Meet the New Parts ("the" solution?)

Not the same as the old parts, that's for sure. In an effort to eliminate some of the more basic issues that could be the root cause of 'the hesitation', I replaced as many carburetor rubber pieces as I could. It seems to have had a positive effect and cured (?) the issue. So far, so good.

Here's what I had planned to replace: (sorry my captions are too small to see/read) that irregular shaped gasket is for the float bowl. Inside of that is the gasket for the carburetor slide cap. Inside of that is an o-ring who's purpose escapes me (it wasn't used). Below the irregularly shaped gasket is the carburetor-to-intake o-ring. To the right of that (lower right) is the intake-to-cylinder head o-ring. In the upper right hand corner is the o-ring and washer for the air/fuel mixture screw. I had previously used Permatex Ultra-Blue to help seal the old float bowl gasket. I opted not to replace that gasket because I did not want to install the richer main jet (I wanted to see if the stock jetting would work appropriately). It turns out I will not need to use the richer (#102) main jet, the NX runs just fine with the stock jetting. At some point, I will replace the old float bowl gasket but there obviously isn't any urgent need. The image of the air/fuel mixture screw (below) shows the new parts on the screw, the old parts to the right and a small hook I made out of safety wire (in the middle). The hook was necessary to pull the old o-ring and washer out of the carburetor body.

Manifold-to-Cylinder Head O-Ring

Carb-to-Manifold O-Ring

Slide Cap "O-Gasket"

Air/Fuel Mixture Screw

Obviously

I finally encountered some knowledgeable inmates over on Adventure Rider. Let me amend that because there are a lot of knowledgeable inmates there. I'm referring specifically to inmates that have experience with the NX. I retrospect, it seems that I might have an air leak, someplace, between the carburetor and the cylinder head.

Normally, the sure sign of an air leak is a slow but steady rise in rpm as the engine warms. Usually a shot of carburetor cleaner or starting fluid on the intake manifold will cause the rpm to increase dramatically (these are flammable fluids, you see). I've never tried this method to try to diagnose the issue because I've never suspected an air leak. The NX is twice as susceptible because it has two o-ring seals; one between the carburetor and the intake and the other between the intake and the cylinder head. What makes it more difficult is that the air leak, minor as it may be, would seal as the parts warmed (expanded). This pretty much explains why the issue was more prevalent when temperatures were cold (20º-50º F). Another clue would have been that the float bowl sealing gasket recently quit sealing. These are the parts, o-rings and sealing gaskets, that suffer the most from age. While mechanical components fair pretty well, these parts still tend to degrade even though they still look good and feel pliable.

So, I ordered a carburetor gasket set (which includes the carb-to-intake o-ring as well as the float bowl gasket) and the intake-to-cylinder head o-ring. If there is an air leak, however slight, this should seal it and resolve the leaking float bowl, too. I would still like to check the valve clearances as well as the compression. I ordered from Honda Parts House in Muskegon, Michigan. They seem have the best OE Honda prices I've found on the 'net and are relatively close to me (Chicago).

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.

Still there, lurking....

The local temperatures continue to climb and the NX continues its mysterious hesitation issue. Now, it almost seems as if it's temperature related. The starting procedure is pretty straight forward; turn the petcock to 'on', apply 1/2 choke, flip the ignition switch to "run", turn on the ignition (key) to 'on' and press the starter button. Usually the NX purrs to life and I allow it to warm up before setting off. Before I leave the driveway, I'm at 1/4 choke. Unfortunately, the first major thoroughfare I encounter has a speed limit of 45 mph (realistically, 50 mph). So, the NX has all of three blocks to get the oil warmed up (not going to happen). However, acceleration needs to be quick and the choke is off completely by the time I'm a few hundred yards down the major road. If I don't completely remove the choke, the motor will start to bog (running rich). Since the motor isn't up to temperature, there is usually some hesitation/stumbling. This is where I cannot tell if it's a carburetor issue, an electrical issue or engine-not-up-to-temp issue. If I'm lucky, the engine will be up to temperature within another mile and I'll know if the motor is "on song" or "off song". I'm supposing it's time to bite the bullet and try a new coil. I've noticed that the TTO Rev Counter (tachometer) jumps around quite a bit, I'm talking thousands of rpm, while the motor idles (either at start-up or while waiting for traffic signals). For instance, I noticed that the tach would register between 960 and 2800 rpm while I held a constant throttle during motor warm-up (first thing this morning). I have to believe there will be some delay with the read out due to the way the tach senses electrical pulses (induction). But, why would it jump all over like that? Perhaps it's time for a call into Trail Tech.

I did exchange one email with Classic Honda Performance in Texas. Lyle, the owner, suggested I try another coil but wasn't sure exactly what an NX125 was. He thought it was a scooter. When I replied with clarification and asked if he recommended one of his products (CHP makes a replacement coil that claims superiority over the OE unit), he never replied to my second (or third) emails. So, I cannot say I recommend CHP due to poor customer service. This was after I spoke with one of his staff. She assured me that Lyle answered all emails on a daily basis. I tried to contact him, over the phone, but he never seems to be in the shop. Disappointed, I am.