Carb Runs Rich Until I Pull Of The Vacum Line!!

[PewterLS1]

Here is what I have:

306 Rotating system (DSS blueprinted and balanced system .030
flycut high comp piston, crank shaft rods, pilot bearing, Federal
mogual bearings. Static compression is around 11.20 to 1
Race prepped block, bored, deck aligned, magnafluxed, re-honed, enlarged oil passages.
Main cap support system ( DSS )
Comp Cams Competition Roller camshaft ( #35-522-8 351w, grind# fw xe282hr-12 hyd )
Edelbrock timing gears set
Trick Flow Chromoly Pushrods (6.550 )
Roller Lifters ( Crane cams hyd lifters )
Roller rockers ( harlen sharp 1.6 ratio 7/16 stud )
Heads ( Canfield power adder Stage 2 CNC match ported)
Radiator ( 3 row aluminum core )
Water pump ( Edelbrock aluminum high vol )
Fuel pump ( Holley Red )
Fuel Regulator 7 PSI (Holly)
Fuel duel feed with pressure gauge
Oil pump (slp high volume )
Carb ( Holley 650 cfm double pumper 4150 style 4777S )
Manifold (Edelbrock Victor junior single plain )
17” Flexilite fan
14” x 4” air filter ( K&N )
Distributor (MSD Billet)
MSD 6a ignition box and MSD coil
MSD wires
BBK 1 5/8 full length headers
BBK short off road h pipe
Exhaust 2.5” over rear end to 3” outs ( Flowmaster mufflers )

The problem is that when Vacuum line is hooked up it pulls 10lbs of vacuum and runs rich as a pig (16:1) all the way through the power band, even after I set my idle screws and fast idle. When I take my main vacuum line off it jumps to 15 and my A/F goes to 14:1, runs just like it should and the a/f is correct all the way through the power band. The cam was advanced I believe 4 degrees when I installed it. Timing adjustments do nothing, idle mixture screws adjust to ideal vaccum and it still runs rich. Is the cam maybe way off and causing this?

The car has been this way for 2 years because it gets driven twice a year, now i want to drive it on the weekends and take it to the track but it runs too rich.

What could be wrong, my father and I build the motor in our garage and after adjusting my original 800 cfm carb and figuring it was too big i just bought the 650 last week.

This is very frustrating and I would appreciate any help you can give me because its no fun to drive a car that stinks of gas!!

Thanks,
Mike

 

[86bluecobra]

the reason you run leaner with a vacuum leak is because you now have more air entering the engine. By any chance is your air filter clean? or have you jetted the carb for your application? seams wierd that idle screws won't at least get the car to run leaner when idling.

 

[PewterLS1]

the reason you run leaner with a vacuum leak is because you now have more air entering the engine. By any chance is your air filter clean? or have you jetted the carb for your application? seams wierd that idle screws won't at least get the car to run leaner when idling.

My point exactly!! Carb is stock out of the box! I ran it with no air filter for a quick run and it did the same thing at idle and in motion, but the filter is new, car has a scoop and even has the filter top so it has a ram air effect, and that does lean it out a bit on the highway but its still rich.

The way I understand carbs is that even if my jets were wrong it wouldnt effect my idle a/f, is this correct. Also this engine with the canfields should have nooooo problem sucking on some air, why so much fuel at idle?

I thinking maybe the cam is installed wrong and that is why I am having the problem, I was hoping someone could verify this so I can feel good about tearing it down with 1000 miles on it!!!!

 

[jrichker]

Check the float level. If it is too high, the mixture will be too rich.

 

[PewterLS1]

Check the float level. If it is too high, the mixture will be too rich.

Float level is perfect, just below the sight window.

I dont have a PCV hooked up, someone told me this might help, I just have breathers on both valve covers. Could this cause the carb to be rich because a PCV is just a controlled vacuum leak!

Cant believe I didnt think of a PCV, that should help some....autozone opens at 9:30 I think!!!!

 

[PewterLS1]

Ok so I hooked up a PCV and it helped a little but not enough. Today I drilled a hole in my 1" carb spacer and just let it pull in air. Car runs good now, adjusted my idle screws so that I am stoich at idle and when im in the primaries and secondaries its almost rich but still in stoich.

I am still going to tear it down to make sure the cam is advanced properly.

Miike

 

[jrichker]

Where's SBFtech? This would be his opportunity to shine.

I am not the resident carb guy, but older Holley carbs have a power valve that is easily damaged by a backfire. Once the power valve blows, the engine runs rich at idle and cruse. See www.mortec.com/carbs.htm or do a google search on Holley 4150 power valve for more carb help.

 

[PewterLS1]

Where's SBFtech? This would be his opportunity to shine.

I am not the resident carb guy, but older Holley carbs have a power valve that is easily damaged by a backfire. Once the power valve blows, the engine runs rich at idle and cruse. See www.mortec.com/carbs.htm or do a google search on Holley 4150 power valve for more carb help.

This is a new carb so it has the check valve to prevent popping the pover valve on backfire, thank you though!!!

Im still thinking I degreed my cam wrong, tearing it down today. I built this car when I was 16, I wasnt as experienced as I am today, but i was still good

Thanks,
Mike

 

[12sec67]

put the 800cfm carb on and see if it still does it. the smaller carb is going to pull more vacuum then the bigger carb which means the carb will also pull more fuel.

 

[PewterLS1]

put the 800cfm carb on and see if it still does it. the smaller carb is going to pull more vacuum then the bigger carb which means the carb will also pull more fuel.

Thanks for the tip, headed out to the garage now to give it a shot!

I will post back shortly and let you know.

 

[PewterLS1]

Ok i put the 800 back on, got it close to where I want it, jettet it back to stock and I will start adjusting from there.

Thank You Everyone For Your Help.

Mike

 

[jrichker]

put the 800cfm carb on and see if it still does it. the smaller carb is going to pull more vacuum then the bigger carb which means the carb will also pull more fuel.

Wong answer.

The amount of fuel delivered by a carb at off idle & cruse is a function of two things:
1.) airflow through the venturi
2.) size of the main metering jets.

Vacuum at idle as it is measured in the intake manifold has nothing to do with carb size.

 

[Dark Knight]

A couple things to check.. Idle vac, what is it? What power valve? If the the idle vac is low, then the power valve might be opening. Are you checking float level with the car running? Can you kill the engine with the idle mix screws?

 

[PewterLS1]

Just an update guys!!!!

Did a teardown and noticed that i had installed my crankshaft timing gear on the 4 degree retard slot WTF was I thinking!!!!

Set it to zero, got it up and running now, runs tit, nice idle, great accel compared to before. I am going to degree the cam this winter and throw a 125 wet shot on it. Can't play too much now, tracks closed so it gets put away tomorrow.

Thanks for everyones help, I have spent many hours trying different things to get it close to right.

Thanks Again,
Mike

 

[86bluecobra]

LOL i did the same thing on my truck cam by accident. Makes me wonder what i did with the cam in my car. Oh well she is running strong so i'm not worrying about it.

 

[86bluecobra]

The problem is that when Vacuum line is hooked up it pulls 10lbs of vacuum and runs rich as a pig (16:1) all the way through the power band, even after I set my idle screws and fast idle. When I take my main vacuum line off it jumps to 15 and my A/F goes to 14:1, runs just like it should and the a/f is correct all the way through the power band. The cam was advanced I believe 4 degrees when I installed it. Timing adjustments do nothing, idle mixture screws adjust to ideal vaccum and it still runs rich. Is the cam maybe way off and causing this?

Mike

You know that 16 to 1 is a lean condition right? Is this just at and idle?
Do you have a Wide Band o2 sensor? My car runs rich 10 to 1 at WOT.
14.5 to 1 or 15 to 1 is a good AFR for an idle. If you are 16 to 1 right through your rpm range i would say you are not giving it enough fuel. If your AFR is 16 to 1 you don't want nitrous you will melt a piston. Nitrous you want around 12 or 12.5 to 1.

 

[PewterLS1]

You know that 16 to 1 is a lean condition right? Is this just at and idle?
Do you have a Wide Band o2 sensor? My car runs rich 10 to 1 at WOT.
14.5 to 1 or 15 to 1 is a good AFR for an idle. If you are 16 to 1 right through your rpm range i would say you are not giving it enough fuel. If your AFR is 16 to 1 you don't want nitrous you will melt a piston. Nitrous you want around 12 or 12.5 to 1.

Yeah I had my numbers wrong, I was using a cheap O2 sensor reader that only has lights and finally set it by vaccum gauge. I have jetted up and down and that gauge never changes at any rpm, even if it stumbles from too much fuel. I need an acurate wideband but there is no money in the budget for it right now.

I know I am giving it close to the right fuel, my jets are now 76 primary and 91 Secondary, I experimented for a few days (about 25 hours) and this combo ran best.

I think the XE282 might be too much cam for my little 306 with the port matched canfields.

I am running 16 initial and 38 degrees of total timing on 93 and have no ping at all, i am thinking of using the old school "turn it up till it pings, then back it off 2" method, or step down a few octane points on the fuel.

What jet sizes are guys running with this setup I listed in the first post?