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05-06-2003, 09:52 PM
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#1 (permalink)
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Join Date: Oct 2001 Location: edmonton, Canada
Posts: 536
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off topic carb problems...
not really my forte as carbs more and more get phased out of existence.. on my car last week i started to get a miss only at idle, off idle still has full power and performance... i hooked it up to the scope and all 4 right side cyl's have no cyl balance decrease..left side has 18% also right side fuel mixture has no effect all the way in or all the way out...
currently 14 in vac
73 buick 350 4bbl carb
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05-06-2003, 11:40 PM
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#2 (permalink)
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Join Date: Oct 2001 Location: Clovis, CA
Posts: 2,481
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I think the mixture screws are "crossed over" on that manifold (right screw feeds left cyls, etc.)
Check for vacuum leak at driver's side throttle shaft bushing. Squirt some oil right on the shaft with engine running. Does it smoke when you do that? (have sombody watch the tailpipe while you do it.) Also, wiggle the shaft around (without turning it) on the driver's side end & listen for changes in idle speed.
If that doesn't tell you anything, check manifold gasket on left. Oil squirt test can show a blown gasket sometimes too.
To check for blown head gasket, look for bubbles in radiator coolant with cap off & engine running. Sometimes they are real small & you can't see them. If you hold a smog "sniffer" over the radiator opening, it can smell exhaust/fuel from a blown head gasket.
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05-07-2003, 01:43 AM
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#3 (permalink)
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Join Date: Oct 2001 Location: edmonton, Canada
Posts: 536
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hey caddmann, i didnt use oil, however i have checked for leaks in all the areas you mention with carb clean... one buddy over the phone asked if my brake boooster is leaking, which it is , but has been for 3 years (small barely audible, and doesnt make for any stumble during application....another said to check my 4 barrels. as i do like to kick em in when i get on the hwy, closed all the way plugs look normal (always have been a little rich , choke pull off doesnt quite do the trick right on those colder mornings .. wire resistance is good , cap and rotor also... this all started on a rainy afternoon with a short start up and straight on to highway for a 1/2 hour journey.. it was there the next startup and i've been chasing it since..i'll look further into the head gasket possibility, thx caddmann
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05-07-2003, 07:39 AM
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#4 (permalink)
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Join Date: Jun 2002 Location: San Antonio Texas
Posts: 714
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Loosen your carb mounting bolts and retighten in x fashion. They can loosen by age. 20 lbs torque all you need.
\o/ Billy
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05-07-2003, 08:31 AM
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#5 (permalink)
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Join Date: Apr 2003 Location: Under the bridge
Posts: 96
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If it only stumbles at idle, I would think its a vacuum leak. But, I would check the fuel pump pressure. The reference to rainy weather leads me to suspect the dist. cap. It may have a hairline crack.
Tarp
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05-07-2003, 09:49 AM
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#6 (permalink)
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Join Date: Oct 2001 Location: Uh, Oregon . . . . y
Posts: 1,441
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I'm looking at having my carb rebuilt on my F150 right now!  I have similar problems and they started out minor and now have become very pronounced.
I took it into the garage and after examining what's going on, was informed the power valve is shot. 
It's going to cost me $200 to get the carb rebuilt and replace the #55's with #52's. (Have to find some way to save on gas! )
It was either this, or rebuild and re-install the Holley 4 barrel, I took off a few years ago. 
Note -- 5.8(M)L that's been bored out! 
Harder
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05-07-2003, 08:30 PM
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#7 (permalink)
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Join Date: Jun 2002 Location: mInN3$0t@
Posts: 1,303
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Sounds like a vacuum leak to me also. If it is lean at idle, you could be seeing misfires from lack of fuel in the unbalanced cyliner bank ( or not enough for proper combustion ).
__________________
do it right, do it yourself. If that doesn't work, prepare to pay for your mistakes.
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05-07-2003, 09:57 PM
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#8 (permalink)
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Join Date: Oct 2001 Location: Clovis, CA
Posts: 2,481
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Yank that brake booster hose off the manifold vacuum port & plug the port good. Does this affect idle speed/quality?
Leaky booster/hose can lead to burnt valves. Bad news.
Problems that start in wet weather almost always relate to high tension circuits. Particularly cap, condenser & wires, but also coil problems can show up. Usually a faulty coil causes no-start or high-speed miss, but it's easy to rule out by swapping in another coil on some jumper wires. No need to remove old one just for that test, unless it proves bad.
Vaccuum advance hose/diaphragm is another common source of leaks.
If electronic ignition model, check for moisture/corrossion in the wiring harness conectors.
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05-07-2003, 10:19 PM
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#9 (permalink)
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Join Date: Oct 2001 Location: edmonton, Canada
Posts: 536
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thx for the suggestions, i didnt get a chance to look at it today, i hope to tomorrow.. btw caddmann it still has points and condensor lol...
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05-10-2003, 11:13 PM
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#10 (permalink)
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Join Date: Oct 2001 Location: edmonton, Canada
Posts: 536
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update: did the intake manifold gasket , problem still there...
the engine is sealed i cant understand. still problem at idle..
has to be the idle circuit in the carb.. i took the top off and the emersion tubes are still attached..
cyl balance at 2000 rpm is 7% all 8 cyl's
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