Jump to content

Dave's shonkers - Grom hits the road (now with added Vespa)


Recommended Posts

It's a totally fair question.

Like you say in sports and "general" motorbikes the most common wheel size is 17". Mopeds and scooters, a lot have 10" but 12, 13 or 14" also exist.

Generally a smaller wheel is lighter and quicker steering, a large wheel is the opposite so more stable, particularly at high speed.

If you think about scooter vs motorbike, the scooter is designed for nipping around town at low speeds, the small wheels are best for this but might start to get wobbly at high speed (in theory), whereas the 17" wheel is more stable at high speed and slower steering/response round town. 

These bikes I guess are designed for something in between, a fun bike to blast around both towns and lower speed twisties but the top speed as standard is only about 65 and it will take a while to get there. So the wheels/tyres are somewhere in between the low speed optimised 10" town scooter and the 70+mph optimised sportsbike.

These bikes don't really fit into a box, most smaller/"monkey" bikes before this were designed badly or made with shitty components and therefore not that good to ride, Honda put a lot of design effort into making these good to ride and the standard suspension etc is pretty decent, which is why they are so popular IMO. 

I've had a few overpowered crotch rockets and while there is a childish satisfaction in giving it the beans, in reality unless you are a super skilled rider or have a weaker sense of self preservation than I do you just can't use anything like 100% of their capabilities.

There isn't another bike on the market (other than copies of this idea) that is as well matched to the real conditions of a normal human riding on UK roads IMO.

Link to comment
Share on other sites

Painting is done. The boomerangs turned out pretty well despite me managing to drip some sweat on one while doing the first clear coat. The mudguard less so, it's got a few areas where the damage shows through but a significant improvement on being held together with cable ties. 


I also had a go at remapping it as mentioned here: 

There are various standalone and piggyback options for the Grom, the general consensus is that an ARacer & wideband logger at ≈£600 is the best solution. 
There are also one or two places offering a reflash of the standard ECU but all US based. 

The software I was trying to make was originally an open source project that the developer took private and now charges $150 for. Totally fair to make a living but I was hoping to manage it for free. I did in the end, by finding an old version online. 

The Grom ECU only has 48kB storage, so there are not a lot of tables. In fact basically just 2, one for fuel and one for timing. 

I've left the timing and added some fuel, and put the rev limit up from 9250rpm to 10000.





Hoping to get out for a test ride later. 

Also inbound this week was this ER6N, which is for my wife who recenty passed her test. 


Link to comment
Share on other sites

  • Dave_Q changed the title to Dave's shonkers - Grom hits the road

Pretty pleased with how this has turned out. 



Headlight boomerang is a part I painted, the side panel is original paint, it's a good match.


You can see in this light some of the wobbly reflections where the mudguard is made of filler, staples and hope underneath the paint. 


The new second hand side panels aren't super mint but that's OK, I can't own anything really nice anyway as I haven't got the time or energy to keep things clean/nice. 

I also changed the oil and fitted half a set of 60% stiffer clutch springs. This was delayed a few days when I found that the oil strainer was missing from the engine. Turns out that the sump bolt was a random bolt that had been cut down, and I guess it was too long for the strainer to fit. 


Just been out for a v.short blast and all seems well. I saw 70 indicated on the speedo on a downhill stretch and could maintain 55/56 on the same stretch back up. I don't think the top speed will be loads different but I reckon that an indicated 55-60mph cruise will be no problem on a flat road. 

Sadly according to my phone gps, 60mph on the speedo is actually 80kmh/50mph, and 70mph is 93kmh/58mph.

Link to comment
Share on other sites

Put the high level link pipe on, it did need a bit of bending to fit but for about £30 all in I'm not complaining.

I've pointed it out to the side a bit so it doesn't melt the number plate or indicator but that has made it look a bit wonky so it might get bent back in. Or I could splash out a further £20 or so on a Yoshimura* can.



Link to comment
Share on other sites

On 9/15/2023 at 10:14 PM, Matty said:

Said I'd never do a bike again, but they look top fun

Well worth a look, much better to ride than you think and small enough to fit in any shed/cellar/house so you don't have to be worried about some scrote having it away all the time.


Need to trim the cables and for some reason am getting no electrics at all out of my new rewired stator (more likely to be the crusty old bike side wiring loom TBH) but sounding pretty good.

Link to comment
Share on other sites

  • Dave_Q changed the title to Dave's shonkers - Grom hits the road (now with added Vespa)

Had a few mins on it between meetings, would be good to get it in for an MOT soon.

The electricity is a bit of a head scratcher, the wiring up to the regulator checks out and if I power the bike from a test battery at the reg connection everything works (except the horn cos DC not AC) but there is no reason the regulator should have stopped while it's been sat.

I checked the output and my meter says it's giving 40v AC which the FB group reckons should be blowing all my bulbs but it's not. Maybe the meter is wrong? It is quite shit. Probably gonna parts darts a regulator to at least rule it out.

The thing also managed to piss a litre or so of petrol out of the carb overflow which can make one very popular when your garage is part of the house. Down to dickhead here not setting the float height when I chucked the refurb kit in the carb, now hopefully resolved and scented candles doing an incomplete job of covering up the smell in the hallway.

Link to comment
Share on other sites

Picked up a regulator today but couldn't run it afterwards to check as all the petrol fell out again.

A combination of having a fuel tap that doesn't turn off, managing to put the float back in with a bit missing and I think maybe a dodgy non-ethanol resistant gasket on the carb bowl led to another litre of fuel on the floor. 

I've had to remove the tank and put it outside for now until I can sort out a tap and on the carb, I'm not sure as the internet is full of shitty Chinese rebuild kits but I would prefer something OEM.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...