possible carb problem, or vaccuum? - Team Camaro Tech
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post #1 of 12 (permalink) Old Dec 1st, 00, 11:57 AM Thread Starter
 
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i have '68rs 327 bored .060 with a brand new holley 750 that was put on about a year ago. about two months ago, the car started running badly after getting on it. timing doesn't help, car smokes black out the exhaust, and pulling out the spark plugs didn't show one bad cylinder to pick on. the car runs better at high rpm's, but not near the power it typically has. a friend suggest that the 750 may have a blown power valve, please help. could it also be a vaccuum problem, or what. i am looking to find the quickest way possible to get my poor baby out of the garage one last time b4 winter hits hard. i really miss driving my 68!!! Another friend has suggested maybe the fuel pump might be bad, 'cause the glass fuel filter is empty and has been sitting for a month. Another suggests looking at the cam on the distributer, and another suggests spraying carb cleaner around the manifold to check for vaccuum leaks. please help, i want to get it running today! okay, since i have now replaced the fuel pump, and sparayed the eyther around the manifold and carb, still nothing. i guess that i am going to have to rebuild the carb, or adjust the fuel idler mixture. i was just avoiding that because i haven't done that before.

[This message has been edited by ahsum68rs (edited 12-02-2000).]

[This message has been edited by ahsum68rs (edited 12-12-2000).]
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post #2 of 12 (permalink) Old Dec 1st, 00, 03:23 PM
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You could have a bad power valve, plugged air bleed, or dirt or fuel residue in the passeges.
I really doubt it's the power valve since the carb is so new.
The newer carbs are protected from blow out by a check valve.
Even the older carbs are not blown that easily.
Fuel can dry out in the bowl and leave deposits that can wash into the metering block.

I'd suggest removing the idle mixture screws and squirting carb cleaner in there. Then squirt carb cleaner on the air bleeds just inside the air horn. Do the primary and secondary air bleeds.

If it doesn't run better, check the float levels and if they are all right, you may have to remove the carb and blow it out.
Make shure the ignition is not the problem.
The black smoke is a tip off to carb richness, though.
David

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[This message has been edited by davidpozzi (edited 12-01-2000).]
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post #3 of 12 (permalink) Old Dec 1st, 00, 03:23 PM
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Black smoke is a sign the motor is running rich. Is your air cleaner good? Check your fuel/air mixture setting on carb. Also a bottle of carb cleaner in the gas tank wouldnt hurt.
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post #4 of 12 (permalink) Old Dec 2nd, 00, 01:51 AM
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sounds like your friend was right blown power valve or maybe a bad gasket or even a needle and seat/ float problem....get a rebuild kit and check it out.better to be safe than sorry.

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post #5 of 12 (permalink) Old Dec 4th, 00, 07:39 AM
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Jim
 
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I'd bet on a blown power valve also. The black smoke says it's to rich. Also check for bad gasgets between teh bowls and plates. These can also cause problems and Hollys can bend for no reason.
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post #6 of 12 (permalink) Old Dec 6th, 00, 09:16 AM
 
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Ill put my money on blown power valve. Ive seen enough holleys blow them. All it takes is one good back-fire and youve got yer black smoke and crappy off idle power.

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post #7 of 12 (permalink) Old Dec 6th, 00, 10:31 AM
 
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ahsum68rs
I'm going through the same problem right now. i have a 1982 Z with a 350 and a Holley 650. I was leaving a friends house and it backfired. I made it home (barely) but the vacuum is way down like around 3-5in in drive. I replaced the power valve with no success. if anyone can help I would appreciate it.
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post #8 of 12 (permalink) Old Dec 6th, 00, 11:10 AM
 
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z head you may want to check for a open vacuum fitting, a backfire could pop off a vacuum connection and that would give you your vacuum drop and bad idle/performance.

If you cant find any obvious open sources, then try systematically blocking all manifold and carb vacuum ports until (hopefully) you find the culprit.

(just a theory)

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[This message has been edited by FoMoCo (edited 12-06-2000).]
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post #9 of 12 (permalink) Old Dec 6th, 00, 07:29 PM
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Also be sure the choke don't have a problem.

Larry
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post #10 of 12 (permalink) Old Dec 7th, 00, 08:07 AM
 
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Well here is the story, the carb backfired and then it ran real rough, low vacuum. I got home and checked the timing, it was right on. The next day, I started it up and it ran (barely) with low vacuum 3-5in in gear. I sprayed carb cleaner down the throat and the vacuum jumped up to 11-13in. I then took off the carb and put a new power valve in. When putting it back together I must have tightened down the accelertor screw too much (the red spring). I bolted it back on & it would not start, due to the flooding. When I figured that out, I fixed the A/P screws and tried again. Now there was a bunch of gas in my oil, when the car started up I was blowing black smoke & no vacuum. I haven't touched it since. I changed the oil (came out like water). Any help would be great. I'm getting to my wits end.
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post #11 of 12 (permalink) Old Dec 7th, 00, 01:07 PM
 
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Gas in your oil??? Yikes! Maybe you blew a chunk out of your intake manifold gasket, or maybe the manifold itself ( )... Seriously that doesnt sound too good.

Do a Compression check first. If the compression checks out ok then your valvetrain /piston rings/ cylinders are ok. Also get the car to run and place your hand over the carb airhorn to reduce the air intake. If the idle raises then youve got an intake leak somewhere. (find it and fix it) If it immediately dies you are too rich, (power valve, jets, idle mix, accel pump, etc, and if it slowly begins to stumble then die you are close to where you need to be mixture wise.

The whole fuel in oil thing sounds a bit extreme to me. So id say you need to remove your fuel pump and check it out. You may have blown a pump seal in the fuel pump, thusly dumping gas into your crankcase. If you didnt wash out your bearings you will at least have a very clean engine!!

Good Luck!

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post #12 of 12 (permalink) Old Dec 7th, 00, 06:05 PM
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my friend had the same thing with his 67, stumbling at low speeds, to fix it i just adjusted his idle fuel/mixture and adjusted his points to the right setting and ran just fine
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