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| carb issues, I'm stumped https://www.slantsix.org/forum/viewtopic.php?t=51331 |
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| Author: | kielbasa [ Thu Apr 04, 2013 6:58 pm ] |
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Just got home at tried to double up the stepup gasket even coated them with silicon sprayto givr them a little better sealing ness. Didnt change a thing. DDidn't really expect it to with how things are going... |
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| Author: | matv91 [ Sun Jun 15, 2014 12:03 pm ] |
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Post subject: carb issues, I'm stumped (Thu Mar 07, 2013 1:15 am) -------------------------------------------------------------------------------- Carter bbs 1964 and down style. Carb has been freshly rebushed. Carb has rebuild kit in it.Gone through all passages. IIdle and main jets clear. Theres no way nothing is clogged. I've pulled it apart 3 times now to tripple check all is good. Float set to 7/32. No intake leaks. Car ran decent before pulled off. Only to fix the leaky shaft. This is what happens: Wont idle where screws were set before.i had to set Idle set screws down pretty far to holdbutterfly open a bit so it would idle like $#!+. Engine revs a $#!+ load higher when I close the choke manually. Mixture screw doesn't seem to change much.. I'm stummped this was suppose to be a easy deal. But of course nothing ever goes that way.. haha. Please help this is my daily driver and its undrivable at the moment. Still like this with all 3 carbs? |
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| Author: | matv91 [ Sun Jun 15, 2014 12:19 pm ] |
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[ main jets clear. Theres no way nothing is clogged. I've pulled it apart 3 times now to tripple check all is good. Float set to 7/32. No intake leaks. Car ran decent before pulled off. Only to fix the leaky shaft. This is what happens: Wont idle where screws were set before.i had to set Idle set screws down pretty far to hold butterfly open a bit so it would idle like $#!+. Engine revs a $#!+ load higher when I close the choke manually. Mixture screw doesn't seem to change much.. I'm stummped this was suppose to be a easy deal. But of course nothing ever goes that way.. haha.] Also leans out as throttle is slowly opened. All this started after new bushings.The following is theory and guess work. 3 carbs all acting the same .Engine is air pump and bigger cams let engine pump more air.. Original carb set up for smaller cam. The wore out carb was leaking enough air to feed big cam and still allowed throttle plate to close to normal low curb idle position, Very little off idle slot below plate and mixture screws still working.Now after no leaks to get enough air to run plate is open to far, too much idle slot exposed making idle mixture screws not effective.Too much slot exposed tends to mess things up. Also as throttle is slowly opened engine leans out more,not enough slot left to run on, and not enough air flow for the main system to start. |
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| Author: | matv91 [ Sun Jun 15, 2014 1:18 pm ] |
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Got an early bbs like yours recently To look at. Also looked at early and late holley 1920s.Looked at carters and holleys side by side, early and late. Early means before cam change In 68 or 69? Late is after. Both brands on early carbs used solid throttle plates no holes. Late carbs both used idle air bypass holes. The holley has a .090 size hole in the throttle plate.5 different holleys all same size hole. Carter uses a separate passage in the throttle base plate,size .100. The off idle slot in the late carter is much longer than early model. My guess is that these changes were made to supply more air because of bigger cam and or emissions changes. |
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| Author: | matv91 [ Sun Jun 15, 2014 1:48 pm ] |
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http://slantsix.org/forum/viewtopic.php ... s&start=30 In this thread on this same issue is picture of base plate. At bottom of red straw,just under it is carter idle air bypass. Think it is picuture no 2. Also notice how long off idle slot is goes all the way to gasket line.At end of straw that little dark sguare is top of off idle slot. |
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| Author: | matv91 [ Sun Jun 15, 2014 2:25 pm ] |
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http://s1275.photobucket.com/user/Dougl ... 2670871949 Better picture |
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| Author: | matv91 [ Sun Jun 15, 2014 2:57 pm ] |
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http://s1275.photobucket.com/user/Dougl ... 1444804375 This is carter with a hole in throttle plate in addition to hole in base plate. |
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| Author: | matv91 [ Tue Jun 17, 2014 7:24 pm ] |
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On the early 60s afbs, carter used an adjustable air bleed [big brass screw] to set idle rpm. Curb idle screw was used to position plate relative to off idle slots only.At least thats how it was done in theory.Some thing like this deal. http://www.carcraft.com/techarticles/cc ... e_stumble/ Any way for testing,made a simple version of this. Put a 3/8 tee fiting in pcv line and ran open port to a plumbing valve. This made for a tuneable air leak. Bolted on 1964 bbs,early carb solid plate,no idle air bypasss, short off idle slot. Backed out curb idle screw completely, throttle closed. Adjusted mixture and tuneable air leak, would idle just fine all the way to 950 rpm. Mixture screw does a lot set up like this. Adjusted air leak down to 700 rpm reset mixture. Drove around,runs fine,wideband says every thing ok. A test like this would prove or dis prove the need for idle air bypass. |
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