Do I need new piston/rings

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Ok, think I'll just ask my question here instead of starting a new thread. So going through a similar rebuild, honed the cylinder out and bought a new piston and head with valves pre-installed and rings pre-installed in the piston....

My question is, when installing the new piston, I see in the service manual that we should be placing the gaps in the rings at specific positions, ie, the top ring gap should be facing forward toward exhaust and the bottom ring should be toward the back, with the two retainer ring gaps, where the oil ring is, should be about 90degrees apart from each other toward the front.... what is the word on this, is this really important? I don't quite understand why it's important as I imagine the rings (gaps) will rotate naturally with vibration etc. while in use so what's the point....
 
You shouldn't have any gap's on a thrust side of a piston, eg top or bottom on a horizontal engine

12RingInstall.jpg



The more end gap's that are lined up with one another, mean's it won't take too many stroke's before there is a groove cut into the bore in that spot.
 
Yeah they will move, it doesn't really matter that much, just as long as they aren't all lined up to start with
 
Ok, but then I'm wondering, given all the strokes of the pistons in all the 4 banger pit bike motors outs there, there has to be someone out there who's piston gaps all lined up at the same time for a short period of time......that would mean you could randomly get a grove worn into your cylinder.....???wtf. Lol.

I'm wondering why there are no gap placements like on 2strokes, the ring basically can't rotate then, problem solved....
 
2 stroke's are more critical, this is due to the inlet, transfer and exhaust port's being in the actual barrel/bore
 
Ok so i went up to a 102 from 100 the exact same thing though. No change.
But i was playing around with the mixture screw and noticed if i screwed it all the way in the bike would keep idling fine that was with the idle turned up a little bit.
Shouldnt this cut the fuel off at idle?
Dunno if that helps work out the problem or not
 
Mixture screw wound all the way in will be as rich as you can get at idle with the #38 pilot jet
Opening the slide will compensate for the over rich idle mixture, but it wont fix it dying at mid rev's

Try putting the mixture screw back to 1.5 turn's out or where ever it was before your last adjustment's and try lowering the clip on the needle onto the bottom notch to richen up mid range
Another thing to try is a thin washer/shim (.8mm or 1mm) between the needle clip and the slide to raise the needle and richen the mid range mixture's
If this help's, it sound's like you may need the #105 Main jet, with the needle clip in the middle
 
Alright i ended up going to #105 main midle notch on the needle now it runs well through the entire range but only whilst the choke is on. As soon as i turn the choke off it starts to rev real high for a bit and then backfires and goes out then it wont start again.
I have also sealed up another leak in the exhaust not sure if this would have made a big difference or not on the issue?
 
Might need a #40 Pilot?
Did it run ok with the mixture screw at 1.5 turns out, or did you need turn turn it in more to richen it?
 
I couldnt get it to run without the choke at all no matter where the screw was.
Im guessing fixing the last leak in the exhaust changed alot then?
It idled almost notmal with the choke on at 1.5 turns out. What is the normal position for the screw for the slide ment to be set at?
 
Idle speed screw once it's tuned should have the slide sitting so it's about 2mm or so off the bottom of the carbys' bore

You might have the idle speed too high and have tuned the mixture screw to suit, sound's like you have the engine running off the Pilot circuit and also running off the main jet
 
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Ok i will take the filter off check the slide hight set it to a couple mm from the bottom and then start again.
So i get that right adjust the mixture screw to run right and then go from there. I will go back through it tomorrow when the neighbors wont get so upset about a bike starting late at night haha
 
Ok so i pulled the carby off checked the slide height and it was only a couple mm from the bottom if i looked at it from the engine side is that the right height or is it supposed to be 2mm from the rear side?
I set it so there was 2mm looking at it from the engine side. Also noticed the clip from the needle had fallen off so that didnt help that is now put back on.
Started it with the choke on it was reving really high so i turned it down slightly more. Let it warm up and when i turned the choke off i got the same effect it started to rev heigher again?
Tuning carbys will be the death of me lmao
 
Having no needle clip will make the carby super lean, so that's why it wouldn't run without the choke on.
So now you'll need to adjust the mixture screw again like you first did, and it should be all good to go.
 
Ok so i have got it idling fine it idles best around 1 1/4 turns out and rrevs well at wot but in between no throttle and giving a quick blip first one is fine second one dies and kills the motor if i hold the throttle open. If i back off and give another blip to half throttle it backfires every blip of the throttle after that.
Would that mean the needle is running to rich?
Or the pilot. Currently pilot is at #38
I dropped the main to 102 thinking it may have been pushing a heap of fuel in there and then backfiring on the next rev but that didnt help.
 
Backfire's/popping is too lean.

Try resetting the mixture again and see if it is the same.
Warm the bike, raise the idle speed a little then adjust the mixture screw till it idle's the fastest and smoothest, then drop the idle speed again.
Remember after each adjustment wait 10 seconds or so till it settle's

I would have thought the #105 main jet and needle clip on the middle notch
Air filter is on when you're tuning it isn't it ?

If it still hesitate's a bit try richening the mixture up, turning the mixture screw in a touch, up to 1/8 turn at a time, then finer as it get's close
 
Yep air filter is on.
Ok so backfiring is to lean got it will give it another go.
 
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