Epiphany of sorts (??)

OK, the NX is not the Ark and we just had a Memorial Day extended weekend that started off damp, got really soggy and then turned into a sweat box. The sweat box continues today and we've already had the obligatory Midwest afternoon thunderstorm (due to hot/humid conditions). This is not 'the epiphany' I had on the ride in this morning.

This is 'the epiphany': Suppose there isn't anything wrong with the NX. Read that once more; there isn't anything wrong with the NX. Why? Well, let's examine the steps taken to figure out what the issue might be; 1) assume it's the carb and remove/disassemble/reassemble/install ad nauseum. Result? No change in performance. 2) Check electronics for possible failure/failing. Result? All components within spec (per Honda shop manual). 3) Maintenance items; check for clogged air filter, check for clogged intake, check carb (see above), check for clogged exhaust. Result? No issues found. 4)Check cam and ignition timing. Result? All within spec (per Honda shop manual). Not much left to check, is there?

Recall that I traded emails with CPW (Carb Parts Warehouse) and their initial reaction was to "bump up the main 2 or 3 sizes". Also, I discovered that by applying partial choke the motor ran better in cold/cool weather. So, isn't it logical to think that the 125cc motor sheds heat so quickly that is never reaches proper operating temperature especially when the ambient temperature is below 45º F? Wasn't my last mpg reading 92? At this point I'm beginning to think that the carburetor is jetted too lean and that I need a richer main jet. I have a #105 (which is one or two steps richer). It wouldn't be hard to procure a #108 & #110 or a #110 and #115. I'm not sure if a "step" is 2.5 or 5 (my old DR350SE took "steps" in 2.5 increments). It shouldn't be hard to find out, though.

How did I discover this? I took a quick ride to "homeowner hell" (home improvement store) Saturday morning. It was in the low 70s and the bike did it's usual hesitation thing until it reached operating temperature and then it ran like gang-busters. I guess it finally dawned on me that I had a simple issue of a lean condition yet I was determined to find something else wrong. I need to check the plug when I get home to see what color the ignition tip is. That's a pretty good indicator of the air/fuel mixture.

Oil Change: I mentioned that the NX needed an oil change and I completed that a couple of weekends ago. The oil looked good, pretty clean and I didn't find anything 'bad' in the screen (no filter on the NX), like metal chips. I did find some type of "snot" lodged in the screen though. It came off with a shot of carburetor cleaner but I'm unsure of what it actually was. It was the same color as the oil but thick enough not to be able to pass thru the screen.

Electrical Gremlins are not home

I finally had an opportunity to remove some bodywork and check the electrics. After chatting with Sudco a couple of weeks back, I may have interpreted the hesitation issue as fuel related. It's possible it might be electrical. So, I exposed as many items, on the NX, as the shop manual mentioned. First up was the CDI and the Coil. There really isn't a test for the CDI box itself. There are some resistance and continuity checks for the wiring that plugs into the CDI. All readings were within spec. Next was the coil. Again, everything was in spec. So, I made sure that the connections were tight and the wiring insulation was free of cracks and/or exposed wires. Everything looked good and nothing untoward was discovered. Next up was the regulator/rectifier. Again, everything checked out as being within specification and all wiring connections were clean and tight. The only thing I was unable to check was the timing. I do not own a timing light and I'm wondering if a timing issue would appear and then disappear like this problem has. If necessary, I can take the NX to the dealer for a quick timing check. I have a call and an email in to Classic Honda to see if anyone there can assist. The search continues...

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.

Old Man Winter - Not Done Yet

I was hoping that I would be able to start my riding season around the same time as I did last year (mid-March 2010). I got about a week's worth of riding in when the weather decided to stop cooperating. This morning finds light snow on the ground and ice on the roads. Temps are supposed to dip below freezing, at night, and only be in the 30s during the day. That, and the fact that the NX has some sort of issue with running above 4K rpm, means the bike will remain in the garage until next week some time. Right now, it looks like Tuesday, March 29, will be conducive to riding.

Now, for that engine issue; it seems that I need to check several things. Fuel delivery; I've already cleaned the carburettor and air filter so I know that's not the issue. But, I need to ensure the fuel valve screen is clear and that the fuel lines are flowing at maximum capacity. Cam Timing; it seems that the cam shaft might be off proper timing and I'll need to double check that. So, this will require quite a bit of disassembly (side covers, seat, tank fairings, tank, rocker covers, cam gear cover, etc.). So, it looks like Saturday will be a busy day. Until the weather improves and I get the bike checked out, posting will be sparse.