Carbureted 302 Off-idle Stumble - Ford Mustang Forum
 
LinkBack Thread Tools
post #1 of 12 (permalink) Old 05-27-2010 Thread Starter
Rookie
 
Jeremy90's Avatar
 
Joined: Jul 2009
Location: St. Peters
Posts: 9
 
Carbureted 302 Off-idle Stumble

Im not one to ask for help but i cant figure this problem out...

I have a 302 with an E303 cam, Trickflow Street Heat heads with 1.6 rockers, Edelbrock Air Gap Intake manifold, Holley 650cfm double pumper carb, MSD 6AL box, blaster 2 coil, and pro billet mechanical advance distributor.. That being said the car starts and idles just fine.. if i slowly roll into the throttle it will rev up just fine.. but if i open the primaries more than 45% open it stumbles and falls flat on its face until i let off.. when i first started it the timing was way off.. i have changed the timing to be at 15 degrees at idle and 36 total timing which comes in around 2600 - 2700 rpm.. that being fixed i moved to the carb.. i have an idle manifold vacuum of 7in Hg.. so i have a 6.5 power valve in the carb.. i changed the squiter nozzles from the 28 that it came with to a 31.. the car is acting like its not getting enough fuel when the vacuum through the venturi system is too low to draw fuel through them.. but ive done what i know to change that but its not helping hardly at all...

any help would be appreciated!
Jeremy90 is offline  
Sponsored Links
Advertisement
 
post #2 of 12 (permalink) Old 05-27-2010
Made Member
5.0L Member
 
bdbolling19's Avatar
 
Joined: Sep 2007
Location: Port Townsend
Posts: 1,465
 
7"Hg at idle sounds really low to me, my setup is very much like yours (but with a longer cam), and I have 14-15"Hg at idle. Might want to check around for a leak somewhere.

What rear end gears are you running?

With that said, trying switching the little plastic accelerator pump cam. A 650 Double Pumper comes with the pink cam installed. For manual transmission Mustangs with low rear end gears (3.73+), I usually use the blue or white accelerator pump cam with a .031"-.037" squirter.

And by the way, vacuum has nothing to do with how well the accelerator pumps work, they're designed to work at 0 vacuum.

If it's not broke, you're not trying hard enough.

1983 Mustang GT T-Top.

New T5 installed, driving my 'Stang again.
bdbolling19 is offline  
post #3 of 12 (permalink) Old 05-27-2010
Made Member
5.0L Member
 
bdbolling19's Avatar
 
Joined: Sep 2007
Location: Port Townsend
Posts: 1,465
 
Oh, and if you have 7"Hg at idle and no vacuum leaks, the 6.5 power valve is probably spending way more time open than it should, which will throw off your accelerator pump tuning. Try a 4.5 or Maybe a 5.5 power valve.

If it's not broke, you're not trying hard enough.

1983 Mustang GT T-Top.

New T5 installed, driving my 'Stang again.
bdbolling19 is offline  
post #4 of 12 (permalink) Old 05-27-2010 Thread Starter
Rookie
 
Jeremy90's Avatar
 
Joined: Jul 2009
Location: St. Peters
Posts: 9
 
I also thought 7in was low.. so i checked for leaks.. couldnt find anything.. i know the acc. pump is made to work when there is no vacuum.. thats why i changed the squirter nozzle to a bigger size because it seems like its not getting enough fuel when there is no vacuum.. It has the factory gears in the rear end.. but i have 4.11s waiting to go in.. but i havent even driven it since ive put it together... i have a 3.5 power valve that i was gonna put in it but just havent tried it yet..
Jeremy90 is offline  
post #5 of 12 (permalink) Old 05-27-2010
SHELBY GT 350 Member
 
302Feen's Avatar
 
Joined: Jan 2008
Location: Norman
Posts: 6,939
 
Have you tried advancing the idle???

Usually stumbling like the is an indication of retarded timing.

I know with carb setups you can usually run quite a bit of timing. So you might try advancing it a little more and see if it helps.

-1994 Mustang GT "The Red Baron": 3.73 gears,K&N filter,GT40 tubular intake,BBK Full Length Headers,modified midpipe & Flowmaster muffs, timing at 12*. Best time- 14.74 @ 93.16
-Check profile for pics of our car collection!
- AmericanMuscle ROCKS!!
- "True Hot-Rods don't have valve covers!"
302Feen is offline  
post #6 of 12 (permalink) Old 05-27-2010
Made Member
5.0L Member
 
bdbolling19's Avatar
 
Joined: Sep 2007
Location: Port Townsend
Posts: 1,465
 
The stock gears are killing you.

I re-read your original post, it sounds like the bog might be in the secondaries, which with stock 3.08 or 2.73 gears is gonna be pretty darn hard if not impossible to tune out with a 650 cfm carb on a 306.

Your timing curve seems pretty good to me, it's the same as what I'm currently running. You just need to get those gears installed.

If it's not broke, you're not trying hard enough.

1983 Mustang GT T-Top.

New T5 installed, driving my 'Stang again.
bdbolling19 is offline  
post #7 of 12 (permalink) Old 05-28-2010 Thread Starter
Rookie
 
Jeremy90's Avatar
 
Joined: Jul 2009
Location: St. Peters
Posts: 9
 
I have thought about advancing the timing a little bit more.. but leary about going too much.. The gears i know will kill it.. but this problem is not even under load.. its while its in neutral.. i havent wanted to drive it while its doing this because the problem will be worse..
Jeremy90 is offline  
post #8 of 12 (permalink) Old 05-28-2010
Made Member
 
KLWorra's Avatar
 
Joined: Feb 2009
Location: Long Beach
Posts: 414
 
You are going to have to find the vacuum leak before you go any further. Pump in too much and you will plate the fuel up bad. I went power valve and accelerator adjustments to clean mine up once I was pulling 15 or so with a much bigger cam.

Ponyless. Maybe again someday, but not today.
KLWorra is offline  
post #9 of 12 (permalink) Old 05-28-2010 Thread Starter
Rookie
 
Jeremy90's Avatar
 
Joined: Jul 2009
Location: St. Peters
Posts: 9
 
Ill look again for a leak..
Jeremy90 is offline  
Made Member
5.0L Member
 
bdbolling19's Avatar
 
Joined: Sep 2007
Location: Port Townsend
Posts: 1,465
 
If it's in neutral too, I'd say start back with the basics. Check your fuel pressure and make sure both the primary and secondary floats levels are set correctly.

If it's not broke, you're not trying hard enough.

1983 Mustang GT T-Top.

New T5 installed, driving my 'Stang again.
bdbolling19 is offline  
post #11 of 12 (permalink) Old 06-02-2010 Thread Starter
Rookie
 
Jeremy90's Avatar
 
Joined: Jul 2009
Location: St. Peters
Posts: 9
 
I checked for leaks again.. none that i could find.. Fuel bowl levels are set correctly and i have 7 1/2 psi of fuel pressure..
Jeremy90 is offline  
Made Member
5.0L Member
 
bdbolling19's Avatar
 
Joined: Sep 2007
Location: Port Townsend
Posts: 1,465
 
Did you buy the carb new from Holley? If not, take the air cleaner off, and move the throttle linkage just a tiny bit. Any movement of the throttle should get you a nice instant stream of fuel out of the accelerator pump squirters.

If the primary squirters are coming on fine, do the same thing for the secondary ones.

It's possible that there's a missing check ball or an incorrect fuel bowl or metering block gasket that would be causing the pumps not to work.

If it's not broke, you're not trying hard enough.

1983 Mustang GT T-Top.

New T5 installed, driving my 'Stang again.
bdbolling19 is offline  
Sponsored Links
Advertisement
 
Closed Thread

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:
OR

Log-in









Random Question

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183