DT175MX Jetting, Plug Chops and Confusion

[Airhead]

OK then.......

Bike...Aircooled DT175MX
Differences from standard?
Gianelli pipe, small pre-airbox removed

For a while now I've been struggling to find the right jetting for my bike, the spark plug has never really given a clue, or at least I didnt appreciate what I should have been reading from it...things seem to have changed over the years...must be this modern petrol!

I was getting this type of reading, you may think it looks weak due to the white insulater and so fit bigger and bigger jets safe in the knowlege that it will begin to go sooty as you get seriously rich, as well as the obvious bogging down 4 stroking malarky. Well no amount of fitting ever bigger jets would give me any sign of a sooty plug, so in the end I just reverted back to a 140 jet 2 steps bigger than the standard 130.

This is thi kind of reading I was getting

anyway I learned from a member of this forum 'Ventura' about A/F gauges, he uses one of these all the time to set his bike up and his little C90 race bike too

Heres the gadget I bought
its an Innovate MTX-L (Digital Air / Fuel Ratio Gauge) and before you get the idea it's expensive...how much is the price of 3 or 4 dyno runs these days?

http://www.ebay.co.uk/itm/230594206021?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_7740wt_1091

So I made a box and fitted it onto my petrol tank, and in the box I fitted a small yuasa 12v battery to power it up...but I found out later I would really benefit from a bigger battery (promptly borrowed from a vehicle jump starter)

The gauge uses a lamda sensor so I needed to weld on the sensor mounting collar to my exhaust...I had to buy a spare steel silencer for this...more expense I know but the hell with it I was having fun

Anyway to cut a long story short, I now have 2 sizes smaller main jet, needle 1/2mm lowered, richer cutaway on the throttle slide and 1 size pilot smaller...oh and a heavily oiled airfilter is now cleaned and lightly oiled.I'd have never got to these settings by feel and plugchopping alone.
Boy Oh boy! the bike is transformed and I 'v got all the gear I need if I try fitting a bigger carb which I have hanging about

Lookin Good

No matter how I've been riding now I have a great plug colour....just hope I dont hole a piston sometime soon...yikes!

However!

the bike seems to run well now but yesterday coming home from the Hope show I was experiencing some serious detonation and boy did the temperature rocket! we have some pretty big hills here in Derbyshire, I don't believe the jetting is at fault maybe theres some truth in what busyeddie posted after all, I was quick to poo poo it...maybe too quick as it turns out. so now I have the FS1E rally looming, I have a bike with detonation tendencies, a thread that needs a new insert and I'm away on holiday...not good!!

My thoughts are to back off the timing a little, fix the thread, put back on a standard unskimmed head and start using super unleaded and hope it improves

[busyeddie]

New petrol.is shit. And engine rebuilds are only fun the first or second time if youre really keen.

[blackhat250]

Well done paul" you"v a degree in Mixture now , . i had knocking with the TS250, i thot it was detonation, turns out a rebore solved it, i had rebuilt the bottom end, and stuck a N.O.S piston in , on the standard bore,,, but she didna like it,,

Am all ready for FS1E run,,, be good to meet up,

[Ventura]

The Innovate A/F gauge must be one of the most useful tuning tools going Paul.

And takes all the guesswork out of setting carbs, especially if you've strayed from the standard setup.

As you say, Ive used mine on all my bikes and my friends bikes too, ranging from vintage Britbikes to litre sports bikes and even racing C90's.

Well worth the outlay and great for peace of mind, especially when setting up 2-strokes.

Worked great on my DT175 too and I'm presently getting it rigged up for my newly acquired RD350.

V.

[DirtyDT]

Paul, Are you sure that all of that overheating isn't due to carrying half a workshop around on the DT?