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vacuum loss 250 crossflow

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paul81mk2
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vacuum loss 250 crossflow

Post #1 by paul81mk2 » Sat May 11, 2019 7:44 pm

took brake booster to brake mechanic ,he said bench tested ok , what would cause or causes be , that reduced the vacuum in a 81 ,250 crossflow with a auto attached??

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xctasy
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Re: vacuum loss 250 crossflow

Post #2 by xctasy » Sat May 11, 2019 8:37 pm

Yes, but only if there is a brake booster failure. That will create a leak for sure.

Use the propane method to find the leak.

The PCV must be hooked up right, the car should be pulling good vaccum. The set up requirements need to be followed.

Fords Ellery Service manuals go through how to tune a 1-bbl carb XD cross flow.

Electronic ignition, EGR and throttle positioner solenoid must be engegised the right way.

If your not doing it the factory way, your doing it wrong.

Check that the flexplate isn't bodgy, and that if it has a viscous fan, its in balance.

1-bbl x-flow 250 Transits and Falcons always had a lousy idle.

If vac isn't right, then you have to find out where the leak is and why.

A one jet supply to both legs of the early 1-bbl intake manifold won't be even, and thats a perenial problem that won't be fixed without a proper 2bbl carb. Propane leak test might help, but its limited as to what you can do to fix it.

There is no four or two corner idle in a Bendix Stromberg 1-bbl carb.

Propane method is this.
http://vb.foureyedpride.com/showthread. ... ost1663147

JACook wrote:The propane enrichment can be done without any special tools, but I will say the tool makes things
a little easier. All you need is a way to repeatably supply a low flow of propane. When I first started
using the propane enrichment method, I modified a regular propane torch by removing the torch bit,
and attaching a hose.

I have altered the factory method just a bit though. Rather than inject the propane into the air cleaner,
I prefer to aim the hose down each individual throat, to make sure I'm getting the same reaction from
all of them. Then I work with progressively lower propane flow rates to fine tune the mixture setting,
while watching both engine RPM and manifold vacuum.

It takes a bit of practice to find the balance, but once you know what feels right, it's much quicker and
more accurate than just using the vacuum gauge.
Image
XEC Ltd ICBE's Inter Continental Ballistic Engines-
FAZER 6Bi (M112 & EEC5) or FAZER 6Ti (GT3582 & EEC5) 425 HP 4.1L/250 I-6
FAZER 6V0 3x2-BBL Holley 188 HP 3.3L/200 I-6 or 235 HP 4.1L/250 I-6
X-Flow Engine Components Ltd http://www.xecltd.info/?rd=10

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JackFish
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Re: vacuum loss 250 crossflow

Post #3 by JackFish » Sat May 11, 2019 9:20 pm

So what are the current vacuum readings?
1978 Ford Fairmont station wagon
1978 Ford Fairmont station wagon
Yup, I bought another one.
1996 Chevy Caprice 9C1 (3)
1999 Dodge Ram 2500

paul81mk2
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Re: vacuum loss 250 crossflow

Post #4 by paul81mk2 » Sat May 11, 2019 10:08 pm

I'm still sourcing a vac gauge that has a numerical reading. would a faulty auto trans modulator lose enough vac to cause my prob, as it is connected to the same t piece as the brake booster. if it all comes back to the booster , the guy checking it , didn't want the work.... and it is a single barrel Stromberg off a Cortina..

paul81mk2
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Re: vacuum loss 250 crossflow

Post #5 by paul81mk2 » Sun May 12, 2019 2:10 am

have plumbed vac gauge to booster . is reading 20 INS/hg at idle 25 after a good rev. drops 5 every brake application , still no boost...booster min is supposed to be 18, max 23??? booster caput.....

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JackFish
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Re: vacuum loss 250 crossflow

Post #6 by JackFish » Sun May 12, 2019 10:12 pm

So you teed into the brake booster line which is manifold vacuum.

I'm not seeing numbers there that indicate a vacuum issue.

I have a cam in mine and it runs quite well idling with only 10-12 hg
Yeah it drops a bit when the brakes are applied.
Are the brakes not working, or is it not shifting correctly?

Describe the drive-ability problem.
1978 Ford Fairmont station wagon
1978 Ford Fairmont station wagon
Yup, I bought another one.
1996 Chevy Caprice 9C1 (3)
1999 Dodge Ram 2500

paul81mk2
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Posts: 9
Joined: Fri May 10, 2019 6:57 pm
Location: adelaide south australia

Re: vacuum loss 250 crossflow

Post #7 by paul81mk2 » Sun May 12, 2019 10:58 pm

when you apply brakes it's like standing on a stone with no real power to stop, I took brake booster to brake mechanic he said booster is fine , it's a vacuum prob... I'm of the view that the booster is stuffed and have been misled. with four spot callipers on the front it should stop on a five cent bit

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