Gas leaking from both carbs
 

Recently, I noticed after a drive where the engine gets all the way up to temp when I stop I can hear boiling in the carbs and gas leaking out of what appears to be the throttle plates. I know I need to check my fuel pump pressure, but could also be floats? is there a tutorial somewhere that shows how to adjust and floats?

These are two new (800 miles) stromberg 97’s.

Re: Gas leaking from both carbs
 

Do you know that 97’s will run just fine with whole tops removed. You can pull the tops off and see the fuel level with the car running.
I would check to see if the fuel inlet valves are good. I hold the carbs upside down and blow in the inlet. There must be no leakage.
The float level is adjusted by bending the tang on the float.
Are these the Speedway carbs?

Re: Gas leaking from both carbs
 

They are genuine strombergs. I did not know I could run the car without the tops on. Thank you for that info.

Re: Gas leaking from both carbs
 

But be very careful and have a fire extinguisher or two handy. Generator brushes can make nice sparks in the vicinity, not to mention the entire secondary ignition system.:eek:

Re: Gas leaking from both carbs
 

What is the float height spec? Is there one?

Re: Gas leaking from both carbs
 

if you aren’t having problems driving it and only noticed this when the engine is off i’d be checking the fuel your using if it has any ethanol in it that’s pretty much the problem it’s called fuel foaming acts like a percolator use a good grade premium or mid grade that doesn’t have ethanol in it it’ll say on the pump good luck

Re: Gas leaking from both carbs
 

I have been running premium (91) in Colorado. I tried 2 tanks of our lowest (85) a while back and it did not run well. I have no idea if the 91 octane has ethanol, but I’m sure it does. I’ll see if I can find ethanol free around me and try it.

Re: Gas leaking from both carbs
 

You measure the fuel level in a 97. Remove the top of the carb and the gasket, measure from the surface that the gasket was on to the fuel. Best done with the motor running. Make a gauge from some sheet metal, or cut a notch out of a 6" steel ruler.
EDIT: (15/32" to 1/2" Corrected by drolston see post #22) the float should sit reasonably flat and level. Check your fuel pressure FIRST!

Re: Gas leaking from both carbs
 

Make sure if you do have the motor running. Don't do it in the garage with the door closed. Park it outside, away from anything that is important to you. Some fire extinguishers can destroy your engine.

Re: Gas leaking from both carbs
 

Instead of running the engine with the tops off try leaving the transmission in neutral, ignition off, and cranking the starter to run the fuel pump. If you have an electric pump you can just turn that on. If fuel spills you have nothing electrical going on to make life exciting. With your freshly rebuilt motor you might want to pull the spark plugs so the starter is not working as hard and the engine spins faster if doing the starter method.

I did the top off and crank with the starter method on a 37 sedan years ago and discovered that the modern fuel needs to have the float set about 1/4" lower than factory specification to get the fuel level correct. I now do this for all carburetors I go through.

I do not like the idea of making the carburetor correct for only ethanol free gas (factory float setting), I can't count on finding ethanol-free on my travels. I can count on finding modern gas that is less dense and will overrun factory float settings. I adjust my floats down for the modern gas and drive many miles with no drama.

Re: Gas leaking from both carbs
 

Interesting observation

Re: Gas leaking from both carbs
 

The density of E10 gas is about 2.3% less than straight gasoline. I doubt that would raise the fluid level in the bowl by very much.



Which raises a question in my mind I have had for years as to why there is such obsession with precision is setting float level. With steep hills and sharp turns and bouncing around on rough roads, the fuel in the float bowl is going all over the place, and yet the flathead continues to run smoothly. The size of the jets controls the flow, not the depth of the fuel in the bowl.

Opinions?

Re: Gas leaking from both carbs
 

I disagree with the statement that jets control flow and not the depth of fuel. I had a Yamaha 150 outboard with 3 carbs and it was a dog until I removed the carbs and raised the float levels to spec - cured the problem. Jet size and float level control the amount of fuel.

Re: Gas leaking from both carbs
 

If you raise the fuel level, your motor will run a little richer.

Re: Gas leaking from both carbs
 

It would be fun if someone with an air/fuel indicator on their flathead ran a test to see how much fuel level in the bowl affects mixture.

Re: Gas leaking from both carbs
 

Interesting chatter about floats!

Does anyone think floats being wrong would cause dripping after running? I haven’t had dripping since I started this thread and I drove it pretty long today (but it’s also now finally not getting hot when idling at lights and such).

Re: Gas leaking from both carbs
 

We have digressed from your problem. More info needed. When you referred to dripping at the throttle plates in your first post, were you looking down the throat of the carb and saw gas on the throttle plates, or are you seeing gas leaking on the outside of the carb around the throttle shafts?

Re: Gas leaking from both carbs
 

I find the alcohol fuel expands more than the old gasoline, and will flood the carburetor after shutdown when the engine is getting heat soaked. Lowering the float eliminates this problem.
Also, my memory is JWL experimented with float settings in his very methodical and documented dyno testing sessions and found fairly large changes in our old carburetors didn't affect fuel ratios. Carburetor design will have an effect on this, and this finding should not be universally applied to other engine types and carburetor types.



I did not do a before test, but I did use my portable O2 sensor test on the 37 after lowering the float to make sure it wasn't running lean (it wasn't). I also found the initial ignition timing advance on the side of the helmet distributor affected idle vacuum and O2 readings much more than I expected. This was 10+ years ago and I don't remember all the details, but do remember being happy with the final result.


This matches my experience. Heat soak causes the alcohol type fuel to expand in the float chamber, running down the carburetor internal passages, pooling on top of the closed throttle plates, and running out the throttle shaft. Lowering the float solved this problem for me. South Texas is hot enough during most of the year that I cannot avoid heat soak.

Re: Gas leaking from both carbs
 

It was visible on the outside of the carb, on both sides (left and right) of the plates. Or actually it was dripping off from the shafts that stick out. I did get 10 Gallons of ethanol free gas after starting this thread and getting the ethanol gas response and I have not noticed it happening since.

Re: Gas leaking from both carbs
 

The Stromberg 97 instruction manual states 15/32 to 1/2"