Author Topic: 650 Demon vacuum secondaries issue (Read 761 times)

71fish · « **on:** June 07, 2009 - 10:01:08 PM »

I tried all springs and nothing. Could it be that their just not enuff vacuum w/ the large cam> It's 292� advertised and 510� lift hydraulic in my 340 9.5:1. Also, I changed to smaller jets and car runs super rich but just a slight hesitation underload.

Is that carb junk for my car?

71fish

422STROKER · « **Reply #1 on:** June 07, 2009 - 10:06:09 PM »

What are the main problems?

Rich? How is the tune? vacuum readings in gear at idle?

Tom

Changin Gears · « **Reply #2 on:** June 07, 2009 - 11:22:17 PM »

Low vacuum with a long duration cam only applies at or near idle, not when the secondaries should be opening. How do you know its rich? If it is, its probably a stuck or misadjusted float. Are you sure the secondaries aren't opening?

Chryco Psycho · « **Reply #3 on:** June 08, 2009 - 01:08:24 AM »

is the port to feed the vacuum pot blocked in some way or leaking allowing air into the vacuum pot
that is the first place I would be looking

matt63 · « **Reply #4 on:** June 08, 2009 - 10:51:21 AM »

I'm not sure I understand the problem totally. If you have low idle vacuum you may well need to change the power valve down to something less than the stock one (probably a 6.5). I've just been through this. If the secondaries are opening properly you won't be able to feel it so it will be hard to tell. With a heavier car I would be using a heavier vacuum pot spring such as the black one to start.

71fish · « **Reply #5 on:** June 09, 2009 - 04:39:17 PM »

I have to get a vacuum gauge.. but that's agood question. How do i tell if the secondaries are opening> I am soo used to a mechanical 2ndaries carb and I can feel the 4's opeing hard. Is a vacuum secondaries more of a smooth transition>?

Also, the car burns your eyes at an idle.. from an idle it shoots some blackish smoke.. but we had it up to 115 on the road the other day.. and no smoke. We have 68 jets in the front and 74's in the rear.

-71fish

matt63 · « **Reply #6 on:** June 09, 2009 - 05:37:43 PM »

I would read this as it answers some of your questions.
http://www.bob2000.com/carb.htm

I've had rich idle problems which boiled down to the wrong power valve. You will need to know the idle vacuum to select the right one or just try a 2.5 power valve to see. There can be a problem with the idle circuit in low vacuum applications (air bleeds) and the attached article talks about this. You can determine if you have this problem by seeing what happens as you turn in the idle mixture screws.

Author Topic: 650 Demon vacuum secondaries issue (Read 761 times)

71fish

650 Demon vacuum secondaries issue

422STROKER

Re: 650 Demon vacuum secondaries issue

Changin Gears

Re: 650 Demon vacuum secondaries issue

Chryco Psycho

Re: 650 Demon vacuum secondaries issue

matt63

Re: 650 Demon vacuum secondaries issue

71fish

Re: 650 Demon vacuum secondaries issue

matt63

Re: 650 Demon vacuum secondaries issue