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Discussion Starter · #1 ·
Hi there, My DBP stalls my engine on Very Hard Breaking.

If I go to four corner Idle, will it solve this problem?

I assume the jet extentions are not ment for this problem. I would also assume you would never want to install jet extensions on the front bowl.... Right?

Mike
 

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check your float level
 

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Hmm.

Not to divert attention from the OP, but my car does the same thing. Float levels adjusted correctly (Holley 650, 351W).

Flick the trans to neutral, bump the starter motor, and it fires right back up, which makes me think it's not flooding...

Any other ideas?

-Jim
 

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Discussion Starter · #4 ·
Very sure my float level is perfect.

What happens on hard breaking is all the fuel is forced to the front of the carb, and the main jets get exposed to air, long enough to kill the main jet flow.

Not sure how float level can be the cause, for 1 second of hard breaking, since the fuel is being forced into places it usually does not visit, and forcing the float to shut off incoming fuel anyways....

This also kills the idle circuit since it uses the same source for raw gas.

I do not think that jet extentions would work in the front, because on hard excelleration, the same problem would happen in reverse. The fuel will be forced to the rear of the bowl, leaving the extensions exposed to air.

So, if there was a 4 corner idle setup, the rear bowl would not be exposed to this problem with breaking, but hard accelleration would be the problem zone on the secondaries.

My question is, will the secondary idle circuit keep the engine running long enough till the front idle circuit recovers from the fuel slosh.

Anyone with a 4 corner idle setup have this breaking problem and the engine stalling?
 

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Don't overlook the brakes. If you have power brakes the big diaphram in the brake booster can crack from dry rot. When you hit the brakes you can hear a noticable hiss or vacuum leak. It can kill the engine. I've had it happen.
 

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Hmm.

Interesting dialog.. Perhaps I'll try a different carb.

Can't be the brakes on my car, I use a hydroboost setup...

-Jim
 

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Bump up your initial timing, and make sure your advance canister is not connected directly to the intake manifold, but to the ported vacuum on the carburetor.

Sometimes lowering the float level will help this problem, too, even if you are sure they are correct now. Can't hurt to try.

Also might raise the idle speed a little bit and see how the engine responds.

Greg
 

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Seems to me that Ive heard this problem before. and i thought the solution was to use the vent whistle in the rear bowl. Under hard braking the fuel sloshes up the rear vent tube and into the carb flooding it and stalling the engine. I think maybe i read it on the holley website.They have a fairly lengthy section on FAQ's . Check them out if you like.
Good luck
 

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Start with vent baffles in both front/rear bowls. Then use longer jet ext in the rear and shorter ones in the front jets. Your fuel is sloshing in both bowls and coming out the vent tubes. You can also run a small rubber hose between the two vent tubes and cut some breathing holes in the very top for air. That's the reason you see those tubes connecting the vents on carbs.
 

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Discussion Starter · #10 ·
The vent tubes.... Yes, I have seen that rubber hose linking the bowls. Sounds like a great fix, if it is truely the fuel shooting up the vent tubes.

My bowls do have those long white plastic spash guards. I can see how it would rush forward in a heard breaking....

Thank you very much.....
 

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Look at it this way, what ever your body is doing on turns, starting stopping, all the fluids in your car are doing. Gas tank, float bowls, oil, diff, trans, all of them.
 

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Discussion Starter · #12 ·
When I slam on the breaks.... I usually do not loose my lunch on the dashboard......(giggles)

But between the bar stool and the floor, yes, I have lost some fluids....
 

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If you already have the white plastic vent baffles in your metering blocks, fuel sloshing out the vent tubes is highly unlikely.

You can find out for sure by taking a piece of scrap fuel line that is long enough to slip onto both the front and rear vent tube at the same time, and cutting out an opening in the top of the line so fuel can go between the tubes and vent without going down the carb throat.

If the problem goes away (I am betting it won't) then you're good to go!

At least it is an inexpensive test.

Greg
 

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Technically, with the correct float level, the car would have to experience around -2g's to uncover the front jets. Not sure how hard he's stopping, but it is likely much less than that!

Greg
 

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Discussion Starter · #16 ·
Hard breaking = 30 - 70 MPH, slam on the breaks and go for shortest stoping distance. It will stall at almost the same time as I come to a dead stop....Just hard breaking.



Normal breaking is fine, no stalling, not even close...bumps, tight turns, high speed offramp turns...sudden breaking...just not hard breaking
 

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Mike, that's precisely my symptom.. Granted, my car does brake hard enough to nearly stop time...

I'm going to isolate the problem this weekend. I'll put the rear axle on jackstands, run the wheels up to 45 or so, and simulate the braking rate. If the motor dies, it ain't the excessive G's!

One thing I've pondered is the possibility of the trans somehow stalling the motor... Anything that I can blame on my FMX auto, I will!

-Jim
 

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Discussion Starter · #18 ·
That sounds like a very dangerous experiment to me. Not sure what information you will get.

The front wheels are stationary, so the porposion valve may not behaive like it is supposed to. Plus there is not load on the rear wheels so it will take a small fraction of the breaking power to stop the wheels. Maybe too quickly and you will snap your driveshaft. Without straps to hold the car in place in event of failure, I would never attempt what you say.

I really hope you are joking.

Remember if you make 100 Hp for 5 seconds to get your car moving on the road, then it will take 100 hp over the same 5 seconds to stop the car to stop the car minus a little loss to road friction. It is time and energy so the 100 HP to stop is spread out over the breaking time, but I promise it equalls the applied energy.

Thats right, in some real hard breaking situation, you maybe exserting the equivelent of over 100 HP to the breaks. On jack stands, I think it will take under 10
 

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The proportioning valve is a non issue, I'd think. 2 separate hyd. systems F+R... But an interesting point.

Since I'm not accelerating the car (and it's associated weight), I think the hp necessary to spin the driveline will be substantially less than 100hp.

I'd speculate, wildly, that if I ran the driveline up to 40 or so and kicked the jackstands out so the car dropped to the ground, she'd probably go about... nowhere. This isn't an engine dyno, where we're running max HP for max wheel acceleration... I'd be surprised if it took anything over idle setting on the throttle to let the unencumbered wheels rotate to any speed.

Speaking of which, ever seen that video of the hotrod on the mobile dyno that hops off the drums? Pretty amazing sight. Stops right @ the edge of the chassis dyno setup, before launching into a crowd of people. Quick reaction by the guy behind the wheel!

-DangerJim
 
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