B-motor – 1200mile update

ok so we’re about 1200miles down on the rebuilt B-motor with rebalanced internals and right the way through break-in miles I felt like the clutch was slipping. I sorta expected this because on the previous motor it slipped from too much power so didn’t really think much of it. Every now and then it did seem to “catch” properly and would dig in and take off but it seemed to be random. For those times it happened though.. wow.

But then at the end of break-in miles since i had to change the oil anyway I put the upgraded clutch (R15 clutch basket with 6-spring boss + uprated springs) from the old engine and it still wasn’t quite hitting the speeds I was expecting. It would get to about 85mph but not any further and given this engine has the power band back in the correct place and screams from about 8.5k right thru the limiter this was unexpected behaviour.

I had been expecting the map to take a while to adapt to the new engine but really it ought to have done that by now. I had recently done a 2hrs each way run which was all main roads so we were in the 8-10.5k range most of that run which meant the autotune had plenty of time to do its thing and sort the map.

The other week I thought I’d just try it on the 14t front sprocket as a test and weirdly it was still not catching right…so I dug into it a bit more and discovered I’d put the clutch cable in a different position from how i’d had it before to see if i could lighten the pull, and then forgot I’d done that. It’s a 1 finger stunt clutch with 3 cable positions so you can vary the travel/pull-weight and as it turns out in the “lightest” position where I had it (which gives the least clutch movement) it was never fully engaging the clutch….

So then I switched it back to the middle position back to the somewhat heavier pull and holy chickenballs what an instant difference.

I also softened my rear suspension a bit as I’d been riding with full panniers before and forgot to adjust the preload back after, so there was no static sag and the rear end was bouncing around which also explained why I was using ALL the fork travel which also seemed weird (back wheel skips a bit then too so you don’t get all the power down)…

So then with a properly adjusted clutch and rear suspension – I had a VERY fun ride on my normal test route and she screamed all the way to the limiter, fork travel was back to acceptable range and I was smiling a LOT.

Then I put the 15T sprocket back on and tested again and she pulled 87 on level ground, best previous was 85.

I’ve still got the wide bars on and a slightly cut down screen and last time the narrower bars and full (double bubble) screen added several mph to the top speed so once I’ve re-polished up the OEM clipons I’m planning to go back to that setup just to see if we can break 90mph, though I suspect we might be bouncing off the limiter at 89 which was the previous top speed (and where I’d previously bounced off the limiter). Gearingcommander.com seems to think we should be geared for 92mph but I’ve hit the limiter at 89 once before on the old engine… but idk.. it seems like it revs a little higher now (can’t explain why) so I’m curious to see how it goes.

On the old engine I’d tried on a 16t front sprocket but it didn’t have the power to push it really but that engine was all low+mid so idk if this will be any different. I guess the ideal solution would be dropping a tooth on the back since that would be a smaller increment, but that’s quite an expensive affair just for an experiment…. but even if she’s happy bouncing off the limiter on a 15t that’s plenty of usable speed and means I’m quite nicely able to keep up with normal motorway traffic, especially since there’s cameras everywhere now too.

So I guess in conclusion – what I was wondering (ever since rebuilding the engine this slightly different way) was whether the changes I’d made to the engine internals by way of rebalancing the crank/piston assembly with the forged con-rod and lightened crank pin were actually better, and the answer to that is HELL YES! 😁😁😁

On the old engine (180cc) the crank balance factor seemed to be about 0.4 vs 0.48 stock and was all low/mid power, very reluctant to rev to the redline…which is unlike the stock engine which likes to scream (which I very much liked).

With the lightened pin + forged rod i make the balance factor about 0.49 so it should actually come on power a tiny bit later than stock and stay on power till a tiny bit higher than stock (though the limiter likely cuts in before the end of the power band) and that does actually seem to be what’s happening… so the maths seems to be solid 😁

This also confirms what I suspected about just slapping a 180 kit on and expecting it to run the same but faster as being false (even with a power commander, cam, injector and all the toys), which also explains why there’s a number of unhappy 180cc owners out there. I guess it’s not really in the interests of the people who sell the big-bore kits to suggest that their product will significantly change the engine characteristics, otherwise people wouldn’t buy their products…but it’s also good to know it can be made to work, and work really well

I think there’s still a bit more power to be had out of the map so am in the process of testing different AFR targets, and there’s still the potential for per-gear maps but that means fitting a hall sensor to the back wheel as apparently the one in the front (speed sensor) doesn’t register with the PCV (i already have it wired in), but this is all really just fine-tuning, the engine itself seems to be about perfect which is a huge relief…given all the research and work/expense which went into figuring that out.

I would like to try tuning the intake tract a bit at some point as the airbox is still pretty much stock (just a k+n filter) and I think it’s still a bit limited by how much air we can cram in there (see carb trumpets/ITBs) but overall I’m now extremely happy with the outcome, and it absolutely WAS worth doing the maths on it and building it that way. 😎

For now I’m just working on finishing up the panels which are nearly done (at long last) and look amazing, and then the bike will be pretty much perfect 🤩😍🥰

In other news – unfortunately I had to separate with my partner over christmas, and with everything getting more expensive I had to take on more work which means much less bike time – so in general, work, life, mental health – pretty much everything is kicking my ass a bit atm but I’m still here and working on stuff, just haven’t really had time to post much about it. Consequently replies to tuning emails are likely to take a bit longer as I’m lucky if i get time to go thru that inbox once a week and my spare time is extremely limited…. and that which I have is spent riding or working on my bikes rather than answering emails.

Otoh whilst I’ve not been able to do much trials riding, on the occasions I’ve been, I have been able to hit balance point a few times now and am booked into wheelie school in June so will try to post about my experience there too 😁

Unfortunately when all the energy prices went nuts I ended up having to switch my main PC & server off which is where I did all my editing so making videos just kinda stopped till I could figure something else out.

Eventually I ended up staying in my (very small) van, which I’d been building out to do little away trips but eventually ended up being warmer and more comfortable than the house… and that’s where I’ve been for the last 6 weeks or so. This was partially for back-pain/comfort reasons, partially because free electricity vs expensive house bills and partially so I can be anywhere I want (now with my trials bike on the back too). With my partner not there the house is just a house which happens to be attached to my workshop so I’m out riding or at the trials club as much as I can be.

It’s taken me a while to adapt but now I have an editing setup I can use in there so can hopefully start going through and posting some of the footage I’ve recorded.

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