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carb CFM

  
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carb CFM

 
jhodson jhodson
New User | Posts: 3 | Joined: 11/12
Posted: 11/10/12
01:48 PM

I have 350 rc vortec with LT4 cam with 2-4s w/600 cfm carbs it runs terrible on back carb 2 barrel, I put a 750 cfm on the back and it runs perfect why??????  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 11/10/12
04:41 PM

Jhodson welcome to CHP:

I'm guessing you have 1200 cfm with the 2X600. Then you install 600 plus 750 and you have 1350cfm. Is that correct?

1.I would check the power valve on that carb it may be leaking.
2.Check the float level
3.Is the needle and seat leaking?
4.How much fuel pressure are you running?
If you are not using Viton Needle and seats, thats what you want..110 Viton needle and seats. High pressures make cheap ones leak.(Like in rebuild kits.

Did you try for a HA,HA putting that carb in the front and see what happens?

How are the mounted? Front to back or sideways?

Do the 600's still have the vacuum secondaries still hooked up that's really a must for a street application.?

The trouble carb may have an internal fuel leak...

Check the vacuum on your intake. THIS IS ONLY AN EXAMPLE:If you have 14inches of vacuum you need a 7.0 power valve.. If 16 inches of vacuum you need an 8.0 power valve, and so on.

Bob  

jhodson jhodson
New User | Posts: 3 | Joined: 11/12
Posted: 11/11/12
09:02 AM

Everything checks out right. It runs perfect when you open throttle up, but when cruising at 60 mph at 1600 rpm on the front 2 of the back carb it isn't getting enough air,with the 600, put the 750 on and it run perfect.  fuel pressure 7#,carbs swapped, etc  

68scott385 68scott385
Guru | Posts: 1990 | Joined: 10/09
Posted: 11/11/12
09:28 AM

have you check throttle linkage adjustment...to make sure both carbs are open the throttle blades at the same time and the same rate  
68scott385 68scott385 68scott385

jhodson jhodson
New User | Posts: 3 | Joined: 11/12
Posted: 11/11/12
01:11 PM

Yes,linkage is set right, but what i'm saying is when i'm on the 2 barrel before anything else comes open is where the roblem is,w/600 runs rough,fuel is right air is not enough, w/750 fuel is right air is enough. it just seems like a lot of cfm for 350?  

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 11/11/12
01:48 PM

If it's lean then your going to have to get some air to that carb.

Just something to look at and forget the carb problem for a minute

If you are usine a vauum advance distributor, it may not be comeing in when you need it at 1600RPM. Its sometime hard to duplicate without a load on the engine. But check the advance. 12* to 16* as base. Then 32* total at 2000RPM try that setup. If you have different springs go to a little lighter set of springs.
It may not be a carb problem at all...

Bob  

Dave632 Dave632
Addict | Posts: 2218 | Joined: 07/08
Posted: 11/11/12
04:01 PM

I always ran my dual quads with the front barrels of both carbs working together.
I never had any trouble running them that way. I had about 4 different dual carb setups that I ran. I did have trouble with idle circuits in those setups having to drill holes in my throttle plates to cure those problems.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

76Skylark 76Skylark
Guru | Posts: 853 | Joined: 12/11
Posted: 11/11/12
05:35 PM

It sounded like you run on the front carb and use the second as a progressive application but they need to be Identical and the vacuum seconds take care of off Idle. check the basics like throttle blade opening and the simple stuff don't be afraid to just stop and start over on adjustments. when we raced Corvairs in the 60's(4 carbs) we used a  UNI-SYN, it sat above the carb and used a rising ball in a tube to adjust airflow they work amazinely well.with Two 600's you don't have an airflow problem,something has gotten out of adjustment... timing or carb.  

skyeking skyeking
Addict | Posts: 2738 | Joined: 08/09
Posted: 11/12/12
04:17 PM

Hi there,
What Inlet manifold are you using???.
Is a dual plane or a 360*.
Yours sounds like an interesting drama..
If it works as is then use it..Practical
is always better than theory....Skyeking..  
skyeking

pepsi1 pepsi1
Guru | Posts: 1718 | Joined: 09/11
Posted: 11/12/12
07:02 PM

Dave:
When you run them side by side thats whats happens. I asked him which way they were set=up but he never answered me as to which way he ran them. Didn't you run 3 stages of Juice with them?

  I ran mine side by side carbs and once I set them up I left them alone. I had to run 7* angle plates under them.
  Like I said I duplicated Grumpy's old 331 Pro-Stock engine. I wanted to run the Nostalgic tour.
  Even with the 2 660's then leaned out when I started to bring up the RPM. It wasn't the Cam coming either it was way below that...

Bob  

skyeking skyeking
Addict | Posts: 2738 | Joined: 08/09
Posted: 11/13/12
03:59 PM

Hi there,
Smokey Yunick redesigned the bowls on the Holleys
to fit the early 2x4 Edelbrock manifolds.
 That is why he was a  "Master of the Game" .  
skyeking

Dave632 Dave632
Addict | Posts: 2218 | Joined: 07/08
Posted: 11/15/12
06:21 PM

I would think the front cylinders would starve for fuel if you are just running it on the back 2 barrels. I don't know of anyone who has run 2 4s that way. Remember air can make turns a lot easier than fuel, even atomized fuel. You want to run the front 2 barrels of BOTH carbs to even out your distribution.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

skyeking skyeking
Addict | Posts: 2738 | Joined: 08/09
Posted: 11/16/12
04:01 PM

A photo would be a great help.
This is a guessing situation
which could end up a tragic mess.  
skyeking