konrad

True, but that will increase the pressure by a relatively small amount -- not from 65 to 200 psi. Did you try jimmyl's suggestion about setting tickover/idle speed? You need an accurate tachometer to accomplish this. I tried to set it with my digital timing light, but the reading was erratic. Ironically, this simple device measures rpm quite consistently: https://www.trailtech.net/tto P.S. I'm curious, what do other 4RT owners use to set their idle speed?

While testing compression are you kicking so rapidly that the decompressor behaves as though the engine is running? That would explain the the high pressure reading. I'm just guessing here, but typical kick-starting speed may be 250 rpm. The decompressor probably deactivates at around 1000 rpm.

The photos in the 4RT manual are not clear. Here is a photo of some of the decompressor parts on a CRF150RB. It may be similar to the 4RT. Does your compression gauge read directly in PSI? Maybe a units conversion error?

There is more to the decompressor than just a spring. There is a centrifugal mechanism to inhibit it from releasing compression when the engine is actually running. Americans call "tickover" the idle speed. There is an adjustment on the throttle body. It should be 1700 to 1900 rpm when the engine is up to temperature. Hard starting can result if set incorrectly. Also check that the valve clearances are set correctly. I see that you've done this already.

Sounds like your automatic decompressor (compression release) is not working. At kicking speeds, the exhaust valves are held open slightly. This system is very common on modern 4Ts. It allows a higher rotational speed for starting and easier kicking. Once the engine fires, the decompressor ceases to operate and the cylinder pressure returns to that of normal operation. The decompressor is built into the camshaft. See the service manual for more information.

Heffergm, did you solve your clutch problem? Your post prompted me to work on my Clake. I installed a new piston assembly and this was a magical fix. Nothing appears to be wrong with the old seals, however they may have grown excessively in diameter. It's a 9.5mm bore. The seal diameter measured about 10mm. Two other used piston seals I have measure 9.7 (from mineral oil) and 9.8mm (from DOT4). So maybe just a lot of seal drag in my case?

Well said! I like riding a variety of bikes and strive to improve all to match the strengths of the best. As Paul Thede says about suspension, "The best you've ridden is the best you know."

I'll suggest one final thing. I have a Clake OLC master cylinder. The free-play adjustment on that is critical. There's almost no range of adjustment between the clutch not slipping and it disengaging completely. And it can exhibit similar lever effects to those you mentioned.

I'm assuming the diaphragm clutch Shercos use mineral oil in the hydraulic system, so this thought is predicated on that being the case. If you're seeing a swelling of seals, this indicates a cross-contamination of fluids. Historically, Sherco used DOT4 in the clutch hydraulics. If, at some point in the bike's life, someone inadvertently put even a small about of DOT4 into a mineral oil system, I could see it causing symptoms like what you are experiencing. If it were me, I'd do a complete flush of the hydraulic system if I found swollen seals. I've also attached a page from Sherco's 2019 press release. Looks like they changed a lot since the prior model year. Can you find a specification for the clutch pack thickness? What does yours measure?

I'm new to the 4RT but often use an oil analysis service to make judgements like that. Here's a link to a service I use in the States: Blackstone Labs As you probably know, Honda says to change the oil & filter about every 15 hours. I imagine that is quite conservative, especially since the engine and gearbox use separate oil systems. I install hour-meters on all my off-road bikes for maintenance purposes. Trail Tech recently upgraded their hour-meter to make it even better! Trailtech TTO

You have to buy the entire connector, but here is a place to get the sealing gasket. http://www.cycleterminal.com/jae-mx23a.html

Seeing that corroded pin is really discouraging. The JAE connector used on the ECU is the sealed type. Is that connector's blue sealing gasket still present? Maybe Hawaii's environment (sea air) has something to do with it the failure? Prior to buying the OSSA, I weighed heavily the fact that most of its electronics were designed/manufactured in Japan (a huge plus in my opinion). P.S. I'm now wondering if the pin snapped off, and then corroded?

I'm feeling a bit sheepish now for having said the signal out of the ECU was unlikely to go bad (I was thinking of just the internal circuitry -- had not considered a broken pin). It's impossible to tell from the photo, but is that pin 17 or 18? (numbers are on the back of the mating convector). Pin 18 is for the injector, but pin 17 is switched 12VDC out of the ECU (which you may be able to work around). An obsolete electronics solder that contains lead would by my choice with a rosin-core flux (if it comes to that). P.S. If you destroy the ECU, don't throw it away. I've been wanting to get my hands on a dead one!

Am assuming diaphragm clutch. Gotta say, I'm not a fan. In my experience, seemingly small dimensional changes cause large changes in operation. I admired Sherco for sticking with what worked for so long.

Possibly the wrong seal for the fluid? The seals for DOT4 versus mineral oil are different. If the wrong seal for the fluid is used, swelling can result.

I now have about 3 hours, over 3 days of riding, on the Dexron-VI. At first I thought the Dexron-VI was a bit grabbier initially (before the fan runs the first time). Maybe the friction plates had to get fully saturated with the new fluid? Now I think that if there is any difference, the HTX 740 may be slightly worse in terms of range of clutch modulation. They seem to perform very similarly. To discern any real difference, I think you would have to ride the bike back-to back under exactly the same conditions with two sets of new friction plates that had only been in contact with the fluid to be tested.

Good diagnosis so far! 1. Yes. 2. Possible, but highly unlikely. 3. Likely nearly impossible to find. Plus it would have to be programmed for your bike. 4. Yes. 1000x more likely than just the injector signal out of the ECU going bad. Have you read my Notebook? https://www.trialscentral.com/forums/topic/69622-efi-ossa-notebook-formerly-tr280i-wiring-diagram-annotated-in-english/ Lots of relevant information there. The industry standard is to provide a "limp home mode" in which the vehicle runs (but very poorly) if one of the sensor inputs is bad. But I don't know if that is true of the OSSA. The ECU provides a ground to one side of the fuel injector when it is supposed to inject fuel (the other side of the injector is connected to +12VDC constantly). Remove the injector from the engine. Disconnect the injector from the bike's wiring and provide 12 VDC to it intermittently. (The injector is not polarity sensitive.) It should squirt fuel as long as there is fuel pressure. EDIT, I see you've already effectively done this test. At this point I would make sure the TPS is working properly.

Here's a link to a white paper by the US firm Lubrication Engineers: https://www.lelubricants.com/lit/news/White%20Papers/simple_viscosity.pdf It's entitled Putting the Simple Back into Viscosity, and I think it adds something to this discussion. I'm not saying anyone here has this misunderstanding, but it's commonly thought that "W" stands for "weight" when talking about oils. As the paper points out, '...the grades denoted with the letter “W” are intended for use in applications operating in low-temperature conditions. The “W” was originally coined for lubricants that were considered “winter grade.” Today, these products are formally called multigrade lubricants, whereas the grades without a “W” are recognized as monograde, or straight grade, lubricants.' I'll also direct your attention to the viscosity equivalence chart for engine oil and gear oil found on page 6.

I knew nothing about Elf lubricants before seeing it was specified for the Montesa gearbox. This Wikipedia entry https://en.wikipedia.org/wiki/Elf_Aquitaine says, "From its very beginnings Elf used motor racing as a means of promotion." Lots of companies do that, but Formula 1 has got to be the most expensive way possible! Makes me wonder if HRC's specification of HTX 740 might have more to do with a business relationship than being the best fluid for the job? I changed my gearbox oil to Dexron-VI last night. Riding in my yard, the clutch seemed less draggy right away (before the fan runs). But as coochb said, the real test will be how it performs in an actual trials. And is it ELF, Elf or elf? Completely inconsistent usage on their own website.

Excellent. Maybe this is a good place to post the following? I'm also very fussy and only change one thing at a time because I want to understand the effects rather than just fix a problem. I'm running 4 clutch springs. As expected, the force required to pull the lever decreased. This is a good modification for me as I have a wimpy finger and use the clutch constantly. Have not noticed any slipping, but when I do it will be time to replace the friction plates (I'll be inclined to use OE or EBC). My bike is currently running the HTX 740. That oil has the characteristic gearbox-specific smell which I find most unappealing. I also think it's an odd choice for the job. Elf says it's designed for very high performance dry clutch applications like 2-stroke GP bikes and shifter karts. HTX 740 is a special-order item in the USA, and costs $50 per liter. I'd like to find a substitute. I often use the BITOG website https://www.bobistheoilguy.com/forums/ubbthreads.php to find 40 and 100 degree C viscosity data for various oils. There I learned that HTX 740 is a synthetic that measures 21.4 centistokes @ 40C and 7 cSt @ 100 C. Also discovered that Valvoline Dexron-VI synthetic ATF is a possible substitute rated 29.5 cSt @ 40C and 6 cSt @100 C. (Which does not seem all that close to me.) I bought the Valvoline locally for $5 per quart, but have yet to try it. I have used my own viscosity measuring setup (shown below) to get a feeling for the difference. I often test suspension fluids by flowing 10cc through a burette at ambient temperature. My result for used HTX 740 was about 42 seconds @ 57 degrees F, whereas virgin Valvoline Dexron-VI came in at 62 seconds @ 57 degrees F. Clearly the HTX is considerably less viscous at 57 degrees F, but possibly has sheared down somewhat from virgin.

I'm new to the 4RT, but have a lifetime of working on bikes. The correct clutch pack thickness is important to proper operation of all clutches. Honda does not provide that specification, but does give a range for the individual plates. My 2016 workshop manual specifies the nominal friction plate thickness as 3.22 to 3.38mm, with a service limit of 3.15mm. In my opinion, 1mm of lever freeplay is too much. The freeplay must be non-zero under all temperature conditions, but I prefer the minimum. I use my clutch constantly. My bike shifts flawlessly, but I can't select neutral without the bike rolling -- not a big deal. I would also suggest bleeding the clutch hydraulics.

Mine says 16400-NN4-J11 (same as 2017 but different from 2015 according to the parts books) and supports dual maps. Is that user programmable?

I recently bought a 2016 260 model. Can anyone tell me where the red Service Check Connector is physically located? The programming software is quite inexpensive at around $31 USD, whereas the interface hardware costs $414 USD. I have a guess as to what the hardware does and would like to experiment with building my own. TIA.

Definitely not super patient. It was done on a late 1980s CNC machine with a "conversational" programming aid. The bolt hole circle subroutine allowed a maximum of 99 holes -- so that's what I did. Still, that's nearly 2000 dimples for a set of 5 steels. I used a #3 center drill, but I don't think the dimensions of the dimples are at all critical (and I could not tell you what they are at this point). I was amazed how well it worked.

Another thought... I suspect new steel plates may work better. With my Shercos, the sticking behavior did not start until the clutches had a lot of hours on them. Since you're already using ATF, it might be worth trying a different type. Valvoline Dexron-VI is an inexpensive full synthetic that has been suggested as a substitute for the very expensive Elf HTX 740 gearbox lube used in the Montesa 4RT.