Stuttering issues with brand new 302

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

whoohoo111

New member
Joined
Oct 6, 2016
Messages
12
Reaction score
0
Hey guys, it's been a while since I've been on here, but about a month ago I installed a brand new ATK 302.  Everything internal is completely stock.  I'm running a Weiand street demon intake and Holley performer 600 carb.  The problem I'm running into is my Bronco is stuttering and trying to die when I slam on the gas or hit high cruising speeds.  It actually sounds like it is fuel starved.   I'm running at 12 degree btdc, and 36 total with advance set in. 

What I've kind of figured out after going through my Holley book and trying to adjust it is that I'm pulling way too much vacuum and the carb can't keep up with fuel output.   At the manifold port, I'm pulling 25inhg~ or more idling at 650rpms.  I figured I should be running at 16-22inhg.   I called Holley, and I was told that I should get their largest pump accelerator, but even though, their formulas show that the pump accelerator should be half of the vacuum that the vehicle is pulling.  The problem is that their largest pump accelerator is only 10inhg.

Is there such a thing as too much vacuum?  I'm not sure if there is an underlying problem without everything being "sealed" too good.  Any ideas where I should go from here?

Thanks,

Rob

EDIT:  Fuel float levels are perfect after stalling out, so carb is definitely getting enough fuel from gas tank.

 
Last edited by a moderator:

Bully Bob

TOP GUN
Moderator
Joined
May 23, 2004
Messages
3,844
Reaction score
12
Location
Boulder City, Nevada (Las Vegas area)
"I slam on the gas"

Do you mean this literally..? (stomp on pedal) If so.., for what reason..?

There's nozzles in some Holley 4 brls. If memory serves, there's different sizes.

But ya.., it sounds line a fuel flow/feed issue.

Sorry, what's ATK 302.?

Is your ignition compatable..?

 
OP
OP
W

whoohoo111

New member
Joined
Oct 6, 2016
Messages
12
Reaction score
0
"I slam on the gas"

Do you mean this literally..? (stomp on pedal) If so.., for what reason..?

There's nozzles in some Holley 4 brls. If memory serves, there's different sizes.

But ya.., it sounds line a fuel flow/feed issue.

Sorry, what's ATK 302.?

Is your ignition compatable..?
No!  I don't mean literally, but I give it enough to accelerate quickly. 

ATK is a brand of motor builders, and I purchased one of their rebuilt 302 blocks.

The ignition is HEI, and it's timed properly.

 

Skitter302

Active member
Staff member
Moderator
Joined
Nov 25, 2012
Messages
749
Reaction score
148
Location
WA
I would make sure that your vacuum advance is not causing the issue. I was working on a jeep earlier this year that acted this way and it was a vacuum issue. Just something I have experienced.

 
OP
OP
W

whoohoo111

New member
Joined
Oct 6, 2016
Messages
12
Reaction score
0
Is there a specific way to check the advance?  I had plugged ported vacuum (advance vacuum) on carb at one point, and hooked the advance up to the full manifold vacuum, and it still did the same thing.  I'm assuming advance means nothing when plugged to manifold port?

 

Rons beast

Active member
Joined
Dec 13, 2007
Messages
1,537
Reaction score
13
Location
Florida..in my mind , sitting on the beach
I doubt the problem is related to vacuum.  A healthy engine will make only so much vacuum and the components ( carb, distributor, and any vac/ run accessory.) are made to be used with it. They could need adjustment.

I'm not familiar with a Weiand Street demon manifold.  Was it on your old engine?  Was the Holley on there too?  How did they work together?

I'm trying to determine if the problem is fuel or ignition and is the manifold/ carb suited for the engine and use.  

Try power braking the engine.  Does it miss or stutter then? (If so it's likely and ignition problem.)  Also try to cruise on the highway at 55 to 60 (legally) then rapidly accelerate ( safely , of course) and see if the engine stumbles.  If it does and continues it is most likely an ignition problem.  If it stumbles but smooths out it is probably fuel related. 

Have you replaced plugs and cap and wires and rotor.?  With a new engine the healthy compression can put a strain on the ignition system and any weakness will show itself.

Good Luck. 

 

Bwonco

New member
Joined
Feb 29, 2004
Messages
7
Reaction score
0
You can try with the engine off, look straight down the venturies while opening the throttle to wide open position. You should see a healthy, long ,even squirt of fuel going down the throat of the carb aimed right at the middle of each primary barrel. if it dribbles or doesn't hit the center, you may need to find out why. These conditions can cause stumble when opening the throttle.

Also if your primary float bowl float level is set too low it could cause a leaning condition at higher rpms.

If you are pulling 25 inches of mercury @ idle, that is very healthy for an engine with new rings and a stock camshaft with little to no overlap on the valve timing. I dont this is the cause of any problem. try another vacuum gauge to be sure your gauge isn't lying to you.

Make sure your dist is connected to ported vacuum source, that slowly increases the higher the RPM's. If it's connected to any other vacuum source, your dist advance will be irratic when opening the throttle, and cause flat spots or lousy performance, and sometimes pinging in warm weather.

~BH~
 

Members online

No members online now.

Latest posts

Forum statistics

Threads
22,509
Messages
135,879
Members
25,108
Latest member
Utahstroke
Top