The pursuit for a brown sparkplug

[Jens Eskildsen]

This is mine (no kit though), a bit of deposits from excess oil, but otherwise tan as Hasselhoff!!

[Irongamer727]

Wow! I'm impressed! I'm now running 290 main jet. Can't feel much difference. My issue is, it does not pull after 3/4 throttle. The revs go up, exhaust getting louder, I brace for the real powerband but then nothing.. Dropping to 3/4 and she goes! But there is definitely power left to scavenge. My next alternative is to try a 270 main jet. And yes I've tried the choke, no results.
Should I really be giving the piston, cylinder full throttle? I'm closing in to 300km.. Shouldn't be an issue right?

[Irongamer727]

This post is deleted!

[Irongamer727]

I've tweaked the oil pump a bit for my Athena, will this dramatically lean the mixture? As I've said, I'm running far bigger jets than anyone I've seen used the big bore kits.

[Darty]

@irongamer727 What is your bike not doing?

I dont get it.

[Irongamer727]

@darty it's not performing well in the upper revs. The jetting is off, I'm steadily climbing in sizes (now 320) but the plug still looks a bit too lean.

[Irongamer727]

And I have a friend running 240 with the kit. We are both running stock Air box and so forth.

[Glynn123]

Are you certain there's no leaks between carburettor and crank case? No head gasket leak, and no leaks in the carburettor itself allowing air in?
I'd say there's definetely a leak somewhere allowing a lot of extra air in.

[Irongamer727]

@glynn123 nope everything is sealing, not leaking etc.

[Calum]

You using the stock carb? Pretty sure they use a powerjet which should be the jet you want to be changing.

[Irongamer727]

@calum yep there is a powerjet. I'll give the really big jets a try first. Because again, I've not heard anyone changing anything but the main jet.

[Calum]

@irongamer727 So the powerjet kicks in at wide open throttle.

You should be doing a plug chop at WOT.

Therefore, changing the main jet won't affect the colour of the plug during a plug chop.

[DTR+NSR]

Pretty sure the power jet isn't changeable on these carbs.

[Irongamer727]

@calum I'm currently going WOT sixth gear and turn ignition off. I can thereby see the plug colour at WOT. And it still looks a tad to white for my taste.

[Darty]

The Powerjet is a fixed system on the TM28,

I used to run 340 Main, 30 Pilot, only because of extensivly modifing the Airbox volume,

And, it was rubbish mostly.

I had to replace my main body Carburettor gaskets because of symptoms near enough the same as you.

I would recomend throughly checking for Air leaks as this is almost certainly your problem!

Dont just throw fuel at this and hope for results.

Work backwards.

[Irongamer727]

@darty how would you check for Air leaks then?

[Irongamer727]

I do have the entire pice where the snorkel existed cut out. So there that as well.

[Darty]

@irongamer727 You donkey,

Why dont you try and restrict Air by patching up a section of the Airbox,

By doing so, i’ll bet a Roast dinner that it sorts out your lean condition.

I’ve played around alot with this, you’ll stuggle to fuel this properly with the TM28

[Irongamer727]

@darty there isn't a good way of doing it, patching the Air box up I mean. In theory, I'll just get a slightly higher fuel consumption than "everyone else". From what I've understood the airbox is quite restrictive.

[Darty]

@irongamer727 True, there are ways around it with Aluminum plate and bolts,

Basically, deal is, you cant complain if you dont see results without trying this first.

If you are determined, Start larger with a main, 350 - work backwards, its safer.

I personally dont recomend having the Airbox chopped completely.

Yes it's restrictive as standard, but otherwise you’ll see a significant drop in torque under 6k.

And without a larger carburettor, insignifcant Power gains at high RPMs without ignition timing adjustments.

Mostly bark, no bite