GPR Camp: Replica Racers

I bought my GPR50 (75) in late 2003. I'd first seen one around 2000 at Competition Accessories in Springfield, Ohio. I wasn't sure what the hell it was, but I was smitten. This one showed up on eBay and I was the winning bidder. The seller was in Indiana where this bike is a moped. Here in Ohio, it's a motorcycle! I took the MSO to the BMV and they issued a title without any argument. It's titled as a 2000, but the graphics and VIN would suggest it was actually built in '98.

I loved it and rode the crap out of it. I ran it twice in the lakeerieloop.com and took first in class on my second attempt. That's 660 miles in a day, WFO across Canada. The Metrakit SP top end I'd installed didn't take it well. I'd added a 2 gal auxiliary fuel tank to cut my fuel stops in half, so it was run HARD all day! It started running poorly towards the end of the day and I limped it to the finish line. It barely made it, but I won my class on just over 13 hours.

Teardown later revealed that the Nikasil had started flaking off the cylinder! It was ugly. I sent it out to have it replated. It was never the same. The bike developed an overheat problem that I just couldn't vanquish. The last time it left me stranded, I almost abandoned it on the side of the road! I was pissed! But I had my wife come fetch me and the bike in my truck. I took it home and pushed it out to my side porch, where it sat unloved for nine years. I couldn't sell it. It was the most fun bike I ever owned, and I've owned a LOT! Last year I finally sold the GPR125 that I'd owned for ten years, and decided it was time to do something with the 50.

For a bike that sat outdoors for nine years (under a cover, on a covered porch), it was in remarkable condition. I already knew the motor was hurt, but a quick evaluation of everything else actually looked pretty damn good!

I tore down the motor and there were no surprises. I started shopping for a new top end, which was more difficult than it ought to be. There's just not enough info out there...in English. I rolled the dice and bought an Italkit 80cc kit. It turned out to be a decent choice. I'll assume it's a race top end. There is NOOOOOBODY HOME below 8500 rpm, but it's a freaking ROCKET from 8500-12,500!

So I rode it a little bit last season trying to further evaluate. It was frustrating. I pushed it home several times! It kept losing spark. By the end of riding season, I gave up and parked it again. I'd talked to a few people who'd all suggested a wiring harness issue. It made sense, and I had a mint condition wiring harness hanging on the garage wall. In the process of replacing it, I found an unsecured ground wire! Holy crap...It suddenly all added up. I went ahead and replaced the harness and secured the ground. I've now ridden the bike a few hundred miles without issue!!

Words can scarcely describe how happy I am to have this bike back on the road...seriously! I've owned a LOT of bikes (about 30), including the very first R1 sold in Dayton, Ohio. This has always been the most fun bike I've ever owned.

So now that it's demonstrated reliability once again, I'm dropping a few bucks into it on various tweaks. Still waiting for a new front sprocket to arrive. In the current configuration, it will pull redline in top gear up a hill! Gonna add a tooth up front and see how that goes. I put a lot of mods into this bike a decade ago. It's definitely the first bike I go to in the morning now. (I also have a VFR1200 and a CBR1100XX out in the garage).

Here are a few pics of the GPR.










Like I said, got a few mods, but still a work in progress. Man I'm glad to have this bike running again!

D Dave

Nice work there Dave!

I have a GRP 75 as well, with a stock top end but 24mm Flatslide and Arrow pipe, and added a tooth up front. With the additional power I think you will like the change. It is a little softer off the line, but once it's rolling I think you will like the taller gearing.

I haven't done much in the way of engine work, other than needing to do some serious carb tuning to get it to run, but I have changed a few things. The plan is to eventually go with a satin silver on the bodywork retaining the blue "Derbi" and a few other stickers.

How do you like those tires? I have some Avons on mine, but they aren't that great. Savas are the way to go from the sound of it, but they seem hard to find in 16s.

Thanks.

I thought I had a thread here somewhere with info and a photo of my GPR, but I can't seem to find it.

This is how it currently sits -


Jay

That's a beautiful bike Jay! I honestly think the 1st gen GPRs are much sexier than they have a right to be. I never get tired of looking at it. Yours looks fantastic. I can't imagine why you'd want to change it.

I've tried other tires on this bike, but still find these stock tires hard to beat. I'd buy another set if I could. There doesn't seem to be much of anything available in these sizes here in the states. TT is a big proponent for switching to the 17" wheels, but I just love the way this bike handles and know that 17s would change that. Hopefully I'll get a few seasons out of these, which are NOS I just installed. Old as they are, they still feel excellent. This is a street bike for me, not a track bike. I'll have to reassess the subject once these are toast. Cross that bridge when I get to it. I have a couple other bikes in the garage I ride regularly, so hopefully I'll get a few years on these skins. I'm continuing to refine the whole package. I love this little bike.

D Dave

Jay you'll find your thread in the projects section.

Dave, you are correct. If you were to source some 17s, and fit them with MC18s from Sava/Mitas it would transform the bike. But in a very good way. The actual diameters of the tire don’t change a whole lot. The benefit comes from better tire design/compounds. It is truly amazing how much confidence you can have going into a corner with these tires. The MC18s were actually designed for these bikes. I’m not suggesting these for track tires, but as street tires. Even on the street you’ll find that great tires make a huge difference.


Sadly they aren’t available in a 16 Inch size. They probably wont go for it, but you could start a letter/email campaign to Sava/Mitas to make the MC18 in the proper sizes for the pre 2002 GPRs. The Sachs MadAss employs the same wheel so you might be able to convince them of the viability. Just make sure you ask for the proper size (90/90-16:Front), 120/80-16:Rear), as the MadAss went to a different size later in production—probably because they couldn’t source a 90/90 front.

The Avons aren’t such a bad tire, but they are an incorrect size for the 16" wheel which causes the bike to handle incorrectly. The 16" front should be fitted with a 90/90-16. If you run a 100/80-16 on it the bike’s handling will suffer due to a incorrect tire profile. The Michelin Pilot Sportys were the best tire I could find for the 16 Inch wheels, but the correct sizes are difficult to find now that the tire has been discontinued.

I suggest reading my post on tire profiles in the tutorial section. There are numerous links, information, and some illustrations to help explain the research, and experimentation I did for these bikes.

toratora wrote: ↑

Tue Apr 16, 2019 9:39 pm

Jay you'll find your thread in the projects section.

(SNIP)
The Avons aren’t such a bad tire, but they are an incorrect size for the 16" wheel which causes the bike to handle incorrectly. The 16" front should be fitted with a 90/90-16. If you run a 100/80-16 on it the bike’s handling will suffer due to a incorrect tire profile. The Michelin Pilot Sportys were the best tire I could find for the 16 Inch wheels, but the correct sizes are difficult to find now that the tire has been discontinued.

Thanks tora - I couldn't recall where it was.

The Avon aren't the right size, and they have seemed to have lost a bit of traction over time when they shouldn't have. We will be taking the GPR out again shortly, and I may start to look around for a better set of tires.

Older Ninja 250s also run 16s, but their sizes are not going to be correct either.

Not sure what would be the best tire choice at this point.

Thanks for the compliments on the bike Dave. I'm just not a fan of the black I guess, and think the bike would be much cleaner looking all one color like silver with toned-down graphics, but yours looks great with the red/silver combo.

Jay I thought your bike looked totally rad with the Racing Emotion graphics. The black and blue made for a very attractive bike. I could see wanting to source a black tail section, but for the most part the black and blue is a very nice look. Blacking out the frame, swing-arm, side stand, and rear sets would add nicely to the look.

toratora wrote: ↑

Wed Apr 17, 2019 7:39 am

Jay I thought your bike looked totally rad with the Racing Emotion graphics. The black and blue made for a very attractive bike. I could see wanting to source a black tail section, but for the most part the black and blue is a very nice look. Blacking out the frame, swing-arm, side stand, and rear sets would add nicely to the look.

Thanks, but there was just too much going on for me, and the black was just too low-budget looking.

Dave's red/silver looks a lot better.

Tonight was a truly monumental night for the Derbi. It made its first highway voyage in more than a decade! No issues whatsoever, other than the shift light being illuminated the whole time, screaming along at 12.5k and 71 mph!
My new front sprocket showed up in the mail today, hopefully that will help once I get it installed. My new mirrors from Easy Parts also showed up today! How the hell does that even happen? It took 8 days to get my bicycle headlight back from Cali, but I get a pair of mirrors from the Netherlands in two days! Holy crap!

Now that the pads are starting to bed in, I'm very happy with this floating front rotor I just installed. Man, the bike is really coming together in great ways. I suddenly remember why it was always my favorite bike, and it's had some stiff competition!

Now to address the tire issue. I've always found the stock Michelins in stock size to be VERY good. Having just spooned on a pair of NOS, that opinion has NOT changed! I have a decently curvy route (by Ohio standards) to and from work everyday. I've been scuffing them gradually and progressively and have begun sticking them a little harder. Despite their vintage, they feel fantastic! I absolutely LOVE how agile this bike is! It's like being teleported between points in space. It just changes directions so instantaneously, it's crazy. At this moment in time I have no compelling reason to switch wheel and tire size.

My confidence in the bike is really coming back, and I'm relearning how to ride a bike that must be kept on the boil all the time. Totally worth it! It's been awhile since a motorcycle made me smile this much. I...cannot...over-emphasize...how happy I am...to have this bike back on the road! I keep tweaking and tweaking and it just keeps getting better. It is absolutely the first one I now reach for the keys for every day. Stoked.

D Dave