Confused about big bore kits... 64mm valve. 69mm valve

[ratdog]

ok, I’m looking at big bore kits.  I want to get a kit that includes the head and cam.  Now they come as “69 mm valve” and “64mm valve”. My problem is of course I don’t know what I have.  But more important, if I’m buying a kit with a new head, and a new cam, what difference dose it make?  I’m replacing cylinder and head, so does it matter how long the valves were on the old head?  And if it doesn’t matter, wouldn’t it be better to get the shorter valve?  I’m thinking weight here.  A lighter vlave ( the 64mm) would be less prone to valve float, and therefor safer at high RPMs

[diynuke]

first of all don't put the intention of raving your bike that high xD Big bore's mostly fail because of they are being abused/ having the wrong carb setup.

Here is an vid about the valve length. : www.youtube.com/watch?v=V_GPI1VIk4o

and if you buy a big bore kit with the head. do keep an eye out that the head isn't a stock head with an small portion milled out. they do work but still isn't really what you want.

And what is your riding style? all the time full open or just accelerating slowly?
this would kind of change for what kind of big bore you need to go for. an 100cc kit (52.4mm) doesn't like to run full throttle all the time while an 72cc(47mm) isn't really bothered that much

And how far do you need to drive with the scoot? This would kind of change the choice of your Big bore. Cheap Chinese bbk kits aren't suited for long rides they just wear out faster than their Taiwanese twins.

And for the valve weight I personally don't think that that little weight will matter If you really want to rev it you could always install some heavier valve springs.

[ratdog]

Every time I hear people talk abot mods on these engines, I think, “with a CVT, why worry about “low end power”, your always running around 7000rpm.  I was thinking about something in the 80 cc range

normaly when I build an engine I do springs with the cam.  So far I have not found anyone the offers stronger valve springs ( I can find vale springs but just lemme vale springs

my biggest problem is that I have no idea what are good parts and what ore junk parts. Most of this stuff looks like the same thing only from a different seller.  For example, I have heard of a number of people having The bearings (cam) coming apart and ofcourse totaling the engine. But I have no idea if one supplier has better cam bearings then another

the bike I have takes a long time to get to 25 mph and about a half mile to get to 30. As it came (new) it was running extremely lean.  I cured this with a different carb with bigger jets and using a pod air filter.  ( yes, I know the pod air filter makes it run leaner). I’m running a 85 main jet right now and the plug sz it a good mixture.  I did not change the coil or cdi, as the few tests I’ve seen on line indicate that the stock stuff is just fine. Not really a good test, but the stock coil will still give a great healthy spark with a plug gap of .035. ( I don’t run that big of a gap, but it was a way for me to “test” the stock coil)

i had not caught that some parts parts are not made in China.  As most don’t say, I’m guessing tha parts made outside of China will be labled as such

just wondering, but do you have any feedback on the parts sold by J&J? ( he has a bunch of vids out there)

thanks!

Craig

[humanshield]

Everything you could ever want to know and more....is buried somewhere here. It's finding it that's sometimes difficult. I have trouble finding topics on things all the time.

I bought my 50mm BBK from 02StarRider (ebay) a few years back and it's still going strong. I think most of the time it has almost as much to do with the installer / tuner as it does with the parts. Just avoid the cheapest imo.

Buy from places like PartsForScooters.com and you'll be assured to be ok.

Good thing is, you can do a full top end change on these things in an hour or so ...versus a car for example, which could take 5 or 6 hours. So I never really overthink it.