Wednesday, September 20, 2017

Minnie the 400 Monster: Not getting anywhere

Man, this thing is just kicking my arse.

What often happens with a project bike of mine is that at some point I go off on a pointless tangent and just dig myself a great big hole.  No point breaking tradition here.

My custom job introduced an obvious issue with the 2 - 1 exhaust, and it has occurred to me that adding the fairing may have played with the fuelling as well.  I've certainly been caught out on that before.

I'd be thinking about what to do about it, and had been getting close to buying another std horizontal header to modify to work with the ceramic coated vertical header and then get a couple of mufflers made to suit.

Thinking about what I had seen with the dyno runs so far, and Dave's comments that i should rejet it to fix the top end richness, I had a look back at some of the runs to see if there was anything to give me hope.  I know from lots of previous experience that top end richness on the Dynojet really kills the power.  Maybe it's richness past the torque peak, as it doesn't seem to affect the power as much through the middle.  A couple of runs caught my attention.

Red is the 2-1 header with the Danmoto muffler and no baffle, blue is the same with one of the snorkels removed to lean it out.  The improvement in top end power with mixture a bit over 13:1 (good for dyno power, but a bit lean on the road imo) was about 4hp.

4hp is about what I'm down from the original headers.  Red is std headers and two Megacycle mufflers, blue is 2-1 and one Megacycle muffler.  An extra 4hp through the top end would be just great, especially with the midrange improvement.

So the obvious was to lean it out.  When I fitted this 400 engine I set these carbs up with the 2001 M400 jetting, which is the same as the M600.  From my video of the slides lifting through the air filter lid, I figured the rich dip was main jet related.  Std is 132.5, and I had 122.5 and 127.5 on hand to choose from.  I was concerned 127.5 wouldn't be enough of a change, so went 122.5.

Easier said than done.  The fairing mounting brackets I made bolt off the bottom of the ignition switch, and all the wiring for the dash, including the original loom sections I needed to hide, are jammed on top of the airbox under the ignition switch.  All of which had to be removed to get the airbox out to access the float bowls.  I'd forgotten about all that guff when I allocated a couple of weekend hours to a main jet change, so it was straight into tanty time from the get go.  Only got myself to blame, on so many fronts.

It's fitted with a heater kit too, so the float bowls are hard to far enough out of the way to get into the mains.

After I had it back together I went for a ride.  Well, first I had to make the dash work again, as disconnecting it made it lose the wheel diameter and the tacho seemed a bit screwy, reading a bit too high.

On the road it felt great, revving out nicely compared to how it had felt before.   Brimming with (over) confidence, I took the chance for an early morning trip to the dyno and typically it went tits up.  On the way there I tried some WOT and it felt pretty crap - flat and surgy - through the midrange.  Turns out it dynod just like it felt.  Crap.

Compared to some previous runs, it gets a bit murky.  The dyno has just had the air/fuel cell replaced, so I don't know if that has influenced anything.  Doesn't explain the difference in how the bike felt though.  Anyway, red is with the leaner 122.5 main jets and one snorkel removed.  Blue is 132.5 main jets and about 5 degrees more ignition advance over std.  Green is the same, but with std ignition advance.  So I really don't know what is going on with it.

The problem is where to go next.  I want to fit some 620 cams to see what happens to the power curve.  I'm hoping that with the early inlet closing, they'll peak the power lower and reduce the need for so many revs.  But, the fact the factory used the 800 cam in the M400ie instead of the 620 cams makes me wonder if that too is just folly.

Before I do that, I want to make sure the result is not tainted by an idiotic exhaust or a wacky fairing.  Plus I have no idea what the original jetting was like with the original headers, which may itself have not been good.  You know where that's going.

Either way, the airbox needs to come out and the 132.5 main jets go back in again which means fighting with the airbox and wiring and other crap and really, I'd have been far better off just leaving the jetting the way it was and fitting the original headers I have.  Joy.

I can always refit the other exhaust when it needs to look good I guess.  I'm even going off that look too.

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