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#1
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Hey Guys, Maybe someone on this board can help tune my Holley 750 DF/DP. First off the engine, 400 pontiac bored 30, trw flat top pistons, crane hydraulic 560 lift w/ 1.65 steel rockers, 1968 #16 heads ported, bowled, 3 angle valve job, holley street dominator. The carb is a holley 4779 750 DP/DF like I said prior with a proform center section, primary jets at 72, secondary at 84. Next the problem, engine just does not want to idle, when you think you have it, it gradually slows down and shuts off. When you increase the throttle screw for a higher idle it seems to hold but fluctuates up and down about 200 rpms. Any help will be appreciated. If you need any other information, post here and I will try to get the answers for you. Thanks in advance for your help guys.
![]() ![]() ![]() You Have To Be Willing To Take It To The Max!
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1965 GTO: 467 (Built By Dan Willever), 400 Block, Eagle 4.25 Stroke, Eagle 6.8 Rods, BRC Pistons, Custom Grind Hydraulic Roller Cam, Edelbrock 72cc Heads Ported, HS Rockers, Doug's Headers, Edelbrock Victor 4150, QTF 850 Carb, TCI Flex plate, AutoGear M22 4 Speed, SPEC Clutch and Pressure Plate, 12 Bolt 3:73 Posi. |
#2
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Hey Guys, Maybe someone on this board can help tune my Holley 750 DF/DP. First off the engine, 400 pontiac bored 30, trw flat top pistons, crane hydraulic 560 lift w/ 1.65 steel rockers, 1968 #16 heads ported, bowled, 3 angle valve job, holley street dominator. The carb is a holley 4779 750 DP/DF like I said prior with a proform center section, primary jets at 72, secondary at 84. Next the problem, engine just does not want to idle, when you think you have it, it gradually slows down and shuts off. When you increase the throttle screw for a higher idle it seems to hold but fluctuates up and down about 200 rpms. Any help will be appreciated. If you need any other information, post here and I will try to get the answers for you. Thanks in advance for your help guys.
![]() ![]() ![]() You Have To Be Willing To Take It To The Max!
__________________
1965 GTO: 467 (Built By Dan Willever), 400 Block, Eagle 4.25 Stroke, Eagle 6.8 Rods, BRC Pistons, Custom Grind Hydraulic Roller Cam, Edelbrock 72cc Heads Ported, HS Rockers, Doug's Headers, Edelbrock Victor 4150, QTF 850 Carb, TCI Flex plate, AutoGear M22 4 Speed, SPEC Clutch and Pressure Plate, 12 Bolt 3:73 Posi. |
#3
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Sounds like a vaccuum leak. Check all parts to make sure they are flat & sealing. Did your carb do this before you added the Proform main body.
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#4
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Scott, I don't think so, but its been at least 10 years since I used it. Upon using the proform center section, I replaced everything outside of the centersection, so it is practically a new carb. I will check for vacuum leaks. Thanks.
You Have To Be Willing To Take It To The Max!
__________________
1965 GTO: 467 (Built By Dan Willever), 400 Block, Eagle 4.25 Stroke, Eagle 6.8 Rods, BRC Pistons, Custom Grind Hydraulic Roller Cam, Edelbrock 72cc Heads Ported, HS Rockers, Doug's Headers, Edelbrock Victor 4150, QTF 850 Carb, TCI Flex plate, AutoGear M22 4 Speed, SPEC Clutch and Pressure Plate, 12 Bolt 3:73 Posi. |
#5
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Sounds like maybe intake leaking. Spray some carb cleaner along the top and bottom of intake gasket and see if rpms increase.
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#6
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With hydrallic .560 cam you are most likely in the
transfer slot on the Holley carb. When you turn the screw to lower the idle the fuel you had from the transfer slot goes away. You also probably have limited control of the idle screws. Try raising the angle of the rear throttle blades first slightly and lowering the front blades to get more idle air flow. evenly open up all 4 idle mixture screws and see if you casn get the carb rich enough to idle correctly. remove the carb and look at the position of the blades on all 4 barrels. If more than .040 of the transfer slot is exposed on the front or rear, drill .090 holes in the throttle blades and reset the throttle blades for < .040 transfer slot to be visible. 90% of the time poor idle with a non stock cam is due to idle blade position being wrong. Tom V. ![]()
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#7
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Poor idle only can come from transfer slots over exposed but fluctuating sounds like vacume leak. If your idle mixture screws work correctly I wouldn't mess with throttle blade settings or be drilling holes........
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#8
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The fluctuating idle with the increased idle speed is probably coming from the power valve.
Check the power valve rating and also make sure it's not bad. johnta1 Pontiac Power RULES !!! www.wallaceracing.com ![]()
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John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
#9
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I too have been having similar problems with my combo for longer then I can remember. I can achieve a stable idle after the car warms up for about 10-15 min. (no choke provisions), but my car idles very rich. It is rich to the point that I get gasoline in my fuel. I have tried everything to lean it out, but when I do the car just will not idle. My car only produces about 7-8in.hg. at around 900rpm. My engine builder says it is because of the camshaft duration, but I don't buy it. I have seen plenty of cars with way more radical camshaft/engine combos. that idle just fine. But enough about my problems. Have you checked your vacuum to see how low it is or if it fluctuates? Are you allowing plenty of time for your motor to warm-up. I know these are basic questions but you have to start somewhere.
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#10
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Also something to think about, is with large cams more initial timing has to be run to get a good idle. I'm runnig approx. 20 degrees initial and approx. 36 total with a solid 265 int. and 276 dur. @ .050 with 619 lift. When I first installed cam, I got the same symptoms as you guys got but when I set initial at 20 degrees, I can now idle it at approx. 900 rpm's. Before that I had to set it as high as 1200. But we are talking a whole different type cam. Checking for vacume leaks and timing first will cost you nothing and about 15 minutes of tinkering....
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#11
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<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by gto70:
It is rich to the point that I get gasoline in my fuel.<HR></BLOCKQUOTE> Man, I hate it when that happens...... ![]() Chance favors the prepared mind. |
#12
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You caught that huh Goatman. I meant to say oil.
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#13
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Hey Guys, Thanks for the help, it turned out to be an intake manifold leak. I tried closing off the heat crossove ports with sheet metal but looks like I failed. Purchased Felpro 1233 intake gaskets and solved the problem.
Thanks again for the help You Have To Be Willing To Take It To The Max!
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1965 GTO: 467 (Built By Dan Willever), 400 Block, Eagle 4.25 Stroke, Eagle 6.8 Rods, BRC Pistons, Custom Grind Hydraulic Roller Cam, Edelbrock 72cc Heads Ported, HS Rockers, Doug's Headers, Edelbrock Victor 4150, QTF 850 Carb, TCI Flex plate, AutoGear M22 4 Speed, SPEC Clutch and Pressure Plate, 12 Bolt 3:73 Posi. |
#14
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As a suggestion to people posting carb issues on the board, it would really be nice if you would describe all of the changes to the intake system
before you post about a carb problem. Carbs get blamed many times for other issues which could easily be addressed if the board members knew the WHOLE story. Tom V. ![]()
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#15
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No "Grasshopper", One must be able to seperate the two.........
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#16
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Quote:
"No "Grasshopper", One must be able to seperate the two......... " Lerry, explain. Thanks. Tom V. ![]()
__________________
"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#17
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The indications told me intake gasket leak because the fact the idle FLUXUATED and he stated that just as he thought he had it, it would stall. Telling me that WHEN he thought he had it (as he stated), the car then reached a hot enough temperature to expand the metals and start gapping the space between the gasket or gaskets. That is the point where the engine would die. Transfer slots overexposed (usually) will still let the motor idle at a higher rpm. Even though the idle mixture screw don't do a whole hell of alot...
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#18
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Tom a "Grasshopper" LOL!
Ya, that's like calling Ccass a "Hobbyist" And Pontiac Dude a "Shadetree Mechanic" Or Goatman "Controversial" Oh wait, scratch that one... ![]() ![]() ![]() ![]() ![]() |
#19
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#20
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Quote:
"because the fact the idle FLUXUATED" I guess I did not pick up on that one as EVERY engine (Pontiac) I have owned, the idle fluxuated! (At about 5 inches of vacuum and .600 lift, I was never smart enough to get that quarter to balance on the intake manifold). Most of the time the hammers were shaking off the walls, the neighbors were complaining about the noise from the open headers, and the cops were driving by to visit, have some coffee, and "shoot the *****." I guess I am a "Grasshopper!" Too dumb to take that "bad" camshaft out of the engine and put on of those "good" 17-18" inches of vacuum camshafts in the engine so the idle would not fluxuate. Tom V. ps If I had known he had one of those "good" cams in his engine I would have immediately ruled out the transfer slots as the air flow requirement would allow closing the blades below the slot. ![]()
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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