I just swapped engines and dropped in the GM Performance 290 hp 350 available at summit and jegs. I put a bow tie 063 intake and an Edelbrock 1406 carb with a street fire dizzy and box.
I'm noticing a slight irregularity at cruise rpm. Whether I am in first, 2nd or cruising at 65 or70 in OD, I notice what I can only guess is a lean surge while cruising or holding steady at 2-3000 rpm. I backed out the adjustment screws on the front just a little and it did seem to help make it just a little better. But after adjusting the first couple "hours" on the screw there was no change. So they are pretty much back to my tuned idle settings and I will leave them there.

I am wondering if this is a lean surge that needs to be remedied with re-jetting? anyone know about this combo and if the stock jets are enough for this engine and setup? Do you know what jets I will need exactly for this setup to work correctly?

Thanks for any help.

 

New fuel pump? A bad pump diaphragm will cause a surge while cruising.

 

pump is newer. I used it for a few months on the old engine and everything was fine

 

Two things I would suggest.

1. Use a vacuum gauge to tune the idle mixture screws in the front.

2. Measure manifold vacuum at idle and replace the springs with a value approx 1/2 of what is measured.

Those two things can make amazing differences with edelbrock carbs

 

Thanks for the tips. I was able to set the screws to max the vacuum at about 13.5 " . I went back and forth to be sure both were set just lean enough to keep max vacuum.
Then I looked at the springs in the calibration kit and picked the 7" spring. I had a stock spring.
I discovered something in my test drive after that. It seemed really good for smooth idle and good power but still had that slight surge at part throttle cruise. But at one point I stopped and made an aggressive turn left while accelerating. not to completely do a donut but definitely on the edge of doing one. the car died. I then noticed the rpms were dropping a little extra low during regular turns on the ride home. I'm wondering if the floats need to be adjusted a little. I had the top off the carb the other day to try the 101 jets but didn't have a 7/16's bit to check the floats so I just figured I would check them later . what are the chances they are very far out of spec from the factory?
any other thoughts?
thanks

 

Usually they are not far off new but it is not unheard of. If you are stalling in hard turns i would check them

 

ok. thanks. should I aim for the 7/16" and 15/16 - 1" measurements or is common to stray from those stock measurements?

 

that is what i use, i also measure with the gasket

 

When you start getting into these surge issues a wideband is really going to help you out.

It might be as simple as a rod change but you need to know how lean it's really going.

 

When you have a 1406 a good place to start is jetting the same as a 1405

 

This chart shows the stock items in each carb. The 1406 is slightly leaner factory than the 1405

http://www.edelbrock.com/automotive_...ors_130815.pdf

 

Agreed

I had to make 1 rod change on my 1405 to get near perfect AFR's at cruse, WOT was pretty good out of the box. 355 with a large cam, good intake and headers.


The 1406 supposedly has the same lean issues as the 1411. According to the Edelbrock tech I spoke with when troubleshooting my 1411 there really isn't a fix for it. My issues were a lean stumble just off idle and even with the largest jets it would still go lean at WOT. Cruse was fine though.