possible carb problem, or vaccuum? - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

LinkBack Thread Tools Display Modes
post #1 of 12 (permalink) Old Dec 1st, 00, 11:57 AM Thread Starter
Join Date: Nov 2000
Location: olathe, kansas, johnson
Posts: 1

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).]
ahsum68rs is offline  
Sponsored Links
post #2 of 12 (permalink) Old Dec 1st, 00, 03:23 PM
David Pozzi
davidpozzi's Avatar
Join Date: Nov 1999
Location: Central California, USA
Posts: 10,125

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.

Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

[This message has been edited by davidpozzi (edited 12-01-2000).]
davidpozzi is offline  
post #3 of 12 (permalink) Old Dec 1st, 00, 03:23 PM
Tech Team
Join Date: Aug 2000
Posts: 63

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.
wrench turner is offline  
post #4 of 12 (permalink) Old Dec 2nd, 00, 01:51 AM
DOUG G's Avatar
Join Date: Mar 1999
Location: Maryland, USA
Posts: 19,629
Send a message via MSN to DOUG G

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.

My '68 Camaro
Doug G.
68 Camaro
406 ci.
DOUG G is offline  
post #5 of 12 (permalink) Old Dec 4th, 00, 07:39 AM
Senior Tech
Codi's Avatar
Join Date: Nov 2000
Location: Kettering Ohio
Posts: 3,165

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.
Codi is offline  
post #6 of 12 (permalink) Old Dec 6th, 00, 09:16 AM
Join Date: Dec 2000
Location: Chandler, AZ, USA
Posts: 5

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.

FoMoCo is offline  
post #7 of 12 (permalink) Old Dec 6th, 00, 10:31 AM
Join Date: Dec 2000
Posts: 4

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.
Z-head is offline  
post #8 of 12 (permalink) Old Dec 6th, 00, 11:10 AM
Join Date: Dec 2000
Location: Chandler, AZ, USA
Posts: 5

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)

Without the Camaro the Mustang would be boring... Without the Mustang the Camaro would be boring...

[This message has been edited by FoMoCo (edited 12-06-2000).]
FoMoCo is offline  
post #9 of 12 (permalink) Old Dec 6th, 00, 07:29 PM
Senior Tech
Join Date: Aug 2000
Location: Ft Worth, Tx USA
Posts: 288

Also be sure the choke don't have a problem.

lnjstreetrods is offline  
post #10 of 12 (permalink) Old Dec 7th, 00, 08:07 AM
Join Date: Dec 2000
Posts: 4

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.
Z-head is offline  
post #11 of 12 (permalink) Old Dec 7th, 00, 01:07 PM
Join Date: Dec 2000
Location: Chandler, AZ, USA
Posts: 5
Red face

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!

Without the Camaro the Mustang would be boring... Without the Mustang the Camaro would be boring...
FoMoCo is offline  
post #12 of 12 (permalink) Old Dec 7th, 00, 06:05 PM
Tech Team
Join Date: Oct 2000
Location: Glenwood,Ut U.S.A
Posts: 90
Red face

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
Marky_24 is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome