1984 Katana 7/11

[pete]

I've ridden it to work both Tuesday and yesterday and the idle is a bit too lean for my liking as it gets to low 14's, so I wound the air screws in a quarter turn last night. Only thing there is if it richens the 1/8 throttle cruise up too much I'll likely need to put some bigger pilots in which from what I've read is not unusual for these carbs. See how it goes today.

[Grimly]

Got mine installed in a temporary fashion today. Just a quick and dirty lash-up that can be removed in two minutes.
I'll make a better enclosure for it; as the one I made, while it does the job just looks totally trashy.



It's not showing mega-lean, that's just it running through its setup routine. Earlier on I warmed the bike up and got some figures from it at least while sitting in the workshop unloaded. It's sitting at 13.1 at any steady rev state up to 3K. Interesting to see the SU enrichment process working when I open the throttle.

[80GS1000]

Got mine installed in a temporary fashion today. Just a quick and dirty lash-up that can be removed in two minutes.
I'll make a better enclosure for it; as the one I made, while it does the job just looks totally trashy.



It's not showing mega-lean, that's just it running through its setup routine. Earlier on I warmed the bike up and got some figures from it at least while sitting in the workshop unloaded. It's sitting at 13.1 at any steady rev state up to 3K. Interesting to see the SU enrichment process working when I open the throttle.

Which AFR gauge is that with the blue numbers?

[Grimly]

Which AFR gauge is that with the blue numbers?

14point7.com
It's the Spartan 2 with the 52mm gauge (extra).

[pete]

Good stuff Dave, how big is the Spartan unit itself? The 14.7 SLC Free is still on my list but that'll now be next year ready for when I rebuild the head.

The quarter turn on the air screws seems to have sorted the idle out nicely without screwing up the 1/8 throttle cruise. It sits nicely at low 13's now with 1/8 still at that mid 12's to low 13's, at least on the commute anyway.

[Grimly]

The controller is barely a bump on the wire, actually narrower than the connector it's attached to.
Caused me a moment of acute anxiety when the damn thing wouldn't disconnect from the sensor lead, and I was worried about damaging the body of the controller.
Moving on... today's results were mixed.
I quickly sussed the default settings I'd been running with were far too rich, but that was good, better than too lean.
After a warm up of around ten miles I jacked the jet up by a turn on the screw and got an idle reading of about 13. Taking off down the highway, it was immediately obvious the bike was breathing better and mid-range responsiveness was improved.
Things aren't right yet, but this was just a settling-in exercise while I did some shopping.
Steady cruise at 4K is around 13.9 to 14.1, cruise at 5K is 14.5, while 6K is getting leaner at around 14.8. I didn't push it too hard into the top end, as the rear tyre feels a bit squirrelly, so that's for later. There seems to be a tendency to lean out as speed rises, so a different needle will be needed. Otoh, the instant reading of the acceleration mix was an immediate drop to 12-ish, which is good.
All in all, I'm quite happy with this purchase, so hope it lasts. I wasn't reading good reports of both AEM and Innovate gauges crapping out, which is why I bought this one.

[pete]

Good stuff Dave, sounds like success is on the way! I'm still keen on giving the SLC Free a go when I get to that point, but it'll be interesting looking at the pure lambda number as opposed to the stoichometric ratio, not sure if I'll choose to use a gauge or just stick with the standard display yet.

These things may be obvious but were things I've discovered along the way... CV carbs are best tuned by steady RPM's as opposed to throttle position which is different to what I'd kept reading, but of course makes good sense when you think of how they work. When tuning the stock loaner carbs I took note of the idle mixture, ~2500 to 3000RPM cruise, ~5000RPM cruise, and then WOT.

With the VM33's though, everything has been done on throttle position... idle, 1/8 cruise, 1/4, 1/2, 3/4, and WOT. The hardest readings to ascertain have been 3/4 and WOT, and the reason for that is purely due to the numbers in red circles posted on our roads here It's really hard to hold 3/4 and WOT throttle long enough to get a good consistent AFR reading and stay in those legal speeds. In fact 1/2 throttle was hard enough in that regard...

In both cases, what I found the most challenging was resisting the temptation to take note of instantaneous number changes on the gauge. You always need to hold steady RPM's or throttle position for probably 10 seconds or preferably more to really get a good accurate assessment. It sounds like a short time, but 10 seconds at WOT on an 1100cc bike is a challenge when trying to obey road rules! My experience says both the VM33's and CV's will lean out noticeably when first changing throttle positions (the VM33's quite dramatically) but the AFR will quickly change once the throttle is steady again. I hope that makes some sense!

Going by your numbers there, definitely seems like something needs richening in the needle department. Over here, our needles from the factory have 5 E clip positions, meaning we can raise the needle very easily by moving the E clip down one notch. Do you have that option or do you only have one notch? If you have one notch, it's possible to insert a shim above the E clip to have the same net effect of richening the needle up. Not sure if I'm telling you something you already know there though.

[Grimly]

This is on the SU, so no fiddling with clips and notches involved.
Instead, there's a world of pain awaits if you go heading in the wrong direction and change the wrong things.
There's the obvious, like the needle profile, then there's the dashpot spring which determines just how much of a venturi you get for a given throttle opening - there's a choice of three or four, although the vast majority of applications usually need one of two. Of course, the venturi opening given by the spring lands you in a different pattern of fuelling on the needle... and so it goes on.
It's entirely possible to think you've got it, but you've gone down a wrong turning and should have done something else. It will work, but not quite right.

At least, that was the case when I was playing it by ear and doing the odd plug chop. It worked ok, and I never did any damage, but I always knew it could be better. Much nicer to see some figures dancing around, showing me exactly what's going on.

I'm going to sort out this 38mm carb for once and for all, then look at putting the 44mm back on, and with the aid of the AFR gauge be able to tame its rough idle and slow-ish mid-range response. The big carb delivers enough fuel for the factory's 80hp, just getting it to do it neatly and cleanly is the challenge.

[pete]

Ah ok, I have zero experience or knowledge of SU carbs. I've heard of them but that's as far as that goes... sounds complicated!

A mate handed me a set of 107.5 main jets on our ride yesterday so I'm hoping to get out for some 3/4 and WOT tests today and see where they put the numbers. Gut instinct tells me it's going to be on the lean side as that's three sizes down from the 115's, but it'll give me a good reference to make a better decision on which size to buy.

[pete]

Test ride observations from this morning's ride with the only change being the mains dropped from 115 to 107.5...


Steady quarter throttle has become a bit leaner, seeing up to low 14's now, 1/2 throttle still good, steady 3/4 and WOT are in the low 12's now.


That would say I could possibly go down another size, not sure why steady 1/4 has changed though.


The standard VM33 issue of cracking the throttle and watching the fueling go lean is now beyond just noticeable, the gauge max's out and the engine basically stalls until the throttle closes a bit.


Given 99% of the time that I use 3/4 throttle and up is for short bursts of acceleration only, I'm going to do what I think is the sensible thing and go up to 110 mains. Steady 3/4 and WOT will be a bit rich but I'm fine with that, will still be much improved over the way too rich condition it has now.

[pete]

Finally got out for a proper ride yesterday with the 110 mains and I'm happy at last. It still gets too rich at sustained 3/4 to WOT but it's made rolling the throttle on up to that point better than the 107.5's were... or at least it seems that way. Keeping sustained 3/4 to WOT around here won't have me riding for much longer

Anyway, I'm really happy with how the VM33's are now, figured out how to ride my favourite twisty road with them, and the acceleration is so much better out of the corners than with the stock CV's. Mind you I got a new rear tyre on Friday and that helps no end as well.

I'll take the AFR gauge off today so I can finally give it back to my mate, shouldn't need to do anything aside from servicing now until I'm ready to rebuild the head.

[zuluwiz]

Spend much time at 3/4 to full throttle and you'll be buying LOTS of new rear tires, that is, when yer not in jail.

[Rob S.]

Spend much time at 3/4 to full throttle and you'll be buying LOTS of new rear tires, that is, when yer not in jail.

Heard that. 5k miles ago (5 years) bought a new set of Pirelli Sport Demons. Front looks absolutely new. Rear has quite noticeable wear down the middle. Hoping to get at least another 2k from it. Front looks like it'll last forever.

[pete]

Hahahahaha yes I like to keep my license and life intact... and make rear tyres last at least a little while

I got about 4500 kms out of that old hard BT45 that was on the rim and it was quite used already, but I suspect that was only due to it being old and hard, and me taking it easy knowing it was old and hard... I suspect this new BT45 may not go so well.

[zuluwiz]

As I recall ........ I got about 2000 miles (3000km more or less) out of the rear Mag Mopus that came stock on my GS1100 way back when. Didn't take long to do it either.