Having a little problem with the restored '79 DT175MX.

With new bore/piston/rings the bike starts and runs very well until it gets warm after say 10 miles or so. At this point if you put the bike under load at speed at say 4000 RPM it sounds as though it is blowing from the head or pinking? once the bike cools down its back to 100% OK. I have had the top end off and all things seem fine (Gaskets, rings, torqued heads, standard factory exhaust,etc), Carb is not blocked. I am running the bike without the autolube at 25:1 mix with quality semi synthetic 2T oil.. Is it running lean and perhaps needs rejetting without the autolube? DO I need to block the autolube pipe? Any other ideas and direction? Tks.

You need to fit some of the autolube pipe back onto the carb oil feed spigot, bend it over a few times and crimp it so it is blocked, or block the pipe with a screw. youre right to be worried

Edit, if it were me I would also be running a bigger jet. an early bike 135 maybe 140 better safe than sorry

Thanks Old git

Blocked pipe and road tested once again. Seems a little faster but began to pink after 5 miles or so when hot so I backet off in an attempt not to hole the piston.

I pulled the choke out when pinking and the noise went away which suggests a lean issue. Took the main jet out and it is marked with 10C ? (the C could be a poorly stamped 0?)

Have ordered a 130 and a 140 and will not ride 'til fitted. Ta again

If it is a 100 jet, I cant think why! That is seriously way too small when standard is 130. I would fit the 140, thats what is in mine.

Your carb should have a ID of 2H500 stamped on it by the way.

Thanks Old git

Blocked pipe and road tested once again. Seems a little faster but began to pink after 5 miles or so when hot so I backet off in an attempt not to hole the piston.

I pulled the choke out when pinking and the noise went away which suggests a lean issue. Took the main jet out and it is marked with 10C ? (the C could be a poorly stamped 0?)

Have ordered a 130 and a 140 and will not ride 'til fitted. Ta again

140 fitted all working perfectly .....Excellent thanks again