Login  /  Register  
  Home  -  Forum  -  Classifieds  -  Photos  -  Links     

  << Previous Topic | Next Topic >>Return to Index  

Brakes are killing me

July 22 2012 at 8:10 AM

Jeff R  (Login chauncy68)
Members

Pardon the pun in the title.

My problem is the engine kills on hard braking. If I do a hard stop from any speed with the clutch in, the RPMs drop to about 700 and the engine stumbles until it dies. Even from 15 MPH! Moderate to slow stops are not a problem.

Details are:

390 +0.40, 10:1, stock Edel heads, Perfomer RPM manifold gasket matched

Holley 750 HP (model 82750) Vac secondary carb with Phenolic 4 hole spacer. Has the vent "whistles" added.

Cam is 250 @0.050 .600 lift, 110 LSA. Draws no more than 10" HG at idle. Brakes are manual.

Ignition is 12 intial all 36 in by 2,800.

Idle speed is 1,000 RPM.

The problem existed in a previous reincarnation of the car when the cam was less, the brakes were power, and the carb was a 70 CJ 735.

Any ideas? I suspect the carb. Should I try the carb forum?


 
 Respond to this message   
AuthorReply

Fred
(Login origincorp)
Members

Re: Brakes are killing me

July 22 2012, 8:22 AM 

prolly gas flooding from the vent tubes...do you have a anti-slosh doo-dad
in the float bowl?

 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Re: Brakes are killing me

July 22 2012, 3:43 PM 

Yes, I do. Front and rear.

 
 Respond to this message   
galaxiex
(Login galaxiex)
Members

Re: Brakes are killing me

July 22 2012, 8:34 AM 

Float level too low?

 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Re: Brakes are killing me

July 22 2012, 3:44 PM 

I will check the float levels later this week. That was the consensus answer from a bunch of my bench racing friends, too.

Thanks


 
 Respond to this message   

BattlestarGalactic
(Login BattlestarGalactic)
Members

Try this...

July 22 2012, 8:35 AM 

set the float really low on the back. Take it for a test drive and anchor the brakes. Does it still stumble? No? Then it's fuel sloshing over.

Could be the front is set too low and it pulling away from?

[IMG][linked image][/IMG]
2006/2009 UMTR Points Champion
1964 Galaxie 2dr 390/6-71/4spd
1964 Country Sedan Wagon 428/5spd
1969 F100 428CJ/4spd
1989 F100 302/AOD
1959 B Model Mack


    
This message has been edited by BattlestarGalactic on Jul 22, 2012 8:36 AM


 
 Respond to this message   

qikBBstang
(Login qikbbstang)
Members

OK here's the opposite: How in the world do you hard core Drag Racers even start to meter

July 22 2012, 9:25 AM 

fuel in a carburetor on a 1-2 second 60foot time under those G's?..... I'd think the fuel's standing sideways and any resemblance to a stationary fuel level in the bowls is purely coincidental?

bb

 
 Respond to this message   

Dan Nelson
(Login 62highboy393c)
Members

BB, use rear jet extensions and

July 22 2012, 9:45 AM 

Connect the front and rear bowl vent tubes together with a vented tube.

 
 Respond to this message   

BattlestarGalactic
(Login BattlestarGalactic)
Members

Actually my car...

July 22 2012, 12:54 PM 

is pretty easy on carb settings. Two 600 Holleys turned backwards on TW intake. I did put jet extensions on the primary side. Never did see any kind of change/improvement.

Hitting the brakes hard from 116 mph does make it want to stumble a bit. Not a problem though.

LarryK

[IMG][linked image][/IMG]
2006/2009 UMTR Points Champion
1964 Galaxie 2dr 390/6-71/4spd
1964 Country Sedan Wagon 428/5spd
1969 F100 428CJ/4spd
1989 F100 302/AOD
1959 B Model Mack

 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Re: Try this...

July 22 2012, 3:46 PM 

I can test that.

If it is, what would the solution be? I don't want to run half full on the secondary side.


 
 Respond to this message   
Anonymous
(Login 391locker)
Members

Re: Brakes are killing me

July 22 2012, 10:07 AM 

Some manual transmission cars came from the factory with dashpots

 
 Respond to this message   
john vermeersch
(Login johnvermeersch501)
Members

Thread not clear on power brakes.......

July 22 2012, 12:37 PM 

IF power, unhook the vacuum line, try brakes.....ruptured booster can cause major vacuum leak, stall engine....

 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Re: Thread not clear on power brakes.......

July 22 2012, 3:51 PM 

Not power, so that can't be. It would add a whole other dimension to the problem, but luckily not in this case.

 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Re: Brakes are killing me

July 22 2012, 3:50 PM 

I bought a Holley dashpot to use on the 735. But I hated driving it on the street. Coming up to a stop it took about 15 seconds to return to anything resembling a normal idle. I have dual springs on and even they could not close it faster.

I also don't think the dashpot will help because if I put the clutch in and establish a normal idle, then stab the brakes it dies.

 


 
 Respond to this message   

Dan Nelson
(Login 62highboy393c)
Members

try this

July 23 2012, 9:04 AM 

this is what i have to do to my 4x4 carbs to make them work n steep ground,also helps on hard acceleration or hard stops, its just a piece of rubber line with an oppening to vent the bowls, try it, if it fix,s the problem then its your rear bowl level too high, if it dose not fix it then the front bowl level is too low.
edit for, also have to use spring loaded needle and seats. it could be a problem with your needle and seat in the rear bowl.


[linked image]


    
This message has been edited by 62highboy393c on Jul 23, 2012 9:07 AM


 
 Respond to this message   

Jeff R
(Login chauncy68)
Members

Picture worth 1K words

July 23 2012, 9:16 AM 

Good photo. I can do that easily for testing. Would rather solve it more elegantly for long term, but sometimes ya gotta do what ya gotta do!

Thanks.


 
 Respond to this message   
Tom P
(Login tomposthuma)
Members

other vent ideas

July 23 2012, 12:11 PM 

Not sure if it is clear here but the only pic i've got on file. The bowl vents face the other way. This is for acceleration, they could be turned around for braking.
When i tried a hose joining the two vents it still dumped gas at the middle. The tall vents threw gas from the front carb directly into the rear carb. The vent angling back over the bowl stopped it all but you can't angle them both or you won't get the air cleaner on.

[linked image]

 
 Respond to this message   
Dave Eames
(Login DEames)
Members

Go on a wiring search in and around the pedal assembly.

July 25 2012, 4:42 PM 

Had a car in the shop years ago with same scenario, hit clutch, vehicle died. We found a jumble of underdash wiring and the B+ wire to the ignition circuit was grounding out on the linkage when driver stepped on the clutch pedal. Doesn't it seem kinda odd that you have the same scenario with two different engines?
Eames

 
 Respond to this message   
 
  << Previous Topic | Next Topic >>Return to Index