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 SR500 sidecar - some setbacks on the way to becoming a usable daily

Admittedly I haven't cranked up quite as many miles as I would have hoped, but definitely have broken the engine enough times during the Summer months, so I guess this kind of evens out. But even then a few things have come apparent: 

The clutch lever I had on there, even though labeled for an SR500, definitely wasn't and I have to find a spare brake lever, but it's this weird ball and socket setup and I have to find out from which bike the master cylinder originally was. 

The other thing that drove me (mildly) nuts was the fact that the exhaust, despite my best efforts, was rattling itself to death and leaked at the joint between down pipe and muffler at the same time. Also, I am a strong believer in touching up the welds, for optimised flow. 

Also a proper joint and not the wobbly mess I had so far did wonders just to how rigid the whole setup felt. As can be seen in the first picture, the original tube had actually been eroded away from the muffler and the down pipe oscillating at different frequencies.

Added a slip joint on the muffler, so the exhaust gasses would have to do a 180 to get out, which makes it a lot more likely to seal up without a gasket than if you put it in direction of the flow.

... and then shortened the header pipe by roughly the same amount, so one would fit into the other.

What followed were a few days of happy thumper-ing along, when my sporty ambitions came back to me (maybe somewhat helped, by rather abysmal starting at even slightly cold weather) and I decided to throw that second hand TM36 back on. Instantly a few more kph of top-speed were found, but something didn't feel quite right. 

At some point, I had a look at the mix screw and found that the actual tip had snapped of inside the carb body. Throw in a few desperate attempts to get that tip out and it was decided to do, what I should have done from the get go.

Get out my wallet and buy a new TM36 and simply enjoy it. 

Not without swapping those JIS-screws out for some stainless allen-heads. (Whilst rejetting to the same jets I used on the previous TM36.)

You may not believe this, but it took two kicks and the SR idled like... well like a bike with a carb that no one has fiddled around with.

So I fitted my elephant ears (even without snow they are super handy to get the wet and cold away from your fingers), put some fuel in my freshly painted tank and...

F*ck.

Removed the paint with fire (don't - I am a professional) and then repaint it with 2K-paint.

As I only had spray-can primer, I pre-heated the inside of the tank until was (very) warm to the touch, which made this whole affair doable, even though it was only about five or six degrees above freezing outside.

And that's it. Put on some wax and then find out if the new TM36 responds well to my jetting efforts or whether my timing might be off - guess we'll find out. (Oh and for those wondering, yes I am currently mostly working on the Lada, but not quite there to show some updates, as in: lot's of work, yet not quite as much to show for it...)

Little addendum: The carb setup is pretty close, starts nicely and can finally take full speed/full throttle for a while, which makes me quite happy.

Everyday TR1 - new TM38 carbs

And one day everything is working fine and going smooth. And you get bored. And you strife for improvement. Now even though I have a set of perfectly good Mikuni VM38-9s, I have had a set of TM38-85 sitting on the shelf for way too long.

But first start with a problem aka. oil-leak. Admittedly I had already bought some aluminium roundstock to repair the lower valve-cover thread. Turns out, those heads leak substantially less, when tightened up properly.

The stock jetting with #22.5 pilots and #230 mains is "a tad" on the rich side, a more conservative #20, #190 was chosen for a first start.

Interestingly the rear of the carb is tapped for a air-jet, but the port is run open. As the parts out of the VM38s will fit, I might give those a shot (6DP4-needle and 0.5 air-jet instead of the stock 6FJ4).

The slide assembly is relatively straight forward, the paper gasket got greased up so it won't stick to the cover or carb body.

The throttle cable holder is vastly different and looks a bit like an afterthought. Those M3x10 screws will have to be swapped out for allen bolts as I foresee them to seize in the aluminium slide in the long run. With that being said, a bit of copper-slip should prevent that for now.

The 51-6506 2in1 throttle cables (available from various XS650 shops), are a bit too long, so shortening by about 10-15mm is due in the long(-er) run or you end up with lots of slop on the throttle-grip. A bit of decent allen-bolt hardware should make maintenance a lot easier.

In order to be able to oil the cable from the top, a bit of shrinkwrap seals the adjuster against the cable.

The cable is too long by about 10 to 15mm, so at the very least the bit from the junction box to the throttle grip has to be shortened. Once I get to sync'ing the carbs, I'll probably have to shorten those as well.

The benefit of the TM38-86 is their 47mm outer diameter on the engine side, which makes them a straight fit in the stock inlet rubbers.

Fuel line routing is dead simple, but squeezing a filter in there might present some challenges as there's really not that much space.

Bit of hose-clamp-magic as I seem to have run out of good quality neoprene fuel hose and the normal stuff gets mushy within days, with the fuel we have available overhere.

So what's the first verdict: Jetting will take some effort. Overall the length is very similar to the old VM38s due to the longer inlet rubbers. The sync plugs on the stock rubbers are a heaven's sent for getting the carbs dialed in and there's once more a lot to learn. First step will be to shorten the cables to reasonable lengths and then play around with various air-jets as the mid-range is running very lean. Mains are too big, which is weird as it's the same size that works with the VM38s, but maybe this is due to the synchronization not being what it is on the other carbs.