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AJP PR4 - Modifications
November 30, 2015 version

 Introduction 

 Modifications 

 Maintenance 

 Crossover Parts 

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                      Alphabetical table of contents  

Bags 
Battery and pigtail 
Battery charger 
Blue 
Carb fuel hose 
Crankcase vent hose filter 
Enduro muffler 
Fork guards 
 
Front brake line 
Front fender 
Gearing/Sprockets 
Handlebars, handguards, grips, and fork guards 
Handlebar miscellaneous 
Headlight 
Hour - Tach Meter 
Kickstand 
Kickstarter 
Lowering the seat CHANGE
Manufacturer stickers and imprints 
Measurements 
Rear fender 
Remove Before Flight 
Shifter bolt 
Tires 
Unused wires 
Weigh-in 
Appearance/Cosmetic mods 3     Electrical/Mechanical mods 16     Reference 6

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Weigh-in

1/24/15 stock, all fluids except gas - 233 pounds.
2/13/15 almost all mods applied, all fluids except gas - 236 pounds.

The enduro muffler swap added 8 ounces.

Adding or changing the following items added weight: nut and longer shifter bolt, clip on fuel line, rear fender extension, headlight, handlebars, handguards, mirrors, hour-tach meter, bags, faux carbon fiber, battery and oil cooler covers.

Removal or changing the following items removed weight: kickstand pin, LiFePO4 battery, faux radiator shrouds, side number plates.

The result: 3 pounds added weight. Not too shabby.


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Measurements

Baseline measurements; stock tires, no suspension changes.

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  Seat height = 36 1/8" (at the lowest point, really)
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  Footpeg height = 16 3/8"

Seat to footpeg = 19 3/4"


Forks

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After mounting the new Kenda K270 120/80-18 rear tire and near-new Kenda K270 3.00-21 front tire, the axle heights changed. I calculated that I needed to lower the triple clamps about 5/32" to get the geometry back in balance.


First geometry change measurements; new tires, triple-clamp lowered.

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  Seat height = 35 5/8" (at the lowest point)
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  Footpeg height = 16"

Seat to footpeg = 19 5/8"
This should match the 19 3/4" of the baseline measurement above because changing the tires shouldn't affect this measurement. Perhaps the seat has compacted the 1/8" difference.

So the seat height is about 1/2" lower. Can I tell the difference? You bet I can. I can touch the ground with both feet without stretching. Will that make a difference? You bet - us short folks welcome any seat lowering we can get...
Also, my Pinto does not lean as much when it's on the sidestand.

 

Fuel tank

The fuel tank holds about 7 liters or 1.85 gallons. However, you don't want to fill it all the way to the top. I had earlier checked the metal cap and it seemed to allow air into the fuel tank, but not out. After filling the tank, I rode around the yard to check for leaks etc and after stopping, noticed that the top of the cap had fuel in one-half. That's not good. Further, when I blipped the throttle, a small spurt of fuel came out of one bleed hole, adding to the fuel already present.

I removed about 100 cc (ml) of fuel and did another check ride - no leaking fuel! So my fill-up procedure will be to fill just below the lip - about 100 cc less. This will result in 6.9 liters or 1.82 gallons of fuel. I'll get an initial MPG figure when I use this tank up.


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Kickstarter

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The zero-th mod was to not install the kickstarter.

Easiest mod evar, and I saved 1 pound 1 ounce.

The kickstarter was never installed, so it was never included in any weights mentioned above.

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I covered the exposed shaft.


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Kickstand

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The very first actual mod was to defeat the kickstand auto-retract. This is easily done by cutting off the pin that extends from the top of the pivot bolt. I used a Dremel - no cost, easy peasy.

And I saved 2 g!


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Shifter bolt

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The stock bolt on any shifter can come loose and then the shifter starts wearing the splines on the shift shaft. I always install a longer bolt and a locking nut on the extended length. That sucker will never come loose. It does add a little extra weight, but it's more than worth it.


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Front brake line

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When I was adjusting the front brake lever, I noticed that the assembly would not slide inboard as far as I wanted. After checking everything over, I noticed that the banjo end piece was jammed against the handlebar cross-brace mount. I cracked the banjo bolt just enough to rotate the brake line downward enough to clear the cross-brace mount, then retightened the banjo bolt. The brake assembly then was able to slide inboard as far as I needed.


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Carb fuel hose

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I like to adjust all the suspension settings to full soft initially so the suspension will break in full-stroke. No problem with the forks; unscrew the adjuster screw on the top of each fork cap all the way out, then in 1/8 turn (there are no detents). The left fork handles compression damping, the right fork does rebound damping.

I had no problem with the shock rebound damping screw either; all out, then back in 2 clicks. But setting the shock compression damping was not so trouble-free. I unscrewed the adjuster knob all the way, then back in 2 clicks. All done, right? Nope. Gas started pouring onto the garage floor. A quick check of the carb showed the fuel inlet hose had slipped off the brass carb inlet barb. The fuel line rests against the shock adjuster knob, and when I was unscrewing the knob, one of the grooves on the knob caught the fuel hose and pulled it free of the carb. I put a fuel line clip on the hose, then reinstalled it onto the carb. Problem hopefully solved.

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You can just make out the reinstalled hose.


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Unused wires

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I had a look behind the headlight to check for any wiring problems, and I found 4 unconnected wires. The wiring diagram shows these as turn signal wires; the US PR4 does not have turn signals. I wrapped the ends in tape to prevent any water-caused problems. Everything else looked fine.


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Battery and pigtail

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I installed an Antigravity LiFePO4 battery, which works quite nicely. It saved about 2 lbs, and all of it up high, above the engine.

The LiFePO4 battery is the thin black slice between the foam, pointed to by the arrow. Yes, it really is that thin. I used high density foam to fill out the battery compartment so the rubber strap would work, but I plan to remove some of the foam when I get a shorter strap.

The extra wiring on the facing side is the battery charger pigtail with it's own fuse. It wraps around below the frame spar then back over the battery and terminates in a big fat red plug. I maintain the Antigravity battery with an Optimate TM291 charger; fancy schmancy. The charger pigtail comes with the charger.

Antigravity Batteries 4-Cell Small Case - about $96.  Amazon
TecMate TM-291 OptiMate Lithium Battery Charger - about $108.  Amazon


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Enduro muffler, blue front and rear fenders, and blue headlight

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I installed the enduro muffler. It is petite and very quiet. At 85 dBA, it is 3 decibels noisier than my CRF230F stock muffler with 82 dBA. I can live with that. The test drive in the driveway was immensely satisfying; the air intake was noisier than the muffler!

It was a bit fiddley to install, but nothing that required super powers. I spent most of the time cutting the header pipe shorter so it just meets the enduro s-bend; two cuts did it. I made a sleeve to fit over the junction; two heavy duty clamps will arrive in a few days to complete the work. I've got two regular hose clamps on there now.

I have to investigate the enduro muffler further in regards to a spark arrester.

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I'll be making the battery and oil cooler covers (in blue) over the next few days. Yeah, it's now a blue AJP.

Like that one over there --->

The enduro muffler weighs 8 ounces more than the MX muffler: 4 lb 2 oz  vs  3 lb 10 oz.

The UFO rear fender came with a taillight, but it had an incandescent bulb. So I swapped the taillight section with an Acerbis LED taillight assembly.


Follow up on the enduro muffler

When I mounted the enduro muffler, I was waiting for some heavy duty hose clamps to seal the junction between the header and tail piece. In the interim, I installed a flimsy aluminum tube and standard hose clamps, and then forgot about it. Eventually the heavy duty hose clamps arrived, but I avoided installing them - too much playing on the trails with other bikes. Then my friend Robert came by asking about my new Pinto, and I pulled it out of the garage and started the engine so he could hear the somewhat noisy exhaust. Yes, the fly in the ointment of the enduro muffler was that it wasn't as quiet as I had hoped it would be. Robert listened for a minute, then said that if I fixed the exhaust leak it should lower the noise considerably. After checking the flimy aluminum tube joint, I discovered that it was leaking badly, plus it had a hole burned through the side! So I decided to install the nicely machined joint tube that another friend made for me.

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Robert tigged the tube to the header (very nicely done) and I installed the header, tail piece, and one heavy duty clamp. Success! The noise was reduced considerably, only slightly louder than my ultra-quite 230F. Thank you Robert.

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That about finishes the exhaust work.

Polisport UFX Free Flow Front Fender YZ Blue - about $30.  Rocky Mountain ATV MC
UFO Rear Fender with Light YZ Blue - 2006 YAMAHA WR250F - about $39.  Rocky Mountain ATV MC
Acerbis X LED Tail Light - about $40.  Rocky Mountain ATV MC
Acerbis Headlight LED Vision HP Blue - about $95.  Amazon


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Handlebars, handguards, grips, and fork guards

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I like Pro Taper SE CR High bars, cut to size, so while it snowed outside, I worked in the garage installing a set. I use aluminum threaded bar inserts to mount handguards so I tapped the bar ends. The short aluminum piece is one such. Several months ago I came across some handlebar vibration reducing inserts (HVRI) which use the same thread tap, so I bought a set for testing (the longer piece is what I'm referring to here). I'll put the regular aluminum threaded insert into one end of the handlebars and the HVRI into the other end of the handlebars. I'm hoping to feel a difference, and if it's good, I'll swap in the other HVRI.

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I found these smaller Cycra hand protectors and they mounted right onto a set of Cycra handguards.

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I'm using the Cycra triple-clamp mount; I liked them on my WR250R and decided to try them again.

I had to get longer fork clamp bolts because the Cycras are so thick. I'm using Hillman Group M8-1.25 x 60 mm bolts I ordered on Amazon.

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And some blue/black Spider hand grips complete the job.

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Faux carbon fiber fork guards. KEWL.
Peel and apply, then use heat gun to bond.

Those curved lines are cast into the stock plastic fork guard; sort of a raised section.

Pro-Taper SE 7/8" Handlebar CR High Bend Platinum Grey - about $60.  Rocky Mountain ATV MC
PMB FASTWAY threaded bar inserts - about $26.  seismiccycles on eBay
Handlebar vibration reducing inserts - about $67.  CheckPoint Off-Road, LLC on eBay
Cycra Series One Handguard Bar Series - Blue 7800-62 - about $54.  Amazon
CYCRA Triple Clamp Handguard Side Mounts - about $45.  seismiccycles on eBay
Hillman Group M8-1.25 x 60 mm bolts - about $14.  Amazon
Spider Grips SLR Open End Grips Blue/Black - about $17.  Rocky Mountain ATV MC
Taro Works 3d Carbon Fiber Vinyl Flex Wrap Blue 60"x12" - about $12.  Amazon


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Hour - Tach Meter

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I hid the hour-tach meter between the handlebar mounts, mostly for protection. No power required; just wrap a wire around the spark plug lead. Works great; you can see the engine's just idling.

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I wrapped the pickup wire around the spark plug lead up near the coil to keep the wire short and out of the way.

TTO Tach-Hour Meter - about $38.  Trail Tech


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Bags

It seems to me that the faux radiator shrouds do two things:
Route air to the air box top and oil cooler,
Make the PR4 look cool.

I figure that all the air that is needed can be provided without the shrouds and I don't care about looks. I am however, interested in a place for my bags.

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There's a battery under that cover.

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The oil cooler is hidden away, and moderately protected.

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Very narrow, almost trials-narrow.

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Nice fit.

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No air flow restriction.

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Showman Royal Blue Cordura Nylon Western Saddle Insulated Horn Bags - about $24.  eBay


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Crankcase vent hose filter

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I replaced the crankcase vent hose (open to the air) with a shorter hose and an air filter. By using a short hose, I've kept the air filter protected from external dust. The hose I used was an old XR250R hose.

Uni Filters Push In Breather Filter; 1/2 inch = 314-9855, 3/8 inch = 314-9854; size depends on hose used - about $15-$16.  Chaparral


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Remove Before Flight

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If you transport your moto in a vehicle to different elevations, fuel may leak from the carb drain hose. If so, use a small black office-supply clamp to seal the line during transport. It does no good to try and drain the float bowl; think about it and you'll understand why. Hint: there is no petcock...

Mine dribbles about 1 out of 3 transports.


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Gearing/Sprockets

I did a preliminary look at gearing when I was first researching the PR4 and posted what I thought were reasonable conclusions, based on what I knew at the time. But as it turns out, I had incorrect information and so my previous conclusions were incorrect. I now have good information based on updated documentation and measurements from an actual PR4 (mine) and so here I go again with some more analysis and perhaps more correct conclusions.

I always have problems bringing bikes to my riding area. I live at 7,400' and ride at 8,000' to 12,000' and bikes always fail to perform well at these elevations. Even when jetted correctly, they do not run as well as at sea level. That's because the partial pressure of oxygen in the air is reduced at this elevation compared to sea level, so motors lose horsepower. To compensate for lack of performance, I have had to gear down the drive system, with smaller front sprockets or larger rear sprockets or both.

To compound the problem, the PR4 has a 5-speed transmission. 5-speeds are not necessarily bad, but in a small displacement motor, there is not enough engine horsepower/torque to properly space gears when trying to design a wide-spaced transmission. The table below shows gear ratios for my PR4 and modified CRF230F (front and rear sprockets and rear tire are different than stock). Although I have modified my PR4, the tranny gears, front and rear sprockets, and front and rear tires are still stock.

The last column (Spread & tire) shows the tranny spread and tire circumference (in inches). Tranny spread is how wide the transmission itself is; it's the first gear ratio divided by the top gear ratio. It's not surprising to see that my 230F has a wider tranny than the PR4, considering that it has 6 gears to the 5 in the PR4. What is surprising is the speed comparison between the two motos (Speed vs 230F). The speeds that were calculated for the comparison are based on overall gearing AND tire circumference and are not shown in the table here; only the resulting comparison is shown (the vs row). The PR4 is actually geared overall lower than my 230F in first gear; it runs 5.3% slower (at any given RPM). That's a bit less than one tooth less on the front sprocket. The stock PR4 will probably climb steeper and more difficult terrain than my 230F! Not even considering that the PR4 is lighter, more nimble, and has a few more horsepower than my 230F.

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Looking at second and third gears, I see that the PR4 runs 3.4% and 3.8% faster than the 230F, just about perfect for more speed as I get out of technical mode and into run-fast mode (if you can believe that either moto has a run-fast mode).

Fourth gear is a puzzler, with the PR4 running slower than the 230F at -.7%. Fifth gear at .01% faster is running neck and neck, but the 230F has another gear in the tranny to allow it to run a higher top speed. But I can live with that top speed limitation; I ride dirt roads and highways as little as possible.

Bottom line - Contrary to my first conclusion that I was gonna need to buy some sprockets, I think the stock setup will suit me just fine for now. The final test will come in April when I get to the tight-single-track trails...


But wait, there's more. In March, I put new tires on the bike, which resulted in lower axle heights and a smaller rear tire circumference and that reduced the overall gearing. To compensate, I calculated that a 14 tooth front sprocket would get the gearing back to stock tire size gearing. But a 14 tooth front sprocket won't fit, so I had to go with a 3 tooth reduction in the rear sprocket, down to a 45T. Here's the new gearing chart with the 45/13 gearing and 77 inch circumference changes.

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The Pinto is closer to the 230F in 1st, and faster in 5th compared to stock - looks good to me.


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Here's the new sprocket and a new DID VT2 chain. The stock chain would have worked just fine, but I like the DID VT2 chain and usually switch to it as soon as the opportunity arises. The DID is the same length as stock, but the wheel is moved back because of the smaller sprocket.

JT Sprockets JTA897.45 45T Aluminum Rear Sprocket - about $27.  Amazon
The DID VT2 chain was in stock in my garage; don't recall the source or price.


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Handle bar miscellaneous

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Parts for making GPSr handlebar mounts.

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Mockup
  and
mounted.

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Enduro jug and watch.

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Finished look.

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With small mirror.


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Tires

My PR4 came with Michelin DOT tires (described below) and I will leave them mounted for the time being. I've ridden them enough to know that I don't like them, and will eventually mount a Kenda K270 front and something else on the rear. I'm very fussy about what tires I use because of the areas where I ride - mostly tight single-track trails and dirt roads. I've found what works well for me on my CRF230F and suspect something similar will work with the PR4. Time will tell.

Front tire

Michelin Enduro Competition MS
90/90-21
3 polyamide plies

Made in Thailand
Tube type

DOT
M/C 54R
Durometer 75

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Rear tire

Michelin Enduro Competition III
120/90-18
3 polyamide plies

Made in Thailand
Tube type

DOT
M/C 65R
Durometer 76

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Front rim  J21 x 1.60 DOT

Front hub bearing  6004 2RS xx mm
Spacers  24 mm od x 15 mm id

Front axle  15 mm

Rear rim  J18 x 2.15 DOT

Rear hub bearings  6005 2RS xx mm  6204 2RS xx mm
Spacers  30 mm od x 15 mm id

Rear axle  15 mm


It's time to change the tires.

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The front tire is done.
 
Now what shall I mount on the rear?
4.10-18              4.60-18                                       stock                                    120/80-18

AAH, I know just which one to mount up...

  

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The stock tire is a 120/90-18, so the Kenda 120/80-18 is the best fit, and it lowered the seat a bit.


Axle heights calculations for geometry correction. Numbers are measured ground-to-axle center-lines.
  
Stock tires  
New tires
Diff
Front
13 3/16  
13 1/8
-1/16
Rear
12 1/2
12 5/16
-3/16

The calculated adjustment is 3/16 - 1/16 = 1/8 front drop. I dropped the triple clamps 1/8 + 1/32 = 5/32      See Measurements for picture.
The extra 1/32 is to account for initial accelerated wear of the rear tire, which I experienced when using this spec tire on another moto. On second thought, the reduced tire diameter is more than likely carcass settling/sagging once it gets to operating temperature a couple of times.

The lower rear axle height also affects the overall gear ratio - the tire circumference is reduced resulting in a lower overall gear ratio. To see the details, have a look at Gearing/Sprockets to see what I did.

Kenda K270 3.00-21 front tire - about $48.  American Motorcycle Tire
Kenda K270 120/80-18 rear tire - about $111.  American Motorcycle Tire


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Lowering the seat

A week ago, I visited the USA AJP web site and discovered that there is a lowering link and shorter kickstand for the PR4. Even though I've installed a lower profile rear tire and lowered the seat from stock, I was still needful of additional seat lowering. Quick as a wink, I called Mike Carlton, the AJP dealer at Dirt Riders West in Scottsdale, Arizona and asked if he could get the lowering link and kickstand and his response was "Yes", so we did the deal and I sat back to wait. Six days later, UPS delivered the parts, all the way from Vermont and in transit over Thanksgiving Day. I can't even get Honda parts that fast!

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The new kickstand is one inch shorter; the new lowering link is 9mm longer. Together, they weigh 72 grams more than the stock parts; that's 2.5 ounces in American.

After installation, I did some measuring. At 34 1/2", the seat is almost exactly one inch lower.

Note - I lowered the triple clamps 11 mm or 3/8 inch to kinda balance the lowered rear end. We'll see how she steers on the tight trails...

Click  AJP Factory Accessories  to see the complete parts descriptions.

Lowering link - about $100.  See your local AJP dealer.
Shorter kick stand - about $50.  See the same dealer.


That's all for now.



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Take-off parts

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I didn't replace or remove a lot of PR4 parts; very happy about that.


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Manufacturer stickers and imprints

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Rear fender.


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Left and Right forks.


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Front sprocket cover.


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Right crankcase cover.


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Frame downtube, below steering stem.


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Tranny, top rear.


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QC on the starter; I'm re-assured that leaving the kick starter off is the right decision. busy


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Enduro muffler imprint (AJP0032), tire side.


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17 character VIN struck into the metal plate affixed to the frame downtube, left side near the oil cooler.
My bike's serial number (in these pictures) has been rendered illegible.


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