carb spitting back at me
Thread Starter
Instructor
Joined: Jun 2004
Posts: 169
Likes: 0
From: Arlington Texas
carb spitting back at me
just curious if anyone knows: Why does my car keep popping back thru itself? timing is right on 34 total but the carb wont idle in gear unless i crank it up to where it will idle at 2400 rpm in park. I hate that but then when I do tap the gas off idle in gear it will backfire thru the carb. it is a holley 780 single pump vaccum sec. choke works fine too. engine is 468 roller BBC with 705/690 lift at 290 duration with 112 separation. everything works great once it gets moving but that pop kills me....and the power valves. carb was just re-built about a month ago.
sorry so long
[LEASE HELP ME!!!!
sorry so long
[LEASE HELP ME!!!!
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Got some wires crossed? I had 5&7 crossed on my 80 and it popped like mad, shooting gas back through the carb. Verify your wire routing.
There *was* a point where the car was running perfect, right?
-Steve
There *was* a point where the car was running perfect, right?
-Steve
Pro
Joined: Dec 2002
Posts: 560
Likes: 1
From: Mooresville NC
Also check to see if the outer ring of your harmonic balancer hasn't slipped so that the timing mark isn't reading true any longer. And see if the distributor mechanical advance mechanism hasn't froze up on ya. Slipped timing chain or very worn?
Like Pacin'California said, was anything changed recently or did this thing rear its ugly head all of a sudden.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Pacin'California
Got some wires crossed? I had 5&7 crossed on my 80 and it popped like mad, shooting gas back through the carb. Verify your wire routing.
There *was* a point where the car was running perfect, right?
-Steve
There *was* a point where the car was running perfect, right?
-Steve
Thread Starter
Instructor
Joined: Jun 2004
Posts: 169
Likes: 0
From: Arlington Texas
o.k. I thought I was sure but I still checked all the wires are in the right order, I think that the idle problem is in the adjustment of the carb. I came out about 2 turns on each idle screw and got it to idle o.k. in gear but it is running REALLY rich. I think I may need a new carb but I am hoping that I can just work with what I have....by the way does anyone have a better carb that I could buy from them??????
I can do most all things with cars but carbs have always been a killer to me.
and yes the car ran perfect when I got it. this problem just popped out of no where.....and I think the power valve is already gone (I put my finger over the vent tubes and the motor died almost instantly)
I can do most all things with cars but carbs have always been a killer to me.
and yes the car ran perfect when I got it. this problem just popped out of no where.....and I think the power valve is already gone (I put my finger over the vent tubes and the motor died almost instantly)
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Proper routing? That's up to you. Proper order is 1-8-4-3-6-5-7-2.
If you're standing by the driver's side door on your vette:
air_cleaner
18
2 4
7 3
56
cylinder order from front to back
driver side, passenger side
1,2
3,4
5,6
7,8
If you're standing by the driver's side door on your vette:
air_cleaner
18
2 4
7 3
56
cylinder order from front to back
driver side, passenger side
1,2
3,4
5,6
7,8
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Instructor
Joined: Oct 2001
Posts: 188
Likes: 0
From: Norwood MA
Thanks Pacin
Sorry to hijack this thread, but I was having a similar problem. I re-did the ignition wires based on info from Pacin California. Just took it for a ride and WOW!!!!!
Runs GREAT and the power is back.
Thanks Again
Pat
Runs GREAT and the power is back.
Thanks Again
Pat
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
[QUOTE=brianlewis60] I came out about 2 turns on each idle screw and got it to idle o.k. in gear but it is running REALLY rich.
Idle mixture screws should be 2.5 to 3 turns out from the seated position. If it doesn't idle with them in this range you may need to drill some idle air bleed holes in the primary throttle plates.
If the engine is running rich at cruising speeds the power valve diaphragm is probably split. Holley carbs are bad for this.
Hope this helps.
BigBlockk
Later.....
Idle mixture screws should be 2.5 to 3 turns out from the seated position. If it doesn't idle with them in this range you may need to drill some idle air bleed holes in the primary throttle plates.
If the engine is running rich at cruising speeds the power valve diaphragm is probably split. Holley carbs are bad for this.
Hope this helps.
BigBlockk
Later.....
