sportsawyer

I believe it's the smaller gear (behind the primary gear), which meshes with the kickstart idler gear, that backs out. Mitani has a writeup about it here: http://mitani-ms.jp/info/2013/09/rtl-f-clatch-outer/ It's in Japanese, but my browser did a good enough job of translation to get the idea. Mitani makes an improved part, but it's not clear how they improve it: https://mitani-kobe.shop-pro.jp/?pid=60396201

The old style pump assembly (2005 - 2015) uses an external vacuum operated pressure regulator so there's a constant differential pressure on the injector. The new pump (2016+) provides constant absolute pressure to the injector inlet, and the ECU adjusts spray duration based on vacuum seen by the MAP sensor. Since the new system ECU is compensating for the varying differential pressure on the injector, I beleive you will need a 2016+ ECU. If you can find a Honda Common Service Manual (2012 or newer printing), look at the fuel injection chapter, pages 9-19 & 9-20 in the 2012 printing, where the difference between these two fuel delivery types (and ECU compensation for absolute pressure delivery) is explained. You'd also need a new (2016+) tank because the newer big o-ring pump mounting is completely different. Not sure about the injector assembly, but the new one has the pressure regulator removed and capped. The vacuum port on the head is not longer needed and must be capped. And there's no fuel return line with the new setup. A new fuel pump, tank, and ECU will likely be pricey, and then there's all the small parts that will pile up. So it may cost less to try and find an old style Mitani / Future Trial / DDM or other lightweight base or fuel pump assembly if you wish to save weight there.

In the past, I suspected the ECU was looking at MAP vacuum to determine the intake stroke and know which crank revolution it was on.

Jimmyl is correct. It's a thermistor that has room temperature resistance of 2.3 – 2.6 kΩ. And it's used by the ECU for FI adjustments as well as telling the fan relay to start. I can't see blocking it out. And if the ECU sees the resistance is out-of-range it may put the bike in limp mode. I know if it's simply disconnected, the bike will go into limp mode. I'd suspect your problem is due to a stopped fan blade. It's happened to me once when a pebble got into the fan housing and jammed the blade. The fan motor kept trying and melted the fan blade around its metal hub. Another time I had the fan stopped because the "purse lock" (what it's called in the parts manual, see Frame F-21 Reference #11) that holds the wire / vent gas hose bundle together a couple inches above the ignition coil had rotated so it stopped the fan blade. I found that soon enough that nothing was damaged. This could be intermittent. These problems were probably seen by others because the fan housing was changed in 2016 to open it up in the bottom (where I had a trapped pebble) to reduce chance of a jam there, and raise the height on the sides so the "purse lock" or wires can't move into the fan blade sweep. If a previous owner took the gas vent hose out of the bundle, and your bike has the "purse lock", it may fit loosely and can rotate into the fan sweep, then rotate out of the way later. Check that first.

In the USA, the set of o-rings is about $16 (no VAT in USA) through online parts. They fit CRF450R and CRF250R for the last 10 years, so they are pretty common. FWIW, at that price, you may want to just order the whole Fuel Filter Kit P.N. 06160-MEN-A31. It includes the big o-rings, the little o-ring for the fuel filter, and the fuel filter. Saw it on a UK online parts site for £55.

There's also the feel of pulling the gauge that I like. The manual calls it "slight drag." Don't think you could get that with wire. For the intakes, Motion Pro makes a "tappet feeler gauge" (do a search) with 0.004" and 0.005". Works great. I also have the 0.006" and 0.008" and set intakes tight on the 0.006" so they're at the big end of the range. They don't make one in 0.012" for the exhaust. I've done as others mentioned and bent a 0.012" gauge leaf. I usually see more change in the intakes. And it's small. Usually only tighten about 0.001" every year or two. But I don't do the wide-open point-and-shoot thing much either. The more high RPM, the more you'll need to check valve clearance.

The map switch modes are reversed between the 300RR / 301RR and 4RT260 models.

Before taking the time to change the TPS stop, what happens if you twist the throttle quickly to high throttle -- maybe 7/8 full throttle? If it does the same thing, I doubt adding a shim for the last 1/32 of opening will make any difference.

See the comment about first year kickstart stop bolt change here.

I think you're right. The Polisport Supermotard UFX Front Fender looks the same.

Can you get a standard MX fender with the "rear ventilation" for the 4RIDE's single, center mounted radiator?

Along with the piston / ring set changing in 2017, the cylinder and left center case also changed. I don't know exactly why each changed. But I'd want to find out what was changed in the cylinder before using a 2017 piston / ring set in a 2016 cylinder. It could be related to side cutouts on the bottom of cylinder, and the oil ring being lower on the 3-ring piston. And if the new cylinder is needed for the new piston, is the new left center case needed for the new cylinder? Part Numbers 2016 --> 2017 --> 2018 Piston: 13101-NN4-L60 --> 13101-NN4-M60 --> Same Ring Set: 13011-NN4-L60 --> 13011-NN4-M60 --> 13011-NN4-N60 Cylinder: 12100-NN4-L60 --> 12100-NN4-M60 --> Same Left Center Case: 11200-NN4-L60 --> 11200-NN4-M60 --> Same

The first-year (2016) 300RRs had a 2-ring piston. They went back to 3-ring piston in 2017. All 4RTs from 2005 to 2020 except the 2016 300RR have used a 3-ring piston.

Banyeres Trials Parts services Showa trials shocks and sells Showa trials shock parts. The Banyeres website lists Showa SS25 as the official rear suspension oil. It's 2.5W. But 2.5W rated oils can vary a fair amount. There are comparison tables online. Honda sells an SS-25 rear suspension oil under the Pro Honda name that may be the same stuff.

The 2020 301RR parts list and manual are available online from Montesa France and Montesa Honda Spain. The numbering is as expected. 16400 is the component code for an integrated TB/ECU. The NN4 is the model code for all 4RTs (250, 260, 300, 301, standard, Repsol, 4Ride), some of the early programmable units had an HRC model code here, but all newer (than about 2007) TB/ECUs programmable or not use the NN4 model code. The M and P are just for the model-year the part first appeared. Any new parts on any 2017 4RT models had an M. The 2018 continued to use the 2017 TB/ECU. The P is for any new parts on 2020 4RT models, so when you're looking at the parts list, scan for the P parts for anything new. The 7 is for parts unique to the 300/301 4ED models, a 6 in that position is for the 300/301 2ED models. The RTL has a slightly different scheme for the last 2 digits for parts unique to the Japanese HRC bikes. And since there was a -H01 programmable in 2010, I'm guessing the -M01 may also be programmable. The Japanese HRC RTL models only come in one flavor per model year, just a competition model in one displacement and no standard/Repsol.