You need to get the carburetor sorted out. No way does the engine require 42degs at idle. no way no how.
Manifold Vacuum Advance what am I not getting?
- Thread starter 340inabbody
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no way pingity pingity ping.
It's a carburetor issue. 99%
I can agree with both of you. The converter is a drivability issue for sure. The carburetor I am sure could use more tuning. This is my first time working with a Holley. I only have worked with a few Rochesters in years past. So I am trying to figure out this as well. Lots to learn all at once…. Wish you guys could come over and just freaken show me. So I will keep trying to learn here and in books etc.
What I’ve done on the carb is float height then idle A/F based on peak vacuum with 1/4 back off from peak. Then took the slack out of the accelerator pump.
You need to step back , take a deep breath and cover the basics again . Check the TDC mark on balancer , set dizzy manual to 17-20* , pull carb and check transfer slot opening ( .025ish …. ). . Probably needs work on idle air bleeds .
No
Sounds right … Turk is giving me good guidance to visit the balancer checking the advance of the motor.
Ive been reading about making sure the transfer slot is like 1/16 no more at idle. The way I understand this is that if there is too much transfer slot opening it will not allow enough flow to the pilot idle path down the emulsion tube/path. Is that what you’re thinking?
I was going to look at the carb after I got it to a point I can run it. Looks now maybe the initial advance is too high at 42°. I e just had it hammered in my head to give the motor what it wants and was using vacuum as part of the process. When is too much I don’t know. Some have said my motor could want as much as 50°???..??
Newbomb Turk
Well-Known Member
Ok, that’s another rule of thumb as far as T slot exposure.
I start with a square slot and then open the throttle to get it to idle.
Once I finalize everything I verify the T slots are not open so far that the mixture screws don’t work.
There is no tuning magic in T slot exposure. They can’t be open so far the mixture screws don’t work but they don’t need to be damn near shut to work properly either.
Edit: if you end up with the throttle blades too far open and mixture screws don’t work, we do t just grab the vacuum hose and hook it to manifold vacuum.
I drill holes in the throttle blades so they shut further and correct T slot exposure.
Resorting to MVA to get one to idle is my last resort.
Because in the end, most time guys end up right where you are. It’s not a fun place for sure.
I just solved an idle issue with my son's truck. One of the primary throttle blades was bent exposing too much t-slot on that barrel. He drives it to work all year, and I suspect he may have had a lean backfire last winter. I initially set the carb up 4 years ago, so I did not expect it to be a t- slot problem.
After you set the Tslot to square count the number of turns it takes to get it to idle (if necessary) and write it down .
But double check your balancer for correct TDC first . Can’t imagine your engine will crank over @ 40+ degrees intial. But you might have a dizzy out of a C-body or such with a 28*ish vacuum advance in it .
You know you can adjust when your vacuum advance starts by using an allen wrench ? You could max it out to see where your static timing really is .
But double check your balancer for correct TDC first . Can’t imagine your engine will crank over @ 40+ degrees intial. But you might have a dizzy out of a C-body or such with a 28*ish vacuum advance in it .
You know you can adjust when your vacuum advance starts by using an allen wrench ? You could max it out to see where your static timing really is .
Certainly, lots of rabbit holes to go down. Maybe what might help me way to figure out what the priority should be based on everything here. I think that would help me a lot. I don’t want to be going from one thing to another aimlessly. I’m already bouncing off the walls trying to get my brakes fixed as well. I’ll be certainly open to any suggestions on how to prioritize this work. Sounds like it might be checking the crank damper timing and then looking at the valves lifters and rockers to try determine the crank is at 0°. Set timing to 24° initial 33° total and then look at the fuel delivery system.
Anyway, that’s what I think I’m hearing
Anyway, that’s what I think I’m hearing
Check tdc first. Do you know how to do this?
340,
You have let yourself be brainwashed by Turk & his nonsense. For the other MVA non-believers, we should say a prayer for them & hope they have a quick recovery......
These people do not understand the combustion process & WHY more timing is needed.
Thousands, if not millions of GM cars, came with MVA. Below is a page out of the 1967 Pontiac manual stating the use of MVA. These cars had 6* initial & 20* MVA added so that they idled with 26*. Small cam, 197 @ 050, 10.75:1 CR.
Your 42* sounds right & do not let some dumb a**e talk you out of it. My own car has 48* at idle, has had it for the last 15 yrs. Another car I tune for drag racing 3950 lb without driver, 3.31 diff, street driven & does 1000 mile return trips, has run 11.65 @ 119 mph. No tuning at the track & the driver was new to drag racing. It idles with 48* via MVA @ 900 rpm in gear.
I did a final tune recently on a 440 I built. TF 240 heads, 10.X:1 CR, Mopar M1 4500 intake, TQ carb. It idles with 42*. I think stunned would be the right word....The owner was stunned at the improvement in idle quality, vacuum etc between 12* at idle & 42*...
You have let yourself be brainwashed by Turk & his nonsense. For the other MVA non-believers, we should say a prayer for them & hope they have a quick recovery......
These people do not understand the combustion process & WHY more timing is needed.
Thousands, if not millions of GM cars, came with MVA. Below is a page out of the 1967 Pontiac manual stating the use of MVA. These cars had 6* initial & 20* MVA added so that they idled with 26*. Small cam, 197 @ 050, 10.75:1 CR.
Your 42* sounds right & do not let some dumb a**e talk you out of it. My own car has 48* at idle, has had it for the last 15 yrs. Another car I tune for drag racing 3950 lb without driver, 3.31 diff, street driven & does 1000 mile return trips, has run 11.65 @ 119 mph. No tuning at the track & the driver was new to drag racing. It idles with 48* via MVA @ 900 rpm in gear.
I did a final tune recently on a 440 I built. TF 240 heads, 10.X:1 CR, Mopar M1 4500 intake, TQ carb. It idles with 42*. I think stunned would be the right word....The owner was stunned at the improvement in idle quality, vacuum etc between 12* at idle & 42*...
What would the mechanical curve on this set up look like?
MobileCustoms
You can twist perceptions, reality won't budge
You say you're having some brake issues... what kind of issues? if you have power brakes, are you sure there's not a vacuum leak to the brake booster? Because that could sure make a HUGE difference here. I also agree that you need a looser converter, which will also make another big difference for your setup and the way it idles in gear.
Lets do a little experiment. I have a digital ignition so it’s easy to modify my curve . I will post the stats on my engine and you recommend a curve . If it runs better without pinging we will know you are correct . Don’t get me wrong … I believe you know your stuff . But it will be a fun and informative experiment. Worst that could happen is my car runs better .
360 based 408
W2 race heads / closed chamber
9.75 compression ...045 quench
246/250 @ .050 .648 lift on 108
Victor W2 intake
TTI 1 7/8 headers theu 3” full exhaust
Pro Systems 850 carb
Daytona Sensors CD1 ignition
Mopar dist with 8.5 VA can on manifold vacuum .
21 intial at 1000 rpm
32 total by 3000 rpm
4sp and 3.91s. 27” M/T drag radials in 69 Swinger.
Did I forget anything ?
Newbomb Turk
Well-Known Member
Yes but dyno testing doesnt cover off idle and low speed cruising .
IABs?
Newbomb Turk
Well-Known Member
Newbomb Turk
Well-Known Member
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