Some jetting and indexing
 

Got the larger jet kit.

Had the Nibbi in and out a few times swapping jets...no real access inframe.

from 40/140 showing lean hi temp on the boao big bore kit.

I jumped to 45/150 with a rich result and a flood out at WOT snap at 50mph ish...sooty plug

went to 42/142 better result but again still a lean WOT stumble at speed... White plug

I now have 40/145 still at mid clip all testing. No ride yet as I am actually trying to be economical with fuel expenses. So next milk and bread run will see...But I feel confident. I do have 148 main to try next if still somehow lean on WOT.

Meanwhile I found the clutch pivot was making contact with the exhaust pipe leg shield which was the likely clutch slip issue...so adjusted that. The pipe was shifting into its preferred hold position...

Also in that vicinity the kick start lever was rubbing the case, hit it with the flap disc for bespoke clearances...

XLCG 250 ADV aka Grocery Getter
 

Added some 'Ghost Racing' semi soft saddlebag/panniers (ebay acquisition) .
Used my old HDPE inner supports from the bicycle bag experiment.

So now the bike is in "Adventure" specification. But mostly for getting some groceries...

Also added a photo just to prove I am actually in Australia if anyone had doubts...

Got home still hitting hesitation WOT...checked plug...still white.

145 to 148main and then its clip position testing.

42pilot 148main 4th clip nice power delivery up until yet again another hesitation stumble at WOT.

plug is a hint of tan...

But getting the tune right on the BOAO dished piston seems to want way more fuel up top...

going to try 152main...

the previous flood out might have been the 45pilot jet when throttle snapped shut.

Unfiltered
 

Trying to work out my carb fueling woes...

taking off the seat, tank, throttle slide and about too remove the carburetor when I opted to inspect the fuel supply system...

was using an inline cheap filter which looked clean and was passing fuel when the supply was open...

But on closer inspection I believe to have found the smoking gun to my top end WOT stumble/hesitation/lean burn condition....

part of the paper filter element has separated from the base and caved in partially restricting the output barb...

I was about to try a 152 main jet from a 148....however seems a test with no inline filter is the next carburetor tuning process...

I am continually amazed that all Australians were not killed off decades ago, what with them driving on the wrong side of the road.....

Natural selection in Oz is on another scale.

No inline filter test...much better response almost running WOT with only stumble at much higher RPM limit.

Will try the 152 main, which will hopefully iron out the last crease...

That is a huge jet! Maybe it will work, but I thought most 250s on this site are running 115 to 130 range?

I wonder if the needle is controlling the mix OK in the midrange but wide open is actually too rich? Could it be possible. I know your logic is based on the idea that you are getting more fuel (no filter). But a 152 main seems like an outlier. If you have much higher airflow, maybe is is needed because the vacuum generated by the venturi is relatively low (compared to a smaller carburetor).

:hmm:

My only explanation is the BOAO dished piston has increased combustion chamber volume so more air needs more fuel with curve demanding more at WOT high rpm...

I'm a little shocked too but that's what the spark plug and bikes running behavior is telling me to do...


I think my other big bore was a 42/135?/3rdclip before it ate itself...

Stock piston 40/130/3rd clip.

Looking at the Nibbi PE28 specs a 150 main jet is already maximum listed tuning specification.

The only other possibility is an inlet manifold leak that develops at WOT the O'ring looks ok though but I might change it if the 152 does not make the stumble go away...the inlet manifold was modified and outsourced alloy welded but I did have to use JB weld to seal some pinholes come to think of it...

Perhaps its a top end phat bog all along...

Sprayed carb cleaner around the manifold with no noticeable change...

I tried the 152...definitely a bit doughy now...I think the pilot and needle is correct for 4/5th of the throttle range...

My overly lean condition was down low from the outset perhaps..?

Checking the plug now is still tanish and can't hold WOT to effect the plug...

So where to try the main jetting from...perhaps back into the mid 130's

135 main...did a full local loop hit 65mph WOT with 1 little hiccup hitting RPM limit...

Definitive result...Also I think my previous flood out experience might have just been a kill switch nudge...

Plug isn't white now but some ash grey...So going to try a 138main...

138main...back to WOT bog above 7k RPM.

Needle clip position testing. heading leaner from 4th to 2nd. If that does not work then the 135 so far is the closest to optimal with only the 5th richest needle position to fall back on.

Though from what I understand needle clip is mid range tuning... So if the 135 main is close to optimal at WOT and the 138 behaves rich again then only a jet a fraction higher or perhaps lower than 135 will be the perfect oatmeal...

unfortunately I do not have any jets in between 130-135-138.

So it seems 135 with clip testing is all that remains in my tuning range.

Needle clip testing is indicating the 4th clip is optimal across the mid range.
might try to find some 133/136 main jets but from all the configurations and over rich main jet bog mistakes at WOT. 42pilot 135main on 4th clip is about as close to dialed in as I can get with a 4*advance key and BOAO big bore kit.

More exhaust pipe modification
 

My exhaust was popping off and not in a good way.

The attempts of using mountain bike seat clamps would inevitably vibrate loose...tried all matter of things to make it work like extra nuts and shims but I've experienced to many pop offs now that its becoming a possible risk.

So I found an old couch seat spring and some cup holder hooks and adopted the spring hanger method...

It can wiggle around and heat expand now with unlikely chance of pop'n'flop.

Also by removing the clamp i gained enough clearance to run the side luggage racks inboard again so slimmed in the profile aka less wide hips

Went for a local loop...exhaust held up with no more detachment concerns.
hit the 100kph/65mph straight and got the stumble/fishbites at WOT again.


135main jet in early summer heat air temps seems to behave rich again at WOT.



Still waiting on the 133main jet to arrive but there's not much adjustment left between 130-135.

Here's Me thinking All was fixed...
 

Go figure...


Went for a Saturday morning jaunt thinking that XLsior (the bikes name not mine) won't let me down on such a nice day...


Well Murphy's law had other plans.


about halfway my exhaust suddenly became a lot louder but my complacent thinking told my brain that there was no possible way it could have come loose after all that went into fixing the slip join...


I get to my halfway destination and park the bike...


Look at where the muffler is supposed to be and it was vamoose.


So closer inspection under the guard leads to a snapped header pipe...


Which implies the muffler hanger bolt came loose and fell out and road bumps found the weak point...(Probably 1 of my welds)


I'm think the days of Aussie muffler might be over for this bike...Well that's what the bike is trying to tell me it seems...



On way back trying not to wake everyone with open header pipe pop-bangs I found the ejected muffler can with the springs still attached and a few deep road scuffs..


Road rest of the way home with tail tucked between legs...


think i'll be looking for a stainless steel complete exhaust package with Aussie muffler going towards the 81 poochie project.