Factory Motocross Bikes—Guy Cooper’s 1988 Honda CR125R

The production Honda CR125R that Guy Cooper rode to four National MX wins.

Although not pristine, Guy Cooper’s 1988 Honda CR125R reflects its owner’s can-do attitude that netted him four overall National wins that year against more refined factory bikes.
Although not pristine, Guy Cooper’s 1988 Honda CR125R reflects its owner’s can-do attitude that netted him four overall National wins that year against more refined factory bikes. (Being bolted to its display stand in his moto/bicycle museum sort of discourages moving it very far.)Shan Moore

Any time you have the chance to visit Guy “Airtime” Cooper, do so!

The former MX/SX pro and off-road hero is somewhat of a collector (though some might dub him a hoarder) and has an astounding trove of old motorcycles and bicycles. A walking encyclopedia of the history of many of those bikes, he's also held on to a number of his old race machines like the 1988 Honda CR125R shown here.

In 1988, of course, the AMA rule mandating the use of production-based motorcycles had been in force for a couple of years, but then as now, the factory bikes still held an edge.

Cooper wasn’t a full-fledged factory rider; instead, he was considered an American Honda support rider with primarily a bikes-and-parts deal and some expense money, unlike factory racers like George Holland. Honda provided Cooper with five bikes for the Nationals, and it was up to him to get them massaged into National-caliber machinery.

After signing the support-rider contract in 1987, however, he broke his leg in an off-season Supercross in Belgium. That forced him to miss the entire ’88 AMA Supercross season and first two rounds of the ’88 AMA 125cc National MX Series. (In order to hold on to his contract, he did try to ride the last Supercross but crashed out in the first turn at the Los Angeles Coliseum. He then got 16th in the first National moto, but hurt his injured leg in the second and did not finish.)

The rest of the season, however, couldn’t have gone much better. In the remaining 10 rounds, Cooper won overall four times, was second overall four times, and took third overall twice—quite the record. Due to missing those first two rounds, though, he could only accumulate enough points to finish third with 433 points for the season behind factory guys George Holland on a works Honda (513 points) and Suzuki’s Donny Schmit (435).

“It was a pretty successful year for a guy who missed the first half of the season (including Supercross),” he notes.

While in town for the Kenda/SRT AMA West Hare Scrambles Regional Championship’s 2nd Annual AMA East vs. West Hare Scramble showdown, we swung by Cooper’s place to see and discuss one of the CRs he rode in Nationals that year. That he still has it is an interesting story in itself since he’d sold the bike to a friend, Dave Shields, years ago. Shields raced it in the local 125cc C class a few times, but when Cooper started putting his vast collection of bikes and bicycles into a more ordered museum, he called Shields to see if he still had the CR and if he’d be interested in selling it back. “I traded him a Chevy pickup and got my bike back,” Cooper remembers. “This is the way I got it back. He left all the stickers on it—the Dunlop stickers kind of pulled off on the sides—but basically this is the way the bike was ridden: same tires, same everything. It’s definitely used, it’s beat up, but that’s my bike so it’s kind of cool.”

So how did “Airtime” turn his stock CR125R into a bike with National-winning potential?

Surprisingly, it didn’t take all that much, due to Honda’s massive efforts in 1985’s works bikes to comply with the AMA’s production-bike rule that took effect in 1986, resulting in 1987s that were remarkably good out of the crate.

“That [’88] right there is nearly stock and it is a good bike out of the crate!” Cooper insists. “The ’88s, the power valve on the 250 was a little quirky, but the 125 was almost the same as the ’87—a great bike! Everything was good about it. A little bit of modification to it or just keeping it fresh [did wonders]. You know, a 125, you could take a brand-new one out every weekend and it had that little advantage over one with three or four hours on it.

“So knowing that and knowing what to replace [and when was important], but I never split the cases on these bikes. All I did was [replace the] piston and ring. If I sucked any type of dirt through it, it was new motor time or go to another bike.

“Hondas were really good, really reliable on bottom ends back in the day.”

And that was important for someone in Cooper’s position since he also performed most of the maintenance between races. “I actually kind of liked working on your bike,” he muses. “You know you worked on it, you know everything’s good. I will tell you something funny about all these bikes: It’s never had a torque wrench put on it! I didn’t own a torque wrench. I didn’t think it was that important!”

One of the trickest parts on Cooper’s bike is the handmade FMF unplaced “cone” pipe. With his being a revver, FMF built him pipes that started out a minimum of 10mm shorter than a production pipe.
One of the trickest parts on Cooper’s bike is the handmade FMF unplaced “cone” pipe. With his being a revver, FMF built him pipes that started out a minimum of 10mm shorter than a production pipe. Note the AMA approval tag signifying the bike passed tech as well as the brake snake and safety-wired footpeg.Shan Moore

A key part of winning on a 125 (and, nowadays, on a 250F) is extracting as much reliable yet rideable power out of the engine as possible. Here especially is where the factory bikes generally enjoyed a marked advantage, but Cooper believed his bike wasn’t far off from that level.

“I used an FMF pipe and silencer,” he begins. “I’d worked with Honda [doing testing] since 1984 so every chance I got, in California I would do their preproduction testing. I’d get paid to go out and ride the bike and that type of thing.

“As a privateer in California, it’s expensive to [go] out there. If I matched it at the right time, I could be paid to be out there and they’d pay for the hotel and give me some money so it turned out to be a real good deal.

“With that [I got to know Honda technician] Eric Crippa and [MX Team Manager] Dave Arnold. The hand-me-down [parts were] always given to me; it was pretty nice to have the works [Showa] suspension. A lot of time it was a year-old works suspension [I’d get] except for twice: 1988 George Holland liked the conventional [Showa works] fork—he didn’t like the upside-down fork.”

“[Honda] was getting pressure from Showa to run the upside-down fork [in Nationals] so I got to use the latest upside-down fork [in ’88], which was harsher, and like I was saying earlier, there were some advantages that I could see [to the upside-down fork]: You could feel the bumps so if you went into a rut, you knew exactly when you got into the rut [since conventional forks flexed and twisted enough to delay that feeling].”

“The conventional works [Showa] forks were the plushest forks on the planet! Everyone—if you talked to Bob Hannah and David Bailey and Johnny O’Mara, they’ll all tell you that the conventional Showa works forks were unbelievably plush! It was definitely like cheating, they were so good! But a conventional fork has a lot of flex in it. Anyway, I got to run the works forks in ’88 as ’88 forks.”

Although these are production Showa conventional forks, Cooper ran much of the ’88 season on works upside-down units, the shock a production item with valving that emulated that found on Holland’s factory racer.
Although these are production Showa conventional forks, Cooper ran much of the ’88 season on works upside-down units, the shock a production item with valving that emulated that found on Holland’s factory racer. Cooper preferred the bend of stock steel Honda handlebars until one set broke when he yanked up on it on the first lap of practice at the National in Virginia.Shan Moore

As the bike sits in Cooper’s museum, it bears production Showa conventionals, as it would have before the start of the season.

In back, Cooper admits, “I don’t know if I ever had the full works rear shock. I know that we had the works forks, but the shock, I think they played with the stock one and valved it to where it was real similar to what George ran because everything [I ran] was based off what George Holland had.

“I never was, technically, a factory Honda rider. I had signing stock (posters) in ’88 and ’89 just like Rick Johnson and Jeff Stanton or George Holland, but I never had that contract.”

Getting back to the engine, Cooper reveals that Crippa would take one of Holland’s works cylinders, study it, then duplicate each port’s dimensions and contours as best he could by his trained hand. According to Cooper, Crippa succeeded each time.

Another key component was replacing the standard 34mm Keihin carburetor with a 38mm version.

“I actually ordered what I thought was a 36mm carburetor and a Honda ’86 model or whatever was actually 38mm,” he recalls. “At one of the events, my bike is outrunning George Holland’s! [Roger] DeCoster keeps coming over [to my pit] and goes, ‘Now what have you got going?’

“And I go, ‘I’ve got an FMF pipe and I’ve got Eric Crippa’s cylinder.’ It was actually at Southwick, in the sand, and my bike was pulling like crazy testing on that Wednesday and Thursday [before the race], and DeCoster’s scratching his head.

“He finally comes over and goes, ‘I want to pull that carburetor and check your jetting.’

“I said all right, and he pulls the carburetor off and he starts laughing. He goes, ‘It’s a 38mm carburetor!’

“So they rushed and got some 38s for George’s bike, but the problem was, that 38 carb had tons of torque and if it was jetted just right, [it was good]. But it was never jetted just right [and] the problem was if you held it [wide-open steadily, it’d lean out and seize]. If you [moved the throttle more], it had just enough of the carb slide moving to where the jetting never found that lean spot and you’d be all right.

“But George’s bike, he’d be in that sand pulling and he was a real steady rider so he’d hold that throttle not wide open but let’s call it 7/8th on the money. Well, it would find a lean spot and he kept seizing it, so they said when they’re not comfortable with the 38, they made me pull the 38 off because they didn’t want to have a Honda not finish. So they gave me a 36 carb.

“But the 38, honestly, if you could get it to where you didn’t have that lean spot, man, they worked good!”

The non-plated FMF pipe is a hand-made “cone” pipe and Cooper explains, “[FMF’s Don Emler Sr.] would always take more millimeters out of my pipe than anybody else because I liked to rev! I wanted that thing to rev, so he would always shorten it.”

While it may sound counterintuitive for a 125, the extra power allowed Cooper to follow DeCoster’s gearing suggestion.

“Roger always talked to me about he’d like to see me run as tall a gear as I could because coming out of a rutted turn, you didn’t have to get your foot under the shifter to get a gear,” Cooper remembers. “So I ran tall gearing. A lot of guys ran 51, 52, even 53[-tooth rear sprockets]. I think I ran a 49 most of the time because you could pull that gear a lot farther. It was a close-ratio transmission, so it would pull the next gear and there wasn’t as much shifting.”

While many of his competitors ran 13/51 or 13/52 gearing, he preferred a taller 13/49 combination for fewer shifts per lap, something made possible with the extra power.
Yes, that’s an 18-inch wheel in back since 19s were not yet in vogue. While many of his competitors ran 13/51 or 13/52 gearing, he preferred a taller 13/49 combination for fewer shifts per lap, something made possible with the extra power. His preferred tire choice was a Dunlop 695 in back and a 490 in front.Shan Moore

While the 13-tooth countershaft sprocket is OEM, the rear is an AFAM—another hand-me-down. Twin Air filters were also items he got when the factory guys had a surplus.

Like the factory team riders, Cooper used Dunlops despite not having an official contract: “I loved the 695! Frank Stacy worked on that tire [design] and got the [knob] angles [perfect for me]. I was a brake-stabber. I would go into the corner and I would stab the brake and I would [brake-]slide and take off. The 695 works fantastic for that.

“I ran a 490 front almost exclusively, even at Southwick in the deep sand. A 695 floated on the sand; a 990 would dig in, and it would knife on me.”

He ran those Dunlops on stock wheels, wheels that he’d even build himself. “I came from a bicycle background so I enjoyed lacing wheels,” he says. “I understood you can overtighten [spokes] and you can [then] break wheels. My wheels hardly ever broke and I did a lot of damage to bikes, but wheels were something that unless it was an absolutely stupid jump, if I broke a wheel, it was because it was going to break no matter what. Even some of the factory guys had me lace up their wheels for them; I enjoyed doing it and they knew that I wasn’t going to jack it up.”

While it looks like a regular production cylinder, the port layout mimics that of George Holland’s factory bike as much as possible, thanks to careful handwork by Eric Crippa.
While it looks like a regular production cylinder, the port layout mimics that of George Holland’s factory bike as much as possible, thanks to careful handwork by Eric Crippa. That and a 38mm Keihin (later switched to a 36 due to orders) helped make this one of the fastest 125s of the year. This seat appears to be the 15mm-taller one off a CR250R—probably a switch that an interim owner made since Cooper preferred the shorter saddle that was standard on the 125s, even putting those on the 250s he raced in Supercrosses.Shan Moore

In something of a role reversal, Cooper preferred the CR125R seat, even on his 250, though the 125 in his possession now has the 15mm-taller CR250R seat for some reason.

Renthal’s Honda CR low-bend handlebar with standard Honda grips and levers provided his primary control mechanisms. (Interestingly, he preferred the stock steel handlebar up to 1986 because he liked the bend, but when he yanked so hard to clear an obstacle on the first lap of practice at a National in Virginia that year that the steel bar broke. Investigation later showed it had a crack and would’ve failed at some point during the day, but he used aluminum bars from that point on.)

Cooper concludes, “[Between] Eric Crippa’s magic that he worked on the cylinder and [Showa engineer] Sam [Mishima’s] working on the suspension for me, I had practically a works bike, although without the fancy mechanic and everything [that goes along with a full works ride].