BHPian ringoism recently shared this with other enthusiasts: My first update after a LONG time here! The Impulse had always been a good bike for the hills/mountains of Himachal. But, had loaded up the long-derelict Impulse and carried it out to Mizoram, where there are countless dirt roads and trails leading out in many cases to agricultural plots/ homesteads, I believed I would be able to have even more fun with it. I wasn’t wrong.Reason For Making UpgradesBike had several years ago been on loan to a pair of youthful brothers who are family friends, one of whom, against my better advice to stick to the ASC an hour south of here, had taken it for servicing to a similarly youthful local mechanic friend of his – who proceeded to really screw it up: He cut slots in my custom foam air filter, allowing all sorts of filth to pass free through the engine. And apparently mis-adjusted the tappets, such that the intake valve burnt (this is rare, it’s usually the exhaust valve that degrades). And who knows what else. So I got the bike back suffering severe loss of power, backfiring through the carb and having zero compression discernible at the kickstart lever. After sitting a few months back at my place, I couldn’t even get it to start at all. After disassembling the top-end and realizing it was going to need some work (including a likely upgrade to either bore size or compression ratio or both – which might require changing the connecting rod as well, since the gudgeon pin of these HH150’s is an mm smaller than most other bikes), I went ahead and removed the engine from the chassis, and put it in a trunk. And for a few years just never got back to it. I had both UCE and AVL 500 Bullets to take care of daily duties, and had found their easily accessed thrust / freight-train-like pull much more practical and pleasing for daily hill use than that screaming yet anemic little 150 had ever been, anyway. A year or more ago, I had finally bought a slightly oversized Hero Honda Ambition piston – the engine of which was in the original CBZ/Karizma engine series – but which in this case had the same general bore range as stock 150’s of the later engine series – and also has the same sized piston-pin, but in flat-top vs. dished – thus providing a significant boost in compression ratio, meaning more air/fuel coming into the cylinder on each stroke, and thus the potential for much better power output. So took that piston and had a capable local machinist do the boring and cylinder-head / valve work. Sometime after this, found out that a friend (who calls himself my pack mule) was heading this way from the U.S., so I also ordered a cheap (Chinese?) big-bore 185cc kit that used the stock sized pin and would allow me to retain the original con-rod. Still (wrongly) thought I needed to split the cases to replace the shifter shaft which had snapped off after hitting a rock along a forest trail… so kept trying to schedule a time with the local Hero mechanic here in the valley, who’s quite into mod work and can take these engines apart and re-assemble more or less with his eyes closed. Back in February I finally got down there with all my parts, and we got to work. I’d pretty well decided to go ahead with the 185cc kit, which he felt was of excellent quality – but discovered that due to carelessness in packing (/my re-packing possibly), the ring set had ended up in the box UNDER the cylinder block, the weight of which had cracked the brand-new top compression ring – AAARGH!!! Karizma has about the same diameter rings as that aftermarket 185cc kit did, but we didn’t have any old Karizma parts available on hand… nor new rings… so the high CR 150 (actually 155)cc it would be! To make a long story short, the bike was re-assembled and apart from troubles stemming from fuel tank that had become extremely rusty after sitting those years, the bike started and ran well. Much more punchy that previously, no need in normal operation to rev it to redline in each gear in order to keep it moving at a decent pace. Having arrived in Mizoram, I got an alloy rear rim fitted (18″ RE Interceptor front one works well) that would match the front alloy 21″ I’d put on years earlier, and a new rear tyre. Surprisingly, the stock spokes from the 17″ work fine for this conversion. Ralco Eco-Racer tyre (weird marketing choice) is surprisingly good for dual-sport riding conditions, with pretty big grooves, lots of siping – albeit not full-depth – and a high-silica compound that is supposed to be superior in the wet. I made a mistake in my online order and ended up with a 100/90-18 instead of the 110 cross-section, so gave up just a bit of GC and width there over what I might have gained, but it’s still giving me about a half-inch more GC than stock, and on the positive side won’t be rubbing the swingarm at all, which with a 110 it might have been getting a bit close to. I think the upgrade to 21/18 over the original 19/17 was well worth it, both in terms of offroad handling and in giving a bit of extra GC. Desi tubeless conversion was also pretty ingenious I thought: I also worked for hours trying to get the inside of that fuel tank cleaned up, fooled a bit with the carb main jet sizing, removed the faded original graphic decals, and saw to other minor required work. In time it was ready to ride, and I was eager to get out for a real test-run. Having studied the satellite images awhile, thought I might have found a way to get from Muthi, a hilltop village and lookout just outside the city, to Tuirial, East of the capital and at much lower altitude, where among other things (the landfill better not mentioned), there is an old abandoned military airfield used for a few generations for driving practice and more recently for organized motorsports events. Headed out sometime after mid-day one Sunday, not really intending to embark on the journey – but as the road down the back side of Muthi turned out to be so badly carved out / eroded, I decided it may be better to press onwards and downwards and find another way out, rather than coming back up through that. Again I was right. I am never in a position to click photos when I’m in the midst of the worst sections, and anyway no point in bragging about what I muscled it through, as others are far more capable riders than I – so will mainly just share some of the beauty of the landscape here: Bike is much improved, but then again, typical Mizoram gradients tend to be steeper than most of what we have here in H.P. Which is to say I don’t feel fully satisfied yet! Main issue is (still) the huge gap in the 1st/2nd gear ratios. I have more torque at 4500rpm now than I did earlier, but still can get bogged down when trying to upshift from 1st to 2nd on very steep up-gradients. I need to shift from 1st at 8500rpm to have it be into the max power range of 5500rpm and up when I go into second. Just no fun having to thrash it like that. Could ride both more smoothly and briskly if my ratios were closer. Same old problem! Both the 125cc Ignitor and Stunner use a close-ratio gearset that should fit into these engine cases, being that these are of the same series. If I can find one of those junked will grab what I need, if not, then met a very knowledgeable tuner / mechanic out there who says the XPulse 4v gearset is a direct fit into the Impulse cases. Those have gearing that’s much closer in 1st-3rd gears to accommodate trail use, while keeping 4th/5th a little higher in order to control revs on highway runs. As there are no real highways in MZ with straights good enough to make riding above 80-90kmph safe, I’d rather have 4th and 5th close-ratio too, which only these 125’s have. But either way, should work. We’re back in HP now, but will keep my eyes open for spare parts, and plan on doing that upgrade next year. I could also probably solve it by just bolting on the 185cc kit, but I still feel the gearing is just “wrong”, and that regardless of how much power I have on tap, it’s going to work out better to have the kind of gearing that it really should have from the factory. Other thing is that I am fully aware the stock pipe is pretty restrictive. Aizawl has become pretty strict about loud silencers, a decision I can support – but I am quite sure I’ll be able to find a solution there that’s both free-flowing and relatively quiet, even if I have to custom fabricate it myself. I was pleased to find out that some of the mechanics and the foreman at the Aizawl ASC are also into racing / modding, and as motocross events have been ongoing out there and the XPulse has become the standard tool for that, there is a LOT of knowledge of these bikes out there. Aftermarket cams, programmable tuning boxes, wide range of final-drive sprocket options, springy gear-levers, and etc, are all very much available and being put to use. Great place for the bike to be, and by the time we (tentatively) shift there next Spring, hope to be hitting the trails regularly. I’m in my mid-50’s now but don’t see any good reason to stop, especially as my kids are getting to the age that they can join me in it if interested (am going to have to build them bikes too in that case!). I kinda like the cleaner look of it without the decals… but maybe that’s just my age talking! EricCheck out BHPian comments for more insights and information.
