Hello, I’m working on my grandpas 72 cutlass supreme, it has a 2 barrel carb on a rocket 350 engine with auto trans. It does have an upgraded pro form distributor as well.






The issue I’m experiencing is the engine hesitating while taking a right hand turn around the block at around 20 mph and sometimes it also hesitates when accelerating hard in a straight line. I believe it is a fuel cut issue possibly due to fuel slosh because when I watch the fuel gauge while turning right it drops down to empty and then as soon as I press on the gas pedal as I begin to straighten out it hesitates and you have to feather the pedal to get it to rev up normally, once or twice it has completely died but will start right back up.

So far I have had the 2 barrel carb rebuilt at a reputable shop called Carb Exchange in El Monte, CA, as well as replaced the fuel sending unit in the tank just earlier today and the sock was beginning to come apart and the ground was very rusty. The tank was previously replaced in 1998 and still looks very clean inside. I took some sand paper and cleaned off the location where the ground wire connects to the body as well to ensure a good ground. After getting it all back together and putting 10 gallons of gas in the tank, I took it for a test drive and still have the same exact issue. It also only seems to happen on right hand turns for some reason. The last thing I could think of to replace is the mechanical fuel pump on the block but it doesn’t make any correlation in my opinion as to why the fuel gauge would drop all the way to empty around a slow right hand corner.

any ideas or helpful information would be greatly appreciated and I hope I included enough information as well. Thanks in advance for reading through!

 

This is a picture of the carb before I had it rebuilt it looks brand new now but I thought I’d add this in in case it helps at all

 

Put another supply line on the fuel pump and run to a 1 gallon can under the hood temporarily. Go drive around the neighborhood and see if you still have the issue and come back to us with update.

Thing is, the car doesn't use the gas in the tank while you are taking the turn. That gas is used maybe ten seconds later or so, there's a fuel bowl in the carburetor.

Check all your electrical connections at the coil.

 

X2 on checking electrical connections at the coil and the ones down to the starter from the coil primary side. You could temporarily jumper battery voltage to the coil to see if the problem changes, don't leave the jumper it will burn the points over time.

Pull the distributor cap and check the black wire to the points and the wire from the points to the condenser. Check the ground wire to the point breaker plate.

Disconnect the vacuum advance to see if anything changes.

 

Thanks for the replies! I’ll try that stuff tomorrow and get back to you.

 

Looked again, your car has been converted to HEI so no points/condenser. Still try disconnecting the vacuum advance. Confirm that there is full battery voltage to the HEI with the car running, very unlikely that could be the issue but it should be confirmed. Occasionally the resistance wire used with points is used to power the HEI but it is around 9 volts vs. full battery voltage.

 

I was wondering about that a bit. But I will check that voltage and try disconnecting the vacuum advance. Could a random vacuum leak be the cause? I did look over most of the vacuum lines and did not see any cracks or splits. But there are 2 metal tubes that go into the carb and I have a feeling they are not sealing into the holes on the manifold. Tomorrow I also plan to spray some carb cleaner around those areas and see if there is a possible vaccum leak.

 

These are the metal tubes I’m questioning mainly, you can’t quite see where they go into the manifold but it’s just under the part that is also encircled in red

 

Have you checked the fuel filter? I had a '67 Delta 88 that exhibited very similar symptoms at one point. I even had just done work on the fuel system as well. It turned out that that work stirred things up, all of which got caught in the filter. Even though I had replaced it during all the fuel system work and it was only a few week old, it was dirty again. Replacing it did the trick.

 

Yes a random vacuum leak could cause it, closely inspect the hose to the brake booster since it moves a little as the engine torques. Is this a cold, hot or any engine temp symptom?

The battery voltage to the HEI has to be checked with the engine running, if there isn't an electrical load it would always read full battery voltage if the factory resistance wire is present.

I don't believe the two pipes a/k/a choke heat tubes could cause a vacuum leak... anyone agree/disagree?

 

John,

The tubes you circled in red are part of the choke-regulating mechanism. The connection at the carb--at the top of your picture--is the source of clean air for the system. That tube from the carb delivers air to the choke stove, which is a depression in the top side of the exhaust crossover through the intake manifold. The depression has a bolted cover that you can see a bit of at the bottom of the circled area.

That depression is only there to heat the air coming in from the carb. It has no connection to anything in the car's gas/air mixture delivery system. It's just a hot box.

The tube on the right comes out of the choke stove and the heated air flows through it to the choke mechanism (the larger item with a black cover in the red circle), allowing the choke plate on the carb to open.

Inside the choke mechanism is a regulated source of vacuum that motivates this air flow. The carb rebuilder made sure the internal vacuum source passages were clear, the O-ring gaskets were in place, and the choke regulation was set.

It's a long way of saying that there is nothing in the red circle that would be a source of your problem. But now you know a bit more about your car.

Gary

 

Fact the fuel gauge drops down to empty when turning right suggests fuel slosh. Completely fill the fuel tank up to the top of the neck then take it for a ride? Does the issue remain, does the fuel gauge drop down to empty in RH turns?

 

More to think about and check or rule out from Mikes carburetors:

 

Ill give that a look as well

 

thank you sir.

 

I put 10 gallons in it after getting the tank back in drive it around the block quite a bit and then I just put another 8 gallons in it today and still has the same issue. So I don’t think it has anything to do with fuel slosh anymore.

 

Jeff - Certainly something noteworthy; yet, it wouldn't explain the fuel gauge reading EMPTY during a RH turn. Suspect incorrect fuel tank sending unit or incorrectly installed fuel tank sending unit.

 

Since the sending unit was recently replaced it would be best to revisit that, particularly the pickup tube and sock position.