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-   -   carb stumble under medium accelation (http://www.hotrodders.com/forum/carb-stumble-under-medium-accelation-165968.html)

hatrecide 10-01-2009 02:47 AM

carb stumble under medium accelation
 
i have a 93 mustang 408w, 790 custom 4150, .576 lift 306 duration cam, 4.10 full spool, fully manual c4 with 3800 stall. stumbles under medium acceleration i can get by the stumble if a feather the throttle and some times will die when switching from neutral to 1st the carb has 40 squirters front and back. 3.5 power valve in front block off in back. pink cam on front and back, 70 jets in front 80s in back car will idle all day just has a few bugs to be worked out any ideas will be appreciated

DoubleVision 10-01-2009 05:10 AM

Have you checked the pump shot? It`s supposed to give it a shot the very instant you move the throttle. Sometimes they can have a dead spot and a bog is the result. You may also want to check the pump cam is in the correct position. In the past when I had a bad pump shot it worked if you very slowly moved the throttle, but if you did so quickly it bogged. I checked the pump there after and found it had a hole in it.

hatrecide 10-01-2009 11:32 AM

i noticed today that when i moved the throttle slow the fuel came out immediately and drips one or two drips with a pause in the middle, when i move the throttle quickly it sprays immediately then a constant spray till open all the way. the cam is in position one

dawg 10-01-2009 11:45 AM

try a cam with a steeper profile.
adjust the pump arm lever at wide open throttle with approx .020 play between arm and adjuster.
once done return to idle position.
there should be no play at all between lever and adjuster.
any movement of throttle the gas should squirt not drip.
if you still have bog then the adjuster spring is weak and best wy to fix is to bent the arm a bit or get a better spring.
or get a higher capacity pump kit.
usually called a REO pump.
look here:
http://books.google.com/books?id=Cly...20pump&f=false

hatrecide 10-01-2009 11:53 PM

could those adjustments fix the car dieing when switching to a gear or is that something different

cobalt327 10-02-2009 12:56 AM

If you are using vacuum advance, be sure to supply the vac. from a manifold (not ported) vac. source.

The engine may also want more initial timing, as well.

dawg 10-02-2009 04:32 AM

a huge vacum leak would cause car to stall out when putting in gear.
if you got a power brake booster disconnect and plug vacum line if it still runs when shifting into gear then diaphram in the booster is blown.
also in automatics if the modulator is blown youll get same symptoms.

sqzbox 10-02-2009 06:54 AM

What kind of intake do you have? Any spacer under the carb? Could be a velocity thing in the plenum. There's also a problem called reversion. With a high lift, long duration cam, when the cylinders are getting more than enough air, the pressure builds up to the plenum and will try to spit excess air and fuel back through the carb resulting in a md-range stumble. Check the under side of the air cleaner lid after a hard run for evidence of fuel on it.
I'm old enough that I can't remember how to correct it :( guess I'll have to read up on it again if I can find the info. :D

hatrecide 10-02-2009 10:55 AM

ill try some of these idea tomorrow because of weather conditions, but the brake booster is brand new like 1 month old, the intake is a edelbrock supervictor 9.2 in between the carb and the manifold is a nitrous plate. it seems like it idels fine then i put it in 1st it die i restart it then it is fine after that

sqzbox 10-02-2009 02:26 PM

Sounds like a mopar! :D

dawg 10-02-2009 05:03 PM

Quote:

Originally Posted by hatrecide
ill try some of these idea tomorrow because of weather conditions, but the brake booster is brand new like 1 month old, the intake is a edelbrock supervictor 9.2 in between the carb and the manifold is a nitrous plate. it seems like it idels fine then i put it in 1st it die i restart it then it is fine after that

I went through 2 NEW boosters before i got one that didnt leak.
In this day and age NEW doesnt mean its good!

cobalt327 10-02-2009 08:31 PM

Quote:

Originally Posted by hatrecide
the intake is a edelbrock supervictor

That single plane intake will require more fuel than 70's, most likely. What are the plugs saying?

hatrecide 10-04-2009 04:16 PM

ok i tried a few options i got a reo pump brown cam position 2 and it seems like the stumbles gone, the car idles 2000 in neutral/park and when i switch to a gear it doesnt stay running almost like its loading up. it seems like everytime i rebuild the carb new gaskets/power valve the problem goes away but slowly returns until it doesnt run in any gear park or neutral.

hatrecide 10-05-2009 09:47 PM

could it be that the power valve is to small and possibly being sucked open the whole time and flooding the engine i dont have a vacuum gauge but i was thinking big cam less vacuum so i got a 3.5 in there

cobalt327 10-06-2009 05:48 AM

Quote:

Originally Posted by hatrecide
everytime i rebuild the carb new gaskets/power valve the problem goes away but slowly returns

Check the metering block/body for warpage.


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