Basic Maintenance - Oil Change

Yes, this is pretty simple stuff but the NX is a little particular compared to some of the other bikes I own (or have owned).

Tools: 1/4" drive ratchet, 12mm & 10mm sockets, 1/2" drive ratchet, 15/16" (or 24mm) socket, oil drain pan, funnel and paper towel or rags.

As you can see, it's very helpful to remove the engine pan (or skid plate or engine guard) and the shift lever to gain access to the oil drain plug (and oil strainer). The drain plug is located just behind the tip of the shift lever.

Use the 1/4" ratchet with 12mm and 10mm sockets to remove the engine pan. The 12mm bolt is at the leading edge of the pan, where it meets the frame. The 10mm bolts (2) are at the trailing edge of the pan. At some point you may consider replacing the hex bolts with Allen bolts. Allen bolts have a tendency to maintain their internal hex shape even if they come in contact with a rock or a curb. If a hex bolt's head is rounded off, it may take a vice-grip to remove it.

Use the 1/4" ratchet and 10mm socket to remove the pinch bolt from the shift lever. The bolt has to be completely removed from the lever before the lever can slide off the splined shaft. Make note of the location of the tip of the shift lever in relation to a fixed point on the engine. You'll need to put the lever back in the proper location so that you can easily shift gears. The splined shaft allows the lever to be replaced in different orientations.

Here, the pan has been removed and the shift lever as well. There's now plenty of access to the drain plug. Remove the drain plug after placing the drain pan under the engine. Be careful when unscrewing the plug. There's a spring loaded strainer (screen) behind the plug. Chances are that the oil will push the screen out and into the drain pan. You really don't want that to happen because you'll have to go "fishing" for the screen in the old oil. If you're careful, you can use the spring to remove the screen (which is about the size and shape of a thimble). Place the plug, spring and screen on a rag or piece of paper towel. Allow the oil to drain completely (this may take several minutes before it stops dripping). I even raised the kickstand to see if tilting the bike further to the left would speed the process. It did, kind of.

Here's the completed job before re-assembly. Old socks make nice rags. I use Honda GN4 10w-40 oil because I got about 12 quarts of it with the bike. I may switch to synthetic once I've exhausted the supply. Right now, I change the oil every one thousand (1000) miles. That may be excessive but the sump is only one quart and the motor revs pretty high (50 mph = ~6K rpm). The transmission also seems to shift better with fresh oil. Always use an oil that's rated for a wet clutch. Automotive oils contain additives which can cause the clutch to work improperly (that is, slip).

Inspect the screen for debris. If there are metal chips you may have more serious issues to address. Be sure the screen is clear. Replace the screen, spring and plug as an assembly. It can be a little difficult to try to push (against the spring) and get the threads started. Be patient and use an extension (3") with the socket, if necessary. Tighten the plug so that it's good and snug but not overly tight. You don't want to strip those threads. I have to use an offset funnel to fill the sump because the fill hole is very close to the frame. Replace the shift lever and engine pan. Inventory your tools to ensure you didn't forget something. Properly dispose of your drain oil (most auto parts stores recycle used oil - my local Auto Zone still does). Start the engine to be sure everything is OK. Other maintenance things to consider while changing the oil: clean the air filter, clean & lubricate the chain, check tire pressures and/or lubricate frame pivots.

Check Everything, Find Nothing, Fix the Problem

OK, remove the side panels, seat, tank fairings and gas tank so I can check "everything". Here's what 'everything' consists of:


Fuel valve: removed, cleaned and replaced. Found some small pieces of debris on the screen but nothing major. Noticed no obstructions, used compressed air to ensure interior passages were clear.

Fuel line (to carb): removed, inspected and replaced. No obstructions found.

Carb: removed, cleaned and replaced. Used carb cleaner and compressed air. Found a little varnish on the valve seat but no obstructions in the passages or in the jets. Double checked the slide action (to ensure WOT) and that the cable wasn't binding.

Air box: Cleaned air sock as well as the underlying screen - a little dirty but not nasty. Removed the internal air horn and inspected the box-to-carb boot. It was clear. Inspected the action of the carb slide (to ensure WOT) and choke butterfly - no issues.

Engine: Removed all inspection ports to check the cam timing. It seems like it might be off 1/2 a tooth. But, there's no way to resolve that. Valve adjustments are within spec. The images show the timing mark and the cam gear marks. The timing mark is very hard to see but it's where it's supposed to be, with respect to the cam timing marks, according to the shop manual. I enhanced the cam gear marks so you can see them with respect to their reference marks (on the engine case).

Exhaust: Removed entire exhaust system to check for obstructions and/or rust. Found nothing. The inside of the pipe is clean and has very little carbon (fuel-air mixture correct) build-up.

After reassembling everything, I started the NX and noticed a pretty high idle (2200 rpm). Since it was pretty cold (35º F), I let it idle at that rpm and took it for a short ride to warm the engine. I came back home and adjusted the idle to 1300 (+/- 100) rpm per shop manual specs. With the motor warm, I revved the motor, in neutral, in the driveway. It went right up to 7500 rpm without issue. I went for a ride and the motor would spin right up to 9K+ rpm (well, there's a slight hesitation around 7K rpm).

So, whatever I did (and I'd like to know what it was) fixed the problem. I'm thinking it must have been something to do with the carb. Perhaps the slide wasn't sitting in the bore properly? I dunno. All I know is she screams now (like she's supposed to). Now, if I could only figure out what to do with 13 hp....ha!

After thinking about it some, I’m going to guess the carb slide was somehow bound up. I noticed when I unscrewed the slide cap that the throttle cable housing spun with the cap. When I reinstalled, I held the cable housing so that only the cap spun. Something was definitely different for the idle screw to be more than one full turn off.


Special thanks to my good friend Russ (who has ridden bikes longer than I've known him) who provided some insight and a list potential things that might be wrong. And, thanks to Joe at Cycle Tech in Summit, Illinois. Cycle Tech rebuilt the motor for the previous owner. Joe was kind enough to spend a few minutes on the phone with me during a busy (for the shop) Saturday afternoon. He pretty much verified the list of things I was going to check.