Recipe - Yamaha XV 1000 TR1 with TM38-86

 The following recipe is not meant as a straight up, blindly follow it and it'll work recipe, but as something that will get that engine moving and save you from going through what is at the point of writing an eight year journey through TM38-land. 

If you just want the jetting that works for me on a TM38-86 (stock settings in brackets):

• Pilot: 17.5 (22.5)
• Main: 190 (230)
• Needle: 6FJ40 (6FJ41)
• Needle Jet: Q2
• Slide cut out: 4.0mm
• No Air jet 

On top of the carbs, I would recommend buying:

• 40 degree throttle cable guide
• 2in1 throttle cable 51-6506
• a set of allen head bolts as the stock JIS are very soft
• 4x M3x10
• 4x M4x16
• 8x M520 
• 2x 90 degree silicone reducer bends going down from 64 to 57mm 
• 2x VM38-200 inlet rubbers 

Assembly:

I started with unscrewing the splitter and then GENTLY clamping the cables in the vice using the splitter as a funnel to oil both sets of cables, as they are almost completely dry from the factory and become a lot smoother, if oiled properly. 

Then hooked up the cable and replaced all the hardware for stainless allen bolts with plenty of copperslip on the threads. Also a bit of grease goes a VERY long way on the paper gasket of the carb top and prevents it from sticking to the carb body and subsequently tearing apart.

The stock jetting of #22.5, #230, 1.5 turns on the airscrew is probably a good starting point, if you run huge velocity stacks or something like that, but after all those years of testing, it is too rich on the pilot and mains, yet the stock needle will cause some serious lean condition in the mid range. 

The difference between a 6FJ41 and a 6FJ40 is basically impossible to spot, which is good, because the needles are very similar in dimensions.

Swapping needles is a bit tedious and quite frankly it is easier, if you unhook the throttle cable from the little doohickey, which locks the needle in place and serves as a mount for the throttle cable.

... and in with those TM38s. Please not the zip-tie on the (short) throttle cables, this turned out to be one of those really important little modifications as it prevents the cables from snagging AND helps a lot with keeping them in sync. The (used to be) red velcro strap holds the cable splitter to the ignition box and again makes sure nothing moves around which helps tremendously with keeping everything in sync.

Conclusion:

When you swap jets, needles and do so many other things and there actually IS a 2-stroke version of the same carb, one can't help but start looking at that one, going with the specification of TM38-102:

• Pilot: 25
• Main:  340
• Needle: 6FJ40
• Needle Jet:  Q2
• Slide Cut Out: 4.0mm
• Air-Jet: 2.5 

In short, one could most likely save quite some money, by buying the 2-stroke version and just removing the air-jet that is threaded into the back of the carb and then only having to jet it to suit.

 

Quite frankly, I have spent a metric TON of hours on setting these and other carbs up and they work really, really spectacularly now. Even the mileage, most likely due to the improved mid-range has improved dramatically. I can ride the bike in a very laid back fashion and I managed to achieve a personal best of 5.77L/100km / 49mpg(UK), but a low 6-ish L/100km / 47mpg(UK) is absolutely realistic with this setup. Oil-temps stay under control on the Autobahn (!), with 160 kph (100mph) power-cruising being absolutely possible now. 

Further reading:

• VM38-9 installation and jetting guide 
• AFRs at idle (a deep dive into what the air-screw does) 
• An even deeper dive into carb tech 

The (flying) brick - a perfectly adequate motorcycle (part 3)

There is a distinct difference between running and R-U-N-N-I-NG. (And also all the variants of the same general topic in between.) As a matter of fact, the BMW was running, but for example it wasn't idleing and it wasn't overly happy to rev up as well. 

So step one was to sync the carbs - this was the starting point, where I had only done it by ear, which I have to say... not too bad. 

 If I held the throttle open far enough, it would run perfectly at around 1100-1200rpm. 

 Which then made me think, even though all the manuals (and the forum) warn against altering any of the mechanical settings, the way the throttle stop is adjusted looked dramatically different to what it is set to on other K75s. So after a bit of tweaking, I simply set it, so it would hold a nice and steady idle at around 1000 to 1100 rpm, when warm and about 850-900rpm, when cold. 

Strictly speaking none of this should ever be necessary on a well maintained bike 

The throttle position switch was completely maladjusted before, as it was almost perfect once I had set the throttle stop so it would idle, indicating that I might be on the right track.

The ignition baseplate is generally meant to be left alone. Clocking it, so it  was set up in the base setting made the engine run much nicer almost instantly. 

 The other challenge was that the overall performance was rather... moderate. As the throttle is geard, it can be set in various positions. Not all of them allowing full throttle.

The result of all those efforts was quite staggering compared to the clip at the top of this post. 

 Bit of tidying up here and there and passing the inspection was actually a breeze.

 As the first ride after getting the bike registered already turned into a wet (and thus cold) one...

I attempted to fit a pair of R100GS handguards. Attempted, because aside from various claims that they are a bolt-on thing, they needed quite a bit of modification to actually do.

The BMW definitely didn't improve its looks, but as I can attest after the first (slightly) longer rideout, it keeps my hands warm and dry. 

 Lastly, given it's somewhat practical nature, yet it not sparking overboarding enthusiasm, I found a name for it: Geraet, which means device or as it is meant in this case, appliance.

The (walking) brick - a perfectly adequate motorcycle (part 2)

So the last post left off with a lot of carnage caused by the fire in the airbox and a lot of broken rubber bits. Let's start this one off with a lot of broken bolts. Starting with a small dab of weld and then progressively larger nuts...

Four out of six bolts that held on the inlet rubbers broke off. 

 

Coolant didn't look too bad, considering it is most likely more than 24 years old. 

 The fan on the other hand has lost a blade over the years. 

 In order to remove it, I had to slightly modify a two-arm puller get the old fan blades off the shaft. 

Apparently at least at some point in the past the motor shaft had come loose and touched the radiator.

Re-assembly was substantially more simple - just press the fan back on and reinstall everything with new hardware. 

While I was at it, a new thermal switch was also installed into the water neck as it would be almost impossible to get to later with the radiator installed.

And because I had to have everything out anyway, I also installed a new fuel pressure regulator. 

Reassemble everything and bleed the cooling system, which to the engineers' credit goes a lot easier than on many cars that I've worked on. It is literally, fill in some coolant, check for leaks, wait for the bubbles and fill some more. When you're done, fill the overflow tank.

Next step necessary to pass inspection: New(-ish) tyres. At least ones, which are too young to vote. 😁 (Front tyre was from the 3rd week of 1992 according to the markings on the sidewall.)
 

The wheels themselves came out without much drama and I have to admit, the mounting on the rear is brilliant. Really easy to get a wheel out. Four wheel bolts and that's it. 

 

 The front on the other side: Started off with two bolts seized in their holes in the forks...

... and this one bolt hidden behind a cover on the back of a fork brace.

Surprisingly (again), the bolts for the fork brace came out with a lot of heat, but could be used again.

It is important to note that those mudguard mounts are not threaded, just packed full of dirt and corrosion. Both from the bolt AND the actual fork leg.

Why all of this? To be honest, just to fit those fork gaiters and be able to reinstall the forks properly again.

 

While the rear wheel came out without much of a fight, the rear drum brake left a lot to be desired. First I marked the lever position on the shaft. 

Then covered the whole shaft in plenty of oil to soften up the caked on remnants of grease and brake dust.

Re-Assembly of the drumbrake is really easy, if you remove the C-clip on the top and just slide everything in place. (No special tools needed.) Don't forget to lube the shaft where it passes through the housing and check the two o-rings, so grease can get into the drum. 

Even after doing the brake fluid (and then bleeding them again) didn't help much, I had a closer look at those brake lines and sure enough... 08/1986. 

 

I still had some leftover brakelines from the TR1 and a local hydraulics shop was able to supply me with a long M10x1.0 banjo bolt. Bit of bleeding and... yep, calipers need an overhaul too, but at least now I can feel the stuck pistons.

Then, lastly, rear wheel out again as the seal of the clutch pushrod had started leaking. When I tried to remove it, it completely fell apart. 

 So this point, the limping brick was at least a walking brick and capable of keeping it's fluids inside of itself.