212 rpm issue

Jason g

New member
Built my son a motor for his race kart.

preditor hemi
Arc billet rod
Arc flywheel
6 degree advance key
Big valve head 32/28
Ported polished epoxy coated
1.3:1 rockers
Nr racing .670 methanol carb
Valves intake set to .003 exhaust .004
Coil spacing everywhere from .020 to .065

our issue is it won’t rev up the most I can get out of it is 6200-6400. Everything says this should pull like a monster to 8000 plus.

any ideas?
 
Keyway is either backwards or sheared or valve springs ?
Arc recommends a pretty big gap definitely not .020 .
Air filter gasket backwards .
 
Built my son a motor for his race kart.

preditor hemi
Arc billet rod
Arc flywheel
6 degree advance key
Big valve head 32/28
Ported polished epoxy coated
1.3:1 rockers
Nr racing .670 methanol carb
Valves intake set to .003 exhaust .004
Coil spacing everywhere from .020 to .065

our issue is it won’t rev up the most I can get out of it is 6200-6400. Everything says this should pull like a monster to 8000 plus.

any ideas?
I didn't see a mention of compression ratio or jetting! Spark plug? Leak down? Degrees of timing? Where are you getting these RPM numbers? Dyno? Track? What track? What gear ratio? What air density?

There may be others that I haven't mentioned.

It's called Tuning. "Tuning is tough" (Al Nunley)
 
What cam are you running? Put a straight up key in the flywheel there's no need to be running 38 degrees of timing.
 
Thanks for the replies. I’m running the mod 2 cam. The jetting that was in the carb is .050 and .029 on the pilot. I’m testing on the kart stand. The head came with 37 pound springs. For kicks I drilled out a main jet to .059 seemed like the same maybe worse. So then I drilled out a jet to .046 seems to rev right up and it went to 7200 rpm. The plug is the ar3910x. I think I covered the questions lol
 
Does it hit 6400 at the end of the straight or does it hit 6400 and just hang there for the rest of the straight?
 
Does it hit 6400 at the end of the straight or does it hit 6400 and just hang there for the rest of the straight?
That’s end of the strait, we have a gear rule. I bought a new bully 2 disk clutch last week, it acted the same with the 3 disk bully I removed
 
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