Carb and Timing Tuning

[Taylorman]

I set the idle mixture screws on my carb with a vaccum gauge, adjusted mixture till i got the highest vaccum. Is setting initial timing to get max manifold vaccum an accurate way to set timing?

[jbone]

I thought someone with expertise would respond.
From what I learned with my recent build up is like you said on the idle mixture. Adjust to highest vacuum.
What I've learned about the timing is set it at your total advance.
I set my timing to 36 deg at 4000 rpm. With the MSD dist, I use the 25 degree bushing and the light silver springs. This gives full advance at at about 3800 rpm.
My initial timing ended being 11 deg at 800-900 rpm.
Good luck.
J

[502 JET]

I set the idle mixture screws on my carb with a vaccum gauge, adjusted mixture till i got the highest vaccum. Is setting initial timing to get max manifold vaccum an accurate way to set timing?
What was your total timing when you adjusted it this way?You should be more concerned with your total timing so you are not running too much at WOT.Unless your distributor is locked out with no mechanical advance.You need to rev it up to check your total timing.
I have never tried setting the carb with a vacuum gauge I just do it by ear and feel.I can tell when I hit the sweet spot.The vacuum gauge method is by the book but who ever reads them.

[GofastRacer]

Always set your timing with the total, the curve depends on the application!.. Setting the idle with vacuum is one way to do it, provided you have a cam that allows enough manifold vacuum at idle I always go by rpm, just turn the screws in and then back them off a 1/4 turn at a time until you reach the highest rpm, done deal!..

[Taylorman]

Ok, then let me re ask the question. Is there a sure fire way to nail down to total timing. My dist is locked out and i have it set at 32*. Idles great and seems to run good locked out. Just looking for options thats all. Im on a quest for the perfect tune up, ie, a/f, timing, plug heat range.

[502 JET]

If your distributor is locked out (no mechanical advance) then you have your total timing set at idle and it should not change when revved up.

[Taylorman]

If your distributor is locked out (no mechanical advance) then you have your total timing set at idle and it should not change when revved up.
I down with that. Im just inquiring about how to set it to the optimum or perfect spot. What measure or gauge do you guys use to know what the best timing is?

[FASTRAT]

I down with that. Im just inquiring about how to set it to the optimum or perfect spot. What measure or gauge do you guys use to know what the best timing is?
Taylor...
i think ur "bored" lol :) IMO the best timing is when it starts easy & runs the best!...i know it runs good rite now sooooo leave it alone & go out & have fun! lol :)
fastrat

[Carnivalride]

I down with that. Im just inquiring about how to set it to the optimum or perfect spot. What measure or gauge do you guys use to know what the best timing is?
If your really looking for optimum it will take some time and patience. I typically start a new engine combination around 34 degrees total timing and then run it. At the race track I go off mph and on the lake I use a GPS. I keep adding timing 1 degree at a time until the mph quits gaining or stays the same. You should also read your plugs and see where the color change is on your strap, it will probably be some where just below the bend before the base. It takes some time to really dial one in but once you do you'll be amazed how much better it runs.
IMO

[Taylorman]

If your really looking for optimum it will take some time and patience. I typically start a new engine combination around 34 degrees total timing and then run it. At the race track I go off mph and on the lake I use a GPS. I keep adding timing 1 degree at a time until the mph quits gaining or stays the same. You should also read your plugs and see where the color change is on your strap, it will probably be some where just below the bend before the base. It takes some time to really dial one in but once you do you'll be amazed how much better it runs.
IMO
Thats what im after. Im about to order a LM-1 a/f meter.

[robertm]

i think youre going to find that 32 degrees of total timing is not enough. but like he said just run it on the gps and keeping stepping up the timing. i have mine set at 38 degrees of total advance.

[Lavey Huffer]

I learned to set the idle screws with a tach.
tap the acc. pump very lightly with your finger
and re-adjust until there is'nt a drop in the idle
bog= too rich
rev=to lean
try to find a happy medium
idle circuit is very important it dictates how the carb will run until WOT

[HP350SC]

Thats what im after. Im about to order a LM-1 a/f meter.
A/F meter is the way to go for jetting. Plan to spend a few hours on the water, hopefully your bowls are easy to remove. Bring a good selection of jets covering a broad range. I cut a qt. oil bottle in half, then pull the lower rear bowl screw first, to drain it each time.
Regarding target A/F mixtures...
Mild cammed motor will idle near stoich 14.7, big cammed 13.0- 13.5.
Assuming you are not knock limited, for mean best torque aim for 12.5 AFR, midway between lean and rich best torque (12.2:1-12.8:1)
On boosted motors that are knock limited, 12.2 if not rich best torque of 11.76 will increase flame speed at very high rpm, with side benefit of surplus fuel to cool combustion.