I am trying to tune a 650 speed demon vacuum secondary with the help of books and the techs at Barry Grant. Anyways I am having a heck of a time with an overly rich idle. I am doing the tuning process as per their direction and it is getting a bit better. Last night I went to start it after making some adjustments and it fired right up running nice and clean with a much higher idle. I thought I had it licked. Then I noticed I forgot to put the pcv hose onto the vacuum nipple on the carb. As soon as I put it on it idled way down and ran rich rich rich. My thinking is that the engine was able to draw more air in thru the open line and thusly lean out the mixture. Am I right?
Anyways I am about to call BG again to find out where to go from here
Thanks for help

graemlins/thumbsup.gif Sounds right, back to square 1 again.Do the same tuning steps you did before- but with all the vaccuum lines connected...

Thanks Joel graemlins/thumbsup.gif

Too bad the Speed Demons don't have screw in air bleeds. I had a similar situation with my HP950. Replacing the idle air bleeds helped greatly with the rich idle condition. Check float levels and also how much of the transfer slot you have uncovered on the primary side.

I find I am getting contradictory advice from BG and from the tune a demon book that they sell.The book states both slots should be .020 if the engine is to idle at 1000rpm or more and if idles at less then that the front slot at .020 and the back just covered. The Demon tech says start at both slots .020 regardless. Well I now have both at .020 and the mix screws are at about 1/3 turn from seated to get my best idle yet, still rich.It is idling about 1250rpm. He recommended today to just close each slot 1 full turn. I will try this weekend, I know that will drop my idle but will it lean it out enough? Time will tell. The book also says that no way should your mix screws be less than 1 full turn from seat, if they are you may have to change idle feed restrictors (wherever they are) The demon tech says don't think about touching them. All in all its been a learning experience just hope I can get this thing set properly

I have been reading your post and I would like to know what your vacuum is at idle.If you still have trouble with it idling try useing a power valve block off,or a lower rated power valve so you can make sure it is not blown or opening from to low of vacuum which would effect the idle circuit.Just a ideal! graemlins/waving.gif

Vacuum at idle is 15-16 . How can you tell if the power valve is toast? The demon specs say the power valve in there would be 6.5. I have bought a rebuild kit with extra power valves I could try I suppose.

Ya know- I might be wrong, but I would BET that a Demon has the "antibackfire power valve diaphragm nonrupturing circuit channel" tongue.gif deal... In other words, a backfire wont toast the diaphragm. I assume its basically a Holley diaphragm..SO, suck on the end with out the spring, and if it draws in, its ok. They have a checker for this, but I think its $40! IF in doubt, just replace it- an extra cant hurt.

Heres a Demon guide I found after doing a search for another post- might be helpful-

http://www.4secondsflat.com/demon101.html

I have also read that article. It goes another route with drilling out the air bleeds??? Don't have it in front of me so I probably screwed up the name. I am going to start from scratch again and go thru this to ensure I have not done something wrong and see where I end up. Thanks for your input

Jerry

You can drill out the pressed in idle air bleeds and tap the holes for screw-in bleeds. This would aid in idle tuning as it seems you need a larger idle air bleed with you relatively high idle vacuum. Most of these performance carbs are calibrated for far lower vacuum. Less vacuum, less pull on the idle circuit. When you start you engine cold is the idle OK? Is it pretty stable when cold then goes rich as it warms up? This would indicate more bleed air is needed for a street application.

Actually RPM, I can't really say. I asked Demon for a carb recommend with my combo and they told me 650 speed demon vacuum secondary. So I went with it. I have been using an edelbrock 600 and I have it working very well even with this new cam, but in my quest for more power or maybe its just my newfound love of tinkering with this car I had to try out a new carb, and I am determined to make it work. Cold start up is still rich and I have to keep it running with extra throttle, I have the choke basically eliminated at this point so I don't have to deal with that too. I thought it would be best to get 1 thing working right then tackle the next
I tried tonight as the demon tech suggested, both slots .020 exposed, start at 1 full turn out on mix screws. Get idle at best possible. Ok, I did this and ended up again at 3/8 of a turn out from seated on mix screws. Still a might rich, kinda burn your eyes. He then said to close both butterflys(transfer slots) 1 full and that should bring idle to acceptable. I tried that but engine died. I tried inbetween, still no good too rich.
Man have I been rambling. Anyways, my uneducated opinion is I either need more air or way less fuel to make this thing idle decently.How I get there is just another adventure.

By the way, I am still having fun, unbelievable

In the article Buzzbomb posted they were talking about the 4 small holes at the top of the carb I believe, drilling these out? Forgive my use of improper terms here. The Demon book talks about the idle restrictors, sounds like an idea buttt, where the heck are they lolThanks for the input

Are you ajusting your idle mixture for maximum vacuum?
If you arent, you probably should be.

And, adjust them evenly.

BTW, your car is very cool looking!

Give us some specs on the combo, it may aide us in assisting you.

You may want to forget about talking to a demon rep, and go by the book you have.

Wow Brian, you are fast. I am sitting here at this darn puter with a rum typing in my woes and bamm, there you are.
Ok maybe you are right, I will post what I am starting with
355ci, 9.75-1,HEI Dist, vortec heads, UD 276H10 Hyd. cam 221/221 @ .050, 454/454 lift, performer rpm int, speed demon 650 vacuum sec, elec choke, hooker super comp, full 2 1/2" flowmaster exh, th350,3.73 posi. Anything else you need to know just holler.
Plus I added a fuel pressure regulater this week because demon tech said I should be at about 5 1/2 - 6 psi fuel pressure. With my stock gm mech pump I was at 8. Now with reg I have it set at 5.75 psi

Must be the rum, forgot to answer 1/2 your questions.
Yes I am using a vacuum guage for this tuning. I also have a tach on my timing light that I watch. I have turned all mix screws the same

blumont,

we are in the same town - shoot me an email and I'll meet you for a coffee and (try to) give you a hand.

Whichever way we need to go with it - if you can't get there with the idle mixture, we can either add fuel or air at idle - I have fingerdrills.

Cheers,

Ryan

On a holley you can have 6.5 to 7 psi, thats where i would start with it.

Set the idle mixture with a vacuum guage, hook up the guage and evenly pull out the idle screws until you reach maximum vacuum.

You're Power Valve should be 1/2 the vacuum reading you get after adjusting your idle mixture.

If your PV is opening at idle (becuase its too high, or becuase its shot) then it'll be pouring fuel into the motor, and it'll be running real rich for no apparant reason.

The adjust your float level so that it's at the bottom of the sight glasses.

I'm not much of a carb tuner (yet), but i've picked up a few tips, and hopefully they will help you out.

i personally dont care to talk to either demon rep that ive talked to. Neither gave me any info that isnt in the book and both seemed agetated by answering me when i questioned there answers like ...
Them: "no sir you cant run that mighty demon carb cause you have more then 260 @ .050"
ME: "Well why not??"
Them: sir we do not recommend.....
Me: Yeah,yeah, yeah, i know what you do and dont recommend but why? what are the internal differences between the 2???
Well come to find out the ONLY difference between the mighty demon and the race demon are that you can swap boosters on the race where the mighty is a fixed booster, and with the race demon you can change the emulsion circuits. Who changes the emulsion circuits, wouldnt you need a dyno or some SERIOUS knowledge????
Now to answer your question you could allways drill holes in your butterflies. That would lean it out, but only do this as a last resort cause you cant change it back if it dosent help. Oh and dont call demon asking them about that cause theyll tell you "no sir WE DO NOT RECOMMEND THAT ON OUR CARBS" well then why in the hell are there holes in the "drag" race demon? then theyll answer "we used to do that a few years ago but we no longer do that" Makes me wish i could just go talk to good ol' Barry himself .....Good luck partner

blumont,

I emailed you my phone number again - give me a call this weekend and I can pop by.

There are a few non-destructive ways to lean out the idle w/o drilling the butterflies, but that works too. I've done that more than once and not regretted it. If you do not have screw in air bleeds, you can still open them up .002 at a time and you will be suprised how little it would take.

Sorry if this been asked/answered above - but do you have vacuum advance and is it working? Is it an adjustable vacuum advance? How much timing does it have at idle? I've had success with limiting the mechanical advance and running more initial timing - cleans up the idle.

So you can get air in there three ways - drill the air bleeds - risk is that you go too far, take baby steps. Another is to drill the butterflies. On a dominator, the best way is to drill and tap holes in the top by the air cleaner stud. Then drill the plugs out. Same as drilling butterflies but it is non-destructive as you can always run a blank. That's how my Pro-Systems carb came. Took the plugs out and I can idle it at 900 now. (286 @ .050")

Dumb question - 4 corner idle or 2?

If 2, you can adjust the secondary throttle stop.

Thanks Ryan, I may take you up on the offer. I am off to Red Deer in the morning and won't be back till early afternoon .Your email to me is in the office, I will try and stop by there tomorrow afternoon, get your number and give you a call. I really do appreciate the help.

I was going to attend the swap meet tomorrow in Red Deer but I have family commitments. I am off to Med Hat on sunday to get the cage recertified.

My email is in my profile - email your number to me and i will call you tomorrow afternoon. I got the engine back together, primed it and fired it, and put insurance on it today. I plan to take it for a short cruise tomorrow if the weather cooperates. Wanna come?

I'm free after about 3pm.

Ryan

:eek: Do I wanna come. Ahhhhhhhh let me think yes please lol. Its 6am Saturday right now and I am going to whip down to the office and get your number off the email. I will call
Dam, Ryan, I can't make it. Thanks for the invite anyway. I am going to call you this week.
I have to see your car

Well, I took 1 more shot at calling BG tech line to look for further solutions to my rich idle. I got a different tech this time and I explained all the sequences I have gone thru with very limited success. He finally told me to try drilling out the air bleeds and recommended a bit size. I bought that size and 2 smaller.(As Ryan, 66-283 said, baby steps) I tried the smallest and it made a marginal difference. The second made a huge improvement. It idles pretty darn good now. I will leave it here for now and maybe experiment with my timing a bit and also float level.I assume float level will come into play more at mid or wide open throttle? Thanks everyone for your input.
Ryan, I am still going to give you a call. I didn't want to bug you for help yet without trying myself.I am a brute for punishment smile.gif
I took it for a little test cruise and seems ok. The new vortec heads and UD 276H10 cam have made quite an improvement.If the weather holds out I will take it out for a bit and maybe open it up some