Signs of valve float or fuel starvation? - Team Camaro Tech
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post #1 of 11 (permalink) Old May 15th, 19, 06:15 PM Thread Starter
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John
 
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Signs of valve float or fuel starvation?

Doing some fine tuning on the 350.
I'm getting some light to med sputtering at high rpms, around 4800 and up.
Just wondering what some quick way to tell if I'm running the bowls dry or it I don't have enough valve spring pressure? When should this cam be done? Comp says 1500-5500.
SBC 350
9:1
Performer RPM non air gap
Holley 600 v.s. (1850)
Mech fuel pump- Z28 spec supposedly
Orig 327 2 bbl fuel lines.
ported 041 heads with 2.02/1.6
1 5/8 headers
Comp HE268, 218 @ .050 and .483 lift (1.6 rockers)
TH350 with 2000 stall t/conv (Hughes GM20)
3.55 gears
26" tire
I have a valvespring pressure checker, and have on eof those cheap vacuum/fuel pressure gauges I think I can plumb in and tape to the windshield and do a run while checking it I guess, but was hoping for what is more of telltale signs of either fuel or valvespring.
Hope I described what I'm trying to check out......

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post #2 of 11 (permalink) Old May 15th, 19, 06:57 PM
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5/16 fuel line? Kinda small for what you are describing in my opinion. Could be almost anything though.

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post #3 of 11 (permalink) Old May 15th, 19, 08:07 PM
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Re: Signs of valve float or fuel starvation?

Did you put those bigger valves in with the old springs ?

More weight and old tired springs ; not a good combo.

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post #4 of 11 (permalink) Old May 15th, 19, 10:04 PM
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Re: Signs of valve float or fuel starvation?

Points?

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post #5 of 11 (permalink) Old May 16th, 19, 04:00 AM Thread Starter
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Re: Signs of valve float or fuel starvation?

New springs when new valves were put in. Valve guides too. Actually they were completely gone through. Seats, hot tanked, slightest milling just to get them flat......
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post #6 of 11 (permalink) Old May 16th, 19, 07:40 AM
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Re: Signs of valve float or fuel starvation?

I would rule out fuel delivery (pressure) problem first.

Hook up a FP gauge and tape it to windshield and go for a sustained WOT run, especially hitting 5k rpm,....if FP drops than that is your issue. If not than valve springs are suspect

most cam cards spec a spring but with using 1.\:5 ratio RR so when going 1:6 you need to do the math to confirm you are still within the springs "bind height" measurement. Your cam lift is not extreme but confirm your springs are up to spec
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post #7 of 11 (permalink) Old May 16th, 19, 08:24 AM
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Secondaries opening ?
Primary only on that 600 my not let the engine go 4000+ Under load.
Just a thought.

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post #8 of 11 (permalink) Old May 16th, 19, 10:44 AM
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Re: Signs of valve float or fuel starvation?

No special equipment is needed to check for valve float. All you need is the tachometer you already have. Best way is to have the vehicle inside where other noises don't interfere with the diagnosis. All you have to do is slowly bring the engine up to and over the RPM where you are experiencing the problem. If you have valve float, you will notice the exhaust note changing when you reach that point.

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post #9 of 11 (permalink) Old May 16th, 19, 04:04 PM Thread Starter
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Re: Signs of valve float or fuel starvation?

Cool. These are what I was thinking.
I'll try these out. Thanks.

- John
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post #10 of 11 (permalink) Old May 17th, 19, 02:48 AM
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Re: Signs of valve float or fuel starvation?

Are you absolutely sure the sputter at 4800 RPM is not ignition related? You may be chasing the rabbit in the wrong hole in thinking its fuel or valve spring issues.

If the distributor is using a box (MSD) with a rev limiter, that could be an issue. Or the module within the distributor is breaking down at higher RPM.

Never argue with an idiot; they'll only drag you down to their level, then beat you with experience.
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post #11 of 11 (permalink) Old May 17th, 19, 03:55 AM
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Re: Signs of valve float or fuel starvation?

spark plug gap
spark plug wires
cap/rotor

Above are the places I'd look first.

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