Holley carb adjustments
 

I'm trying to dial in my 4160 600 cfm 4 barrel carb on my 350 in my 67 c10. It's a list number of 1850-01.

When I bought it used it had 65 main jets with a 25 squirter and 6.5 power valve. It was very sluggish at a steady cruise going 25mph. It also was very hard to keep running on the road from a dead stop. I called Holley and they told me to up the jets two sizes. So I bought 67's. It made a pretty good improvement. It still was tough to keep running from dead stop. I bought a 31 squirter which seemed to help a bit, but same issue. I then bought a 35 squirter and 69 main jets. Still having same issues. Finally installed 71 main jets and kept my 35 squirter.

I've hooked up a vacuum gauge and I got my vacuum up to about 12.5. I set my curb idle screw and idle mixture screws. My spark plugs are telling me the engine is still running lean. I have 71 main jets and a 35 squirter. I have my accelerator pump shaft set correctly.

It still is tough to keep running when I slow way down and when I start from a dead stop or am cornerning. After I am cruising and floor it it runs pretty good. I know I need to up my jets another size or two, but am unsure on my immediate acceleration problem. Do I up the squirter another size? Or turn up my curb idle screw? I like it low so it doesn't drink my gas. 35 seems big enough since this came factory with a 31.

Holley tech told me I shouldn't need to upsize my accelerator pump cc's until you start needing a bigger squirter than a 41??

I have not messed with my carb cams I'm assuming they are stock...

Re: Holley carb adjustments
 

What other mods?
What intake?
What cam?
What tranny?
What gears?
What’s your timing like?

Re: Holley carb adjustments
 

Intake is an edelbrock performer
Cam is stock
Th400
3.73
Not 100% sure on timing. Just had this engine rebuilt and brought the pickup to a shop to get the whole pickup looked at and timing set. I don't have a timing light to give exact numbers.

Re: Holley carb adjustments
 

Likely there’s your problem.
Lack of timing.
You should have 18 hg of vacuum at idle.
All the mods to your carb
aren’t helping.
You need to figure out where your initial is and fine tune it.
What’s your idle rpm in park and in gear?

Re: Holley carb adjustments
 

18"?? Where did I come up with 14.7"? :/ I don't have a tach. I should probably get an auxiliary one and wire it in to see where I'm at. where is a good number to be in park on a carbureted engine? I know it drops in gear. Maybe that is some of my issue is it's too low in park then in gear it wants to die.

I might call the shop I brought it to and see if I can bring the pickup back over there tomorrow night and throw a timing light at it.

Re: Holley carb adjustments
 

Timed right with your stock cammed motor it should idle at 700 rpm in park and 600 in gear.
You likely need about 14 to 16 initial.
Let us know what it’s set at?

Re: Holley carb adjustments
 

Wow that is lower than I thought as far as rpm's! I will report back when I know more! Not sure when I'll be able to get in there hopefully tomorrow evening.

Thanks

Re: Holley carb adjustments
 

Roadkill Garage had a nice episode a couple of months on tuning the Holley.

Re: Holley carb adjustments
 

May I suggest saving the money you would spend for the shop to do the timing and invest in a dial back timing light? You will likely be money ahead.

Re: Holley carb adjustments
 

The shop said they will tune/time it for free. I tried tuning the holley by myself to learn how to. I took it the pickup in and found one of the idle mixture screws wasnt working. I thought I checked both of them, but when he turned the passenger side screw down the engine didn't die. I brought it back home and pulled the carb and brought it back to him to look at. He took it apart and thinks the metering block is too far gone. He thought he had a spare at home to swap it out with so I should be getting it back Monday. Then I'll bring the pickup back and work on the timing more with him. I'll let you know what I found out.

Re: Holley carb adjustments
 

If a mix screw acts like that it means you have your primary throttle too far open exposing the transfer slot. You need to adjust it back closed. Either more initial timing or crack the secondary open a touch more.
Info here on the transfer slot.
About 1/2 way down the page.
http://www.crankshaftcoalition.com/w...EI_distributor

Re: Holley carb adjustments
 

Make sure you double check that timing with vac advance disconnected and plugged at the intake. below throttle plate is suggested for vac on your advance.

Re: Holley carb adjustments
 

Look for Roadkill Garage, Episode 29. "Carb Tuning and the Tater Truck!"

Re: Holley carb adjustments
 

Thanks for all the replies. I got it back now and it's running so much better. It's timed correctly and it's pulling the right amount ignored vacuum. It's got 74 size jets in it now. I took it out for a 60 mile road trip and it kinda feels like it's starving for a bit of fuel. Or it could have been the heavy winds pushing the truck. I'll have to pull a plug and see how they look. I appreciate all the input that was given. The truck is finally driveable. I'll have to tinker on it some more next spring since it's starting to get cold here.

Re: Holley carb adjustments
 

Timed correctly, eh!
What’s your initial timing?

Re: Holley carb adjustments
 

Someone is over looking something. The carb should have been just about perfect in stock form. Did you buy it new or second hand? I'll repeat what the others said, your timing must be correct first. Also make sure it proper fuel pressure and volume.

Re: Holley carb adjustments
 

Have you checked float levels front & rear?