tuning my new Holley Ultra

[Patronus]

I have to tune a new carb for my 383 AT. A new Ultra 750cfm manual/manual. The 383 is stock as far as I can tell with a performer intake, TTI headers and I noticed a B&M valve body in the trans. Its running real rich out of the box. Im thinking going down 2-3 jet sizes. (holley states one for every 2000 elev.) Im in Boulder, CO at 5300 ft. But I have a few questions. First off, should my vacuum advance be running full manifold vacuum or to the port on the metering block? (hope that wasn't too stupid) Then I want to know, should I jet it and then check vacuum and then choose a power valve? Any tricks to draining the bowls?

[Patronus]

After much searching, there still seems to be some debate. Are you guys running port or manifold vacuum for timing advance? (stock to mild cam)

[tan top]

for our type of cars  mainfold vacuum  , ie  the port is below the throttle blades    is the one you want to connect the vacuume advance to

timed vacuum , i think is for emisioned controled  stuff  , i believe  & of no use to our type of ignition set ups !!
  , 

[Patronus]

Thanks TT, I knew you'd help out. I think its referred to as "ported" vacuum.

[Patronus]

So I took out the main jets, kind of odd, I was expecting the same size but its 72 in the front and 80 in the back. Is this common? I will go down 2 from each and try. Plus, the fronts were really tarnished..!? I have a new carb, new tank, and new gas...??

[greenpigs]

From what I have been told you want the timing set first before messing with the carb, what are you running initial & total timing?

After you set that are you running a double pumper?

If so I don't think that is the best for a mostly stock 383 but I guess it can be made to work with enough tuning.

[Patronus]

I've set the initial timing at 10-11 BTDC. How do you come up with the total timing? I was under the assumption that 750 cfm was pretty good for the 383. Its close now, certainly the jetting helped a lot. Then last night the first night drive left me with a dead battery so I have a few more gremlins to work out....   

[440]

Hmmm, maybe it's a mopar thing but I thought vac advance was supposed to be metered... If it was straight manifold vacuum you'd have full advance with the throttle plates closed. And initial timing is always set with vac advance disconnected and plugged.... Maybe I'm wrong but 

[Patronus]

Most of my searching says ported vacuum is for Fords...? I see your point though. Im still wondering how to check total timing. How do you measure 30 some degrees on a scale or pointer that goes to 10? Also, am I supposed to be checking timing at 2000-2500 rpm?

[oldschool]

Hmmm, maybe it's a mopar thing but I thought vac advance was supposed to be metered... If it was straight manifold vacuum you'd have full advance with the throttle plates closed. And initial timing is always set with vac advance disconnected and plugged.... Maybe I'm wrong but 

you are correct sir. you want the metered port.

[Patronus]

From Holley installation instructions #6B: "The timed spark fitting in the choke side of the primary metering block provides vacuum for the operation of the distributor vacuum advance."
Learning is such a bitch.

[tan top]

 oh crikey  , looks like i  might  have got them  mixed up then & round the wrong way    , sorry guys if this caused any confusion    , going to wait for my bus
  knew i should of just copied the oem avs port , but  went by the eldelbrock , instructions
  desconected the vacumme advance ,  because was thinking need one with less advance , & had not bothered looking it to it yet   , just set it up with mechanical advance only  . as too much advance at part throttle

ok got to go !!   my bus is here   .......
hmmmm

http://www.youtube.com/watch?v=Gj2utt1oSQE&feature=related

[greenpigs]

I've set the initial timing at 10-11 BTDC. How do you come up with the total timing? I was under the assumption that 750 cfm was pretty good for the 383. Its close now, certainly the jetting helped a lot. Then last night the first night drive left me with a dead battery so I have a few more gremlins to work out....  

You are setting it 10-11 past TDC right?

 The way I do it is hook up a vacuum gage & get the motor to operating temp then advance the distributor till you get the most vacuum. On my 72 low compression 440 I run 21* timing, that is advanced or after TDC. The factory timing specs suck don't use them. If the motor starts easy & doesn't ping you found the sweet spot, there is no need to advance the timing past the point of increased vacuum. Or once you don't see much gain in vacuum stop & you want 32 deg or so at 2500 RPM, with the vacuum advance not hooked up.
 Plus you want the ported vacuum for your advance on the distributor.
 Still learning myself but that should help.

[Patronus]

No, its set at about 11 before.

[greenpigs]

Most of my searching says ported vacuum is for Fords...? I see your point though. Im still wondering how to check total timing. How do you measure 30 some degrees on a scale or pointer that goes to 10? Also, am I supposed to be checking timing at 2000-2500 rpm?

  I have a degreed balancer with the marks on it but some use tape too show the 30+ degrees timing. Some timing guns may be able to do it also but I don't know for sure about that.
   You do the initial timing check at idle, 850 RPM then check the total timing @2500

   Your idle will go up as the vacuum increases & then you will need to adjust the idle back down, this is normal.

[greenpigs]

No, its set at about 11 before.

Try setting the timing like I described, I bet that 383 likes it.

I like to use the cap from a rattle paint can and put it under the lowest bolt then back the bolt out and it will catch most of it, you should do this when its not hot of course.

[oldschool]

quote: Try setting the timing like I described, I bet that 383 likes it.


i bet it does'nt..

[frederick]

 

"On my 72 low compression 440 I run 21* timing, that is advanced or after TDC"
Greenpigs, You're mixing things up, advancing the timing is increasing timing before TDC, not after.

You don't want the timing to be after TDC at all, always before TDC.

[Patronus]

Well, Im on to an alt. issue right now. I did change to metered vacuum though.

[greenpigs]

"On my 72 low compression 440 I run 21* timing, that is advanced or after TDC"
Greenpigs, You're mixing things up, advancing the timing is increasing timing before TDC, not after.

You don't want the timing to be after TDC at all, always before TDC.

  Not what I have heard & when I went from the stock setting to what I described the motor responded VERY well. I think your mixing things up or getting confused as to what I am trying to say.
  If you think running all your timing before TDC is the right way go for it.

 

[Patronus]

Timing aside, I have another couple questions. Checking vacuum, should I really be adding 1 unit for every 1000ft. above sea level? I would think thats right as Im only getting 12 so +5 = 17, which is more what I expect. And then divide by 2 for an 8.0 power valve? (I haven't tried getting more than 17 yet...)

[greenpigs]

That is new too me adjusting for altitude by adding a set amount of vacuum to the base.

 Not sure but if you are getting 12 I would go with the motors actual output instead of compensating, & going the easier route 12/2 & get a 6 power valve.

[Patronus]

There's a 6.5 in it. The only real issue I have is a stumble on full throttle. Squirters were 31f 28r and I switched em. Its still think its rich, plugs are medium brown.

[greenpigs]

Dunno.....some help right? 

Tuning a Holley is still a learing process for me but I have 0 experience with a double pumper.