Previous Thread
Next Thread
Print Thread
Runs better with vacuum leak #1981022
01/01/16 01:20 PM
01/01/16 01:20 PM
Joined: Jul 2007
Posts: 2,554
Maryland
wally426ci Offline OP
master
wally426ci  Offline OP
master

Joined: Jul 2007
Posts: 2,554
Maryland
71 challenger driving me crazy with nothing but problems this year. Got the charging issue figured out then had start issues. New distributor runs fine but I was checking vacuum for timing at the brake booster. When I pull the cap it smooths out.

I've never noticed that before and trying to figure out the issue. Could the carb be too rich? New plugs helped previous hard start and smoothed it out but I just want to drive this friggin car!

Re: Runs better with vacuum leak [Re: wally426ci] #1981040
01/01/16 01:50 PM
01/01/16 01:50 PM
Joined: Nov 2006
Posts: 1,074
Manitoba Canada
67autocross Offline
super stock
67autocross  Offline
super stock

Joined: Nov 2006
Posts: 1,074
Manitoba Canada
I had a late 70's Chevy 4x4 that ran better with a leak, drove it like that for years. I'm sure someone here will have some ideas on how to fix your car ....but if it runs with the leak and you really just want to drive close the hood and go.


A new iron curtain drawn across the 49th parallel
Re: Runs better with vacuum leak [Re: wally426ci] #1981158
01/01/16 03:54 PM
01/01/16 03:54 PM
Joined: Dec 2003
Posts: 4,951
northwest USA
N
NANKET Offline
master
NANKET  Offline
master
N

Joined: Dec 2003
Posts: 4,951
northwest USA
OK so it idles better with a vacuum leak, how about cruising down the road? It may be too lean and damage things. Is you vacuum hose coming off carb base affecting all 8 cylinders, or just the #8 intake runner affecting only one cylinder?

What do you have for a carb, camshaft, compression ratio, leak down numbers, tell us about the whole engine.

Is you power valve bad, cam to big, idle speed too low, fuel pressure too high, ignition system all goofed up? here we go, the snowball is picking up speed.

Re: Runs better with vacuum leak [Re: wally426ci] #1981170
01/01/16 04:07 PM
01/01/16 04:07 PM
Joined: Jul 2007
Posts: 2,554
Maryland
wally426ci Offline OP
master
wally426ci  Offline OP
master

Joined: Jul 2007
Posts: 2,554
Maryland
Haha thank you. I will touch base in a bit, installing trim in basement.

Re: Runs better with vacuum leak [Re: wally426ci] #1981199
01/01/16 04:45 PM
01/01/16 04:45 PM
Joined: Aug 2003
Posts: 43,127
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 43,127
Bend,OR USA
It sounds like you may have a issue of hot fuel boiling over into the motor when you shut it off, that will make them hard to start work You will have to grind on the starter and hold the throttle wide open to get it to start and run if that is the problem. I've had that problem recently with todays crud they call gasoline runaway One way to verify that problem is to remove the air cleaner after driving it far enough to get the motor up to temps. and heat soak the engine compartment and watch for fuel mist coming out of the top of the carb. from the boiling fuel. Have you tried leaning the idle mixture screws down enough to get the motor to sart to die? If not I run my motors as lean as possible on the idle circuits, adjust the screws slowly inwards. closing them, to make it start to slow down on the idle RPM and then add 1/8 to 1/4 out to make it richer richer scope thumbs A leaner motor is way happier than a rich or fat motor will be twocents

Last edited by Cab_Burge; 01/01/16 04:47 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Runs better with vacuum leak [Re: wally426ci] #1981292
01/01/16 06:38 PM
01/01/16 06:38 PM
Joined: Jan 2003
Posts: 15,315
Omaha Ne
T
TJP Offline
I Live Here
TJP  Offline
I Live Here
T

Joined: Jan 2003
Posts: 15,315
Omaha Ne
Originally Posted By wally426ci
New distributor runs fine but I was checking vacuum for timing at the brake booster. When I pull the cap it smooths out.

I've never noticed that before
and trying to figure out the issue. Could the carb be too rich? New plugs helped previous hard start and smoothed it out but I just want to drive this friggin car!


If you are running the vacuum advance, AND depending on where it is hooked up ( IE: manifold or ported)_you may have too much timing at idle thereby creating a misfire. The distributor change may have impacted this. Creating a large enough vacuum leak would lower the manifold vacuum there by retarding the timing

Other wise I would go for thee mixture adjustment. twocents

Re: Runs better with vacuum leak [Re: wally426ci] #1981314
01/01/16 07:01 PM
01/01/16 07:01 PM
Joined: Dec 2003
Posts: 4,951
northwest USA
N
NANKET Offline
master
NANKET  Offline
master
N

Joined: Dec 2003
Posts: 4,951
northwest USA
We know nothing of his combination. Any advise is just a WAGuess at this stage.

Re: Runs better with vacuum leak [Re: wally426ci] #1981315
01/01/16 07:04 PM
01/01/16 07:04 PM
Joined: Jul 2007
Posts: 2,554
Maryland
wally426ci Offline OP
master
wally426ci  Offline OP
master

Joined: Jul 2007
Posts: 2,554
Maryland
I do have a miss that I am getting to the bottom of. At the moment, I need to get rid of the old fuel and start fresh.

I have a stroked 360, .30 over, eagle crank and rods with Keith black pistons. I need to find my cam card but I believe I ended up around 10 or 9:1

750 edelbrock

Cr ran fine for me but I got into my charging problem, then the starting problem which is fixed. New plugs, old were fairly black.

My fault for the car sitting so much but that's what happens when your house was built right after the civil war....

Re: Runs better with vacuum leak [Re: wally426ci] #1982116
01/02/16 04:54 PM
01/02/16 04:54 PM
Joined: Dec 2003
Posts: 4,951
northwest USA
N
NANKET Offline
master
NANKET  Offline
master
N

Joined: Dec 2003
Posts: 4,951
northwest USA
Old fuel will make it difficult to solve anything. How much idle,vacuum, at what RPM does it idle hot? What coil and ignition?

Re: Runs better with vacuum leak [Re: wally426ci] #1982287
01/02/16 10:14 PM
01/02/16 10:14 PM
Joined: Jul 2007
Posts: 2,554
Maryland
wally426ci Offline OP
master
wally426ci  Offline OP
master

Joined: Jul 2007
Posts: 2,554
Maryland
Yes, fuel is my first fix. Car ran great before the charging issues. Stock coil, and I have a known good electronics box on it. Low,idle around 900 and it was bouncing around 15 vac







Powered by UBB.threads™ PHP Forum Software 7.7.1