Kymco ZX50

[zombie]

Oh yeah I did Bro! We appreciate the Kudos. You even got another person to post their first. That's the coolest part of the forum for me. Everyone has their own experience, and tips to bring to the table. There is something else I noticed in your Pict. The burn marks on the piston dome are in line w/ the transfer ports. That reinforces the jug is too high, and not closing the ports soon enough. The heat on the piston may be igniting the charge before it gets compressed. These little bits are all adding up to a well tuned kit tho. Get the jug lowered, and re measure the squish. That will modify the mill that should be done. If you can get a gasket down to .02mm that would take another .03 of the mill spec bringing it to .07. I think in ball park #'s you would be around .06-.08 squish. See what you can get for the base gasket, re-measure, and we'll take it from there. Heres another tip: I used a friends Band saw table, and 600 grit emory cloth w/ PB Blaster as a lube to shave .5mm of my head. I checked the table for true w/ a straight edge, put the cloth down, and rubed in a circular motion, It only took 20 minutes from start to finish.

[sidthesloth]

I have ordered the piston kit which has gaskets with it, but I think I will hit the auto parts store for some gasket paper to lower the jug, though I am a bit dubious taking it apart again without replacing the head gasket, I think it has been 3 times already. See, what you are reading from the photo I have no idea about, but again, is all learning. I don't have a band saw but at work I could stay back on A/S and use a drill table or similar for that.

[Shaka]

Sid-  I have taken my head off a bunch of times without replacing the gasket.  I wouldn't worry a whole lot about it.  I think the next thing you need is a leak down tester!  It's about the only way to tell for sure!  Maybe I'll get around to posting pics of that soon too!

[zombie]

A drill press table is just as good. Just MAKE SURE it is FLAT. The transfer ports are the holes inside the jug on the sides. When you lower the piston in the jug see if the burn marks line up w/ the holes. That will tell if the jug needs lowering. (I think it does). You will most likely not find thin enough gasket paper, but aluminum will work fine w/ a good sealer. Permatex/Indian Shellac/OMC Perfect seal...I have used beer/soda cans for gasket stock dozens of times. You MUST use a sealer tho

[sidthesloth]

What about permatex aviation form a gasket under the jug with no gasket? would be the lowest we could get.

[sidthesloth]

Righto, removed gasket from under jug, piston sits about 1~2 mm above, so that has answered my previous question. Previous gasket was 0.81mm after having been in service, new gasket is 0.4mm prior to service, piston is almost flush, perhaps just proud but not by enough for me to measure. Will try to put some pics up.

[sidthesloth]

Here is a pic of the head

[sidthesloth]

Took scooter for a ride and performance is down quite a bit detonation is at it's worst. After installing the thinner gasket there was still no squish reading using the 1.2mm solder, checked at 4 points, 1 at each bolt. I have been reading Gordon Jennings' 2~Stroke Tuner's Handbook, though a lot of it is way above me it is giving me a much better understanding of the workings of the engine, thanks for the link zombie. Am now waiting for the engine to cool enough to remove the head and try trimming the face a little.

[Shaka]

Jennings book is great!  I wouldn't recommend trying to change anything until you have a good understanding of what he is saying though!  If it makes you feel any better, I don''t have a full grasp of his entire concepts yet!  I'm working on it though!  I would be leery of shaving the head before I knew for sure that is what was really necessary to meet the formulas Jennings set forth.  To me shaving the head is something that should only be done if you know exactly what you are doing.  It is something irreversible that if done too far cannot be un-done!  I have no problem doing what Jennings formulas call for, but I would not attempt to "half ass" meet my vague understanding them!  I don't mean to scare you out of tuning your scoot, but only to have a good understanding of what you are doing, and do it right!  Good luck Sid!!!

[sidthesloth]

No, I'm not trying to follow his formulas, I dont have the mathematical skill, just trying to get the scoot sorted. today was an experiment, tomorrow I will raise the jug a little higher to see what happens

[zombie]

When you measure the piston height the jug as to be bolted down. That will compress the base gasket, and give the tru reading. I don't understand how the sqiush could not be measured tho. You could try taping a piece of solder across the head, torquing the head down, and checking that way. The compression on that jug may be wicked high to begin w/ and that would explain the detonation returning. Have you done a compression test on this set up? Try those 2 things, and post back.

[sidthesloth]

After removing the head the piston was about .5mm above the gasket face, used feeler gauges. put solder on piston at 4 points and torqued head down. given the drop in performance tomorrow I was thinking of raising the jug a little higher than it  was previously, just for experiment. with this set I have only ever got 95psi but that may be the battery was not strong enough, tomorrow I will try with a drill. I am starting to feel like a gynaecologist. (a scooter one, that is).

[zombie]

I'm following a thread on Scoot invasion that is a 250cc kit, and Josh is just about to scrap the supplied jug as the timings on it are all out of wack. Check out the progress on that to see if you are using a similar kit. I give you alot of credit as you are sticking w/ it, and starting to see how it all works. The 95 psi bothers me tho! It should be over 100-110. With the piston sitting proud of the jug, it makes no sense to me that you can't measure the squish. Have you tried turning the engine over by hand? This just may turn out to be a mis match on the con rod/piston for the jug timming. You can keep trying to adjust the jug height to get the best compromise from it tho.

[sidthesloth]

Yeah, I think the supplied gasket may be the best but I just feel like I gotta at least try, after all, if it is no good, I can allways go back. that sounds interesting, I will have a look. I will stick with it, though it can be a little frustrating it is good to get results. I may have done more damage on initial setup than I thought, but I only have my self to blame, call it learning. for what it is worth, we had a little bit of rain the other night, the road was wet, I did not in my wildest dreams expect any wheel spin, but I sure got some!

[sidthesloth]

Did a comp. test before removing the gasket, 120psi using the kick starter. Tried both gaskets but was way too high so went back to the original one. Detonation is still there, not as bad but is definately there, must be from rubbing the head down at a guess, so I will try to find a thicker shim for a gasket.
After putting the original gasket back was about 110psi but that was without the exhaust ( I don't know if that will make any difference). So on it goes, it feels as though the engine has a lot more to give than I am getting from it, I just have to try to figure out how, with my lack of experience it could take a while.