Kymco ZX50

[sidthesloth]

G'Day, did a plug chop, finally, since raising the needle yesterday it is a lot better but I think it needs to go up one more, what do you think?

[sidthesloth]

Can't see too much with that photo, here is one of the plug I have been using.

[Shaka]

Really hard to tell in that pic.  I can't tell if it's all the light or it is really lean.  That one looks leaner than the last, my guess is the pic though.  How long are you running the plugs for?  Just a tip, but I did end up re-using some of my initial "real lean" plugs for later plug chops after I knew it was running richer than before.  It just added color to the previously white plug.  I'm still trying to use up all those darn plugs!

[Shaka]

The second pic looks pretty good.  Is that your all around plug?  My guess is that you're good on everything up to WOT.  Which indicates too small of a main jet.  You might try to go one jet larger and drop the needle.

[sidthesloth]

The needle was on the second notch and yesterday I raised it to the middle one, do you think I should try going up one more or just order a new jet? The pics were taken in the daylight, (beautiful weather at the moment, hence yesterdays ride).

[Shaka]

The needle only adjusts the fuel flow from about 1/4 - 3/4 throttle.  At WOT the needle is not a factor.  You have the needle pulled all the way up out of the jet.  If you are running lean at WOT the only thing you can do is to increase the jet size.  The needle position is really to adjust the mid-range and the transitions into and out of it.  I may have already given you this link, but if not check out the small blue graph of what "circuit" of the carb is operating at which throttle position.  This is a good visual of where you need to make adjustments.

http://www.mopedarmy.com/wiki/How_To_Tune_PHBG_Carburetors

[sidthesloth]

Yeah, after I posted thast post I realised it might be something like that. what about when cruising, just backing off to maintain speed? it seems to have a rattle there. Maybe a crabked ring, with the heating and seizing issues in the start it could be possible?

[sidthesloth]

I will check that link when I get home. (on mobile phone at the moment).

[zombie]

Hey Guys! Fell off the planet for a couple days. Amazing how much happens! Sid, I think those chops look great. The rattle MAY be pre-ignition. Do you have any photos of the head before you installed it? (combustion chamber) Are you running Hi Test fuel? My scoot has a funny rattle to it at idle, that I just live with. I re-checked everything 10 times, and figure it is just the harmonics of the set-up. If you cracked a ring you may be able to either see it or feel it thru the monstrous exhaust port on that jug. there will be a score in the jug if a ring broke. It only takes seconds for a broken ring to leave its mark. Well a plug chop at full throttle will get you set on the main jet, as the photo did look good. You may want to go 1 step colder though. For a new jug there should be a little more oil showing. the plug is showing how the cylinder looks, and I think it is a little dry for break in. Have you posted a link for the kit you have? I would sure like to see that.

[sidthesloth]

G'Day zombie, sounds like you need the antigravity boots.  I have mixed the fuel oil @ about 33:1 (300ml.oil/10.00litres petrol). I don't know what high test fuel is but am using Shell V.Power which is 98RON. (the highest available here). I don't have a photo of the head. The rattle is at cruise as you back off to maintain speed, it was worse before I raised the needle so I am thinking a larger jet, (is a 107 now) have emailed seller for a larger one, will also check local bike shop as I think it looks like a mikuni jet he showed me last week. here is the link, hope this works.http://cgi.ebay.com/ebaymotors/Honda-DIO-82cc-90cc-Big-Bore-50mm-cylinder-kit_W0QQitemZ330416972035QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item4cee62e103

[sidthesloth]

Right, found main jet to be same as keihin, so changed to 120 (also have a 125). took for a ride and a little sluggish so dropped needle back to original position, second notch. jet was easy to change through a plug in the bottom of the bowl.

[zombie]

I told you I live where it $uck$. Grav boots would make it $uck more. Hi test is slang for the best you can get at a station. The photo from the link helped quite a bit. The head has the correct orientation of the cooling fins for the shrouds, which is a good sign. It also has an offset plug/combustion chamber which is another +. The bit about the rattle does sound like pre-ignition, and that would explain why the plug has good color, but is soooo dry. I forgot to say how cool that pipe looks on the scoot. It has a massive header pipe. I can say I felt a chill... Not to sound like I read a book, and got smarter... BUT have you checked the piston to head clearance? (squish) Most people seem to agree that .5-.8mm is best. Shaka had alot of trouble w/ gaskets on the bottom of the jug, and at the top to balance the cyl.

[sidthesloth]

G'Day zombie, I did check the clearance of the piston to the top of the barrel, though I didn't measure the gap, there was clearance there.I am going for the big one and am trying to post 2 pics. Plug with 120 jet.

[zombie]

Too Lean. See the crackle on the electrode? That is pre-ignition! Was that a w.o.t. chop?

[sidthesloth]

Still thinking of trying the 125 jet. Hey, that carb. needle just turned up as I was writing this post, thanks zombie but  the new carb is in.