How do you know if your carb is too small ?

[87BlazeLS]

Hey, Just wondering - how do you know if the carb on your engine is too small ?

I have a 350 GM crate motor (290 h.p) EB 600 EB RPM intake. I purchased the calibration kit for the carb and a rebuild kit.
So far I have found that the carb had the OEM components. I made a swap to the larger metering rods and pink spring combo.
This helped the motor alot as far as hesitation goes. Still it had a little bit of stumble at part throttle.
changed to the orange springs and it got worse, Changed to the silver springs and it is much better. The best overall selection for far. Now the idle mixture was set to a variety of settings= 1 1/4 - 1 1/2 - 2 - 2 1/2 and now 3 turns out.

Seems this is where the motor wants to run right.

I do know that the GM specs for this motor called for a 670 cfm carb. All my stuff is set up for Edelbrock

I did the carb chart for my motor and it comes out to like 590 cfm. It is stock from GM except for the headers.

Would going to a larger carb help ? And what brand would work with my Current EB linkages ?

87BlazeLS

 

[MightyCarlo86]

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[Jshock]

Check your exhaust output temperatures. If the temp is way too high your not delivering enough fuel. I had the same issues wih an EB 600 had to go to a 750. Using orange springs right now.

 

[FE3X CLONE]

Hook a vacuum gauge up to manifold vacuum. Under WOT you should have 0" of vacuum. Anything more than that and its possible the carb is a restriction.

 

[79MaliCrazz]

I have a Holley 650 double pump on my 350 it runs almost like if I had fuel injection.But I had a tuner that is well known for tuning carbs do it.I would suggest finding someone who knows a lot about tuning carbs.It will safe you a lot of headaches thinking if its right or good enough.

 

[Doug213xrj]

The motor will stop pull at a lower RPM . A 350 should have no problems being shifted a 5000 to 5500 RPM. I think 600 CFM is to small to run at that RPM. Try a 750 Edelbrock carburetor. My 600 Holley couldnt keep up with my 305 H/O.


Doug

 

[87BlazeLS]

Thanks all, I have had some reservations about this carb. It seems to have a good strong pull off the line and as long
as your in the gas. At running temp, Idle is good and smooth. Just above idle is where the motor wants to jump around in the frame. (shake just a bit) I moved the idle mixture out until this stopped ( now 3 turns out)

Cold starting is good Choke seems to work correctly but alot of gas fumes. Timing is set at 10 Degrees BTDC
30 degrees all in @ 3000.

After warm up shut it off and restart is sometimes difficult. It acts like it's flooded. Seems like it needs a half pedal
to get going again.

Blaze

 

[jrm81bu]

Might be an issue with heat in the carb. You could try running a wood or phenolic spacer to keep it from boiling fuel.

 

[Bar50]

I always ended up tuning most of my 600 cfm Edelbrock carbs with the kit for the 750.....
The big thing is patience and only changing one element at a time. Focus on power valves springs first, then to the range of metering rods then to jets if you see an improvement. Some of them seem to have an off idle stumble for me. Make sure your hot start is not a timing or actual heat soaked starter.

 

[Mikes84GP]

Open the hood and have a woman take a look at it. If she looks down, points and laughs- and you hear "Awww, it's so cute!", then that would be a good indication that your "carb" is too small.

Okay, now that I got that out of my system-

Are you running a 1406 with electric choke? This is what I'm currently running and I've been tinkering with part throttle acceleration for a few months now. I've richened the light throttle cruise, but I still have a bog before the rods step up to the power circuit. I played with the step-up springs and the silver worked best for me so far. The next time I get a warm day I am going to go with a larger primary jet and go another stage richer on the cruise circuit. I think I'm 2.5 to 3 turns out on the mixture screws and I also have hot start issues. My hope is that with the jet size increase I can turn in the mixture screws and cure that problem.