Carb Help - Car idle slows and dies after being run for a while

[PeterB]

My car starts fine with the choke on and idles well for a while with the choke off, well after the engine is up to temp. Then if I contiune to let it idle or drive it a little, the idle seems to slow and the car stalls. Then when I go to start it, it has a hard time to start. I recently had my HS6 Carbs rebushed and then I rebuilt them in my BJ7. I checked the timing with an advance light and I am running 15 degrees as in the book. Distributer seems to be fine. I initially tunes the carbs after the car was warmed up so I am not sure what I am missing. Could it be vapor lock? Any thoughts.

Thanks as always for the help.

 

[pkmh]

One suggestion is to disconnect the fuel line to the carbs, but have line empty into a safe container and observe fuel flow while having the ignition in the on position, thereby activating fuel pump to ascertain if pump is working properly and or if fuel filters are clogged and or if fuel tank is clogged.

I had to totally redo my entire fuel line starting with the tank to rebuilding my carbs. All I can say is its a step by step process. Others here will be more specific as well.

Good luck.

Paul

 

[steveg]

My car starts fine with the choke on and idles well for a while with the choke off, well after the engine is up to temp. Then if I contiune to let it idle or drive it a little, the idle seems to slow and the car stalls. Then when I go to start it, it has a hard time to start. I recently had my HS6 Carbs rebushed and then I rebuilt them in my BJ7. I checked the timing with an advance light and I am running 15 degrees as in the book. Distributer seems to be fine. I initially tunes the carbs after the car was warmed up so I am not sure what I am missing. Could it be vapor lock? Any thoughts.

Thanks as always for the help.

When it stalls, can you undo the float chamber lids and see if the chambers are empty? That would confirm you've got a fuel starvation problem.

If you drive the car without idling, will it stall as it does at idle, or will it keep running indefinitely when you drive it? If the latter, no fuel starvation.

I rebushed my own HD8 carbs with new teflon bushings and the car would gradually die at idle, like yours. When I had Tom Bryant rebush with his solid Delrin bushings, the problem went away. He's a Volvo guy, so he's done that to hundreds of HSs.

When the car's idling, try squirting something around the throttle bushings. If your idle changes up or down, you've got an air leak at the bushing.

Edit:
According to this Joe Curto video there are 3 different float designs for the HS, with the possibility of the wrong float being used with a given cover - leading to a float that shuts off too low, causing fuel starvation.

See (starting around 10:00):
http://joecurto.com/su-float-bowl-covers

 

[jimmyr]

After many fuel related problems over the years, pumps, filters, clogs, etc, I have added a nice small fuel pressure gauge. Located it out of the way behind the hood brace, I cad quickly see if a fuel related problem has occurred. Thus localizing the problem to a fuel delivery or ignition etc.

 

[PeterB]

Thanks for the ideas, I will check them out this weekend. What leads me to the vapor lock it that the car runs fine at start up and for a while after that. It's only after 20 or 30 minutes of idling or stop and go does it start to act up.

 

[pkmh]

OK PeterB,
Possible about vapor lock. and aside from that, I heard something about gas caps having issues, too.

Question...When the vehicle stalls, it takes a little while before you can start her over and runs, yes? And then it stalls again after some point, yes?

If yes to both, then chances are it might be a clogged gas filter (in my opinion and was for me, anyway). There are filters, one right after the gas tank and one just before the carbs (if installed). Any others I missed?? Then your fuel pump might need looking into, as well. One step at a time.

Fuel filters are easiest to check, in my opinion (next to leaving the gas cap off?). Just my opinion.
again, good luck and keep us informed.

Thanks.


Paul

 

[red57]

Your first post is not clear whether it dies while driving or just when idling? If it is mostly at idle that you have a problem, I would consider it might be a little too rich and slowly loading up the plugs. I suggest let it idle until it dies and pull some plugs and see if they are sooty or wet or dry or whatever - that may tell you something about what is going on.

In my experience, most of the time vapor lock will happen when the car is fully warmed up after driving for a while and you shut it off to get gas or a short lunch break. Because there is no air movement the heat from the engine then soaks into the float bowls and heats the fuel. When you re-start it will pop & snort & spit and backfire for a while because it is trying to run on fuel vapor rather than liquid fuel. After a few minutes running, when it gets some cooler fuel from the tank and air movement cools the metal of the carbs a bit, it will settle down and be normal again. Lots of cars (like Datsun 240z) attempted to cure this by having a return line to the tank so there was always a source of cool fuel to the carbs.

This normally doesn't happen while continually driving because there is cool fuel and lots of air flow - but there can be exceptions and other explanations.

Dave

 

[PeterB]

Dave, I would say mostly at idling. I was trying to adjust my brakes after new shoes so I warmed up the car and was running it back and forth down a 400' driveway after my adjustments but there was a lot of idling involved. I will try again and pull the plugs as suggested.

 

[PeterB]

I think I found my problem. Running way too rich. Pulled the plugs today and they were black and just about dripping. I ordered a colortune to help me lean it out. I’ll let you know who I make out when it comes in.

thanks

 

[steveg]

I think I found my problem. Running way too rich. Pulled the plugs today and they were black and just about dripping. I ordered a colortune to help me lean it out. I’ll let you know who I make out when it comes in.

thanks

Tom Bryant has a good step-by-step on tuning the HS6. He's a Volvo guy and a lot of them have dual HS6's.

https://thosbryant.wordpress.com/2015/10/04/su-carburetor-tuning/

 

[John Turney]

I think I found my problem. Running way too rich. Pulled the plugs today and they were black and just about dripping. I ordered a colortune to help me lean it out. I’ll let you know who I make out when it comes in.

thanks

When you turn the key on, does the fuel pump stop clicking before starting? If the pump keeps running, the carb float needles may have some crud in them and leak.

 

[steveg]

When you turn the key on, does the fuel pump stop clicking before starting? If the pump keeps running, the carb float needles may have some crud in them and leak.

In this case, gas would probably also leak out the manifold drains.

 

[bob hughes]

Over-fuelling could well be the problem, I have experienced that - had to change the needles in the end. Also check the integrity of the low tension wire from the coil to the dizzy, I experienced a problem with that, the car would run for a while then stop, let it cool and it started up again, traced it to that wire - barely hanging on by the insulation let alone the wire inside.



Bob

 

[kozelding]

I agree, running super-rich can definitely foul things at idle.

Also, to veer back to the other side of the engine, I've seen a lazy centrifugal advance do something similar: after idling a few minutes, the weights in the distributor unstick and retard the timing beyond where you thought you set it.

 

[steveg]

I agree, running super-rich can definitely foul things at idle.

Also, to veer back to the other side of the engine, I've seen a lazy centrifugal advance do something similar: after idling a few minutes, the weights in the distributor unstick and retard the timing beyond where you thought you set it.

Interesting about the sticky distributor weights.

Shouldn't checking the maximum advance to be 35 degrees at 3000 rpm validate that if it's the case?