Valve Float

#1
Hey all, running into an issue with valve float. This is on a Hemi Predator 212cc. Specs are as follows....

Head is stock other than .050" shaved and 26Lb springs
+.020 billet rod
ARC speedway billet flywheel.
26mm chikuni carb
.010 head gasket
CM Grind cam

Bike is a doodlebug with geared at 5:1

Issue comes in that it seems to hit valve float at 6600 RPM free revving I think i am going to drop to a 6:1 to gain a little more acceleration off the line but with the engine shorting me 1000 RPM from what is expected I am hesitant as I'm kind of a speed freak....

Guess its an open ended question... I haven't played with jetting yet as the plug has had a clean electrode with a sooty exterior so I'm leaning that it is jetted fairly close. Lash is set at .003 on both intake and exhaust.
 

delray

Well-Known Member
#5
if them springs are set right. no way your valves would be floating at that rpm. 26 pounds will hold up 8500 when set correct. I'm not there to see it or here it run,but my guess would be you have to much fuel coming on. if that's a true 26mm bore carb. really should go with a 22mm carb. maybe try to jet it down first.
here's a 22mm carb....



 
#8
I am i ny and do not have access to my spring chart but maybe delray can post it. Going from memory installed height of .840 is around 26lbs seat pressure. Predator install height is less i think around .820. With those springs and a install height between .850 to .820 unless you have a bad spring it should rev to 8000 with ease. Do not try to free rev it to high rpm.
 
#9
I am i ny and do not have access to my spring chart but maybe delray can post it. Going from memory installed height of .840 is around 26lbs seat pressure. Predator install height is less i think around .820. With those springs and a install height between .850 to .820 unless you have a bad spring it should rev to 8000 with ease. Do not try to free rev it to high rpm.
Thank you ole, next time the head come off for porting I will defenitly pay attention to this!

Now to derail the original post are there any great write ups on porting that are worth the read. I did a couple searches but wading through them is taking a while.
 
#14
Three good books on porting and cylinder head development but all cases you need a flowbench and bench tools to develop a port. First two books are must read third has a lot of car specific info that is of no use in single cylinder engines. First is how to port and flow test cylinder heads by David vizard. Next is engine airflow by Harold Bette’s. Third is practical engine airflow.


 
#15
I had posted a hemi head rework thread on hear a few years ago on porting and testing a hemi 28.5/25. It is a bit dated but you can get the general idea.
 

65ShelbyClone

Well-Known Member
#16
Issue comes in that it seems to hit valve float at 6600 RPM free revving
What exactly does it do at 6600rpm? Does throttle opening have any affect? You have a cam and springs good for 8000+rpm unless the installed height is way more than it should be(and it's probably not). I'd be looking at fuel or ignition first.
 
#17
Doubt you are floating the valves. My bet is you are running rich. You have greatly increased compression with the .050 milled head and longer rod. I would go to a smaller jet and see where that gets you rpm wise. If RPM increases then go smaller. If RPM decreases go larger on the jet.
 
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