Jester

I've been trying to get my idle mix adjusted properly. I just got a new O2 sensor for my gauge that actually works..and found it wasn't adjusting too easily. At 1 turn out, it's too rich. At 1/2 turn, it's so lean it stalls. Inbetween it doesn't idle that well and and the AF readings are very erratic, going back and forth between lean and rich.

I'm running a fairly big cam..only pulling beween 9 and 11" of vaccum. The Carb is a Holley spreadbore 650 DP.

Do I need to drill holes in my throttle plates or is there another problem?

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

sleeper

sounds like a vacuum leak... did you check all your lines?

FastBroker

I'd say the same thing, a vac leak OR the idle speed is too low for your combo OR your carb has some internal probs and needs a rebuild OR PCV valve stuck open/partially open from the low vac of the cam. Need a PCV with a weaker spring but noone ever changes it. The strong spring in the OEM PCV you have now should be overcome by engine vac at idle. If idle vac is low, the valve will partially open anf low a lt more air, mesing your idle/misture majorly. If you cannot find a performance PCV, put a restriction in its line, a piece of brass witha small hole, to limit the flow at idle and partial throttle...

[This message has been edited by FastBroker (edited August 01, 2001).]

Jester

I don;t think it' a vacum leak. I removed and plugged all my lines except for the vac gauge and the reading didn't change. I don't thintk it's a leak from the manifold gaskets or under the carb...everything is torqued down good with new gaskets.

I don't have a PCV valve at all.

I also don't think it's a vacuum leak because I can close the plates till the engine stalls no problem. In fact, I noticed that once I lowered it to a bit under 500 and stalled, I still had several turns left before the plates closed completely. I think I'll drill those holes. It may or may not fix the problem, but it seems like it can't hurt.

I'll double check for any internal blockages or leaks while I have it off to drill the plates.

Idle speed is about 1000, I don't think it's too low...then again I might be wrong.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

[This message has been edited by Jester (edited August 01, 2001).]

kevin v

JESTER -BEFORE YOU DRILL ANY HOLES. WHAT IS THE DURATION OF YOUR CAM AT .050 ?

Jester

234/244 .510/.544 114LSA

it's a spreadbore carb to, so the primaries are tiny. I think that has something to do with it.


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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

Biochem

And here I'm asking YOU for help! Sounds like you have the same problem as I do...

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

Jester

Yeah..but I've actually checked the stuff I've told you to but you never do



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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

kevin v

a 1000rpm idle is a bit high for a cam that size. sounds to me like its to lean at a lower idle rpm. try turning the idle down as you lay your hand over the primary side of the carb to see if it continues idling. if that's the case then the idle circuit needs to be richened by way of idle feed or idle air bleed. also, how much initial timing are you running? the more initial you use the better the idle quality too.

greearhr

I don't think those small primaries can handle the air flow you need at idle. Some times a bigger carb can actually give better idle because you don't have to open the primay so far. Just my opinion.

Bear Tracks

kevin v

the small primaries really don't have much to do with it. the idle circuit itself just has to be right. i've seen small cubic inch super stock engines with late style q-jets idle at 1000-1100 rpm with about half of the tranfer slot exposed. duration at .050 around 280. engines don't need a lot of air to idle. most of the time it's a lack of fuel that causes bad or erratic idle problems with bigger cams.