuel levels.

Try lowering your float in the carb to about 1/2 inch, as long as you don't keep your foot buried in the throttle you will see a major increse in MPG, my 73 f-100 (360 auto) went from grandma 6mpg to 2000
pound past capasity of 12.5 trip average from Washington state to Texas (2400 miles) and the truck burns(& leaks) 3 quarts of oil every 100 miles.

Your only limit is the floats hitting the bottom of the bowl. You may think 'The bowl will run out of fuel' if your that hard on the petal your not in the habit of getting good mpg anyway. Just use reason give your floats room to open the needle valve but not fill the bowl all the way up. The reason you get better mpg is greater levels of suction are needed to pull the fuel up the stem 'ripping' the fuel apart on the way up the high speed nozzle for more air contact (surface area)."

Christ · 03-11-2010, 10:45 PM

Is your Turkey carb'd? Maybe you could try it out?

bgd73 · 03-11-2010, 11:52 PM

tercel will take a weber...

...but that float level stuff..keep it as high as it will go. for every bottom out there is a lack of stoich, and it will dump it trying to gain it back. The goal is "float".

never ever drop the float.... EVER.

suspectnumber961 · 03-12-2010, 04:18 AM

Moi...does not drive a Turkey...but a POS.

I am going to try this soon...since I need to take stuff off to fix a coolant leak....where I'll be installing a 192F thermostat. Will also put in a new float/valve while I'm at it.

If you read what he says...your limit is the float bottoming. This carb has a sight glass in front...last I looked the level ran slightly below the line...so it might not adjust any further down. Doubt if it's going to "dump" fuel at any point...if adjusted too low you simply won't get enough fuel because the valve won't open enough.

Not afraid to try it...just don't want to be taking the top off the carb when I can avoid it...which is why my carb rebuild kit has set in it's box for a few years.

luvit · 03-12-2010, 09:22 AM

i think i need pics. to see what you're doing.
i was messing with my carb before the cold weather set-in.

suspectnumber961 · 03-12-2010, 02:20 PM

Took a look at the manual...says not to mess with the center tab that actually actuates the valve...says that this carb is set up for strict emissions....and since by the sight glass it runs a little low already...I might not mess with it.

I'd probably end up having it off there several times before it ran right again.

Changing the float level might more likely work on US carbs on the bigger engines?

LaPointe mentions soldering the power valve shut.

I've rebuilt carbs before...but it can be hit or miss at times.

Frank Lee · 03-12-2010, 02:32 PM

By all means, do whatever La Pointy says!!!

Christ · 03-12-2010, 10:30 PM

I've brazed the power valve on quite a few carbs... on older 4 cylinder cars, it really doesn't affect anything unless you intend on floor it and go - type fuel delivery.

Several Kei-Hin carbs were known for their ability to randomly flood engines when you hit the gas too heavy, too quickly. The fix is to close the accelerator jets off, and use the throttle at bit more sparingly (or listen to a backfire every time you hit the pedal too quick).

The only way that you can run lean by moving the float in the bowl is if the bowl starts to get empty. I find it highly unlikely that you'd get better fuel economy by doing it, considering that no matter how many times I've adjusted the floats on any of my industrial engine carbs, they still run for the same amount of time on the gallon fuel tank they have.

Of course, they're steady state engines, too. Maybe something's different there.

Frank Lee · 03-12-2010, 10:54 PM

When anyone is ready to get serious about adjusting the mixture leaner, they'll rejet it.

Christ · 03-12-2010, 11:00 PM

Quote:

Originally Posted by Frank Lee

When anyone is ready to get serious about adjusting the mixture leaner, they'll rejet it.

I thought this to myself, but didn't mention it, because "Frank-Lee", if you're not willing to take the carb apart to put a few gaskets in it, you're probably not going to be interested in re-jetting it, either.

Me, on the other hand, I'd be the one trying to make my own jets on a lathe.