Can't get it to idle.
#3043348
05/18/22 05:30 PM
05/18/22 05:30 PM
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Joined: Sep 2017
Posts: 342 Red Deer, Alberta
Greenwood
OP
enthusiast
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OP
enthusiast
Joined: Sep 2017
Posts: 342
Red Deer, Alberta
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After disassembling my carb, blowing out the air bleeds, and re-assembling, I finally got it running sort of properly. I can get it to idle down to about 1200-1300, and it sounds and smells nice and crisp. However, even after getting up to temp, it will suddenly drop off and not recover. It should actually idle about 900, and I've been sneaking the timing back closer to a proper initial, but the only way I can keep it from randomly dying is to keep the idle up past 1400. The carb is an older BG 750 DP, with no choke or air horn, and downleg boosters. I set the idle mixture screws at 1 1/2 turns out, as a baseline. It starts great. Half a shot of gas, hit the button, and it's running. Just can't get the idle sorted. ??
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Re: Can't get it to idle.
[Re: Greenwood]
#3043380
05/18/22 07:00 PM
05/18/22 07:00 PM
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Joined: Jan 2003
Posts: 2,923 A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,923
A shed in England
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Was it OK prior to the carb re-assemble ?
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials. 9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge. RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: Can't get it to idle.
[Re: B1MAXX]
#3043454
05/18/22 11:20 PM
05/18/22 11:20 PM
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Joined: Aug 2003
Posts: 43,184 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,184
Bend,OR USA
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All the cars I've work on that had the idle speed screw up far enough for the throttle plates to expose the transfer slots ran rich and stunk like unburnt gas out the tail pipes. I can remember seeing a post about intentionally exposing the transfer slots on here several years back, really bad suggestion The transfer slots are their for adding additional fuel at light part throttle changes from under 1200 RP up to around 2100 RPM The idle circuit is tunable by using the idle air bleeds as well as the idle mixture screws Don't make it idle on the transfer slots
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Can't get it to idle.
[Re: Cab_Burge]
#3043463
05/19/22 12:31 AM
05/19/22 12:31 AM
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Joined: Sep 2017
Posts: 342 Red Deer, Alberta
Greenwood
OP
enthusiast
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OP
enthusiast
Joined: Sep 2017
Posts: 342
Red Deer, Alberta
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Okay. I had some self-induced carb issues last summer. I did solve them, but I also had the carb apart for new gaskets. I kind of overthought my first fire-up issue, solved it (crossed wires. Doh!), and then it was all over the place on the next fire up. Thought for a bit, and pulled the carb apart, blew out the bleeds on a hunch. I set the throttles at about .040 of transfer slot visible, and set the idle screws at 1 1/2 turns out. Right now, the timing's at 32 at 1500. Can't get a shot any lower, but in the past it has idled nicely at 10 initial, with 36 all in. Cab, am I reading it correct that I should close the throttle blades up until the transfer slots are NOT exposed? I also suspect I could bring the idle screws out a bit more, so I will try that tomorrow night when the neighbor's at work.
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Re: Can't get it to idle.
[Re: Cab_Burge]
#3043521
05/19/22 09:39 AM
05/19/22 09:39 AM
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Joined: Mar 2003
Posts: 2,505 PA
moparacer
master
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master
Joined: Mar 2003
Posts: 2,505
PA
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I've been sneaking the timing back closer to a proper initial How much cam? Might need to go the other way to get the idle where you want it.. Crank the initial up and take some centrifugal out to get your total. Sometimes if the cam is big enough I have had to locked the distributor out, set the total and roll with it.
67 Barracuda street/bracket car 11.27-119 68 Dart 502 BB 8.70s-152 414 cid SB Dragster 7.65-174
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Re: Can't get it to idle.
[Re: GomangoCuda]
#3043639
05/19/22 03:45 PM
05/19/22 03:45 PM
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Joined: Jan 2003
Posts: 14,499 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,499
So. Burlington, Vt.
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That cam will like more timing at idle. Try 20° or more. Then adjust the Carb. Agreed. Fundamentally, I like to have the basic ignition curve sorted out before trying to dial in the carb.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Can't get it to idle.
[Re: justinp61]
#3043784
05/20/22 01:05 AM
05/20/22 01:05 AM
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Joined: Jul 2005
Posts: 707 California
BigDaddy440
super stock
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super stock
Joined: Jul 2005
Posts: 707
California
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Many carb problems have been fixed by correcting the timing. This has been true in my experience once or twice. If you don't run enough timing, you'll have to turn the idle screw beyond the idle circuit of the carb -causing problems. By advancing the timing which increases RPM, or making sure you're running the proper initial timing for your engine, you should be able to idle within the idle circuit the way the carb was designed to run. This is the first thing I'd confirm before moving forward.
Last edited by BigDaddy440; 05/20/22 01:05 AM.
1969 A12 Roadrunner 1970 Plymouth Cuda 1968 Dodge Dart
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Re: Can't get it to idle.
[Re: lewtot184]
#3043849
05/20/22 10:25 AM
05/20/22 10:25 AM
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Joined: Jan 2003
Posts: 14,499 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,499
So. Burlington, Vt.
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If the timing situation seemed to be close to what I thought I’d end up with(20-25 initial/32-38 total), then “my” next step is to just grab another carb off the shelf to see if a different carb solves the problem, or at the least changes the idle characteristics.
I realize a lot of people don’t have that option........ but I haven’t had only one carb on hand for many many years.
I find that swapping to “known good” parts is a pretty effective way to troubleshoot.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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