White smoke coming from carburetor/exhaust

[Black66]

My 66 C10 has a 350 SBC in it and a Holley 650 double pumper carb. It ran fine the other day then I tried starting it today and it has very rough idle and won't stay running. If I don't have it choked at least half way and let it idle, it will idle very roughly and eventually stall. I checked the exhaust and there's thin, whispy white smoke coming from it and it does smell like gas. I popped the hood, took off the air filter and there was a bunch of smoke coming from the carb. I took a video and could upload it to youtube if that would help.

The needle on the primary bowl had a worn o-ring so I bought new ones from Holley and they should arrive later today. Some gas does come out of that set screw in the front that's on top of the needle and I heard that could cause flooding? I set the floats to the levels in the Holley manual. I haven't done anything with the two black screws on either side that control lean/rich adjustment yet.

Any help would be appreciated!

[Chevy Fleetside]

is your engine stock and if so why have a double pumper on it. You might have even blown a head gasket or maybe the base gasket on the carb. It could be a vacuum leak also. Get some carb cleaner and spray it at the base of the carb and along the intake. if the idle goes up you have a leak. A small amount of white smoke coming fron the exaust isn't bad but if it becomes a cloud then you have a blown head gasket. Another way to tell is with a cmopression test and you can also pull the dipstick and see if it looks like a chocolate milkshake. Maybe i will take a picture of the one I have so you get the idea.

[Kenfuzed]

Agree with Chevy Fleetside, could be head gasket but I'd first check for a vacuum leak. Check the base, any cracked vacuum hoses (brake booster, PCV hose, trans vac line if auto). On motorcycles we always use propane to check vacuum leaks. With engine idling take a small propane torch and turn on gas. DO NOT LIGHT. Wave the tip of the torch near possible sources of a vacuum leak listed. A vacuum leak will draw in the propane gas and typically drop the idle. If the idle changes you have located your leak. Did I mention not to light the torch? Also keep away from any flame and use caution

[Black66]

I put in the new o-ring (Holley #26-37) on the needle, and fired her up. She's still idling rough and if I don't keep some gas on it it will stall.

These are the o-rings:



Now there's gas pouring out of the tube that I drew the red arrow to.

The red square is where I put the new o-ring on the needle which I thought was causing the problem.

What does it mean when gas is pouring out of that tube on my carburetor, all over my engine?

[Jimal]

Stuck needle causing flooding. Take the bowls off, clean them out, replace the needles and seats, put it back together and you should be good to go. Still too much carburetor, but it will run.

[LVPhotos]

Judging by picture you need to replace vacuum caps and what ever is that clear line. The rusty fuel line and gauge could be a problem. The choke looks like it's not opening all the way. How is the carb to manifold gasket? Fuel filter? Dirty air filter?

[Jimal]

Originally Posted by LVPhotos

Judging by picture you need to replace vacuum caps and what ever is that clear line. The rusty fuel line and gauge could be a problem. The choke looks like it's not opening all the way. How is the carb to manifold gasket? Fuel filter? Dirty air filter?

Possibly, but while those items might cause rough running, they won't cause flooding. Did you readjust the floats after installing the o-rings? The flooding to me indicates debris in the needle and seat or a float way out of adjustment.

[Kenfuzed]

Aside from the mentioned problems there are some other things going on in that picture of concern. As stated by others, should replace the vacuum caps and that clear or white tubing as a vacuum line to the distributor advance should not be used.

Also you should relocate that one spark plug wire so it is not resting/rubbing on top of the throttle linkage.

[joedoh]

have you replaced the fuel pump recently? I see a pressure gauge on the fuel line, do you have an electric pump by chance? an electric fuel pump can overpower the floats if the pressure is too high, and if that gauge is part of a regulator setup your regulator could be bad.

[Jimal]

To get back to something you mentioned in your original post, you should not have fuel coming out of that set screw. Have you checked your float levels? Joedoh is right that too much fuel pressure can overpower your floats, but let's start with the simple things. If you remove the brass caps from the brass side of the float bowls, my guess is you'll have more gas pour out. Let that drain, then start the truck and see if fuel shoots out of those holes. If the float level is correct, a slight amount of fuel should trickle out of those holes.

[imjeff]

The o-ring you replaced will not affect how it runs. That assembly is used to adjust the float and is not under pressure. The tube with the arrow is the front bowl overflow tube and will only have fuel coming out of it if the primary needle is stuck open or adjusted incorrectly. This sounds like it started out as a vacuum leak and became a float adjustment issue when you replaced the o-ring. I wouldn't tear anything apart until you adjust the float and fix the vacuum issues. There is most likely a cap or hose that came off to suddenly have a problem.

Jeff

[geezer#99]

That tube with the arrow is a vent. You need air over liquid to get it to flow. Otherwise you'll get an airlock in the bowl of the carb. Put an air cleaner lid too tight to the vent and see how your carb acts.
However since it's connected as a vent, fuel likes to flow out when the float is set to high.

[GASoline71]

The screws on top of the hex nuts on the float bowls are for float adjustment. The screw is used to lock it in place, after you set the float level by turning the hex nut.

The float is waaaaayyyyyy out of adjustment if you have fuel coming out of the vent tube.

https://www.youtube.com/watch?v=ge-mIk6nEYQ

Gary

[Longhorn 70]

also the little brass screws on the sides of the float bowl are sight plugs to see how high the fuel is in the float bowl.

This may help you. It explains how to adjust Holley floats easily.