1970 454 Engine surge while braking
Thread Starter
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Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
1970 454 Engine surge while braking
I have a 70 with the 454 in it, manual transmission. It runs fine once warmed up but when coming up to an intersection if i am costing lets say it idles near 800ish but if i get on the brakes hard(manual brakes) the engine RPM goes to about 1400rpm, if i step on the gas it will go down. Any thoughts?
Thanks
Thanks
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
Agree. I'm thinking 'float issue'.
I'll take a WILD stab in the dark and guess that if the RPM's go up, the primary float is set too low and admits air into the front jets.
I just went through having a 'float issue' where mine were set too high. Had the exact opposite of your symptom.
May be something else, but we're all about the guess here.
I'll take a WILD stab in the dark and guess that if the RPM's go up, the primary float is set too low and admits air into the front jets.
I just went through having a 'float issue' where mine were set too high. Had the exact opposite of your symptom.
May be something else, but we're all about the guess here.
Thread Starter
Advanced
Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
The car is stock so I have the original Rochester Quad on it. I assume a float issue as well but im not sure if it is too high or too low. The car engine is sluggish when i step on the gas like it is flooded, at least until it clears up. I have been messing with the choke thinking that was the issue but at this point i am all but certain it isnt the choke.
Last edited by bill69; Sep 16, 2015 at 10:48 AM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
If the float is too high, you could have fuel sloshing out of the vent tube on hard braking.
I just read another thread that mentioned a baffle in the fuel bowl that was supposed to prevent this. maybe your baffle fell off.
I just read another thread that mentioned a baffle in the fuel bowl that was supposed to prevent this. maybe your baffle fell off.
Thread Starter
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Joined: Mar 2003
Posts: 98
Likes: 3
From: Oglesby Illinois
There is no baffle based on the repair manual I have and I don't see a place for one either. I checked the float level and it was already high so I lowered it below spec and I still have the problem in exactly the same way so the float is not the issue nor does it seem to be a contributor. Any more ideas?
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Ha, it IS possible your big wide shoe is catching the edge of your gas pedal upon braking because I found my wide shoe was doing that. To cure the annoying problem I cut 1-1/2" off the right side of my brake pedal. I used a jig saw to do the cutting then used a disc grinder to smooth the cut and put a radius on the corners. After I cut my brake pedal I found many others have also cut their brake pedals because of the same problem caused by their big wide shoes.
Last edited by toobroketoretire; Sep 22, 2015 at 08:52 AM.
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
I would think that you would have a stalling issue if it was the float, not a surging issue (either flooding if the float was too high, or fuel starvation if the opposite). The fact that you can right the problem by hitting the gas would suggest something else. Have you had a hard look at your linkage all the way from the pedals to the carb?
Last edited by Brcmpbl; Sep 22, 2015 at 08:55 AM.
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Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
A lot of people have trimmed off an inch or so off the right side of their brake pedals because of their wide shoes catching their gas pedal so that could be your problem. Something to consider anyway...................