Carburetor question

[bradrenea]

I'll start off by posting a little about my setup. I am running a 440ci BBC, with 12.5:1 compression, .595 lift Lunati hydraulic cam, closed chamber rectangle port GM heads, Team G intake, and a Quickfuel 850 Professional Series carburetor. The carb is stock, nothing has been changed.

Here is my problem. When I leave the line the car runs sorta crappy and pops and misses a little bit. At about 6-6500 RPM it will clear up and run smooth. At the same time it clears up, it starts to puff a little black smoke. It does this through all three gears. Best I can tell, it is running lean up until the 6-6500 RPM range and then it starts running a little bit rich for some reason. Has anybody ever had a problem like this? What do I need to change to fix it? Quickfuel's tech guy just told me to start jetting up, but I am afraid by the time I get it jetted right in the lower RPM range it will be WAY too rich above 6 grand.

And by the way, when I say it runs crappy up until that point, it does not run REALLY bad. (8.60 1000 ft/ 3500 lb car) It is just bad enough to notice, and I know it is not right.

Thanks in advance!

[rustbucket]

You may have to send it back and let them tinker with the air bleeds unless you feel comfortable messing with them. Ive had 3 quick fuel carbs and one of them was a pain in the butt, but the other 2 are awesome. I usually talk to Zack @ quick fuel. Hes really helpful.

[sunsation540]

do you know what jets are in it ? what if it is droping a cylinder at lower rpm the black smoke is the loaded up cyl cleaning out. quits poping and stuff when it cleans up that cyl how old are the plugs ? mine did this just felt lazy ran 10.30s3 passes changed plugs just cause and went 9.90s i know it sounds stupid but at that power level you can hardly tell it drops a cyl an 850 without power valves should be around 88-90 78-82 with PV one test bring it up aginst the converter 2-3 times when its cool like 160 just flash it let it fall off the converter and idle it in the shop/ drive pull the plugs then if one is weak this will show up pretty quick what kind of ign,,?

[bradrenea]

The primary jets are 76, the secondarys are 84. The plugs look good, they are almost brand new. I thought I might have a bad one so I changed them with no effect. I have also used an ignigtion analyzer to check the voltage to the plugs and they are all the same.

The ignition is an MSD ProBillet distibutor, MSD 6A box, and 8MM Taylor spiropro wires. It's all brand new. Plugs are Champion RN9YC. Those are what my dad told me to run, he ran them in this particular motor for about thirty years before I got the car from him. He said that's what he always had the best luck with.

I ended up increasing jet size by two front and back, and it ran smoother up to 6 grand. I couldn't really tell much above that. I will have to wait till I can get back to the track to see what the timeslip says.

I know what you mean about not being able to tell you have dropped a cylinder at this power level. I don't know how many times I have done something to the car and taken it for a couple passes up and down the highway by my house and thought there was a huge difference, only to take it to the track and find out it was the same as the last time, or slower!

[bradrenea]

Any more ideas?

[jones_performance]

off the line may be a accel pump issue.

[bradrenea]

I thought about that, but it does it in all three gears. About the time it starts running smooth, its time to shift and it craps out again.

On that subject though, the carb has 30cc pumps front and back. Do you guys think those are big enough? Sorry if it's a dumb question, I have never ran a Holley style carb before. The car had a Predator on when I got it from dad, but had to pitch that due to hood clearance issues when I got the new intake.

[sunsation540]

you pitched the predator but what did it run before ? you could be looking at a worn cam lobe weak valve spring and again the fuel system do you have a vent hose on the top of the fuel vents in the carb,, how close to the hood is the carb?

[bradrenea]

Best time with the Predator was 8.71 /1000 ft. But at the same time I changed the carb I also changed to gapless rings, went with a little smaller cam with a much broader powerband, and got a better intake, and had the converter freshened(slipped so bad the shift light would stay on all the way down the track) . The new intake is a Team G, old one was a Edelbrock Torker (The one with the angled carb flange)

The cam and springs are both new and I have double checked the rockers.

The fuel system consists of dual holley red pumps ran parallel, with 1/2" line, and a System1 inline filter.

I dont have a vent hose on the top of the carb. Are you talking about a piece of hose running between the two with a slit cut in it? I have seen them before, but was not sure what purpose they served. Do I need one?

The top of the air filter has about 3/4 clearance from the hood. It it a 1" drop base, 3" K&N element, with a K&N filter top.

Also, the 8.71 I ran on the old setup was with a 250 shot (average was 8.8x's) , the 8.60 I ran on the new setup was with a 200 shot. And I have only made one nitrous pass on the new setup, second pass I broke a u-joint. So I know the changes made an improvement, now if I can just get it running right.

[sunsation540]

what does it run like off the bottle?

[bradrenea]

9.70's

The problem is worse off the bottle, I am assuming that is because I have not fine tuned the nitrous system yet, and it is too rich, which is helping out the lean condition?

[sunsation540]

jet it the other way on mtr 76 ft 80 rear the nitrous may be trying to clean it up run it down the road and pull a plug to get some idea off the hose you need to fix it N/A first

[bradrenea]

Right, that is the plan, I just could not wait to make at least on pass on the spray!

Back to the carb vent......... Do I need one?

[sunsation540]

it is always a good idea to have a slosh hose on the carb but if you use a air cleaner this may not be needed have you ran it with the air cleaner off sometimes this can pull vacuum on the vent tubes if the filter has to much restriction. make a fuel slosh hose cut 1.5 in out of the center half way through 5/16 line frome one vent to the other..

[Wayne Carroll]

Brad:

OVERLEAN CONDITION
I'm not too sure that you may be running out of fuel by volume - not pressure - but volume.

YOUR RACE CAR
A couple of things make me come to that conclusion. First it is an 8 second car so it really hauls. If you are lean coming out of the light it is because you are against the converter at WOT and under full fuel demand by the time you launch. If you are draining off fuel under full demand and don't have enough fuel in the carburetor when you first release the transbrake. Then the car leaves without fuel in the bowls. Apparently, the fuel level slowly fills again at the top of the gear and gets a little better. You pull the next gear but the same problem starts all over again.

BARRY GRANT - WEBSITE
Go to the website for Barry Grant carburetors and look up the suggested plumbing and fuel requirements links. It will help to tailor what you need for your particular combination. I think that will give you all the best information Anyway, it explains this stuff much better than I can.

Good Luck;

FUEL DELIVERY TEST
Barry Grant will ask you to take the line off as it goes into the carburetor. If it is an 8 second car it should pump one gallon of fuel in to a one gallon tin can (not plastic) in 15 seconds. If it does not you have a volume problem. I doubt that your Holley Red Pumps will meet the test. They are street pumps - go to the Holley website for the best pumps for your application, it will not be the ones you have.

NO NOS
Off the bottle, you would still need 1 gallon in 25 seconds for a 10 second car. And, remember, the demand on a single 4BBl is greater - than 2X4BBl's.

If you don't get the required volume in the time to fill test:

I would remove the Systems I filter - increase lines size from you pumps at least to 9/16 to a fuel log and then 3/8 to each bowl of the carburetor. I would also suggest you have an inlet to your pumps at 5/8 I.D. That is from the tank to the inlet side of your pumps. This may sound big...but, with fuel delivery it can never be too much, you can only err if it is too little. Either way, make it at least one or two sizes bigger than what you have now. Use reducers from smaller to larger lines fittings just to make it easier for test purposes. You will certainly find out if you get a better result. Then do the final system when you can afford big changes. For now, just these tests will do.

FUEL VOLUME INCREASE CHANGES
Remove the Systems I fuel filter. Don't use filters for this test. Use -8 line (3/8 I.D.). Strain the fuel when you put it in your tank. I would split the lines to run one pump to each bowl of your 4BBL Holley. Believe me, it is not overkill. Then run the car with high float settings at about 1/2 way up the sight glass (higher than normal).

VENT HOSE AT CARB VENTS
Put the vent hose on the top of the vents...that is a very good idea. You can run from one to the other vent with the proper i.d. hose and cut a clean slot at the very top. The guys are giving you great advice on that idea. Do it at the track and see another car with the same idea if you want to see how to cut the vent hose.

FUEL STALL
You may have fuel stall if the car leaves hard, so you really should have better pumps so the car doesn't go into a lean condition for that problem either. That can come later when you get better fuel pumps.

5" MINIMUM AIR GAP ABOVE THE CARB
You don't have enough space above the carburetor for a good feed of air. It must be a minimum of 4" above the air horn - preferebly 5" - lose the air filter for test purposes. Just get simple, straightforward and with as variables as possible.

AUTOLITE PLUGS - OR NGK
Change your plugs to the range suitable for racing without NOS to make the tests (about 2 stages colder than street) - don't use Champions - they are very good and work well with a narrow band of performance under constant wide open throttle for the NASCAR and SCA crowd driving their cars in a much different way than drag racers. We are on and off the throttle in burn outs and staging slowly then full blast after a few seconds snap throttle shut to exit the track back to the pits. AUTOLITE and NGK have a broader heat range that is much more suitable for your application.

So, read Barry Grant's website - change a few things I suggest and the website tells you. It is good because you can do all this without spending much money and then go for it!

Let us all know how things turn out. If I'm wrong, at least it was cheap and you didn't have to go broke to get the car better and faster. It will be better and faster.

Finally, don't tell your DAD that I asked you to change the plugs to AUTOLITE or NGK against his advice he may have a fit!..but, you are no longer running the Predator Carburetor - tell him the Holley needs different demands than a "gate type" or door venturi A/F metering induction system. He will understand...I hope.