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1978 yz80


rockout12001
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update again. tore it down today. i was not happy with how it was running. compression was low so it spent a whole 10 minutes and ripped the piston out. took it to the bike shop down the road and he measured and checked wear on the cylinder. he felt it was ok with just honing it out and replacing piston and rings, bearing, gaskets, etc. i suggested boring it out, but he rechecked it and said if it was his, he would just re ring it. i ordered a new piston just because i didn't like just reringing it. oh yeah, both rings were broke too. cleaned, cleaned cleaned. going to paint everything tomorrow. now my question to the techs out there. i don't have a manual, what is the head torque? now i have a stupid question-what do you run in the gearbox? the kid at the counter suggested 80wt. gear/trans lube. i drained it out and it had red fluid that resemebled transmission fluid. maybe someone put the wrong stuff in before i picked the bike up. hoping to have all of the parts by this weekend, but not holding my breath. put a new clutch in the dt100. took it out for a little test drive and what a differance. might rebuild it too. little low on compression too, but runs really good. not the most powerfull thing, but still starts with 2 kicks. starts easier than my kx125.

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any suggestions on pulling the magneto off. i have a 2 jaw puller, but it doesn't want to budge. i am wanting to replace the points, but can't get to them.

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any suggestions on pulling the magneto off. i have a 2 jaw puller, but it doesn't want to budge. i am wanting to replace the points, but can't get to them.

you will need a special tool which are common to all mags.

looks some thing like this

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i pretty much all but gave up on this forum. i ran to our local harbor freight tool store and bought a new set of 2 jaw pullers. first one out of the box popped it off like nothing at all. i just needed a new one with longer "teeth" that could get in behind and grab ahold of the hub. doesn't seem to be too many interested in old beater dirt bikes and giving information out on them. i bought a manual and will just finish the project with my son. he really enjoys "working" in the garage. our next project is rebuilding his 4 wheeler. needs a piston too-low compression.

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  • 1 month later...

i was bored and decided to check out this forum again. same as always, no interest from anyone on old small vintage bikes. well, i got the girl running, but didn't have 1st or 2nd gear. took the motor back apart and split the cases. gears stripped. found a good set on ebay for 25 bucks, so i replaced all of em(mixed and matched to get the best) and replaced all of the case seal (which fixed my idle problem from another post). took it out for a little spin and i am so glad i decided to keep it and fix it up. first off, my son and i have something to talk about besided cleaning his room or not pissing his mom off somehow. we got to spend some great quality time together and i hope he was able to learn something besides the cuss words when i couldn't get the thing to idle. only bad thing is- he broke his collar bone playing football and can't ride it for a few weeks. we now have another project- a vintage ktm 125 to restore. we rebuilt his quad and i just re did my beater quad. now i want to restore the dt100. it does run great, but looks like crap.

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  • 1 month later...

[any old yamaha is worth restoring .........................................................

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i was bored and decided to check out this forum again. same as always, no interest from anyone on old small vintage bikes. well, i got the girl running, but didn't have 1st or 2nd gear. took the motor back apart and split the cases. gears stripped. found a good set on ebay for 25 bucks, so i replaced all of em(mixed and matched to get the best) and replaced all of the case seal (which fixed my idle problem from another post). took it out for a little spin and i am so glad i decided to keep it and fix it up. first off, my son and i have something to talk about besided cleaning his room or not pissing his mom off somehow. we got to spend some great quality time together and i hope he was able to learn something besides the cuss words when i couldn't get the thing to idle. only bad thing is- he broke his collar bone playing football and can't ride it for a few weeks. we now have another project- a vintage ktm 125 to restore. we rebuilt his quad and i just re did my beater quad. now i want to restore the dt100. it does run great, but looks like crap.

Hi, You have my interest here. I am restoring a YZ80D and have it all together thanks to donor parts from a 78 yz80E. Trouble is I have no spark and am wondering what to do as this part of a bike is not my forte'. I can telly that it has a magneto and that there is no spark. The key was broken off of the shaft that the magneto is held on with and I made a new one. Beyond that' I'm stuck. Any thoughts? Places I could find a how to on the magneto ignition system. I've beat up google pretty bad and have found nothing....

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