212 open predator RPM problems

I have a 212 non hemi predator with a rpm issues at about 7200-7300 ish. The build is 212 non hemi predator with stock bore, .040 longer arc rod with a stock hemi flatop, F275 DYNO cam, stock crank, clone big valve ported head with 32mm intake 28mm exhaust valves, 1.3 ratio gauge rocker arms, green stripe dual valve springs with titanium retainers, 28mm mikiuni on alcohol. The problem I'm having is around 7200-7300 rpm it acts like vavle float it will not rev past that rpm it kinda sounds like a lo206 hitting the rev limiter. I have changed coils have 45 thousands gap no difference changed plugs checked cam to make sure the dot was lined up with the crank. It ran that way last year I freshened it up for this year and it's still doing the same thing pulls very hard all the way up to 7200-7300 rpm doesn't stumble or anything just at a loss what to check next I want to send the head off and have the spring pressure checked cause right now the spring intalled height is around 1.0" maybe more like 1.1" I'm at work so I can't check it right now that's why I'm thinking it's floating the valves cause the installed height is more the I think it should be any ideas would be helpful
 
If you have a lot of room prior to coil bind, you might gonahead and shim
Them a bit and see if it goes away. Easy enough to try. At high rpm its either float or ignition break up. You sound like you have a pretty good handle on it. Shim a little. Try it. HTH.
 
The cam you are using calls for 32 lb springs with standard rockers. More will be required with 1.3 rockers. That should be the pressure required to move the valve off the seat.

The proper check will be to get the seat pressure needed for your setup, then check for how close you are to coil bind.

May require a little thinking to use things you have on hand to check the seat pressures as installed.
 
This is what arc says when u pull up the Dyno dual vavle springs, Approximately 42lbs at .840 installed height and 80lbs at .275 lift(.620" install height). Will coil bind above .400 lift without modification. I had problems with the aluminum retainers when I got the head my rocker arms were barely touching the edge of the retainers I didn't notice that checking lash cause it wasn't much but it wore out the aluminum retainers it was pushing the valve out the bottom of the retainer so I bought titanium retainers and they weren't rubbing at all after that but my intalled height is just over 1.1"
 
I'm thinking you'd want to be in the .850-875 installed range. (guessing around 38 lbs) I saw they make .200 longer valves for the predator hemi. If valves are too long, that would explain rockers hitting the retainers. Geometry is likely off. Roller tip should start closer to edge of valve tip, roll across the center, and may be be slightly off center at max lift. Are guage rockers a shaft type, or similar to the stock rocker, with ball pivot? If ball pivot with adjusment made at the pivot, may need longer pushrods if you keep the longer valves.
Just some things to look for.

Do you have lower retainers on the springs?
 
What size of shim would u think I should try and shouldn't the installed height be less than. 1.1" more around .900 or something?
I just checked my preditor with a spring pretty close to what you have. My installed height is .850” (nom) I believe I have around .020” shim. The points brought up about a long valve stem would certainly explain your pain with a quickness.
 
The builder I bought all my parts from builds these engines everyday so I'm pretty sure the carb is jetted properly, my valve spring retainers are sticking out past the mounting surface for the valve cover and when I push on the valve with my finger there is hardly any pressure, I used to have a open animal big valve ported head 308 cam with dual springs and those were very very hard to move with just your finger pushing down on the valve with no rockers on, and the rockers are shaft mounted they pivot on the same shaft
 
Are the adjuster screws sticking well above the locking nuts? With the pushrods up to the bottom side of the rocker?

The 38 lb springs on our animal can no way be pushed down with your fingers.

Stuff happens.
 
Stock clone valves are 2.525 and 2.555 long max according to NKA rules. Pop one out and take a look.

If you decide valves are too long, you may need longer pushrods after you change them.

Just trying to think ahead.
 
I think he decided the hemi valves were used in a clone head. He shimmed the springs .150- .175 and the engine ran better. He ran good for the first half of the season. Hven't seen him the last half.
He was going to send the head back to the builder to see what happened for sure.
 
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