Vacuum

[Coolio]

I have a Pontiac 400 with 600 Holley carb; Holley red electric fuel pump; nitrous xpress regulator with gauge; and a as far as I know stock 700r4 torque converter. The problem I am having is that the brakes are stiff even when the car is running also I was told that the carb couldn't be adjusted fully an it's not getting enough vacuum to the carb,because the cam is to big(I'm not sure of the exact specs). Bare with me I worded it the best way I could.

 

[foxtrot]

What are you getting for vacuum now? If you are measuring in the 15-20 range, your power brakes should operate just fine and its possible that your booster is bad. Also, could have an issue with the vacuum line to the booster.

 

[84cutspreme]

I added a canister inline with brake booster with check valve

 

[Coolio]

What are you getting for vacuum now? If you are measuring in the 15-20 range, your power brakes should operate just fine and its possible that your booster is bad. Also, could have an issue with the vacuum line to the booster.

Last time I checked it was about 10 not sure what it's at now. Could this prevent the carburetor from getting adjusted properly.

 

[bob64]

One sign that the engine(big cam) isn't producing enough vacuum is when the car is running and you put your foot on brake you'll feel it slowly go to the floor. Feel almost like a brake line leak.

As for adjusting the Carb, yes you need atleast 14psi of vacuum to adjust it properly or it will idle like crap.

You may have to buy a electric vacuum pump, but make sure that you have no other choice there pretty pricey, atleast the one l got was!

 

[bracketchev1221]

10" of vacuum is iffy on a power brake car. I have 10 on my chevelle and the power brakes work ok on the first or second stab, then the pedal becomes rock hard. I have a new power booster and a vacuum can with the check valve siliconed in to prevent leaks. As far as the carburetor and vacuum, you adjust the carburetor to establish highest idle vacuum. As far as the carburetor not being able to be adjusted due to low vacuum I'm not sure what that means. Its most likely not the vacuum you are fighting, but that you can't idle it low enough and it runs rich at idle. What I would try doing is raising the idle ignition timing as high as you can, and reducing the idle speed through the carburetor. Then use the idle mixture screws on the side of the carb to get the highest manifold vacuum.

 

[Coolio]

10" of vacuum is iffy on a power brake car. I have 10 on my chevelle and the power brakes work ok on the first or second stab, then the pedal becomes rock hard. I have a new power booster and a vacuum can with the check valve siliconed in to prevent leaks. As far as the carburetor and vacuum, you adjust the carburetor to establish highest idle vacuum. As far as the carburetor not being able to be adjusted due to low vacuum I'm not sure what that means. Its most likely not the vacuum you are fighting, but that you can't idle it low enough and it runs rich at idle. What I would try doing is raising the idle ignition timing as high as you can, and reducing the idle speed through the carburetor. Then use the idle mixture screws on the side of the carb to get the highest manifold vacuum.

Thanks.I'll give it a try

 

[565bbchevy]

If you verify everything in your vacuum system is functioning fine I would start by adding a vacuum canister first since they will add reserve to your current system and they are relatively inexpensive and if that helps but not quite enough you can add on a vacuum pump for brakes something like this.
https://www.summitracing.com/parts/ssb-28146/overview/

 

[Coolio]

If you verify everything in your vacuum system is functioning fine I would start by adding a vacuum canister first since they will add reserve to your current system and they are relatively inexpensive and if that helps but not quite enough you can add on a vacuum pump for brakes something like this.
https://www.summitracing.com/parts/ssb-28146/overview/

Is it a such thing as a cam made specifically for manual transmissions?

 

[565bbchevy]

Is it a such thing as a cam made specifically for manual transmissions?

The camshaft has to be matched to the engine and it's application, although certain cams might work better with a specific trans I would say no they are not trans specific.