New jets needed?

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ClarkDart70

ClarkDart70

Street Machines Limited
Joined
Mar 17, 2011
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Location
Plainfield, IN
Just finished installing my new Summit 600 CFM carb with electric choke and Weiand Action Plus 4 BBL intake.
All is fine at idle and mid to high RPM but I am getting a hesitation at take off.
So far I've adjusted the air/fuel mix and have maxed my vacuum at idle and have adjusted my curb idle and timing to about 800 RPMs.
Is the next step looking to rejet the primaries to get rid of the hesitation?

Also, on a side note, my car shifts out of 1st between 15-18 MPH... is there an adjustment to make it shift alittle later?

Thanks,
Clark

PS on the Summit carb.... I really like. Easy to adjust and seems to like a quality product!
 
Oh if it makes a difference.... I'm running the stock LA 318 heads with a stock cam. timing is about 5* advanced... vacuum reads 20 on the dial.
 
Try this first..........Accel pump adjustment.........

[ame="http://www.youtube.com/watch?v=w3F3ssOb8lg"]Accelerator Pump - YouTube[/ame]
 
As far as the trans. you have to make sure your kickdown rod is all the way back at wide open throttle. Should be very little movement. Just enough to not bind the linkage at WOT. Also not sure how parallel your linkage is. Should run parallel frt. to back with the valve covers. Summit and Holley carbs are more narrow then Eddy/Carter types and sometimes require this adapter..........

http://www.summitracing.com/parts/HLY-20-7/


Here's a short vid showing too much rearward play in the kickdown rod.....
[ame="http://www.youtube.com/watch?v=U0tsQ06EyOs"]440/727 kickdown linkage - YouTube[/ame]
 
I have it pushed back as far as it will go at WOT with very little movement. My linkage runs apparell with the valve cover after a bend was needed in the arm. I can't get it to down shift under hard acceleration either. I might have to play with it to get it right.
As far as the accellerator pump video... it suggests I have a nozzle size 35-40 for a lighter car.... think a 37 is a happy medium?
 
ClarkDart70 said:
I have it pushed back as far as it will go at WOT with very little movement. My linkage runs apparell with the valve cover after a bend was needed in the arm. I can't get it to down shift under hard acceleration either. I might have to play with it to get it right.
As far as the accellerator pump video... it suggests I have a nozzle size 35-40 for a lighter car.... think a 37 is a happy medium?
Click to expand...

I put up the vid for adjustment purposes only.

I just looked up the specs for that carb......Nozzle #35, Prim. jet #67 and the source of your hesitation......6.5" power valve. Nozzle size is more then enough with a dual plane manifold. Increasing the nozzle size would just be a crutch for the PV. You may need to jet up a size or two at some point, but that's not the issue right now.

With 20" of idle vacuum you'd have that around at cruise rpm also. So what's happening is you need way too much throttle opening (vacuum drop) for your part throttle enrichment. I'm gonna suggest you switch it out for a 10.5" valve.

Also, don't be shy about upping your initial timing. I'd think that engine would be alot happier at 12-14*

As far as the trans, i cant go much further then the linkage adjustment. Hopefully one of the trans guys will chime in on that.
 
Your welcome. Those carbs tune just like Holley's and one other small thing i like to do is when you have your mixture screws tuned for maximum vacuum, as you've done, i like to open them both about a 1/16th of a turn just to keep off that lean edge of adjustment. Good luck & let us know how it goes. All new ones need some dialing in, but i'm sure you're gonna love it.
 
maybe you guys already covered this buy i had the same issue with my holley 650 and just swapped secondary springs and it took care of it. im assuming this is a vac sec carb
 
It is a vac sec carb. Just out of curiosity )and a lack of being able to link it together in my brain) how did changing the spring affect the hestitation at take off with the primaries?
 
took nearly 1/16" of play out of the accelerator pump arm adjustment... hopefully it corrects the issue but I didn't have time to drive it today to check (stupid job got in the way!).
It now has a snug .015" gap as per the video. Thanks again!
 
Ok, I richened the air/fuel adjustments, backed off the curb idle, and bumped the timing to 10* advanced. Its a lot better off of the line. Rick, I already ordered a 9.5 and a 10.5 power valve from Summit.... at this point would I have anything to gain by swapping one in for the 6.5 or should I just return them and leave the 6.5 ride?
 
Since you adjusted your pump you should be able to just move your throttle linkage by hand and see the squirter work, it should be immediate when you move it, if it is it will work fine.
 
Glad you made some improvement Clark. As long as it feels comfortable now off idle and at moderate cruise acceleration, i think you could wait on the PV swap. As inexpensive as the power valves are, i think i would keep one of them just incase down the road it could benefit you. Not sure if you have headers or manifolds now, but if you upgrade the exhaust it will lean it some and at that point it may be necessary to do the switch. Get some driving under your belt with the current configuation to confirm your good to go. And no, i hate spending money, especially other people's. So if it turns out you don't need the PV then i'm truly sorry.
 
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