Boggs down under hard acceleration.

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  #1  
Old 03-29-03, 08:25 PM
360hp350
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Angry Boggs down under hard acceleration.

I built a pretty healthy 350 about 2 months ago. Here are all the specs. 1972 350 bored .040", 4 bolt mains, stock cast crank cround .010/.010, stock "X" rods, 9.6:1 compression ratio, "041" heads with 2.02/1.60 valves and 64 cc chambers. The cam is a L82 corvette cam with .450" of lift on intake/.461" on exhaust and the duration is 224*. On top of it all I have an Edelbrock RPM Air-Gap which powerband is 1500-6500. And I have a electric choke vac. secondaries 750 edelbrock. Ok finally got that out of the way! Now when I am at a complete stop and push it to the firewall it boggs down real bad sometimes it backfires or almost dies or completely dies. I have tried everything and am getting discouraged. The oil smells a little gassy. Do you guys think some smaller jets might help? Or should I just buy a 650 Holley?? Thanks for all the help I really appreciate it! Sorry about the novel!

-Jake
 
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  #2  
Old 03-30-03, 03:50 AM
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I ran your numbers. For a 350 with a 90% V.E. you would need 547cfm with a redline of 7000rpm. I doubt you engine runs and 90%, but it is always better to have more than you need than less. You have to much carburetor on it, but I think you should be able to make that one work with some tinkering with jets and timing.
If you want to figure you CFM your self use following Calculations.

First Get you Maximum CFM

(CID/2) x (Maximum RPM/1728) = Maximum CFM

Next Figure Your Volumetric Efficiency

Volumetric Efficiency = 5,600 x HP x 100% / (RPM x CID)

Then
(CFM) x (VE)

If you get a VE over 130% on a naturally aspirated motor you more than likely messed up you calculations.
 
  #3  
Old 03-30-03, 05:44 AM
Joe_F
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Make sure no fuel lines are hitting anything or pinched . Does it do it when it's cold, hot, etc?

My vote: Pitch that God awful carburetor you are running and go to warmed over Q-jet. You'll get better throttle response, performance and fuel economy.

A 650 Holley is a waste of money, gasoline and looks butt ugly on a GM vehicle. Stick with the General's parts.

Like an old Pontiac guru said, "Rochester doesn't have to advertise, they sell 5 million carbs a year" (in the heyday).
 
  #4  
Old 03-30-03, 07:59 AM
360hp350
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Check out a picture of my plug there is something wrong because they are black and smell gassy. I don't know what this means but I'd guess it is rich. I have an old Rochester QJet lying around I bolted it on and it did the same thing. If I get time today I might bolt it on again and see what happens. I am going to ask a couple of my buddies if they have a 650 Holley I can borrow and see if that helps. Thanks for the replies!
 
  #5  
Old 03-30-03, 08:02 AM
360hp350
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Ok it didn't ket me post a picture just click this link----->http://www.blazinlow.com/forum/attac...?postid=148914
it actually looks more black than it really is.
 

Last edited by 360hp350; 03-30-03 at 11:04 AM.
  #6  
Old 03-30-03, 08:42 AM
jamoke
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ok i got a ???? are the plugs black or tan hehehehe
i see the pic it looks tan but kinda wet tan is good however we all know wet is not. but in your other post u said they were black.
Im just tryin to paint a picture here
 
  #7  
Old 03-30-03, 11:03 AM
360hp350
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They look black I don't know why the picture made it look tan but they are black. It also floods easily. I am going to buy some different jets and try that before I spend several hundred dollars on a new carb. I have no clue on what size I have or what size I should get!
 
  #8  
Old 03-30-03, 12:29 PM
jamoke
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how long have these carbs been sittin and or the gas tank in that thing for that matter??? and do u have an inline filter to them ??
i know a quadrajet has internal one . but if u r gettin trash in it and it keepin the needle open thus flooding . hard to really say with out it in front of me .
 
  #9  
Old 03-30-03, 03:11 PM
360hp350
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I have a clear inline fuel filter and there isn't any trash in it. It is a 1974 Blazer so I bet there is all sorts of crap in the tank. The carb I have on there now is brand spankin new.
 
  #10  
Old 03-30-03, 03:53 PM
Timorama
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Here are a few more ideas: Check that your vacuum advance is working properly. Check the timing, with the modifications you've made you can't use a factory spec for timing. Try bumping it up 2 degrees at a time until it knocks under hard acceleration, then back it off until the knock stops. If you put in an electronic ignition distributor make sure you've got a full 12 volts going to it. The factory used a resistance wire in older vehicles that originally used a points type ignition. Make sure the carbs you are trying don't leak, or maybe have a sticking power valve. The power valve only opens under full throttle, so if there was any crud in the float bowl it is going to go right through the power valve, possibly hanging it up. Also make sure the float height and drop are set, or it will leak fuel down the venturies. Remember, if you look down the carb with the engine running PLEASE use a mirror and not your face to see what's happening. If you can actually see fuel "dripping" onto the butterflies when it's idling your float is set too high or the needle and seat aren't stopping the fuel from coming in. Your combination of parts sounds good. I also prefer the quadrajet carbs. You should make good bottom end torque and strong midrange power, and nothing beats secondaries the size of beer cans!
 
  #11  
Old 03-30-03, 04:03 PM
jamoke
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well if the filter has no trash and its new carbs
is the choke opening up ??????
 
  #12  
Old 03-30-03, 04:38 PM
Joe_F
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Verify all that's presented here, good advice.

Start with freshly rebuilt carbs, old ones kicking around have rotten parts and tend to be wasted from kicking around.
 
  #13  
Old 03-30-03, 05:34 PM
360hp350
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Q. Is the choke opening up
A. Yes

Q. Is the vaccum advanced working?
A. I unhooked it because I have enough mechanical advance

Q. Check the timing
A. My motor builder said 34* at 2000rpm

Q. Check to make sure 12 volts is going to the dist.
A. Haven't done that yet. The truck is a 1974 Chevy Blazer 4x4

Q. Check the float and power vlave
A. I will have to check the power valve etc.

The distributor has a new control module, new cap and rotor bug, new wires, and new Accel plugs.

Thanks for all the help guys! I adjusted the kickdown today so it is more peppy but that is just because it shifts down now when I goose it.

Just incase you are curious as of what my K5 looks like click here--------> http://www.blazinlow.com/forum/attac...?postid=130612
The tires were my christmas present.
 
  #14  
Old 03-30-03, 05:41 PM
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Make sure your vacuum secondaries are not opening up too soon? You might also try calling the guys at Edelbrock http://www.edelbrock.com/automotive/index.html
 
  #15  
Old 03-30-03, 10:07 PM
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I agree with Stevo, i think you secondarys are not functioning
correctly.
 
  #16  
Old 03-31-03, 11:34 AM
360hp350
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Is there a spring I can change to adjust when they open?
 
  #17  
Old 04-01-03, 01:11 AM
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I should have been more specific. You could change the secondary vacuum spring to adjust how the secondarys act. If that dose not fix it could be your secondarys combined with vacuum created by motor could be causing the fuel that should be atomized for combustion to be used to wet the carburetor. The fix would be to upgrade to 50cc accelerator pump kit. Either way these kinds of problems are always hard to track down, I hope this helps and sorry it took so long.
 
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