Hesitation on throttle

65 riv , 401 , edelbrock carb.

I changed the acceleration pump jets to a smaller diameter. and changed the metering rods and primary jets to the next smaller size than stock (edelbrock sent me the pieces).

Now if the throttle is at idle and you give it gas (just enought to take off from a light guick - not racing) it hesitates badly then jumps off the line. same thing for up til 20 mph then you can stomp it and it runs fine.


I checked the new acelleration pump jets and the seem to be squirting plenty. when the car is off.

Did this sound like an accelerate pump or smaller jets?
How do I know if I leaned it out too much?

I could have screwed some of the linkage up when I took it apart.

 

Sounds like a problem with your off-idle circuit.

It's been a long time since I studied carb theory and I don't have any experience with Edelbrock's improved AFB. What cfm carb and size primary and secondary venturi's you running?

JR

 

So I screwed something up when I took the top off to change the primary jets and accelerate pump jets?

Its a 600 but I dont know the size of the jets. It is supposely a size less than stock.

 

Sounds to me like you have a lean condition, (not enough fuel), maybe try puttin the old accelerater squirters back in, what is the reason that you took the old ones out? o No:

 

I messed with the accelerator jets and primary jets because it was getting bad mileage (10) and exhaust smelled rich.
When I looked at the acclerator pump, it seemed to squirt way too much gas in (not very strong but just a large stream).


I didnt think a lean condition would make it surge only at idle. above 20 mph it runs fine.

 

You have a good point there.....usually things act lean all the way through. I guess what i was thinking is that it's not gettin enough gas just off the go.....maybe i'm not making sense....that wouldn't be anything new...lol :laugh: ou:

 

My 64 with a 425 and a Carter 9635 (625 cfm) gets 13-16 mpg, so you've got something going on. I'd check two things: 1) Vacuum, 2) Spark plug color. Almost sounds like you've got a vacuum leak somewhere, can be P/B and A/C as well as gaskets. Plug color will tell you if you're too far rich/lean. Did you check that the primary metering rods are free to move against the springs? They're under the little covers on the air horn assy. I take them out and put them back in separately when I take my airhorn off, so they don't get bent tips.

 

I just changed the plugs so I will check in a couple of tanks.

I did check that the rods are moving freely.

I will check for a vacuum leak. I will block off all the vacuum lines and see if it helps.

My secondaries are completely closed . Isnt that wrong? I thought they were closed until I stomped on them. or they would suck gas thru the secondary jets.

 

There should be some sort of color on them now, just pull a couple and have a look.
Secondaries have an air valve right under the venturi assemblies. It's normally closed by counterweight action, when the engine is revving enough to use the airflow, that air valve will start to open.

 

You need to put the original accelerator pump jets back in, but keep the smaller main jets you put in. It just isn't getting enough fuel when you push down on the accelerator. Accelerator pump is only a very small contributor to your fuel mileage. The main jets being too large is why you were getting poor fuel mileage.

 

Well now when I got ready to change out the jets, it stopped "stumbling". it runs fine now. I do worry about it being too lean. I dont want to burn up my exhaust valves.