Carburetor lags when I punch it

[melhilburn]

I have a 292 with rochestor 1bbl - I have rebuilt the carb and the engine runs fine - It just bugs me that the motor stumbles for just a slight moment when you punch the gas pedal - Any ideas what could be causing this?

[Big Fenders]

Possible accelerator pump adjustment
Bob

[geezer#99]

Timing or
Cold intake!!

[oem4me]

Look down into the carb with a flashlight and hit the accelerator. You should see a healthy stream of fuel squirt into the throat. If you do not see that upon working the accelerator, then your accelerator pump is bad, or more than likely it's outlet is plugged. Clear the hole with a wire and away you go.
If however you do see a squirt, then look into your timing.

[melhilburn]

Thanks it has to be related to the accelerator pump - engine runs smooth as silk otherwise - I just replace the heater riser valve spriing and it works perfectly - I'll take the carb apart and give it another go.

[sigshooter]

Same story here on this end...... I have checked mine and it is not squirting the fuel, I just haven't had time to tear it apart. I chose to drive it all I can since it runs fine otherwise.

When I rebuilt mine my 5 year old was "helping" me and I think we might have gotten the two small round steelie balls in the wrong holes. They are a different size and wont seat properly if they are switched.

Might check those also.....

A friend of mine built his and the "T" shaped retainer that holds the long ink pen looking spring in place...... well he put it back in a way that is blocked a very small hole and prevented the fuel from being able to be drawn to the accelorator pump. Took him several tear downs to figure this one out.

Good luck and let us know what you find

[63burban4x4]

Originally Posted by oem4me

Look down into the carb with a flashlight and hit the accelerator. You should see a healthy stream of fuel squirt into the throat. If you do not see that upon working the accelerator, then your accelerator pump is bad, or more than likely it's outlet is plugged. Clear the hole with a wire and away you go.
If however you do see a squirt, then look into your timing.

X2. IIRC, the fuel normally is drawn into the carb barrel by the venturi effect. Air rushing down the barrel past the venturi, draws fuel into the airflow. When you stomp the pedal, the throttle plates instantly allow more air, but it takes a second or two for the venturi effect to provide more fuel. The accelerator pump overcomes that momentary lack of fuel with a little extra fuel "pumped" in, That little squirt of fuel provides enough fuel until the venturi effect takes over. Easy then to understand the "stumble" , if the accelerator pump isn't working. It's been a while, but I think the accelerator pump has a rubber diaphram, which is pushed down by the accelerator pump linkage, pushing a little fuel in front of it. That rubber plunger can dry out, crack, and fail. At least that's how I remember it...LOL. The real mechanics here can correct me if I'm wrong.

[Wrenchbender Ret]

I agree its probably the accel. pump. Sometimes raising the float level a small amount helps.

[luvbowties]

..."engine runs smooth as silk otherwise"...

You are talking about idle circuit above--completely different from power circuit which seems to be giving trouble. Sounds like carb needs 'soaking' in carb cleaner for a few hours, cleaning all orifices with gas welding cleaning tips and air pressure, and a quality rebuild kit--paying CLOSE attention to adjustment specs. Nothing beats all these steps in carb-tuning.

As another poster mentioned, you may want to raise floats a tad above specs if all else fails.

Also, verify vacuum advance is working properly; if not, it can cause your symptoms as well as kill gas mileage.

[luvbowties]

Originally Posted by 63burban4x4

X2. IIRC, the fuel normally is drawn into the carb barrel by the venturi effect. Air rushing down the barrel past the venturi, draws fuel into the airflow. When you stomp the pedal, the throttle plates instantly allow more air, but it takes a second or two for the venturi effect to provide more fuel. The accelerator pump overcomes that momentary lack of fuel with a little extra fuel "pumped" in, That little squirt of fuel provides enough fuel until the venturi effect takes over. Easy then to understand the "stumble" , if the accelerator pump isn't working. It's been a while, but I think the accelerator pump has a rubber diaphram, which is pushed down by the accelerator pump linkage, pushing a little fuel in front of it. That rubber plunger can dry out, crack, and fail. At least that's how I remember it...LOL. The real mechanics here can correct me if I'm wrong.

Dunno why you mentioned "real mechanics" above--sounds like you gave quite a good & thorough explanation of just how it works!

[melhilburn]

I agree it must be related to the accelerator pump system (either the pump seal or blocked passage way) - I'm a clear on the venturi effect - This creates a instant leaning of the fuel mixture when you punch it - The only wat to over come this is whit a small aquit of fuel provided by the accelerator pump - I'm going the break it down this week and soak it carb cleaner over night then put it back together paying close attention to each step and part - Not clear on comments regarding raising the float level?? - How would this help just curious??

[T2vigil]

All of these answere are spot-on. Weather you are book learned or shade tree like most of us a real mechanic is one who can get the job done. I for one appreciate all of the advice the "Mechanics" provide on this forum.

[63burban4x4]

Originally Posted by luvbowties

Dunno why you mentioned "real mechanics" above--sounds like you gave quite a good & thorough explanation of just how it works!

Thanks, luvbowties. That's just how I remember it.....although I haven't really had a carb apart in many years, it's fairly easy to recognize a probable acc pump problem.

exactly 43 years ago, (1969) I had a "Class A" smog licence in California...to repair the very early vehicle smog systems. The stuff I learned in that training stays with ya (well, some of it anyway) like, how a carb works!

I try to contribute when I can, but it certainly wouldn't be the first time I've been corrected ...LOL.

[63burban4x4]

Originally Posted by luvbowties

Dunno why you mentioned "real mechanics" above--sounds like you gave quite a good & thorough explanation of just how it works!

Thanks, luvbowties. That's just how I remember it.....although I haven't really had a carb apart in many years, it's fairly easy to recognize a probable acc pump problem.

exactly 43 years ago, (1969) I had a "Class A" smog licence in California...to repair the very early vehicle smog systems. The stuff I learned in that training stays with ya (well, some of it anyway) like, how a carb works!

I try to contribute when I can, but it certainly wouldn't be the first time I've been corrected here...LOL.

[Sillyoldman]

Look for vacuum leaks.

[HouldenCaulfield]

I am experiencing the same thing. I solved all vacuum leaks. I just rebuilt the carb. I haven't got it back on to see if it helped or not. The accelrator pump looked ok. I replaced it anyway. I did however, notice my floats were dropping around 2" instead of the 1.75" I believe they should drop. So, hopefully that will help also.