Inconsequential ramblings of an Old Git

[Scuffmark]

Arr, you've been further into your forks than I have . Interesting to know.

I've not ridden my smc since altering my forks so it'll be Interesting to see if its made a difference.

[mangocrazy]

It's more than a bit annoying - with the forks in pieces, now would be the perfect time to dig into the compression shim stack. But I'm totally certain that the part I need to butcher wouldn't be available as a spare part, so I'm a bit girly scared of doing anything too brave.

Be very interested to hear your feedback on the air gap mod when you get the chance to ride it. How much did you change it by?

[Scuffmark]

It's more than a bit annoying - with the forks in pieces, now would be the perfect time to dig into the compression shim stack. But I'm totally certain that the part I need to butcher wouldn't be available as a spare part, so I'm a bit girly scared of doing anything too brave.

Be very interested to hear your feedback on the air gap mod when you get the chance to ride it. How much did you change it by?

20mm ...Airgap is now 120mm

The manual has the smc as 100mm +/- 20mm so not exactly out of spec but just thought I'd give it a try.

[mangocrazy]

Be very interested to hear your feedback on the air gap mod when you get the chance to ride it. How much did you change it by?

20mm ...Airgap is now 120mm

The manual has the smc as 100mm +/- 20mm so not exactly out of spec but just thought I'd give it a try.

Hah! That was exactly my reasoning - air gap on my forks is specified as 80mm +/- 20mm, so I'm going with 100mm.

[mangocrazy]

I finally plucked up the courage to attack the staked end of the compression stack with an Aldi Dremel clone fitted with a diamond burr. This allowed me to remove enough of the staked material to permit removal of the end nut. Once I'd removed that I was able to measure the thread pitch, which came out at a scarcely believable M6 x 0.5. I've encountered M6 x 0.75 before, but never M6 x 0.5. That is a ridiculously fine thread.

Anyway, I was then able to measure the shim stack and relay the results to a suspension guru I know. To reduce the harshness of the high speed compression damping he suggested that I remove the shim closest to the shims around which the shim stack deflects to see if that improves matters, although his view was that the piston itself may well be the problem, not flowing a large enough volume of oil.

Anyway, it's something to try (along with increasing the air gap), so it wasn't a totally wasted exercise.

[mangocrazy]

So while I had the forks off the bike and drained of oil, I thought I might as well see what the rebound (RH leg) shim stack looked like, if only for reference purposes. This time the staking on the rod was only done in a half-hearted manner and the nut came off with only a small amount of resistance. I cleaned it up with the die, in the same way I did the rod on the compression side. I spread all the components out on a piece of clean towel on the bench and measured everything up. What was noticeable was that the shims closest to the piston were what I would best describe as triangular. I guess this was done to reduce obstruction through the return side of the piston as much as possible. Any way here's a picture of a shim stack, if that floats your boat...

DSC_4972.JPG (461.14 KiB) Viewed 1224 times

[mangocrazy]

Did some messing about with oil levels, and I've decided that I'm going to take the path of least resistance and just put 500 ml in each leg (manual says to use 534ml). That means I get full use out of a litre bottle of oil - not that I'm cheap or anything...

Can't put everything back together yet as I'm still waiting on some slightly softer fork springs to go with the softer spring I fitted to the shock last year. I have a very sensitive derriere, I'll have you know. Having the bike up on stands is really annoying, as it means I can't get at anything in the shelving rack behind it. I definitely need some bike therapy as I'm finding myself getting annoyed at the slightest thing at present. Ho hum.

[Supermofo]

I definitely need some bike therapy as I'm finding myself getting annoyed at the slightest thing at present. Ho hum.

Definitely helped me last week. Home schooling, work and lockdown are a grind for sure. Hence why mine will be used today for errands, I'd be on my own in the car as well but it's just not the same.

[mangocrazy]

It's a bummer having 2 bikes in the shed, neither of which I can use. The Duke is up on stilts with its forks out and the petrol tank on the LC has been lined internally with an epoxy coating to inhibit rust and is sat in front of the radiator quietly curing. Even if the LC tank was usable I wouldn't be riding the bike as it's awaiting its tax and MoT-free status which is due on 1st April 2021 (bike was first registered on 8th August 1980). I'll be down the Post Office first thing on that date to get it sorted! It'll probably piss down for the entire month of April knowing my luck...

[Supermofo]

If it does (rain) we'll know who to blame!

[Skub]

If it does (rain) we'll know who to blame!

Yeah,we have his card marked if the weather is shit.

[mangocrazy]

A bit more detail on the 690 Duke (R). It's a 2017 model (the last of the line of the R models) with the latest, twin balance shaft, engine. It's Euro 4 and the slow speed fuelling has always been snatchy when running in the closed loop part of the map. To meet emissions targets it has to run impossibly lean in the closed loop, leading to rideability problems. Euro 4 compliance hits big singles the hardest, which I suspect is one of the reasons why KTM have called time on the Duke 690 range (the engine lives on in the SMCR , Enduro and Husky bikes).

Back in November 2019 I took the bike to Andy at BSD Performance to try and fix the low speed fuelling issues. The dodgy-by-design fuelling was compounded by the rather aggressive nature of the fly-by-wire throttle, which gives an instant reponse to the throttle in all gears, including the lower ones. On one of my favourite roads, which has a lot of hairpins and 2nd and 3rd gear corners, a combination of the above meant it was difficult to maintain smooth progress. In the higher gears it was great, instant grunt, but it was all a bit too much in the low gears.

Unfortunatelly Andy found that all the maps on the bike were write-protected. He could read the maps but not alter them, so all he could do was disable a couple of sensors. However a year later when I contacted him, he told me that he now had software that could defeat the write protection, giiving him modify access to all maps. So not only was he able to correct the low speed closed-loop fuelling, he could also modify the throttle behaviour in the lower gears, making the initial response softer and more gradual. Full gas in all gears was still available at WOT but the 'slope' of the response was gentler initially, ramping up the more the throttle was opened. He also managed to find a couple of extra horses lurking at the top end, bless him...

Here's the dyno trace. 72.61 bhp at the rear wheel is not shabby for a 690cc single. What it does show is that there's precious little to be gained by hanging on after 7000rpm. Best to change up at 7k and use the fat part of the torque/power curves.

Duke_690R.jpg (94.36 KiB) Viewed 1170 times

[mangocrazy]

If it does (rain) we'll know who to blame!

Yeah,we have his card marked if the weather is shit.

Ya bastids....

[Taipan]

Remaps are aces. My F800R had awful low speed/part throttle response. Real choppy like a lot of Fi bikes. Gary at Mototuning said he could sort that so I sent him the ECU. He turned it round quickly and I refitted it. Not only did it sort the snatchiness into a smooth progressive throttle action it really fattened up the bottom end and mid range. It made short shifting along the torque curve an absolute joy. Look forward to hearing how your road test goes!

[mangocrazy]

Remaps are aces. My F800R had awful low speed/part throttle response. Real choppy like a lot of Fi bikes. Gary at Mototuning said he could sort that so I sent him the ECU. He turned it round quickly and I refitted it. Not only did it sort the snatchiness into a smooth progressive throttle action it really fattened up the bottom end and mid range. It made short shifting along the torque curve an absolute joy. Look forward to hearing how your road test goes!

I've mentioned it elsewhere, but I could even notice the difference in throttle response when loading the bike into the van. I always drive the bike up the ramp (being a lazy old sod) and previously I had to be careful with the throttle or I'd find myself dragged up the ramp faster than I intended. After the remap the throttle could be modulated so much easier and I had really fine control. So the omens are good...

[Supermofo]

I think me (and Weeksy IIRC) are one of the few that don't have an issue with the 690 throttle, I find the fueling on mine fine.

Maybe I have expert throttle control


Or the feelings of an axe murderer

[mangocrazy]

I think me (and Weeksy IIRC) are one of the few that don't have an issue with the 690 throttle, I find the fueling on mine fine.

Maybe I have expert throttle control


Or the feelings of an axe murderer

You're both just way too butch and I'm a pansy. I know, I can live with it...

It could well be that the Akra map I had loaded on it when I de-catted the bike just has snatchy low down fuelling. Or it could be that it was the last of the line motors where they'd gone all in on the Euro 4 compliance - I dunno. But I know that on a road which could have been designed for it, it felt jerky and snatchy off the throttle or on a constant or light throttle and I couldn't attack the corners as I wanted to. It's also a pain in town, but then I try and do as little town riding as possible. The only 'town' stuff I have to do is getting out of Sheffield into the Peak district etc.

If it still feels bad, then it's definitely me...

[Taipan]

I think me (and Weeksy IIRC) are one of the few that don't have an issue with the 690 throttle, I find the fueling on mine fine.

Maybe I have expert throttle control


Or the feelings of an axe murderer

Kine was fine if riding it normally, it was slow speed/part throttle cruising where it was snatchy as fook. Booster plug helped there, but still wasn't anything like a remap. Great bikes though and I miss mine is some ways...

[Supermofo]

I think me (and Weeksy IIRC) are one of the few that don't have an issue with the 690 throttle, I find the fueling on mine fine.

Maybe I have expert throttle control


Or the feelings of an axe murderer

You're both just way too butch and I'm a pansy. I know, I can live with it...

It could well be that the Akra map I had loaded on it when I de-catted the bike just has snatchy low down fuelling. Or it could be that it was the last of the line motors where they'd gone all in on the Euro 4 compliance - I dunno. But I know that on a road which could have been designed for it, it felt jerky and snatchy off the throttle or on a constant or light throttle and I couldn't attack the corners as I wanted to. It's also a pain in town, but then I try and do as little town riding as possible. The only 'town' stuff I have to do is getting out of Sheffield into the Peak district etc.

If it still feels bad, then it's definitely me...

I don't doubt you, loads of people mentioned it on the KTM forum. I think I'm just weird

[mangocrazy]

It seems to me that their is more variance with KTMs than most bikes in this respect. Andy at BSD reckons that every KTM is different, and he's seen plenty.

But of course it could just be that you and Weeksy are weird...