Thinner base gasket: improved low end.....Rich?

[binthedirtnow]

Well, I'm gonna have to ask you about this one too Rich, because I know I'll get a proven answer from you. I was advised that if I went to a thinner base gasket, it would improve the low end. Again, I took it from another post...Bike: 2002 kx 125, stock except for fmf pipe and new top end.....

Please inform me about this: If I install a thinner cylinder base gasket, what am I accomplishing and will I have to use race gas? I don't want to use race gas. Also, to offset a compression increase I don't think I can install 2 head gaskets because the '02 kx 125 uses a steel shim gasket and, let me know if I'm wrong, I think using two would invite leaks. But, I just thought of something - I might be able to get a thicker head gasket from cometic, but that might be defeating part of the gain (increased compression) from using a thinner base gasket? True?? Or False??
B.

 

[bikepilot]

I'm not rich and don't claim to know even half as much as he does, but here goes ...

A thinner base gasket will lower the cylinder in relation to the crank and pistion. This has two main effects. The first is increased compression, which typically gives more low end power and may induce pre-ignition and/or less over rev/high rpm power. IMHO, a thinner base gasket will not increas compression enough to cause pre-ignition or much difference in top end power. The second main effect of a thinner base gasket is lower ports. Lower ports should give a bit more low end power at the expense of top end power. these are just my observations and I am not expert. I am thinking of installing a thinn base gasket on my wife's KX100 and look forward to reading Rich's comments.

cheers,

josh

 

[binthedirtnow]

Rich????????

OK, Rich class is now in session....... :worship:
B.

 

[marcusgunby]

a thinner base gasket gives better bottom end but its only a small change as the drop in cylinder height is only about 0.2mm , you need to drop it about 0.5mm to really make a difference.

 

[binthedirtnow]

Cometic High compression gasket kit???

Cometic makes a high comp. top end gasket kit. What is the difference between that and the regular top end gasket kit? Does that kit lower it an appreciable amount like you say is needed? Would I ned to use race gas with it?
B.

 

[marcusgunby]

The difference i guess is its thinner somewhere to raise compression, how much im not sure, but the thin cr base gasket is onlyt 0.2mm thinner than std, generally gaskets can be used to fine tune only, they wont make a big difference, will you need to run race gas? i have no idea how close you are to detonation so its hard to answer.Some models like the cr detonate without raised compression.

 

[binthedirtnow]

Thanx Marcus

I'll probably not bother with the thinner gasket then - it was suggested by someone else to boost low end or shift the band lower. What I'd like to do instead is get a pipe for low end, but the only company that seemed to make those was Noleen racing, and they appear to be out of business.... :(

I've decided I don't really want to port, I'd rather just play with what the motor has already, until I can just get another bike.
B.

 

[bikepilot]

I'm probably going to try it on my wife's kx100 just for kicks. Will post the results whenever I do the mod. Might even try no base gasket and use a little high temp spray copper stuff to seal it up:)

good luck

 

[marcusgunby]

A thinner base gasket and a spacer for the pipe may bring it up in bottom end power, try a 5mm spacer where the pipe bolts on to the cylinder.You may have to make one yourself.

 

[Matt Fisher]

A spacer between the reeds and motor will also increase bottom-end. I think Moose racing makes one for the KX100, or you could make your own.

 

[binthedirtnow]

Mixed opinions on the reeed spacer

I've read mixed opinions on the reed spacer as to whether or not it works with certain motors. Even Rich said there was no way to know unless you try it. So, it may not do anything in your application. Best to ask if anyone has done it to the same kind of motor you have and get their feedback before spending the money on one.
B.

 

[bikepilot]

Thanks for the input. At this point, its got a stock pipe, shorty bills silencer, 12oz flywheel weight and a 3mm spacer in the exhaust (I had one lying around that fit perfectly). I think I am going to leave it like this untill we get a chance to ride it a little. Then, depending on the results of a test ride I will probably try a thinner base gasket, re-test and then perhaps a reed spacer and/or another 3mm spacer in the exhaust. I also want to play with the pv a little. Unlike the bigger KX's there is no spring to hold it shut at low rpm. There is a little play in the linkage so it can move a little at low rpm. Also, the govenor opens it very suddenly, its really either wide open or closed, no inbetween. I would like to try some type of small spring that would hold it shut, but not over power the govorner. Any ideas?

thanks,

Josh

 

[BDAY]

i accidentally left out the base gasket on my bike and just put silocone on it. it gave killer low end comparatively but lost so much top end and detonated occasionally. it took me forever to figure out why i gained 30 psi of comp. i changed it back.

 

[Moto Squid]

how do you accidently leave the base gasket off but have silicone in there?? Why are you siliconing at the base anyways...

I did the thin base gasket on my 02 cr125 and I thought it helped...but then again it had a new top/bottom end and that made the biggest difference in better power