konrad

I'm fairly new to trials myself (6 years), but why not just use standard tubes on both wheels? I think there are rear trials tires specifically made for use with a tube.

True, if you use the belt method. I would suggest poking a wire into the keyway slot, as it might be difficult to see if the key is there or not.

Front wheel should have a tube. Rear wheel is likely tubeless. Because trials tires use very low pressures (maybe 4 - 6 psi), checking tire pressure before each ride is necessary. Many inexpensive pressure gauges won't read accurately at low pressures. Experienced riders check pressure by feeling the deformation of the tires with their hands. P.S. Check the wheel bearings.

Dirt bike rims get dirty inside. Glass bead blasting is fairly extreme, but would likely solve the problem. I've used a bench-mounted wire wheel on corroded rims.

Ohh, I like this! We call it a strap wrench in the States. But actually using a belt and clamping to the footpeg make a lot of sense!

There is another way to hold the flywheel, and that's by jamming soft aluminum between the primary gears (in fact there is even a tool made for this purpose): https://www.motionpro.com/product/08-0427 Of course, you would also need to remove the clutch housing.

Agree with above. If it were me, I'd clean/rebuild the old wheels. But then, being retired, my time is worth nothing. Lacing/truing wheels is not for the impatient. To be truly worthy of the moniker Caferacerman, it seems a necessary skill, no?

If you don't have a flywheel holding tool, you can use an "impact wrench" to remove/install the flywheel nut. These tools can be pneumatic or electric. See: http:// https://www.ingersollrandproducts.com/en-la/power-tools/products/impactools.html You will also need a "flywheel puller" with threads specific to your flywheel. I always lap the crank/flywheel taper with valve grinding compound to ensure optimal torque transmission. The Woodruff key is intended for location, not torque transmission.

I don't know anything about the TR80, specifically. How does the tank vent currently? At the risk of stating the obvious, drill and tap the fuel cap for a hose-barb fitting and install a vent with a one-way checkvalve like this: https://www.ebay.com/itm/MOOSE-RACING-ALUMINUM-VENT-CAP-FUEL-HOSE-SMALL-ONE-WAY-VALVE-COLORS-ANODIZED-MX/232728408990?hash=item362fb1b39e:m:m8S6mTDXwRrxYJaRgZoaXUQ:rk:1:pf:0 One caution, I've found some of the Chinese copies may look like the above, but don't actually contain a checkvalve.

It's great you reported back on your progress. (And very considerate of you to think about the next guy with a similar problem.) I'm assuming your ignition timing measurements relate to an arc at the perimeter of the stator plate (which is obviously a relative measurement). I hope this does not come off as "preachy", but a more meaningful way is to specify an absolute measurement in degrees BTDC with a timing light, or mm BTDC with a dial indicator against the crown of the piston. But, ultimately, it does not matter because trials is all about feel. So, I would encourage you to experiment with other ignition timings so long as you have some way to reference each one and are able to return to it.

With the username "Sine", I'm guessing it will be an AC motor?

Your assessment regarding stuffing is correct. I don't know if it was OE or not, but "modern" 2T trials bikes use high primary compression ratios. This yields a lot of torque at low engine speeds at the expense of greater pumping losses. The exhaust systems are usually quite simple and don't benefit from a large crankcase volume. The holes are for balance factor, so if they are plugged, it's with a low-density material. Often, a sheet metal cover (think automotive frost plug) is pressed into place. I have seen cork epoxied into place as well. The fact that it's still there says the material has decent longevity.

Below is a graph from SAE paper 790429 that shows exactly that. Although, somehow, they labeled the units of Reid Vapor Pressure in pounds instead of psi. But this does not seem to cause much of a problem if the system is sealed. For example, I leave E10 in my chainsaw (in a cool garage) all winter without ill effects. I also over-winter gallons of E10 in a sealed plastic container for use in a 4T backup generator. You would think that if all the light ends had gotten out, it would affect cold starting, but I really don't notice anything. BTW, I read your clutch fix a long time ago (a friend showed it to me when she was having trouble with a Beta clutch). The format gave me the idea to make .pdf files for use on message boards. So, thanks for that! Here is a link to my thoughts on ethanol (and lead) in gasoline.

Our "natural" gas is mostly methane. It's also called CNG (compressed natural gas) and LNG (liquefied natural gas) depending on how it's stored/transported. Propane is also know as LP (liquefied petroleum) gas. +1 for Cat Stevens.

This is good advice! I suggest putting everything back together, and setting the TPS to about 0.6 volts as measured between the TPS center pin (wiper) and chassis ground. If the bike still runs poorly move the TPS slightly. Don't move it randomly. Move it in increments of about 0.02 volts. Try both increasing and decreasing. It is possibly your injector is dirty and leaking into the engine. Some automotive repair shops can clean injectors. But, you really must have the diagnostic system. Here's how to build the interface cable: https://www.trialscentral.com/forums/topic/69670-building-an-ossa-ecu-diagnostic-cable/ Others on this forum have offered the software. A lot of reading on this forum will help.

Yes, you have the original fuel injector. I paid about $20 USD for one via Aliexpress.com There are many choices: https://www.aliexpress.com/wholesale?catId=0andinitiative_id=SB_20190224120228andSearchText=FBYCG80 Also, lots of information in my OSSA EFI Notebook that could help you: https://www.trialscentral.com/forums/topic/69622-efi-ossa-notebook-formerly-tr280i-wiring-diagram-annotated-in-english/

I found plenty in the US on eBay by searching "Mahle KL97" . As I recall, peterb mentioned the same filter is used in the OSSA (but is much less convenient to replace).

My first trials bike was a TXT 321. It took 8+ kicks to start from dead cold. As I'm sure you know, the enrichener (choke) jet is replaceable in the Dellorto. Mine came with a #60 (0.023" orifice). I drilled mine to a #70 (0.028") and it started much better from cold.

Poor scavenging.

Perhaps too late to help you but for future reference, operation of the "vacuum" or "pulse" type fuel pump is describe here: www.walbro.com/wp-content/uploads/2015/12/FPC-pump-8-20-12.pdf

No. Idle jets are an M5 thread, main jets are M6. P.S. A rich mixture does not cause 4-stroking, but it can exacerbate it.

I'll add that trying the standard jetting is usually a good place to start with a stock bike. I don't think there's any shortcut to jetting. A lot of test-riding is needed to judge the changes. Jets are cheap, and having an assortment on hand is a big help. Some of it depends on the local fuel, and how picky you are. Luckily, with trials bikes it's usually pretty easy to get at the carb. I often use a 0.5mm shim under the jet needle clip to get things to my liking.

Change the ignition timing first (which will affect the perfect mixture strength). Retarding the ignition timing will make the engine more willing to rev. Make one change at a time to understand its affects. Hard to start from cold is likely the choke (enrichener) circuit. (But retarding the ignition timing may improve this.) You may be able to just flip the reeds over to make them seal. (My Shercos seem fairly tolerant to imperfect reeds.) Based on your statement regarding "running in" jets, I assume you are familiar with 2T MX bikes (which have an air screw for the mixture strength). Despite begin a 2T, the Dellorto has a fuel screw, which I find has a smaller effect on generally rich 2T engines than an air screw. Regarding feeling both rich and lean at the same time, it's possible the "transition hole" (engine side of carb from bore into idle circuit) is clogged. Make sure every passage inside the carb is scrupulously clean by spraying carb cleaner and compressed air thorough all the orifices. Don't be afraid to gently use a fine wire as well. I rarely make a jet change of more than 1 size at a time. The main jet only affects fueling from 3/4 to full throttle. Since you're using a slow throttle tube, this may not be much of an issue.

Swept, your encouraging words in my first post here meant a lot to me. You seemed quite willing to share your vast knowledge -- I'm sure your input will be greatly missed. Here's wishing you the best, and hoping you'll be back!

I just measured one at M6 x 0.75