GSXR250R (GJ73A) Race Bike Build

Well to be honest mate I've never considered myself that great with electronics! I've certainly never attempted something this big before, but really it wasn't that hard once I had the harness completely stripped out and just went one circuit at a time. I've now tidied up the wiring for the dash, put a single inline fuse for the main power feed circuit and got the neutral and oil lights working again. Only problem now is the starter motor just spins and doesn't crank the engine over. It doesn't appear this bike has a separate starter solenoid and it was working fine during the last test I did and not much has changed since then. so I'm more inclined to believe it's not an electrical problem. I will will have to pull the LHS engine cover off and see what's going on.

Fork seals arrived today and the job is done on the RGV forks, but the replacement seals I got from Pyramid Parts were a very poor fit and I'm really disappointed that I ordered 2 sets as I will have to send the other one back. Firstly they just pushed straight in, no need for a seal driver so the OD is obviously a bit small. Secondly the upper side of the seal has a stepped edge rather than being flat on top, so the clip that holds the seal in place sits about 2mm higher than the seal, which meant it was sliding back and forth with the action of the fork. I managed to cut the top out of the old seal and use it as a spacer above the new seal to hold it in place but its far from ideal and I won't be surprised if they leak around the outside of the seal. To top it off the dust seals don't fit properly either so I had to clean up as best I could and reuse the originals. I am very disappointed with Pyramid Parts, I've read of problems with their kits before but thought I would give them a chance when I saw this site would get a a kickback if I ordered thru here, but now I'm kicking myself I didn't just go OEM.

 

Actually I may have jumped the gun there... just checked my invoice, I thought I ordered seals specific to the RGV VJ21 but it was actually the GJ73A. So I looks like I will have to strip the GJ73A forks sooner rather than later to see if they will be OK.

Simon to answer some of your questions; and good ones they are too!
I have considered removing the alternator and starter and going total loss but for stage 1 I plan on keeping it all in place. As I'll only be racing the 250 for fun I don't want it to cause too many hassles on race day when I need to switch to the 600 or vice versa. Charging batteries and using a roller starter would probably take up too much time. Also my local circuit has a fairly steep hill and removing the flywheel may cause it to loose torque off the corner preceding it, but won't know if this will be a problem until I get out there. But if I ever get serious enough with it to take to the Island Classic I'll probably look at doing all the mods to wring every last bit of speed out of it!
Its hard to say what sort of weight it will shed, but I think 20kgs is not out of the question. I have a ZXR750 that I have removed about 40kgs from and its still street legal so a lot is possible! The fairings and headlights weigh a ton and I ditched the entire rear seat section so there's a good start. Oh yes and a good piece of news, I test fitted tire warmer on the rear and it fits fine, guess the actual rolling diameter of a 190/55 17 is about the same which is surprising to me.

Thanks so much for the service manual, I have just donated to get access to the manuals and will grab the copy kiffsta is compiling

 

Well, today I found why the starter wasn't turning the motor over. I'd only gone and hooked the battery up the wrong way, so the motor was turning in reverse! Geez I felt like a tool, guess thats what happens tho when you are in a rush and working in a dimly lit workshop lol

But turns out I have bigger problems, removing the alternator cover has revealed the magnets on the flywheel are braking up. 2 rather large chunks have come loose and at least one more is cracked. Looks like I might have to run total loss after all, its either that or try gluing them back on and see how it goes. I called a mate who runs total loss on his VFR400 and he said he had nothing but improvements in acceleration and engine braking (less) after ditching the flywheel, so maybe its the way to go. I will have to do a bit more research on it I think...

 

A bit more progress made over the weekend. Got the front end assembled with the RGV clipons and hooray I have set of brake lines that now fit! Both sets of calipers are still filthy, I wiped the worst of it off but these things need a serious clean, not especially looking forward to it but gotta take the fun jobs with the bad I suppose. What's great about the RGV clipons is the bar is separate from the clamp so I will be able to install a brand new set of lightweight race bars I have spare. Only problem is one of the threads is stripped so will have to get a helicoil put in there. Also my Litetek carb kit came in so I rebuilt those and refitted to the engine. It took a fair bit of cranking to fire up again but once warm the engine ran smooth and seemed to rev more freely than before.

The JB weld seems to be holding the broken flywheel magnets fine. I am still only getting 13.56v max from the alternator but this is enough to charge the small lithium battery so all good I hope. The wiring seems all OK and most of the harness is taped up now. It was great to hear it run again and give it a bit of a rev, she is a real little screamer alright but has a deeper note compared to the higher pitched CBR250 I recon. I'll have to pull the carbs back off though as I want to try and soften up the rubber intakes somehow as they are a bit stiff and I don't want them cracking. Other jobs on my radar will be to get the front brake system refurbished and back together and maybe start organising a battery box and tray to accommodate the remaining electrics.

The broken magnets, repaired with JB weld

Carbs all stripped, cleaned and ready for new seals

RGV VJ21 complete front end and fairing stay bolts straight on, original GJ73A gauge cluster fits perfectly

 

Progress update: After a lot of scrubbing the calipers are now clean.
Before After

I spend a lot of time cleaning the pistons and working rubber grease into them, all but two were very tight so it took a lot of pumping them in and out with air pressure and applying grease. They are a lot better now, I want to avoid having to rebuild the caliper seals as funds are tight at the moment so hopefully they will work OK with no sticking. These calipers are from the GSXR, the RGV calipers are worse and definitely need rebuilding so this will happen at some point and I will swap them over. The bad news is after test fitting them with the lines and master cylinder reveal that with the forks fully extended, the brake line I hoped to use is about 1cm too short. Also the forks are leaking oil past the seals already so they will definitely have to be done again

Better news though, after taking the carb rubbers off they were actually still nice and soft with no cracks, so I just cleaned them up and put them back on. I also turned my attention to the under seat area and tried a piece of high density foam to house the battery, starter relay and igniter.

This could probably be made to work but I decided it was a bit too flimsy and would be difficult to make brackets to mount it properly, will be easier to make a fibreglass tray.
So I made this pattern piece out of cardboard
I will coat it in tinfoil to make a mould, it doesn't have to be pretty so should work out OK hopefully. Progress may be a little slow over the next week or so though, need to turn my attention to the CBR600RR, it needs a few upgrades before the next race round in 2 weeks time...

 

LOL Mustard! I think you already have the competitive advantage starting with a Honda but seriously if you want any of the high density foam I have lots of it! I think to compete with the faster bikes in our class I am gunna have to get the GSXR finely tuned and the chassis really dialled in to carry maximum corner speed. All the tests I've read have put the engine back a peg slightly compared to the other 4cl bikes.

Yes I am definitely still a Honda man, but the little GSXR has really grown on me and I always like having a bike thats a bit different from everything else. Its been sitting there teasing me in the corner of the workshop all week, can't spend any time on it though, still have heaps to do on my 600 to get it race ready, valve clearances need changing and I noticed today the forks are leaking...