Hello hello
sorry to post this but I need to decide if I should just keep riding the machine or do some proper measurements of parts in the head.  I took the head off sometime ago and did a visual inspection but didnt measure things as there was no scoring on the piston or cylinder and no blow by on the rings.  However the bike makes a 'rattling' sound at around 6.500 to 7000 rpm especially on decel.  I even wonder if this is 'pipe' noise but I dont know.  Fairly metallic sounding.  I was under the understanding that worn rings cause the piston skirt to 'rattle' at all rpm's which is why Im asking before taking it off again and putting in new parts if necessary.  Trying to get ready for some really long rides ahead.  (3 to 4 days in a row and far from the home base) Currently I can ride the bike all day but it does have this rattle?  Cheers if you have any comments.

(again should I post this in the 1977 MX section or is it ok here? cheers)

Good ya getting out & riding it but idealy we need a good video for a listen. In the end the only way to be sure is to measure the skirt clearance & they don't run much clearance so will rattle pretty quick if it's up past 2 thou on the skirt.

If its rattling only on the overun, I would be looking to the crank and little end first.  Unusual for it to be at a specific rpm though.

 

OK thanks again so much. I have moved the needle to one richer setting to see if it runs better and its not 'pinging' at all. (will probably ride out next week to check) Like you say Tinkicker Im feeling that the little end needle bearing could have some slop so I think I will change that sometime soon, and perhaps with a wrist pin as well, then if that really isnt what the problem is I should finally check speck on the skirts. I just never seem to have the right diagnosis for problems so I dont want to change what isnt the problem,
thanks so much

Thank you thank you. A small update and again any and all input back is very very much appreciated Tried to make a phone clip but the sound was just junk. I moved the carb needle up (richer) / one clip down. It feels a tad better and definitely not worse. At 17 degrees (outside temp) bike starts on choke with a little throttle, take it off choke after a minute runs great. Revs cleanly to red line in all gears (dont really need to in 5 and 6), pipe makes quite a dang dang sound going down a steep hill in mid to low revs. There is the slightest surge at low rpms being in a gear too high. If I pin it at 6000rpm it changes sound to a bit like a chain saw, above or below it sounds like a 2stroke. It's a little (in my poor opinion) slow to come down on revs and settle at idle
It's a 600usd bike and apart from a set of tires, I've spent less than 20usd on it so far I reckon (and all that is one plug and 2 cans of paint!)
If it needs a good proper overhaul I will get to it, but it goes and has good power so I'm still feeling could any issues still be 'tuned out', maybe, maybe not, will real life prove me wrong !

Yeeeeeeeesss, made a lot of progress thank you everyone. Perhaps I have been overly cautious. I hate messing up carb settings if I'm not super sure about what I'm doing. I shall probably continue this on my restore thread but for now things are not absolutely perfect but pretty close. All the down hill banging is gone, nearly all the cla bang sound is gone and the bike feels smooth and peppy and like a 2 stroke dirt bike should feel and sound

The solution was I moved the needle to the richest clip setting. Needle up (bottom clip engaged) Like having a NEW bike, feels so good. So hopefully some real trail riding to come, catch you all next time.

Good news that going to the richest actualy fixed it.
Bit unusual to need to go so theoreticaly rich unless there's something hidden causing it.
Anyway, it works so best result. Thanks for posting.

Cheers RT, yes maybe something blocked in the carb. I did 'clean' out the intake and exhaust a little, I wonder if its more fuel hungry? I just never quite had this 'sound' before and convinced myself it was more mechanical. A few more ride outs will tell, but its night and day right now. Glad to have so much support on here because it helped a lot patiently thinking things through.

Hopefully it continues to run great and gives you many more enjoyable rides, I will say when I was in my teens over 45 years ago we were always tinkering with carbs, plugs, different 2T oils and basically doing whatever we could do to keep our bikes running with very very limited money, parts and knowledge and the occasion or two when they ran great and we said WOW it’s never ran this good it was usually short lived and the piston would seize up or burn a hole in it usually within a minute or two after our comments, we usually blamed it on the 30 wt. recycled oil we bought from the 7-11 for .69¢ a quart that we used in the injector tank on our DT’s or used it in the pre-mix for our YZ’s

Lizeec sounds like you had lots of fun and learned lots too! I use the cheapest 2T oil in the oil tank and often check the clutch side oil dip and if I hear noises I dont like I dont force things. It's not fun pushing a motorcycle home