The kit I bought and put in my Predator came with 18lb valve springs. I put them in the same time I installed a billet flywheel and rod. However, my engine doesnt seem to rev any faster, and in fact sounds like it misses a few cycles at WOT. Stock springs are supposed to be 10.8lbs. How should I measure to be sure what I put in was 18 lbs? Or do you think I am just running out of cam? What cam would be a good replacement? This is for a yard kart btw.
how would you check valve spring rate?
- Thread starter Scout
- Start date
- Status
OzFab
New member
To test them accurately, you need a spring rate tester (expensive & very technical aparatus) but, there are less accurate ways...
One way is to set up a stable rig (as in, it won't fall over or fall apart under weight) & simply load it up with weights until the spring starts to compress; that will give you a ballpark figure...
It's very possible the stock cam doesn't like the high RPM, however, replacing it with a high RPM cam will mean you will possible lose a bit of low end torque...
One way is to set up a stable rig (as in, it won't fall over or fall apart under weight) & simply load it up with weights until the spring starts to compress; that will give you a ballpark figure...
It's very possible the stock cam doesn't like the high RPM, however, replacing it with a high RPM cam will mean you will possible lose a bit of low end torque...
I'd get a cheapo dial indicator and set some known amount of weight on the spring. You may need to make some type a jig for it all, but it shouldn't be too tough and will give you down to the .001" of deflection, so you won't need much weight or displacement.
Ok. So I'm not sure what's going on since I changed several things at once, billet flywheel, billet rod, valve springs. It sounds like the motor misses at full throttle. I was thinking that the stock cam may not be able to handle ungoverned rpms. The new valve springs are 18 lb pieces, and the "missing" is rather random so I don't think it is valve float. I also wondered if maybe the coil gap is wrong, even though I measured it and set it to spec, but it runs strong right up to WOT.
Any ideas other than valve float?
Any ideas other than valve float?
Louie The Lot Lizard
New member
One way to check your valve springs is with a Harbor Freight arbor press and an electronic scale (preferred).
Set the scale with the spring under the arbor. Rig a couple of gauge blocks with a parallel bar across them, like a bridge over the scale pad and next to the spring. (Scrap will work OK if its true). Rig the "bridge" so its height is equal to the installed height of the spring.
Its then a matter of compressing the spring with the arbor until it contacts the bridge and read the value on the scale. CAREFUL, you may need to rig another parallel bar under the arbor to make it wider and more stable. If the rig is cockeyed the spring can fly out and hurt you.
Commercial valve spring raters work like this only without all the rigging.
Set the scale with the spring under the arbor. Rig a couple of gauge blocks with a parallel bar across them, like a bridge over the scale pad and next to the spring. (Scrap will work OK if its true). Rig the "bridge" so its height is equal to the installed height of the spring.
Its then a matter of compressing the spring with the arbor until it contacts the bridge and read the value on the scale. CAREFUL, you may need to rig another parallel bar under the arbor to make it wider and more stable. If the rig is cockeyed the spring can fly out and hurt you.
Commercial valve spring raters work like this only without all the rigging.
KartFab
Active member
Check your spark plug gap? Flywheel key? Camshaft gear lined up correctly?
thebroketeenager
New member
It could simply be a lack of fuel to the motor. Run at wot a little after cleaning your spark plug. If it's white, you may need to get a new main jet or drill out you're existing one. Imao though I'm not a professional lol
Sent from my KFOT using Tapatalk
Sent from my KFOT using Tapatalk
- Status