Carb physics
 

I was not good in science. Am sure that is faulting me now. Here is the setup. I have a long driveway to my garage. the last 100 feet is 45 degree grade down into the garage. I back my car into the garage. When its colder out, say 50 and below, i can back down the grade with no issue. When its warmer out, as i begin down the grade, the tripower starts acting up, sputtering, and usually the car conks out and I have to glide the rest of the way down the hill with no motor.

What would cause the carb to act this way, only when its warmer out?

Due to the laws of nature things expand when they heat up., and so does the volume of fuel in a Carbs fuel bowl .
This means that what is a good level of fuel cold when the car is at that revers angle is too much when the motor is hot and it discharges into the motor and floods it out.

The problem is trying to determine which carb is the one that has its fuel level set too high.

You will have to get the motor to act up and hopefully you can look down into each Carb and see which one looks wet in it’s throttle bores and then reset the float level in that carb..

Check for proper choke settings/action.

Inclined to sputter:
In theory; a Fuel puddle in the Intake Plenum would tip fuel into a runner.
In practice; a float is set too high.

45 degrees! I hope you never get any ice or snow on it and try to back into the garage!!

I've done quite a few 2JET carbs over the years and although I'm not able to test them on an engine I do use an electric pump to fill the bowl and make sure the N/S holds and there aren't any leaks. I did some "tilt" testing with them and you'd be surprised at how easily they start leaking from the boosters when tilted backwards.

I was perplexed by this the first time I tried it, and even took the carb apart to check the float height and it was right on the money.......FWIW......

Thanks for feedback guys. I’ve messed around with these floats a lot over last couple years and believe they are pretty dialed in. Maybe I need to go a little on low side.

Yeah, its a heck of a grade cliff. Those carbs are way tilted. And my garage opening is not very wide -u can see in my profile pic. So I lose power steering going backwards down a hill and aiming for hole perhaps a foot and half wider than the car. Always interesting moment when warmer weather rolls in. Drives perfect on flat surface.

That is a terribly incorrect explanation/guess. I guess there wasn't anywhere else on the internet for you to copy and paste on this one. The fuel level is determined by a balance of the height of the float (and float buoyancy) vs. the needle and seat and the fuel pressure. Outside temperature should change this negligibly. As far as determining which carb it may be, are you serious? I'd say it has to be the center carb unless he's hammering it full throttle in reverse.

Back to the problem in question. I'd check the choke (as has already been suggested) or exhaust heat riser (if it's still in place and functional). Maybe have some vapor lock going on? Winter fuel blend if you live North?

Also. I think it may be the laws of physics instead of nature.

I have seen 2-Jets where the seal between airhorn and floatbowl is lost due to owner using "gorilla arms" at the aircleaner wing nut, bending the airhorn out of shape.
When this happens fuel will spill over the edge of float bowl into the venturies at acceleration, more with nose up.

With a propane torch and a shop press you may put the airhorn back in shape.

45 DEGREES? Are you sure it is not a 45 PERCENT GRADE? That would be a little under 25 degrees. Still real steep.

45%!!!!
Percent of grades like used on Railroads , would since there rated at a 100 ft lenght would mean a rise of 45 ft in just that small 100 ft run!!

That’s massive !!

That property may need fuel injected cars.

I may have to use that line with my wife if I’m ever in market for fuel injection

I agree 45 PERCENT is massive, but the 45 DEGREES quoted from the first post is almost twice as steep.

45% is 24.23° inclination equals 45 cm height per 100 cm distance.

45° angle is 100% inclination equals 100 cm height per 100 cm distance.

My vote is for 24.23° steepness.

Agree!

Most have seen the Movie "Bullitt" with Steve mcQueen and the 1968 Mustang.

The hills for example in San Francisco are some serious inclines.

Here is the order for the worst hills:

Here, according to the city Bureau of Engineering, are the steepest of the steep in descending order:

1. & 2. Filbert between Leavenworth and Hyde; 22nd Street between Church and Vicksburg, both 31.5 percent gradient.

3. Jones between Union and Filbert, 29 percent.

4. Duboce between Buena Vista and Alpine, 27.9 percent.

5. & 6. Jones between Green and Union; Webster between Vallejo and Broadway, both 26 percent.

7. & 8. Duboce between Divisadero and Alpine; Duboce between Castro and Divisadero, both 25 percent.

9. Jones between Pine and California, 24.8 percent.

10. Fillmore between Vallejo and Broadway, 24 percent.

Parking on the foregoing is, in most cases, perpendicular to the curb and sidewalks are stepped to give pedestrians a better footing. The intersections at their summits have been graded for 20 feet or so to prevent cars from scraping bottom at the crest.

The "Hill" at the Romeo Proving Ground

https://www.pinterest.com/pin/340303315563203538/

30% grade

45% grade, I do not think we are using the same terms

Tom V.

We had a steep driveway when growing up: the 2-bbl and 4-bbls always did well, but we always drove up and drove down well. Rarely/never in reverse, because we could turn the car around at the bottom for the "running start"

Those carbs are way tilted. And my garage opening is not very wide -u can see in my profile pic. So I lose power steering going backwards down a hill and aiming for hole perhaps a foot and half wider than the car. Always interesting moment when warmer weather rolls in. Drives perfect on flat surface.

For sure you need to lined up pretty good if/when you loose power.

Speaking of garage stories a very dedicated Pontiac enthusiast asked me to build a TH400 for him about 20 years back, but he chose a local "builder" instead. Somehow during the process of firing it up and filling it with fluid it was in reverse and it backed off the jacks, out thru his garage door, across the alley and into the neighbors garage! I guess the "builder" had installed some type of reverse VB and somehow it was in reverse instead of neutral and he wasn't using a neutral safety switch........

I thought that in road work the "percent grade" was a way of using the tangent of the slope angle as a way stating how steep it is. That would make a 45 degree angle a 100 percent grade. And if you ever had to drive one that steep you would be wishing for a carb off an old acrobatic airplane.

🔰 I totally agree with JSchmitz...
 

Totally agree, the end carbs don’t have anything to do with idle, as they only dump gas. There’s no fuel ‘circuit’ on them. The center carb does everything that’s important.

To the original poster: I’ve experienced accelerator pump ‘sticking’ issues...although your not really ‘accelerating’. I remember mine used to ‘stumble’ when even the slightest gas/accelerator was applied. Check to see if the accelerator pump is binding...

I tend to agree that the choke may not be warming up the fuel. Have you tried installing an electronic choke ?

Go San Francisco
 

You haven't lived till you have driven some of those streets in SF. They are scary big time.If you are ever out here go try them in a rental car if you have not driven.

On the fuel starve/ or flood, I will tell you of a common problem when hot out.
Our 65 GTO with four barrel, would stall out on a steep grade. The problem turned out to be a cracked rubber fuel line in the back where the tank outlet hooks to the steel line going up front. Could not draw enough fuel to keep things going.

I have seen scary rubber fuel lines on the same car. These were lines I thought were fairly new. NOT! The rubber lines at the fuel pump and the lines to the fuel filter and carb were also badly cracked. Change you rubber hoses at least every 5 yrs and be safe.