Good to hear that you seem about sorted Flyday58 and that the bike is a runner again.
Ive been struggling a little to fine tune the jetting and tuning on my '79 DT175 since rebuilding it and find the above comments about jet sizing very interesting.
While I was running mine in, with stock 130 main, it was fine and dandy up to 4,500 rpm, but when I took it over this I first started to experience very"boggy" (rich) running then at 5500 rpm the dreaded "flappy" over-lean noises!! Not good!!
As I had a spare Gianelli silencer I welded in a bung and fitted the A/F gauge I have for tuning my other bikes.
This is when the sniffer screws in.....
The A/F results I got were very interesting.
At tickover to 4500 revs, while riding in all gears, the A/F was spot on around 13:1 which is roughly what we aim for.
Very soon after 4500 the bike went suddenly ultra-rich (around 10.3:1) and bogged down to the point it was 4-stroking.
Feathering the throttle got it thro this, but at just over 5500 revs it then went ultra-lean (15:1) till the revs went over 6200 then went rich again to the point at WOT where it was running at 11.5:1
This sudden over-rich and then over-lean running, in such a short rev range, must have been a product of some strange resonant harmonics going on in the airbox and/or exhaust as it came and went in such a short time. Not something that would happen if down to just jets and needle position.
I couldn't get the mid-range bogging sorted until I removed the top cover of the air box which, altho it still goes rich, now doesn't badly effect the running too much.
The over-lean part at 5500 revs has been much improved by raising the needle.
But the interesting thing is that the stock 130 main is, if anything, a bit on the rich side already.
The way Im running, and the results Im getting, at the moment I could easily drop down to a 125.
If you guys are running 155/160's then from the above you must be running very rich at WOT.
Unless of course you have a pod filter or the likes and have binned the airbox?
I have recalibrated the A/F gauge so no inaccuracies there and have now refitted the stock silencer which hasn't seemed to effect things too much.
The running-in, lean running, problems I was having were obviously due to the fact I was limiting the bike to run in that short 5500 - 6000 rev range which was causing all the lean issues!!
More food for thought!! ..................