Problem at the track...

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atth2o
Posts: 3
Joined: Tue May 10, 2011 10:44 pm

Problem at the track...

#1 Post by atth2o » Wed May 11, 2011 11:49 am

Here is my set up-

68 Camaro
454 .30 over
Steel Crank
Keith Black Hyper Pistons
9.5 to 1 comp
781 cast large oval port heads
1.7 roller rockers
crower springs
850 Proform race carb 1/2 inch fuel line
Mallory 140 electric fuel pump
Comp Cams XE284H 574/578 lift 240/246 duration
Edelbrock RPM intake
MSD Ignition dist,coil 6AL box- Dist has med springs and red bushing and vacuum is locked out
Hooker Comp headers 3 in exhaust
TH400 - 4000 stall
12 bolt 4.56 gear
cal tracs
28 x 15 x 13 M/T ET Streets



the car is backfiring through the carb when it hits around 5300 rpm under load, but if you feather the throttle it comes out of it.Its not laying down, or nosing over like a valve is floating, its still pulling hard, goiing through the traps at 6300 the car is still charging
things i have tried and checked:
I have a constant 8lb fuel pressure during WOT- mallory 140 pump/ 3/8 line from sending unit to filter/pump then 1/2 fuel line to regulator up front then 3/8 to carb
I changed carbs to see if the problem went away and it does the same thing/ currently on the car is a quick fuel 850 jetted 78/84===I have mesed with the jetting at the track before up and down and it does the same thing
Ignition is all MSD- 6AL box- have swapped out the box, coil, distributor, wires, with another, changed plugs and no change,- it has a good ground too
I checked all the valve springs and nothing is broken that i can tell/ it has crower springs on it.
I can't figure this out I need some wisdom..this is pissing me off .lol

let me know what more info is needed if so....

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10scnd70
Posts: 24
Joined: Tue May 10, 2011 9:37 pm

Re: Problem at the track...

#2 Post by 10scnd70 » Wed May 11, 2011 3:29 pm

Are you sure you've got enough valve spring for the lift? Has the car always done this, or did it start all of the sudden? What is your total timing? Have you tried any othertiming?

Frank
Just another 10 second Camaro...

want-a-be
Posts: 189
Joined: Tue Feb 05, 2008 11:04 pm
Location: Southern Illinois

Re: Problem at the track...

#3 Post by want-a-be » Wed May 11, 2011 3:30 pm

What spring pressure are you running? How did you measure it?

Are you running a power valve? How high are you running the floats? Might be running a tad too much fuel pressure. How far is the regulator from the carb? The 3/8 line from sending unit to pump may be a bit restrictive. What squirter size?

You mentioned the ground being good. How are you running your ground and does it run to both the block and ignition? How much timing are you running? Is the distributor locked out or are you running some advance? Initial if you not locked out? Timing all in by what rpm?

When you hit 5300 and you stay in it,....does the backfiring continue on up to 6300?

Don

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atth2o
Posts: 3
Joined: Tue May 10, 2011 10:44 pm

Re: Problem at the track...

#4 Post by atth2o » Wed May 11, 2011 8:14 pm

i dont know what spring pressure I am running. After the motor was built, my builder said no more than a 600 lift cam, and told me he put Crower springs in it. He may be full of crap I dunno. I am just explaining what is happening. It had a smaller Crower Beast cam matched to the springs last year in the motor and it did the same thing. Before I put the Xtreme 284H cam in I called him and he told me it will be fine. SO I pulled the cam and put in another, i didnt change the springs. But as i said it did it with that set up
BUT he may be wrong i guess..lol

No Power valve in the back. there is a 8 in the front in the Pro Form that was on the car. The Quick Fuel I know is blocked in back too but not sure on the size in front The floats are right to the bottom of the window.
regulator on the fender well
squirter size is 33/33 have tried 31/33

ground is to battery for the box and the battery is grounded to the frame and the block with 1 AWG

have played around with the timing up and down, I dont remember the initial but its all in by 3k and has been as low as 32 and high as 38 doesnt really change the problem regardless of timing
backfiring continues when your in it from around 5300 all the way to around 6300 then it stops and pulls again.....but as you know, thats killing me

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10scnd70
Posts: 24
Joined: Tue May 10, 2011 9:37 pm

Re: Problem at the track...

#5 Post by 10scnd70 » Wed May 11, 2011 8:26 pm

I wouldn't take anybodys word on the springs. I would start by checking them myself. You've eliminted some other possibilities, but I don't understand why it would pull through this at higher RPM's. What is your shift point?
Where is your fuel pressure guage plumbed in to your system? Is your guage inside the car where you can watch it during a run?

Frank
Just another 10 second Camaro...

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atth2o
Posts: 3
Joined: Tue May 10, 2011 10:44 pm

Re: Problem at the track...

#6 Post by atth2o » Wed May 11, 2011 8:38 pm

fuel pressure guage is plumbed in right at the dual fuel line on the carb..one of my guages is on the cowl outside the car so i can see it during the run, the other is right off the regulator

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BracketNova
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Re: Problem at the track...

#7 Post by BracketNova » Wed May 11, 2011 11:38 pm

What do your plugs look like? What are they gapped at?

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Dave Yonemura
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Re: Problem at the track...

#8 Post by Dave Yonemura » Fri May 13, 2011 7:12 am

Raise the float level, 1/2 to 3/4 in sight windows. Ground the heads from side to side, and then to MSD box mounting screw, sanding off any paint at grounding points. Set the total timing at or above 3000 RPM, @ 38*

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