67 commando 273 issue

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fireguyfire

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I rebuilt my factory 273 commando engine from the 67 barracuda I bought last fall. I have broke in the camshaft and lifters, set the timing etc and the engine runs and sounds beautiful.
Today I started the engine and let it idle to get another heat cycle into it while I tweaked a few things under the hood, and I noticed that when the engine is hot and I shut it off, you can hear fuel boiling inside the 4 bbl carb and if you look into the barrels you can see it leaking fuel down the barrels when it’s “gurgling”.
Obviously this is an issue I need to sort out for several reasons.
I can’t remember when I rebuilt the carb what type of base gasket was on the car, but now I am just running the thin gasket that came in the Carter bbd rebuild kit.
I’m wondering if it should have a laminated thicker insulator type base gasket on these 4 bbl commando engines?

I double checked timing, confirmed that the heat riser valve is working (I’m going to disconnect the exhaust and confirm that it’s not 180 degrees out).
I’m looking for advice on what my issue might be and other things I need to troubleshoot as having fuel boiling in the carb is clearly not acceptable.
 
fireguyfire said:
I rebuilt my factory 273 commando engine from the 67 barracuda I bought last fall. I have broke in the camshaft and lifters, set the timing etc and the engine runs and sounds beautiful.
Today I started the engine and let it idle to get another heat cycle into it while I tweaked a few things under the hood, and I noticed that when the engine is hot and I shut it off, you can hear fuel boiling inside the 4 bbl carb and if you look into the barrels you can see it leaking fuel down the barrels when it’s “gurgling”.
Obviously this is an issue I need to sort out for several reasons.
I can’t remember when I rebuilt the carb what type of base gasket was on the car, but now I am just running the thin gasket that came in the Carter bbd rebuild kit.
I’m wondering if it should have a laminated thicker insulator type base gasket on these 4 bbl commando engines?

I double checked timing, confirmed that the heat riser valve is working (I’m going to disconnect the exhaust and confirm that it’s not 180 degrees out).
I’m looking for advice on what my issue might be and other things I need to troubleshoot as having fuel boiling in the carb is clearly not acceptable.
Click to expand...
Interesting you are hearing what I have heard and described on many threads here about hard starting, vapor lock and fuel evaporation. For the naysayers, it's a real thing. Like 4 spd recommended, an insulator will help. Keeping your engine temp down may help a bit as well. Do yourself a favor and run regular non ethanol gas if you can find it. Even 10% ethanol can worsen the issue.
 
Use non ethanol fuel and this boiling in the carb will not happen.

I'd bet that the 273 4 bbls use a thin base gasket. Seemed like that thick base gasket all started in 1970 when they changed the choke thermostats to the raised dome kind and the cup underneath with a gasket.
 
The cast 273 intake absorbs a lot of heat, it has a very short plenum and the AFB's are really prone to fuel boiling. The bowls are quite small and directly over the base and the hot intake. @fireguyfire, if you are running stock manifolds, make sure the heat riser is open when the engine is warm and that the passage under the intake is open.
 
273, 2 BBL, no insulator.

No fuel issues especially on ethanol free gas
 
Yes, I was just pointing out that everyone says you have to run the insulator even on a 2 BBL. But you do not.
 
Can we see a picture of how you have the fuel filter attached, please?
 
used a vent line from a 71 Duster to run to the tank.

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So I picked up the suggested edelbrock 9266 spacer and the bolt pattern on my AFB and factory intake are quite different.
I could maybe butcher this spacer but it won’t be ideal just the way the correct gasket overlaps the 9266 for comparison.
Am I missing something?

My buddy who is a retired mechanic said to just make one out of 1/2” plywood as that is the way they used to do it all the time in the old days, but I’m a little leery about putting a flammable item where all of the fuel and air comes together.
 
fireguyfire said:
So I picked up the suggested edelbrock 9266 spacer and the bolt pattern on my AFB and factory intake are quite different.
I could maybe butcher this spacer but it won’t be ideal just the way the correct gasket overlaps the 9266 for comparison.
Am I missing something?

My buddy who is a retired mechanic said to just make one out of 1/2” plywood as that is the way they used to do it all the time in the old days, but I’m a little leery about putting a flammable item where all of the fuel and air comes together.
Click to expand...
An old racer friend of mine had wood spacers on his tunnel ram with no issues. In fact this one is wood fiber and has a dual bolt pattern. THis one is Edelbrock 8723.
Yes, the carb base is smaller on the early smaller cfm carbs. Apparently the spacer didn't have double holes drilled like the carb bases are. The bypass fuel filter pictured above will help if you are having vapor lock while the engine is running butt as soon as the engine is shut off there is no flow and the gas can still boil in the carb.
1726606790886.png
 
There is gas boiling, and dripping down the barrels, but if the bleeds are plugged, that can cause "syphoning" which also causes dripping after shutoff.
Find and clear air bleeds, reset/check float level, check for sunk/heavy float, might be considered.
Good luck
 
Inertia said:
There is gas boiling, and dripping down the barrels, but if the bleeds are plugged, that can cause "syphoning" which also causes dripping after shutoff.
Find and clear air bleeds, reset/check float level, check for sunk/heavy float, might be considered.
Good luck
Click to expand...
It sounds like the gas is boiling in the bowls.
 
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