[65fbmustang]

Hello,
I have a 600 cfm Holley w/ vac secondaries (model 1850-1) on a 289. The car has a 4 spd top-loader tranny. I have reduced the jet size from 66 to 64 (b/c of altitude) and have a #31 accel pump squiter with tubes/horns in it--the original was a #25. Since the car was always running rich and the primary butterflys were open too much, I drilled one 3/32 hole in each one. Now the car doesn't run rich, but is bogging when starting to move. If I slip the clutch quite a bit and rev it up, then it does ok. The car is rather high geared, not sure exactly what ratio.
The question I have is, should I start looking at accel pump cams or a larger squiter? I am on a bit of a budget (I am a teacher), so I don't want to just start buying parts.
Also, the car bogs when the secondaries open for a moment, then runs fairly well. I have bought a spring kit, and currently have the black spring installed w/ the ball installed as well. It got better w/ each spring, but the black one is the last one--any suggestions?

 

[killerformula]

if it bogs you need a less agressive squirter or pump cam, don't get a bigger pump!

If it bogs when secondaries come in you need a different secondary spring.

K

 

[lluciano77]

You shouldn't have drilled the butterflies. That almost always isn't necessary. There was probably some other problem you overlooked.

With the butterflies drilled, you are running lean off idle. You need a bigger pump cam to overcome the excessive air at idle. It may help, but you will always be tuning around the drilled holes that shouldn't be there.

289s and 302s have a dead spot from idle to about 2,500 RPMs. They like a little more accelerator pump shot to get through that range anyway.

It sounds like you need to adjust your throttle position also. Set the primaries so that the transition slot looks like a square from the underside of the carb. Then, adjust the idle with the secondary screw. It can be a pain, but you will get the most from your transition slots this way.

Make sure you have instant accelerator pump shot. As soon as the throttle opens there should always be pump shot.

 

[65fbmustang]

lluciano77
Thanks for the reply. I got a book from the library and had done the adjustments on the secondary screws as you suggested, but the book then told me that drilling was a option if adjusting the secondary screws worked. I will look with accel pump cams instead of a larger squiter, as you suggested.
Does anyone have any ideas about the secondary spring--I have the stiffest one in the kit (black) installed, and it still stumbles a bit--it is definitely better, but the stumble is still there.

 

[65fbmustang]

under jetting a carb

Hello again,

What are the effects of under jetting a carb? Would this possibly cause both the bog at off idle and when the secondaries kick in? Or is this completely off base?
Thanks.

 

[lluciano77]

The stiffest spring will make the secondaries come in later. That usually won't cause a big bog. It will be more like a wide range flat spot in the mid to upper RPMs.

Jetting a carb too lean will cause surging at cruise speeds. The best way to jet for the street is to check for lean surging. Start with the stock jetting. If your car is surging increase the jet size. If you are already jetted up, jet down two sizes at a time until you feel a lean surge. Then, increase two jet sizes.