Best Way to set the idle mix on a 4160

patrickt · #1 (**permalink**) 10-04-2018, 08:02 AM

Here are two pics that seem to vanish from time to time.

steve meltzer · #2 (**permalink**) 10-04-2018, 05:50 PM

Patrick, an off idle question. 4160 on my '67 'Vette. Car starts great, runs great, idles great, but even a modestly brisk touch of the accelerator pedal and the car dies. So off idle response is zip. Correct squirter is a 26, I think. Moving to a 31 didn't help. can't recall the color of the cam, nor what is called for (it's a list 3180...and Holley tech couldn't tell me what cam was correct). I think the issue is the cam, but could this be a float issue or timing?
I need to confirm that the advance weights are moving, but the "pump shot" is good (even tried a new a/p diaphragm). Any thoughts? thanx. steve
(oh, yeah, my Cobra is still for sale).

patrickt · #3 (**permalink**) 10-04-2018, 06:14 PM

It's not a float issue. Pull the distributor cap off and inspect the springs and weights, then put a timing light on your marks and watch the movement of the marks as you rev the engine up to 3000 or so. The curve, of course, is based on the spring choice but you should be able to see the marks move smoothly up to a total of 34 to 36. I don't think it's a timing issue though. How do you know your pump shot is working well? Have you put some towels under the squirter, so you're not just dumping fuel down the carb, and then, by hand with the engine off, give several pumps on the throttle linkage and see the gas squirt out with your own two eyes. Do that several times and see if you can get a "dry pump." All pumps should be nice and "streamy" until your float bowl is empty, which is a whole lot of gas. Now, remember, you're working on a cold engine. An imaginative solution would be an accelerator pump diaphragm that only fails to hold pressure when it gets hot. A little GoPro zip-tied to show what your squirts look like while actually driving would disclose that goofy scenario. My money is on a failure to squirt properly.

patrickt · #4 (**permalink**) 10-04-2018, 07:44 PM

Before I even thought about disassembling the carb, I would switch the one on the Cobra over to the Vette and take her for a quick ride. If the problem vanished, then I'd be pretty sure it was a carb problem.

Gaz64 · #5 (**permalink**) 10-05-2018, 03:45 AM

Quote:

Originally Posted by steve meltzer

Patrick, an off idle question. 4160 on my '67 'Vette. Car starts great, runs great, idles great, but even a modestly brisk touch of the accelerator pedal and the car dies. So off idle response is zip. Correct squirter is a 26, I think. Moving to a 31 didn't help. can't recall the color of the cam, nor what is called for (it's a list 3180...and Holley tech couldn't tell me what cam was correct). I think the issue is the cam, but could this be a float issue or timing?
I need to confirm that the advance weights are moving, but the "pump shot" is good (even tried a new a/p diaphragm). Any thoughts? thanx. steve
(oh, yeah, my Cobra is still for sale).

Steve,

Perhaps your list number is a 3810 not 3180, since 3180 does not exist?

A list 3810 is a 585 cfm 4160, runs a 65 main, 25 pump, a purple sec spring, similar to the average list 1850 600 cfm with a 66 main, 25 pump, and plain sec spring.

Alas I can't tell you the cam yours should have, but most 600s come with a white cam.

Although this pic shows a red cam:

http://www.chicagocorvette.net/item....m=7232&rc=1437

And this one is also red:

https://www.ebay.com.au/itm/67-Corve...oAAMXQMTlRcPsX

So looks like Red could be correct, but run the smallest pump cam that gives throttle response with no flatspot. White is 17cc or 19.5cc, Red is 18.5cc or 20cc.

You could have some seizing advance weights.

Verify the float levels are correct, then a timing light on the balancer to check the advance is happening from say 1100 rpm up.

Gary

davids2toys · #6 (**permalink**) 10-05-2018, 05:04 AM

Quote:

Originally Posted by patrickt

Here are two pics that seem to vanish from time to time.

Very nice, thank you.
Sorry for the double post

steve meltzer · #7 (**permalink**) 10-05-2018, 03:18 PM

thanx guys for all of the advice. will try to get to it tomorrow. thanx again. steve

steve meltzer · #8 (**permalink**) 10-05-2018, 03:19 PM

oh yeah...Gary, pardon my (recurrent) dyslexia, yes, 3810, not 3180

patrickt · #9 (**permalink**) 10-05-2018, 03:21 PM

Quote:

Originally Posted by steve meltzer

thanx guys for all of the advice. will try to get to it tomorrow. thanx again. steve

No, you should do it today. We're not sure you're working hard enough; yep, we think you're just goofing off.

steve meltzer · #10 (**permalink**) 10-05-2018, 03:29 PM

ah jeez Patrick, i was hopin' to get lucky today. s

steve meltzer · #11 (**permalink**) 10-06-2018, 03:24 PM

OK, did manage to get out there a bit today...

watching the pump shot while my helper stomped the pedal, shows a great squirt X 5 or so. no failures, no dry pumps. plenty of fuel. Orange cam with screw in #2 slot. Base timing was 2° and should have been 10° BTDC. So, I actually set it at 12, but may go back to 10. Not suer why the timing was so retarded. let me drive her and see how we do, and i'll post the list. thanx again. s

patrickt · #12 (**permalink**) 10-06-2018, 04:13 PM

Quote:

Originally Posted by steve meltzer

Base timing was 2° and should have been 10° BTDC.

Hmmm, must have been elves. They sneak in to garages at night and monkey with the carb settings, goof around with timing settings, loosen bolts, and perform other automotive mischief. I've actually sat up at night to try and catch them, but they're very clever and somehow know if you're waiting for them. One day I'll catch them though and then they'll pay....