The pursuit for a brown sparkplug

[Calum]

It's not really appropriate to be judging the fueling on break in, you need to put that engine under load and perform a plug chop to really understand how the fueling is doing.

Once it's bedded in, perform a plug chop and report back what the plug is doing then.

I'd say that plug looks a tad lean to me.

Easiest way to tell is to restrict the air flow into the bike, if it performs better then you know you need to increase the fueling.

[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.