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Old 07-17-2019, 03:15 PM
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Default 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.

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Old 07-17-2019, 03:17 PM
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Have a AEM wideband ...but of course it s out of commission...

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Old 07-17-2019, 03:24 PM
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Float level and bowl vents? Got a "whistle" vent in the secondary metering block?

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Old 07-17-2019, 03:40 PM
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Quote:
Originally Posted by Skip Fix View Post
Float level and bowl vents? Got a "whistle" vent in the secondary metering block?


That is what I was thinking too. Car might be flooding on hard braking.


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Old 07-17-2019, 03:40 PM
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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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Old 07-17-2019, 03:51 PM
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Tried adjusting fuel pressure???

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Old 07-17-2019, 05:39 PM
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Quote:
Originally Posted by Skip Fix View Post
Float level and bowl vents? Got a "whistle" vent in the secondary metering block?
Here are some of the Holley Vent Baffles "Whistles"

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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Last edited by Tom Vaught; 07-17-2019 at 05:46 PM.
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Old 07-17-2019, 06:12 PM
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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 ....

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Old 07-17-2019, 09:30 PM
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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.?

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Old 07-17-2019, 10:09 PM
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Lower the secondary float and see what happens.

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Last edited by ta man; 07-17-2019 at 10:14 PM.
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Old 07-18-2019, 07:23 AM
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Quote:
Originally Posted by Torquewar View Post
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.?
Stock HP Metering Block White Plastic Whistle length is approximately .900" from the metering block to the end of the whistle.
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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Last edited by Tom Vaught; 07-18-2019 at 07:52 AM.
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Old 07-18-2019, 07:53 AM
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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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Old 07-18-2019, 09:49 AM
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Quote:
I will try dropping the primary side again
Ditto what Steve said, also ta man.
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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Old 07-18-2019, 10:15 AM
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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....

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Old 07-18-2019, 10:53 AM
Tandyman Tandyman is offline
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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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Old 07-18-2019, 05:10 PM
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Quote:
Originally Posted by Tandyman View Post
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 .
LOL, that sounds almost as fun as someone leaving out the secondary diaphram check ball...

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Old 07-18-2019, 05:20 PM
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Quote:
Originally Posted by Tandyman View Post
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 .
The correct way to do it is to install the new umbrella seals and take a side cutter and cut the stems completely off. I have seen issues where the float level was never right because the stem interfered with the float. Without the stem the float should have complete travel in the bowl.

Tom V.

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Old 07-18-2019, 07:53 PM
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What's your idle rpm?

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Old 07-18-2019, 09:02 PM
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Hey AG..idel is about 850/ 875..in gear 750.

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Old 07-18-2019, 09:05 PM
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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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