Author Topic: Secondary opening too soon or late?  (Read 2658 times)

Offline 68rs/ss

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Secondary opening too soon or late?
« on: August 31, 2018, 06:45:36 PM »
After a rebuild with the help of Cliff and company, I have the ol' Q-jet working pretty good. Actually, it's the best carb I have even had on any of my hot-rods.
There is one last thing that I think I can get better. When ever I put my foot into it, the secondary's seem to open quickly giving a sudden surge. I would think there should be a smooth progression between the primaries and when the secondary's open. There is no bog, or at least I don't think its a bog.

So am I right that they are opening too slow?


I have roughly a one second delay in the choke vacuum pull off and have the secondary flap spring tension adjusted as per Cliff's book.
 

Offline Cliff Ruggles

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Re: Secondary opening too soon or late?
« Reply #1 on: September 01, 2018, 12:12:03 PM »
A one second delay is pretty quick for the pull-off, so you may need to add just a tad more spring tension to get them in smoother.  Usually with a well timed pull-off about 1/2 to 3/4 turns past where the spring just contacts the pin will get it........Cliff

Offline 68rs/ss

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Re: Secondary opening too soon or late?
« Reply #2 on: September 14, 2018, 04:50:17 PM »
Put a little more restriction in the choke pull off vacuum line to slow it down to almost 2 seconds. Much better.

Also would like to mention. Took the old Camaro on a road trip recently. Checked the gas mileage and was pleasantly surprised that it got 23 MPG on mostly highway driving. Very happy with that.

Cliff helped with engine combo and carb tuning.
10:1 350 with dart heads, GM 350hp cam, headers, Q-jet RPM with 3:73 gears and 5 spd overdrive.

Happy happy.

Offline Cliff Ruggles

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Re: Secondary opening too soon or late?
« Reply #3 on: September 15, 2018, 03:12:47 AM »
Good news there.  What kind of idle quality are you getting with the 350hp camshaft in that build?

How about the power curve?   It should have a broad/smooth/flat power curve till you feel like shifting it........Cliff

Offline 77cruiser

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Re: Secondary opening too soon or late?
« Reply #4 on: September 15, 2018, 06:09:56 AM »
Put a little more restriction in the choke pull off vacuum line to slow it down to almost 2 seconds. Much better.

Also would like to mention. Took the old Camaro on a road trip recently. Checked the gas mileage and was pleasantly surprised that it got 23 MPG on mostly highway driving. Very happy with that.

Cliff helped with engine combo and carb tuning.
10:1 350 with dart heads, GM 350hp cam, headers, Q-jet RPM with 3:73 gears and 5 spd overdrive.

Happy happy.
Sounds like a nice running combo.
Jim

Offline 68rs/ss

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Re: Secondary opening too soon or late?
« Reply #5 on: September 16, 2018, 10:09:28 AM »
Idle quality is good. Fairly smooth. Vacuum is up from the original extreme energy Comp cam of 11in/vac to 15in/vac at 750RPM with the Speed Pro CS-179R cam you had recommended. Easier to tune to highest vacuum and does not stink out the pipes.
 I did put it on a chassis dyno a couple of years ago. Just the way I drove it in, it put out a nice flat torque curve in the mid range. Peak torque was 324 and HP was 292 @ 5200 rpm. It showed a little lean on the upper end, but have since increased the fuel pressure to 6ish from the tested 4.5lbs.
I know the numbers are not staggering, but remember, that was at the wheels. I've been told you can add 20-25% to get a flywheel number, which would put it around 350-360HP and 380-390 ft/lbs of torque.

I have since added 1.6 rockers and changed the mufflers. The unknow make of mufflers that was on the car were 2.5" inlet/outlet. But looking down the inlet, the pipe was expanded from 1 7/8" to the 2.5". The replacements were  true 2.5" all the way through. It feels like it picked up some, but have yet to go back for another dyno run. Hopefully it gained with those changes. Some timing adjusts might help too.

This is a street car and works very nice.
Thanks

Offline Cliff Ruggles

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Re: Secondary opening too soon or late?
« Reply #6 on: September 17, 2018, 01:34:37 AM »
I've never been the least bit impressed with any of the Comp XE camshafts.  They show some "bling" at idle, stinky exhaust but come up short beyond that.

The chassis dyno numbers look good, and the addition of 1.6 rockers will make even more power......Cliff