aussiechris

Yes, I was aware there are some fuel pump issues. I'm guessing it's the same problem affecting millions of bikes and cars worldwide fitted with Denso or Assen pumps. Somehow the material used for the impeller absorbs fuel causing it to swell. Road vehicles in many countries are subject to recall and a free replacement (my Honda road bike is one) as it's a safety issue. I've seen no such recall on the Montesa so I'll just keep riding until it fails I guess. But thanks for the heads-up.

I found this snippet from a Honda PGM-FI development document... It's not identical to ours because it's off a scooter but close enough. It notes that the Pb sensor reads manifold vacuum and is mounted downstream of the butterfly valve (point 3 at the bottom).

From the service manual... 1700 rpm is fine. The DC voltage is 13.5v from way below that. It has a very powerful alternator (compared to other trials bikes). I did this testing mostly out of curiousity but it does make a difference if you're trying to attach a tacho that reads off the spark plug wire. There's been discussions about spark timing and fuel injection in the past and I felt the debate was never conclusively settled. In any case, it doesn't hurt to have some baseline data from when the bike is new to help troubleshoot problems down the track.

Yes, that's exactly the way I was thinking. During start up, it would be relatively easy to detect the first sudden pressure drop as the inlet valves open. That would tell the ECU that the next crank trigger pulse requires a spark and the one after requires fuel and so on. I agree. I think the PB sensor incorporated in the throttle body is actually a MAP sensor. Just as an aside, this is part of the ECU wiring from my current model Honda Goldwing. It has both a MAP sensor (in the intake manifold) and a baro sensor (under the seat). Notice that the MAP sensor goes to the input labelled "PB" at B29 whilst the baro sensor goes to "PA". Coincidence, or is this Honda's terminology. I think PB is a MAP sensor.

That's certainly a possibility Konrad. I know my six cylinder car does that so it can detect a misfire and log a code indicating which individual cylinder is missing. It could explain why there's a row of trigger holes in the flywheel rather than a single slot like other bikes. But I was thinking of another possibility. And yes, too curious for my own good!

Warning: long message with copious amounts of techno-babble. I was reading an old discussion on this forum about whether the 4RT runs a “wasted spark” ignition (that is one spark per revolution of the crankshaft) rather than a more conventional (four stroke) one spark every 2nd revolution. It was also suggested that the fuel injection is not sequential but rather injects fuel continuously. Certainly Honda are not averse to using wasted spark ignitions - many of their multi-cylinder bikes do just that. And given the engine does NOT have a cam position sensor, both the above would be reasonable assumptions. However, I think I have managed to prove that the engine does only fire the spark plug every second revolution and the fuel injection also occurs every second revolution timed to intake valve opening (which makes sense given the location of the injector). How? Let’s get technical… I made up some test harnesses to enable me to intercept the wiring at the trigger (pulse generator) coil, the ignition coil, and the fuel injector so that I could view what’s happening on an oscilloscope. At my (slow) idle speed of around 1700rpm, the crankshaft is rotating 28.3 times per second or once every 35 milliseconds. The crank trigger coil sends pulses to the ECU every time a hole in the flywheel passes by. The flywheel actually has a row of holes/slots that pass the trigger coil, then a gap with no holes and that gap or burst occurs every 35mS. The pic below shows the output of the trigger coil on Ch1 in yellow. The blue trace (Ch2) is the ECU signal going to the ignition coil primary. You will note that it only occurs every 2nd burst of trigger pulses. The ignition coil pulses are about 70mS apart (each grid square being 10mS) so that is about 14.2 times a second or 850rpm. That’s half the crank rpm of 1700. So what about the fuel injection? Unfortunately I only have a two channel scope so in the following image, the Ch1 yellow trace is now the fuel injector signal. The blue trace is still the ignition coil showing the relationship between the two. You can see how the fuel injector fires in between each ignition pulse. This is always the case regardless of rpm. The injector is firing every 70mS just like the ignition coil except one crank rotation out of phase. I did some measuring and the injection pulse* occurs 34.8mS before ignition spark… Given the time for two revolutions (720°) is70ms, then fuel injection is commencing about 358° before the spark which sounds about right - just before the intake valves open at the end of the exhaust stroke (taking into account spark advance and valve overlap). The injector pulse duration (the negative bit) at idle is about 2ms long (just over 20° of crank rotation) but is visibly longer when the throttle is opened. So, in summary, this engine definitely fires the spark plug every second revolution (at the end of the compression stroke) and injects fuel sequentially just prior to the intake stroke. That just leaves one question for ya’ll to ponder… Since the engine does not have cam position sensor (or points), how does it know which stroke it is on? It would be easy to suggest it just fires the spark plug every second crank trigger but it has to pick the correct one to align with the camshaft otherwise it wouldn’t run. I have a theory on how it might achieve this every start but wondered if someone else would like to offer an opinion. Looking forward to your comments. * Note: the above traces are referenced to the +13.5v power. Both the ignition coil and fuel injector are switched to ground by the ECU. The spark plug fires when that ground is removed (the end of the negative pulse) but the fuel injector opens when the ground is applied (start of the negative pulse).

I would think so. Obviously it would need painting afterwards. Having said that, the original bracket looked like unpainted cast/forged stainless steel when new but it did go rusty later on. Some stainless steels do rust. Be warned, the spring will be a bear to get back on after moving that perch point 😠

My 2015 260 was fine with regards to the side stand. But my 2022 301 was not. It came with the self retracting stand -supposedly for safety reasons but doesn't work so well with a right side stand if you mount/dismount from the left. Anyway, before even riding the bike, I removed the side stand bracket for modification. As you can see, the spring perch is slightly behind the pivot... I hacksawed it off and re-welded* it forward of the pivot... Works fine now although the spring is stretched a bit more than it should be. It now stays extended until I kick it up... * The bracket is some sort of steel or possibly stainless steel. I TIG welded it using stainless filler wire.

I'm a bit late to the party but I thought I'd mention that I used a rod kit from HotRods for repairing my 2015 4RT 260 and it worked perfectly. Their part number is 8616. Original rod on the left... Specs are on the lines for CRF250R or CRF250X... Sources might be: https://www.allballsracinggroup.com/8616-connecting-rod-kit Or in the UK: https://www.motocrosspartsuk.com/honda-crf-250r-x-2004-2017-hot-rods-connecting-rod

Good luck with that !!! Honda/Montesa don't supply a rod kit as a spare part. They expect you to buy the entire crankshaft assembly for some hideous amount of money. I recently replaced the rod on my 260 4RT and used a rod kit from Hot Rods in the USA. Fortunately it is the same rod as a Honda CRF 250X or R (04 to 08). The Hot Rods part number is 8616 and the dimensions are - centre to centre 90mm, small end bore 16mm, big end bore 38mm, small end width 15mm, big end width 17.8mm, pin diameter 30mm, pin length 52.85mm, big end bearing 30 x 38 x 18mm, side thrust washers 1mm. The rod kit includes big end pin, big end bearing, and thrust washers but not the piston pin or clips. It is stronger than original (slightly heavier but runs smooth). Photo shows the original rod on the left. Parts with KRN on them (or KRN in the middle of the part number) come from a CRF250. Hope that helps.

All the guys I ride with run 100:1 (usually Motul 800 full synth) in modern liquid cooled bikes and have been for the past 15 years or so. And most of our bikes are between 5 and 10 years old now with no oil related problems. On the odd occasion we've pulled an engine down, there is tons of oil on the piston/crank etc. Feel free to run richer mixtures for peace of mind but I am yet to see any evidence that 100:1 has caused any premature wear or issue. And replacing or repacking clogged mufflers is a hassle I'd rather put off as long as possible.

If it is a crank seal, you should notice the bike consuming gear box oil. When my pro did crank seals recently, I was adding about 50ml of gear oil to bring the level back to half way up the sight glass for every tank of fuel. New seals/bearings and it no longer smokes or uses gear oil.

It's the map switch. Large button selects normal ignition map for dry conditions, pressing the small button selects a softer map for wet conditions. But in my opinion it's makes little difference.

Also check the primary (clutch) cover gasket after removing the skid plate. It's possible for the cover to get moved slightly on impact thereby breaking or dislodging the gasket.

Thanks Oz. I don't know who makes the Race Tech bushes, I assumed they were their own aftermarket jobs. If that was the case I would be happy to try them. However, I have not managed to find a dealer who could supply the Race Tech parts for reasonable postage rates or at all. I have tried to register on the Race Tech site so I could order them directly but something broke and I'm now locked out. Emails to both info@racetech.com and distsales@racetech.com (overseas sales) have gone unanswered. In desperation, I have ordered a pair of bushes and seals from the Splat Shop in the UK. They were showing the bushes under the old Honda part number so I thought I'd take a chance on them. They'll be another week or two away. The new bush and seal I installed the other week only lasted one ride. That same fork is leaking again but not too bad. I have a competition this weekend so it will have to do. Assuming it is a manufacturing fault (and I think it is), it's unfortunate that there appears no way for dealers or customers to tell if new stock is good or bad. The dealer seemed to indicate that the factory are just saying it's not a warranty issue. But I'm sure we're all happy to pay for new bushes ourselves but would like some certainty that they are good ones. I'll also be checking the fork tube to ensure it's not bent next time it's apart. But it was sliding freely last time I re-built it. The teflon just doesn't seem to be stuck properly to the metal. I've had numerous bikes with huge mileage and never had a problem like this - and never gone close to even wearing out a bush. Other than that, the bike is great. And I still think nothing comes close to the Showa suspension both front and rear.