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#1
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Carb quirk..
Hey guys I’ve been getting ready for Norwalk and have had a carb issue which is stumping me.
Issue is a 4150 custom built ... Been persistent with regards to stalling. Starts runs around town when I have it on and at the track it down right works. Ran a best with it and the RPM testing 2 weeks ago.. Issue.....stopping the car . Slowing down even at 20 mph on the street and hitting the brakes hard it wants to die. At the track well ..its dangerous..got to hit neutral and clear it up. Floats are perfect ...mix screws good idel 850 ..12 vacuum. Electric pump at 6.5.. Played today with everything and went for a drive....same deal. Ideas?.... Note run a Quad with a rpm and its flawless. |
#2
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Have a AEM wideband ...but of course it s out of commission...
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#3
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Float level and bowl vents? Got a "whistle" vent in the secondary metering block?
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
#4
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Quote:
That is what I was thinking too. Car might be flooding on hard braking. Sent from my iPad using Tapatalk
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
#5
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I know you say floats perfect but that sounds like classic fuel flooding.
Did you adjust floats while the engine is running? Drop the float level a bit more than bottom of site holes and see if it improves. Add a section of hose to the secondary vent and see if it improves. Like Skip Fix asked, if you don't have a whistle vent some fuel could slosh out. Anti-bounce float spring? (Mostly for off-roading but it doesn't hurt)
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Only a pawn in game of life. |
#6
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Tried adjusting fuel pressure???
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#7
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Quote:
1st Picture metal (brass) or Plastic baffle 2nd Picture Screen baffle 3rd Picture Short "Hot Rod" Plastic Whistle (may allow fuel to get to air horn on hard stops due to short length 4th Picture Long Plastic WHITE Whistle (if this whistle is trimmed to the length where the upper roof notch is and then the roof notch is duplicated again in the Modded length Whistle, the fuel control is excellent for braking/acceleration/ turning corners). This keeps the length longer vs the Hot Rod whistle and also works better on braking and turning due to the length being longer vs the Hot Rod whistle.
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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. Last edited by Tom Vaught; 07-17-2019 at 05:46 PM. |
#8
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Thanks for the quick responses...first fuel pressure is at 6.5...never moves . I run a Aero motive stealth in tank system. Always dead reliable and a aeromotive reg .
Yes I have the whistle block in both sides. Now ..Tom I believe its the 3rd one . Will check. The longer unit makes a ton of sense to me... Yes I set the floats wth engine running and I will try dropping the primary side again. It’s below halfway mark in the window now. Surfsma ..anti bounce spring...very interesting. Something I have never dealt with.. Was thinking about fuel slosh and wondered about erratic float movement. I will dig up some hose shortly and vent up couple inches. I will do the easiest thing first...primary float drop... Again thanks all .... |
#9
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Well spent some time tonight on tests..
Lowered the front float to about the bottom of the window. Had some tubing and extended the vents. Went for a spin..No change .. So off comes the carb and its apart . The vents are not very long. Blocks are 4412 XP They only extend past the metering blocks about 7/8 of a inch. The bowls are HPs so to reach near the back I need another 3/4 in.minimum.These are Press in vents. Question how far back should they go?..and can I get them that length.? |
#10
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Lower the secondary float and see what happens.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 Last edited by ta man; 07-17-2019 at 10:14 PM. |
#11
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Quote:
That is too short on the length. Old School 4781 850 carb white whistle is 1.5" long from the metering block to the end of the whistle. It has a .300" cut-out on the top of the whistle. the front edge of the cut-out is 1.200" from the metering block. The modded Whistles (I modify and use are .300" shorter in length but I redo the window). 1.200" long on the total Whistle length from the metering block. The length of the upper cut-out is still .300" and cut into that length so the edge of the opening at the top of the whistle is .900" from the metering block with a total length of 1.200" long from the metering block. 7/8" length whistles are not going to do it. Get the stock white whistles and mod them per above dimensions. Tom V. There are LOTs of Holley Aftermarket Parts that do well in "One Mode" (example Acceleration) and then the engine dies at the top end of the track when you hit the brakes. Old School Holley Guys tried to compromise and get the best of all modes. The really short plastic whistles are better than the Screen or the Brass part on the metering block but do a poor job typically on the braking (especially with the larger volume and length Race Bowls or bowls used with "spacers" to get extra volume. The Spacers were used for a while because the fuel pumps could not keep up with the flow demand required by the carb. More volume and maybe you can make a full run under power.
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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. Last edited by Tom Vaught; 07-18-2019 at 07:52 AM. |
#12
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If your running a air cleaner or not a Holley Carb , or any Carb needs a minimum of 3/4" of room above each fuel bowl vent to meter fuel correctly.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#13
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Quote:
The rear is where it would probably be dumping gas out of the vent into carb. Any jet extensions on jets?
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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 |
#14
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Great replys everyone. Thanks for the info on the vents Tom , i searched around for some and called my local speed shop . Guy on the other end didnt get it and I dont speak Manderine Chineese hes hard to deal with on occasion. . He finally odered a pair that hopefully will work and i can modify. Getting those Saturday morning.
The air cleaner assembly has lots of room above it..Big conical filter dome top and ive tried it without ..same result. The rear block has jet extensions. I did use couple chunks of hose to extend the vent tubes to try to eliminate the fuel dump last night. Will play with secondary float levels tommorow. Had holleys before but never this deal. The investagation continues.... |
#15
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Had a similar issue once . Check the accelerator pump umbrella seals for a stem that is broken but not completely so the nub inside the bowl flops around and interferes with the float .
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#16
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LOL, that sounds almost as fun as someone leaving out the secondary diaphram check ball...
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#17
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Quote:
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. |
#18
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What's your idle rpm?
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
#19
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Hey AG..idel is about 850/ 875..in gear 750.
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#20
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Texting a freind tonight... mentioned the secondary rear adjustment. Just wondering about getting a litttle more air in.
Know that the trassition slots need to be carefully looked at . This is a mechanical secondary unit.. Its another item to look at. I need to mention after i went for my spin last night about 5 miles the plugs were definatley showing a rich condition . I cleaned them before the test. |
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