Honda Mr175
HONDA MR175
Cycle World Road Test
A Sheep in Wolf's Clothing
WITHIN THE PAST two years, since the introduction of the Honda Elsinore line of two-strokes, people have come to expect quite a bit from any ring-ding manufactured by the Big H. The Elsinores certainly weren’t a letdown; the MT250 wasn’t, but the MT125 was. This year Honda has introduced the new MR line, premiering the MR175 tested here. The MR line, which next year will be expanded to include a 250, is billed as a cross between the CR motocrossers and the MT trail bikes. While there is neither a CR nor an MT 175 from which to obtain a cross, it isn’t difficult to pinpoint which parts were influenced by which machines.
The chassis is mild steel but proved surprisingly strong. Its single downtube splits into a twin engine cradle at the tube’s base. The cradles sweep back under the engine and then upward to end at the upper shock mounts. The backbone of > the frame comes rearward from the steering head and then splits into two struts that drop to meet the engine cradles at the swinging arm fulcrum. The frame is finished in conventional black.
The motor is based on the engine cases of the MT125. Stroke length is shared with the 125, but the bore is 10mm larger. Two additional plates have been added to the MT’s clutch to handle the additional output of the new motor. The ignition is identical to the MT’s, with the exception of the absent battery-charging coil. Since there is no battery, it is not needed.
The transmission is a five-speed unit that operates beautifully. Shifting the MR is a dream. Lever throw is short, positive and need not be accompanied by disengagement of the clutch.
Fattish and green, the 2.9-gal. tank holds enough pre-mix for about 90 miles of frisky riding. Oil-injection has been eliminated on this machine to help keep the retail cost down and to eliminate one more thing that needs adjustment. As far as that is concerned, the Honda is one of the easiest machines to work on that we’ve ever come across. The engine is a breeze to wrench, and adjustments are really kept to an absolute minimum. As for regular maintenance, such things as air filter cleaning are child’s play. The airbox is very large, thanks to the room made available by the absence of an oil-injection tank. Breathing through a snorkel-type intake beneath the seat, air is filtered through an oil-wetted foam element before entering the 28mm Keihin carburetor. The Keihin on the MR is very Mikuni-like in appearance and performance. The MR was always easy to start and carbureted well throughout the test.
■ WE COMPETED SUCCESSFULLY in a couple of enduros on the MR175. Once in stock form, during which our staffer found it necessary to ask the Honda to rev to unheard of rpm and to ride it on the ragged edge of both reason and safety just in order to stay on schedule. But stay on schedule he did. Then, after modifying the motor in the manner we’re about to describe, another enduro was attempted. This time the bike was much more up to the task, requiring less of the rider. Both of these enduros were of the “family” type with one easy loop for beginners and kiddies and one bust-your-tail loop for the more experienced riders. Degree of difficulty was virtually identical in both enduros.
After our experience in the first event, we knew that something had to be done to the machine if we were going to successfully compete on it.
We discussed at length with Honda the feasibility of installing a six-speed transmission from a CR125 in the MR cases. They told us that the cases would have to be machined to accept the wider gear clusters, but that it could be done. The resulting set of ratios, however, would have given us a first gear taller than the standard one and a sixth gear lower than the MR’s fifth. They said that some of their R&D people had also tried playing with existing ratios from other suitable transmissions, swapping back and forth trying to come up with a better gearbox, but they just couldn’t find an ideal set of ratios. In the end, we decided to leave the transmission alone. More torque and horsepower were sought.
We took the cylinder to Mike Christianson of Precision Motorcycle Services (soon to be with Premier Yamaha as head of the competition department). Mike did a time/area value chart to define the exact timing of the ports and see where they were deficient. After studying it, he found the intake and transfers to be deficient at the peak operating rpm of the exhaust port. He remedied the situation by porting the cylinder to the specifications provided with the port layout drawing.
This cure is only partial. Our test machine had to be returned before we could experiment further, but Mike plans to continue trying to get even more power by playing with larger carburetors and developing a more efficient exhaust pipe. If you need help with your MR, give him a call at (714) 536-7555.
When we got the engine back together, we found that we had to lean out the mid-range by dropping the needle all the way and then fatten up the top end by going to a 122 main jet (standard is 118).
Very little of the low-rpm pulling power was sacrificed. The mid-range was much stronger and the top-end power was really neat. Now the MR could handle the second-to-third shift with ease. In sand, we had to climb the walls of the sandwash and then dive back down in order to get the engine to fourth at a point where it could pull, but it would pull it. Ten minutes straight running WFO fourth gear (about 50 mph) up a sandwash left the motor no worse for wear. Fifth gear was still a problem, but at least it was occasionally usable. It is our opinion that the MR should have at least as much power in stock form as our test bike did after this one simple modification. It still retains 95 percent of its foo-foo power, but now has enough in reserve to make use of the fine suspension and excellent tires that come as part of the standard package.
There are also a few more things that the average rider can do to make his machine more enduro-worthy. Installing an aluminum CR shift lever is one. The stock lever sticks out prominently, inviting rocks to take a bite at it. The CR lever is malleable and can be easily straightened. It also doesn’t stick out as far. We suggest that you also cut away part of the left sidecase to expose the countershaft sprocket for easier changes and replacement of thrown chains. CR125 footpegs are about an inch shorter on each side and make picking your way through rocks much easier.
Suspension-wise you can purchase a forward-mounted shock accessory swinging arm designed for a CR125. Redline Mfg. and DG both have excellent units available. To install it you must machine 5mm (2.5mm on each side) from the swinging arm’s pivot since the CR swinging arm measures 176mm across its pivot and the MR only 171mm.
The MR 175 Honda is a fun little bike that can be made more competitive with additional expense. Of course, the more performance you want, the more you have to pay. If you want something that runs like a Can-Am or Penton, then buy one of those. You can spend enough modifying an MR to have purchased one of the other two, yet they’ll still scoot past you when they want to.
But if all you have to spend is $895, or if all you want is an MR175, then Honda has the bike for you. gl
Suspension is handled fore by a pair of CR125 forks with heavier fork springs, and aft by CR250 shocks. The forks are set to provide 5.7 in. of trail, which works well in conjunction with the 31-degree rake. There is a tendency to search slightly at speed, but since the little MR is anything but a rocket, we gladly accept this slight hindrance in exchange for the excellent steering. Besides, the mild wiggle at the bars sets itself into a rhythm that is kind of like music as you ride. It never gets anywhere near troublesome. If the MR had about eight more horsepower, the speeds attainable in rough terrain might make the stability a little sketchy, but as it is, we loved it. >
PREMIER YAMAHA COMPETITION DEPARTMENT
Those wishing to take their MRs out to these porting specs should have the work done properly by a competent dealer. Porting a cylinder is not just a matter of sitting down and whittling away at the port windows. Unless the port is opened up all the way through, flow will not increase and velocity will drop. For this reason, we suggest that you spend the extra cash and make sure that it's done right.
The porting specs here are designed for increased torque and top-end horsepower, peaking at 8000 rpm. They are designed for operation with either the stock carburetor or a 30mm Mikuni. With the stock carb, we found it necessary to go to a 122 main jet and lower the needle all the way. The power increases are substantial, but would be greater if a new pipe were built to work in conjunction with the new ports.
The MR has a really light feel for a very good reason. It is light. Weighing in at 214 lb. with a half a tank of gas, the little 175 is lighter than most 250 MXers, and even lighter than a couple of 125s we can think of. Couple this lightness to the positive steering characteristics and you can see why the MR can be flicked about tight trails with ease. In fact, with the super-low first and second gears, picking its way through ridiculously tight paths is the MR’s forte. It would be hard to find a 175 anywhere capable of cutting a swath through the twisties better than this one. That’s good for the MR, because every other 175 we can think of would blow its doors in out in the open country.
The problem that the MR175 has is two-fold. And it all has to do with piddling engine performance and transmission ratios as wide as the Grand Canyon. The motor runs like a strong 125 Enduro. As a 175 it is underpowered. The power spread is broad, but there isn’t much power. First gear is low enough to climb telephone poles. Second gear isn’t much faster. When in these gears, the engine works neat. But the jump to third gear is too deep to be pulled in sand or on a mild grade. So you scream the engine in second, shift to third, bog, go back to second and scream it, bog third, etc. Quite frustrating if you have to do it for very long. The jump from third to fourth is the same way. And you can forget fifth. With a 200-lb. rider, the Honda was faster in fourth on a fiat dirt road than it was in fifth. What the bike needs to be competitive, apart from at least a half-dozen more horses, is a six-speed transmission.
PARTS PRICING
HONDA MR175
SPECIFICATIONS
$895
POWER TRANSMISSION
DIMENSIONS
SUSPENSION DVNO TEST FRONT FORKS
Description: Honda MR175 fork with HD 315 oil Fork travel, in.: 6.75 Engagement, in.: 4.0 Spring rate, Ib./in.: 24 Compression damping force, lb.: 8 Rebound damping force, lb.: 26 Static seal friction, lb.: 4 REMARKS: The MR comes with too much oil in the forks. It should have 140 instead of 160cc. Damping is correct for the spring, but the spring is too heavy for the motorcycle. The result is a rough ride over small bumps and washboard surfaces. A softer spring (18 lb.) and lighter oil is the cure. Static seal friction is only 4 lb.; this is outstanding, since it allows the forks to move smoothly without binding. Travel can be extended a maximum of 1 in.
REAR SHOCKS
Description: Honda shock, stock oil Shock travel, in.: 3.5 Wheel travel, in.: 4.75 Spring rate, lb./in.: 77/1 22 progressive Compression damping force, lb.: 4 Rebound damping force, lb.: 86 REMARKS: The MR shocks were dyno tested after two enduros. At that point, they lacked in both compression and rebound damping, although the ratio between CD and RD is about correct. Excessive bottoming and some topping of the rear suspension was the result. To make damping ideal, CD and RD both need to be raised about 11 lb., for a total of 15 lb. compression and 97 lb. rebound. Changing to an oil with more viscosity will help achieve this. Spring rate is fine for a 160-lb. rider. Tests performed at Number One Products
But Honda had 20-hp six-speed prototypes before it settled on the current design. Obviously, it wanted the machine to be more of a foo-foo bike than an all-out enduro mount.
The reasons are simple. Foo-foos with only five speeds are cheaper to build and sell more than high-strung slingshots. As such a machine, the MR is a success. It is harmless. You have to ride off a sheer cliff in order to get into trouble on it. It is perfect for a super-light kid stepping off a minicycle onto his first motorcycle. The light weight is an obvious benefit here. But there is so much on the bike that says “ride me hard” that we kinda wish that the rest of the machine was up to par.
Just to see what could be done with a few extra dollars, we had our test bike hopped up. The accompanying sidebar will give you the details and the results.
The name MR is itself a cross between the MT and the CR of the trail and racing Hondas. Some people have dubbed the MR the “Mister” 175. Actually, that is about the best way to sum it up, Mr. 175 ; capital M, small r. J5J
