Idle drop by 500 rpm?

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Ironracer said:
Timing is @22° according to a Matco dial back, still pulling vacuum in park @1200 rpm.. need to locate a piston stop..seems like she wants more timing. Fires right up, no drag on starter
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Now wait a minute. Up there ^^^ you say you have it idling at 650. So which is it? 650 or 1200? Why would you idle it up to 1200 if it'll idle at 650?
 
George Jets said:
With your secondaries cracked open you are loosing all of your vacuum at an idle, then in turn your vacuum advance is doing nothing because there is no vacuum there to pull the vacuum advance so it dies when the idle drops when you put it into gear.

Over the internet diagnostics, no easy task . . .
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He was advised to crack the secondaries open slightly because he was pulling vacuum on the spark advance port at idle. That's an indication that the T ports on the primary side are too far exposed, so to make up for it, he was advised to pull the carburetor, get the primary T ports square and crack the secondaries very slightly. It's a very, very common practice people have done for decades, along with drilling the throttle blades. I don't like drilling the throttle blades, because that's irreversible. Playing around with the T port exposure is not.
 
Ironracer said:
Well, just finished dinner. Went back out, fired it up, gave it the smallest pedal w/ foot brake, and it stayed running in gear. Probably just need to close the secondaries back up, and leave it the heck alone! I'm not a professional carburetor tuner I may be trying to get this thing dialed in " too much"... lol. I know I had less problems when I didn't mess with it! Thanks George!
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Sounds to me like you are closer now, but have at it. I sure wish we were local. I would figure it out for you.
 
Ironracer said:
I closed the mix screws, brought em to highest idle (2.5 out) and messed w/ the timing...
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2.5 out? should be 1.5 max.
I think you should look for a vacuum leak.
Holley 750's are factory spec'd for 396 Chevy. if anything it would be rich for a mild 340.
 
fishmens67 said:
2.5 out? should be 1.5 max.
I think you should look for a vacuum leak.
Holley 750's are factory spec'd for 396 Chevy. if anything it would be rich for a mild 340.
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When I pulled the plugs, after pulling it from the ol 66 Sat, they were healthy grey...with points. It the carb I got when. I built the mill. Ported heads, oversize valves, 155 psi, full Grove mains, 8 qt pan ( never again, lol) ARP rod bolts, std bore TRW forged pistons, high volume oil pump, strip Dom, just a fun Lil mill, w/ reliable street ability...
 
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fishmens67 said:
2.5 out? should be 1.5 max.
I think you should look for a vacuum leak.
Holley 750's are factory spec'd for 396 Chevy. if anything it would be rich for a mild 340.
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The damn thing was fine.. the only odd thing was, I gave er a Lil wing, and a spit out the primary popped out. Never before w/ that combo....
 
RustyRatRod said:
He was advised to crack the secondaries open slightly because he was pulling vacuum on the spark advance port at idle. That's an indication that the T ports on the primary side are too far exposed, so to make up for it, he was advised to pull the carburetor, get the primary T ports square and crack the secondaries very slightly. It's a very, very common practice people have done for decades, along with drilling the throttle blades. I don't like drilling the throttle blades, because that's irreversible. Playing around with the T port exposure is not.
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Thank You fer articulating that properly...
 
If it only started doing this since u cracked the secondaries open wouldn’t it stand to reason to close them back up? And if ur pulling vacuum where it shouldn’t be the carb surely needs a rebuild at least. May have worn throttle shafts also. It it was great with points try installing them again. Kim
 
oldkimmer said:
If it only started doing this since u cracked the secondaries open wouldn’t it stand to reason to close them back up? And if ur pulling vacuum where it shouldn’t be the carb surely needs a rebuild at least. May have worn throttle shafts also. It it was great with points try installing them again. Kim
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It's 12 years old. Seen some dragging, and a few years of street use, daily, I'd hate to think i killed the Throttle shafts...what's odd is the Darn thing, after following RustyRatRod and Mattax instructions, to a t, she fired up and idled at 650, then dropped to 450 in gear.. then I tweaked the idle mix screws out, that raised the idle... checked w/ a light, timing was to advanced, so I retarded the timing. At some point, I gave it a little gas, and got a pop outta the primaries. SOB never idled since... Thanks Kim, hope all is well, Chuck
 
Ironracer said:
It's 12 years old. Seen some dragging, and a few years of street use, daily, I'd hate to think i killed the Throttle shafts...what's odd is the Darn thing, after following RustyRatRod and Mattax instructions, to a t, she fired up and idled at 650, then dropped to 450 in gear.. then I tweaked the idle mix screws out, that raised the idle... checked w/ a light, timing was to advanced, so I retarded the timing. At some point, I gave it a little gas, and got a pop outta the primaries. SOB never idled since... Thanks Kim, hope all is well, Chuck
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You might should have tried the idle screw instead of the timing. So where are you now with it? Will it still not idle?
 
Ironracer said:
It's 12 years old. Seen some dragging, and a few years of street use, daily, I'd hate to think i killed the Throttle shafts...what's odd is the Darn thing, after following RustyRatRod and Mattax instructions, to a t, she fired up and idled at 650, then dropped to 450 in gear.. then I tweaked the idle mix screws out, that raised the idle... checked w/ a light, timing was to advanced, so I retarded the timing. At some point, I gave it a little gas, and got a pop outta the primaries. SOB never idled since... Thanks Kim, hope all is well, Chuck
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I'm no holley expert, but a pop can break some parts. Mostly the power valve I'm told.
Might be worth a look-see. Lots of instructions in how and where and what to look for on google.
Supposedly holley "fixed" the power valves to not fail after a pop, but if the pop preceeded your issues... Well, there it is.
 
Does it have power brakes? Or does it have some vacuum caps? A lot of times, when one pops, it'll blow off a vacuum hose or cap and induce a manifold vacuum leak. Ain't gonna idle like that.
 
RustyRatRod said:
Does it have power brakes? Or does it have some vacuum caps? A lot of times, when one pops, it'll blow off a vacuum hose or cap and induce a manifold vacuum leak. Ain't gonna idle like that.
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Good call. I had exactly this happen before. Didn't even occur to me!
 
RustyRatRod said:
Does it have power brakes? Or does it have some vacuum caps? A lot of times, when one pops, it'll blow off a vacuum hose or cap and induce a manifold vacuum leak. Ain't gonna idle like that.
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Yes. Has some Viton (or whatever) caps. And darn power brakes. Newer master
 
Phreakish said:
I'm no holley expert, but a pop can break some parts. Mostly the power valve I'm told.
Might be worth a look-see. Lots of instructions in how and where and what to look for on google.
Supposedly holley "fixed" the power valves to not fail after a pop, but if the pop preceeded your issues... Well, there it is.
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It has the power valve blowout protection... but I guess I can get some gaskets and rip it apart.... unfortunately I'm supposed to work today
 
Ironracer said:
It's 12 years old. Seen some dragging, and a few years of street use, daily, I'd hate to think i killed the Throttle shafts...what's odd is the Darn thing, after following RustyRatRod and Mattax instructions, to a t, she fired up and idled at 650, then dropped to 450 in gear.. then I tweaked the idle mix screws out, that raised the idle... checked w/ a light, timing was to advanced, so I retarded the timing. At some point, I gave it a little gas, and got a pop outta the primaries. SOB never idled since... Thanks Kim, hope all is well, Chuck
Click to expand...
With your engine combo and converter the idle speed in park should be more like 850 -875 rpm.
 
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