Gas Running Out When Hot
I am running 3- 94 carbs stamped ford on carbs on my 56 Y block 312 with an aftermarket intake manifold. They run fine but now leak onto manifold. When I shut down I can see gas dripping out of center discharge tube in all 3 carb. throats. Hard starting also.
Touch the carbs when he sees them doing this. If they are too hot to comfortably touch, then they are indeed probably heat-soaking. Unfortunately, if they are heat soaking, about the only thing he can do is to try to find non-ethanol gas (which may not solve the problem entirely) or get the engine compartment heat level down (lower heat range plugs, bigger radiator, bigger fan or electric fan, lower temp thermostat, retarded ignition timing, Water Wetter . . . all of the above . . . )
If they are not heat soaking, his fuel pump pressure (including after shut-down) may be too high. Tell him to reduce it to 5 lbs. or less. But I’m betting on heat-soak . . .
What Power Valve to Use on Tripples
2.5HG seems to work best for most.
Surges
Surging is usually an indicator of a lean-running condition. Check for vacuum leaks at the carb base, the intake manifold where it installs to the block (or the heads if not a flathead) and any vacuum-driven accessories and their hoses or pipes (even a leaking 1/4″ wiper motor or trans modulator hose/pipe can affect idle characteristics). Worn throttle shafts/bushings will do the same as well.
Here is a question from a customer:
I have a gmc 302 engine with a Holley aa-1 carburetor. I have done a compleet rebuild of the carburetor with your parts and took it apart again last week, to make sure I have done it al correctly.
I have this problem of the engine surging.
The carburator was cleaned in an ultrasonic bath. Checked everything inside and al is good, as far as I can see.
But the idle mixture screws have very little effect when turned in or out. De engine even keeps running with the mixture screw fully in.
I have good vacuum but to be sure I changed all gaskets to make sure it doesn’t have a leak. Engine picks up good. Sparkplugs are black.
Checked ingnition which should be 5 degrees before TDC and was correct. Adjusted timing to 9 degrees before TDC because I run 102 octane, and it has no ethanol in it. Checked Valve lash and adjusted it to specifications. Put new spark plugs in and also new ignition cables.
But surging still exists. Don’t know what to do else, maybe a new carburator because I think it’s fuel related. Do you have any idea what to check to solve this surge.
My Answer:
There is some information on this page. See Surges
With black plugs, it tells me too much fuel.
Did you test the fuel pump for too much pressure? Should be about 4 lbs. A new fuel pump is especially suspect.
The idle mixture screws don’t make a difference because there is too much fuel at idle. Check the idle jets #44 on this page.
They may be plugged and not venting enough air.
I like to spray carburetor cleaner spray through all the small passages to make sure they are clear.
Check for leaky needle & seat by blowing into the fuel inlet with carb upside down. Remember no more than 4 lbs of air. If you suspect a leak, wipe the needle with mineral spirits to remove any residue. The needle could have been damaged when adjusting the float.
Flooding, or Too Much Fuel
- Test the needle & seat – crud may have gotten into the seat. Sometimes blowing some air into the fuel inlet will dislodge it.
- Be sure the gasket under the seat is completely removed. I have been known to leave the old gasket in place by accident.
- Test fuel pump – check your manual for the correct setting but should be 3-4 lbs.
- Check the float level
- Test your float. Nitrophyl floats need to be weighed. Brass floats may have gas inside which you will hear when shaking. The float could have a pinhole. Test brass floats by heating up a pan of water just prior to boiling and immerse the float. Any leak will show up with bubbles.
- Move the float up and down to determine if it is rubbing, or binding.
- Power valve leaking. Test by blowing on one side or the other to determine if the bellows has a hole.
One or Both Idle Mixtures Screws Doesn’t Change Anything
- One or more passages are plugged. Pay special attention to the idle circuit passages.
- Too much fuel, or not enough fuel, which could be due to a lot of things. Refer to flooding above.
- If the engine has been sitting for a period of time, then the gas may have turned and varnished the inside of the carburetor.
Car Sits for Months, Now Doesn’t Run
When cars that sits for months, the gas will turn to varnish. You can usually smell it when close to the carburetor. The gas will coat the inside of the carburetor, the fuel lines and the gas tank. This can cause the carburetor to flood, or not get enough gas.
The tendency is to just replace the gas. This might work early on, but usually the varnish chips off the sides of the gas tank and ends up in the carburetor.
The best way to fix this problem is to rebuild the carburetor, cleaning it thoroughly, get the gas tank cleaned out by boiling it out at a radiator shop (if you can find one), or use a kit from POR15, or other similar company.
When cleaning be sure to blow out the small passages as they will be plugged up with dried varnish. Spray carburetor cleaner should also cut the varnish.