Please help with Engine Problem

[Derrick]

Car is acting weird lately. Can't keep the carb tuned. Car will idle and run fine and then get progressively worse after driving for 10-15 miles. The car will also miss out randomly, and more consistently around 3k rpms.

The car will idle up an extra 5k rpms by pumping the brake several times quickly. Does this indicate a vacuum leak?

Any ideas would be appreciated.

 

[baxsom]

pull the hose going to your brake booster and plug the carb to see if it gets better.

just remember that your brakes will not work as well as before if you go for a test drive.

 

[LVMYVT76]

check mounting bolts, they can get loose. spray around carb with wd-40(?), if engine rpm increases, vacuum leak apparent. Check fuel filter. Check fuel, filled up lately? Check screws in carb, may be loose allowing air.

 

[howard blackburn]

rpm going up when you press the brake pedal quickly a number of times is normal.the servo uses vacuum each time you press the pedal to boost hydraulic pressure in the brake line. sounds more like electrical fault. check the rotor arm. i had similar fault turned out to be center conection on rotor burnt through.

 

[Derrick]

Thanks for the replies fellas. I'll spend some time this saturday checking out your recommendations.

It'd probably make sense for me to check the tuning on the Holley carb also. How would I go about resetting the idle mixture screws? I read that one idea is to screw both all the way in and then back both out 2 full turns as a good starting point. Then based on the how the engine is running back out or tighten up the screws 1/2 turn at a time. Does this seem accurate?

 

[minifridge1138]

I think the base mix is all the way in and then 2 or 3 turns out.

Then I hook a vacuum gauge up and make 1/4 turn adjustments (usually in to lean the mix). Go back and forth between the two screws making these adjustments.

As you do this:
Vacuum should increase, then hold steady, then start to drop.
Just when it starts to drop, back 1/8 of a turn.

Good Luck!!!

 

[JohnZ]

It'd probably make sense for me to check the tuning on the Holley carb also. How would I go about resetting the idle mixture screws? I read that one idea is to screw both all the way in and then back both out 2 full turns as a good starting point. Then based on the how the engine is running back out or tighten up the screws 1/2 turn at a time. Does this seem accurate?

Just leave them where they are, then connect a vacuum gauge to full manifold vacuum and adjust the idle mixture screws for highest steady vacuum. You're already at a reasonable baseline setting, or it wouldn't run at all.

 

[Derrick]

Checked the tuning this weekend and found that it was 3.5 turns out on one side and 1.25 turns out on the other. I got it running better after resetting to closer to 2 turns out on both sides.

I also found another issue with the carb......I noticed the fast idle lever on the holley carb won't reset itself even after it sits for several hours. This this prevents the electric choke from working too. Does the choke need a new cap/thermostate?

 

[JohnZ]

I also found another issue with the carb......I noticed the fast idle lever on the holley carb won't reset itself even after it sits for several hours. This this prevents the electric choke from working too. Does the choke need a new cap/thermostate?

Have you tried adjusting the choke cover? The rich/lean adjustment determines how long it takes for the choke to open the blade fully, and the plastic fast idle cam must move freely on its pivot. What's the LIST number stamped on the front of the choke air horn?

 

[Cruzen]

I see you live in Texas so I am assuming the ambient temperatures are mild. That choke will take more than a few hours to reset. How fast or slow it resets is dependant on the underhood temperature. Expect it to take more like seven or eight hours if the underhood temperatures stay warm. I live in Arizona and if the outside temperatures are above 50 which they are for most of the time, the underhood temperatures takes quite a while to cool and chokes do not reset for 10 to 12 hours. But then under such warm conditions you don't need much of a choke to get the engine started.

Remember, that running on the choke leads to a rich condition which is not a desirable condition. Besides glazing the spark plugs, it tends to thin down the lubrication on the cylinder walls and when done consistently can lead to premature cylinder wall wear.

Denny

 

[JohnZ]

An electric choke on a Holley will reset to its "cold" blade position in minutes, not hours. The only thing that keeps the blade fully open in the "hot" position is current flowing through the bi-metallic coil element inside the choke housing, which heats the element continuously as long as the key is "on". When you turn the key "off" and the current flow stops, the coil element cools off quite rapidly and the choke blade will move back to its "cold" position.

 

[Derrick]

thanks for the comments guys. I think I've got things in order now. One problem I had with the choke was that the choke lever was hitting my air cleaner just enough to keep it from opening and closing smoothly.

The other thing was some of the pivot points were gummed up. After modifying the air cleaner and removing the gunky areas the choke seems to be working good again.