GP125 Seat

July 7, 2013

To be perfectly honest I had completely given up on this frame. With the engine in pieces and being worked on for my RS125/GP125 swap, this bike no longer has a heart.

I’ve always loved the simplicity of classic flat top frame bikes and after my usual internet trawl of delicious bikes this week, things started to brew again. I cut the end off the frame to shorten up the working area and started playing with a template for a steel seat. With no real intention to build something permanent I got to this point and I’m wondering if I should progress with it, I kind of like it. It’s not perfect as I didn’t intend it to be used and I don’t have any real sheet metal working tools (folder, band saw, roller etc) so I had to be a bit creative with some thick steel and some g-clamps.

I do have a gripe on the GP125s styling. The tank side profile is fairly nice on the eye but it’s chubby. If I was really keen/wreckless I’d cut about 80mm out of it’s width and follow suit with the tail piece but… I’m not to fond of the idea of cutting and welding a fuel tank.

On the RS/GP front, I have ordered a small dentist drill and some carbine tip burrs to port the 2 stroke cylinder. Otherwise, I’m just waiting really.

RSGP125 BUILD3

May 19, 2013

Suzuki GP125 engine strip down

Here are some more internal photos of the GP engine as I pull it down. I ended up drilling most of the phillips head bolts which hold the casings together as they were corroded down the thread. What a stupid idea it is to use a phillips head, honestly.

This last photo is of the tiny GP gearbox assembly. I wanted to show it to give you an idea on how a motorcycle gearbox works (although similar to a car) in translating the up and down movement of the gear changer to a change in gear. When you push up or down on the changer, a mechanism spins the grooved barrel in the top of the photos. In those grooves are the gear selectors which move left and right depending on the groove. The selectors move the gears on the input and output shafts which engage with each other to drive different combinations of gears and therefore ratios.

RSGP125 BUILD2

May 6, 2013

I swapped the Honda NX4 RS125 tailpiece from my 4 stroke onto its rightful home on the RS125 chassis.


A few NX4 RS125 expansion chambers also turned up on my door this morning, thanks Jesse! I know they’re not matched perfectly to what I will be doing to the GP engine but Rob has shown that they work well enough to get some great power figures from them. It’s also easier to use an RS one to get it going and rideable instead of stuffing around building one that is likely to be crap. I do plan to build a few in the future though…

RSGP125 BUILD1

May 6, 2013

I spent some time at Tim’s (a fellow F4 racer) place on Anzac day talking crap about bikes and figuring out how we can get some economies of scale going on with our GP125 builds. Being the good bastard he is, he gave me some… ummmm… used GP125 cases and a test bed GP100 cylinder for some time on the grinder before jumping into mine. THANKS TIM!
I started undressing her the other night and took some photos along the way:

Factory Suzuki GP125 crank case as provided by Tim

Tim’s degree wheel for port timing

Port side

Factory timing marks

Starboard side

This happened about two weeks ago and I can’t get it off my mind. I dream of building and racing motorcycles (hopefully for a living one day) and this is just the first step forward in many that are required. It is partly why I’m selling of my Datsun gear. This is a NF4 Honda RS125, a GP bike of the days when 2 stroke 125cc bikes were raced on the world stage. I’m unsure about the exact year of this bike but it’ll be approx the mid 1990’s.

The Honda RS125 was a bike that could be purchased directly from Honda by any club racer or enthusiast, they’re the peoples racer of sorts. The later model variants have a revised rear suspension system and a thicker main frame (basically overall better), but that does not detract from how awesome these little bikes are.

The plan: take the engine from my Suzuki GP125 and with some guidance from Team ESE and Tim modify/tune it to produce a chubby power curve (approx 20hp would be fine) to tackle the F4 kart tracks. Then I will squeeze it into the tiny frame and learn to ride a real race bike. I am not planning to sell my Suzuki FXR150, rather build a new exhaust and keep it serviced as a backup if the unthinkable should happen and the ‘stink wheel’ (as they call them) fails. Last week I bought all new fasteners for the frame as the original ones were looking pretty shot. I also woke up to a fairly new set of Dunlop slicks at my door. There are many things I still need to get for this bike but I’m working through them all slowly. Here’s to the beginning of a life of 2 strokes!

MT WELLINGTON NOVEMBER 12

November 20, 2012

Rick and Henk on the F4 sidecar onto the main straight, look at the concertration! These actually go pretty well with two people believe it or not


Photo of myself by my dad Simon

Last Saturday I finally got my engine back together and running after being sprawled over the benchtop all week. We didn’t get a chance to have practice before the October meeting so were allowed an addition practice and fun day last Sunday. I was frothing to get out there and by 1pm I was stuffed, too much track time, not enough muscle strength/endurance. I managed to drop my PB time down to a 33.35, 0.75 seconds from my last meeting, which I am pretty stoked about!

This Saturday there is the north island series round at Mt Wellington and on Sunday a 40 lap b-grade endurance race followed by a 2 hour endurance race (team of two, 30 minute stints). With the weather looking like it’ll stay dry for the weekend I’m more than keen! It was my birthday on Monday and my parents were nice enough to buy me some italian Gaerne GRW boots! No more fear of broken ankles! Whilst we were searching around for boots I bought myself some Revit! racing gloves too so I’m all geared up and ready for some more track time. Last on the list is another tune to make sure the engine is running at optimum, some physical training to get my strength up and someone to point out how to improve.

Keep an eye out for some more photographs from the coming weekend, fingers crossed on a good result

RACE MEETING #1

September 18, 2012

After torrential rain through the night I didn’t think this event was going to happen. Auckland’s weather surprised me again by clearing out and bringing the sun to dry up this notoriously slippery track. I went out with my old man who shot a few photos of me trying to get used to the bike, I really wish I could have made practice on Saturday.

The fastest lap time is in the 30 second mark with the top guys lapping consistent 31 and 32 seconds. The lap times the class I’ve started to race in are approximately 33 seconds to 34 seconds. I started the day out slow to get my bearings and ran a 37 for the first 10 lap sprint. The next was a best of a 35.6 then a 35.0. The last race session I put my best time down as a 34.0 which I was fairly happy with. The bike has plenty of power and I know when I get better I can start to hustle a bit. I need to find about 0.8 of a second per lap to be setting times up near the top of my grad but it’s the racing skill that counts and the ability to pass. Again, I’m frothing to get some experience under my belt with the rad guys who race every month.

Huge thanks to the guys who put this on whilst racing too, it’s hugely appreciated!

RACEBIKE – THE SPANIARD

September 15, 2012

Finally! Man that took far too long… that is for me to own a race motorbike. So my dad and I picked her up today for a very good price considering the work that has been done (spec list below). Honestly I think Suzuki FXR150s are pretty damn ugly but even when they’re almost stock they are very good value for money. There are limitations however and this bike has already had a few of them scratched off.

At this time it’s pooring with rain outside and the monthly bucket race meeting is this weekend. I missed the practice today because we had to pick this up but I did get a chance to give it a punch down the deserted country road and was very pleased. These make approximately 16hp from the factory and this one has been dyno’d at 20hp with a healthy torque curve which is the main thing given the nature of the tracks we race at.

I took a few things off the bike tonight and swapped the sprocket for a larger one for tomorrow but I also started to plan a new colour scheme. I’m a bit bummed I don’t have fairing space to play with – because they’d just get obliterated – but I did a quick photoshop for myself and I’m psyched to make this thing my own. I bought a back protector today so now I just need some proper boots and gloves and I’m set with gear.

Spec/modification list and other stuff I picked up:

After market high lift cams and heavy valve springs (3 meetings on these)
Ported head
64mm piston (6 meetings on this) and copper head gasket
28mm Keihin flat slide carb
Custom stepped header and muffler (plus a very good but loud mega phone exhaust included)
12 tooth front sprocket, new 47 tooth rear sprocket and new chain. 48 and 49 tooth sprockets included
GSX250R wheel conversion with Dunlop slicks
Standard wheels with wet weather tires
Raised footrest hangers
Clip on bars
KX125 quick action throttle
And a bunch of useful spares

The person I bought it off had this to say about it: “The bike was used for the north island series with several wins and top 3 placings, finishing second overall. There is plenty more scope for development but is still up there with the best”. I’m stoked,let’s get out there.