mcman56

Earlier Beta 4ts had a slightly quicker throttle, at least in the initial stage. I think the change happened around 2019. I have a 2016 and when I went to the later throttle is made operation with small throttle openings easier to control. I'm not sure if you can still get the old model from Beta. However, when looking for a replacement tube for my 2016 throttle, I found that the one used on KTM 50 4t was exactly the same. This may be it but the description is odd. https://dominoracing.com/shop/off-road/domino-4t-throttle-system/ https://dominoracing.com/shop/off-road/4t-spare-parts/

Attached is a scan from an old Hotrods catalog. It shows all rod/ pin dimensions for a number of YZ250 engines. I would be curious to hear if one matches your engine. The catalog also shows pins available by size but it is from 2007. I see that Hotrods is now part of the Allballs group and still sells individual pins. https://www.allballsracinggroup.com/p126-crank-pin Scanned Document.pdf

That should come with the rod kit.

I ended up going to the Tubliss system and the issue appears to be gone. I expected mounting to be quite difficult but it was not bad. I see their claim about it being lighter. I did not weigh anything but I would say... maybe and it probably depends on the thickness of the 4:00 x 18 tube you are running. The 18" tube and two rim locks go away. You add a skinny bicycle type tube, plastic cover and lightweight rim lock/ pressure valve. Provided plastic tape replaces the rim band.

"bounced me backwards just a bit pulling on the throttle." That is exactly what I would describe as the throttle getting away from you. In that situation, a smaller front sprocket makes the bike run out of RPMs quicker so it can sort of choke off or minimize the "getting away from you". It is cheap and easy to try.

A couple of years ago, I bought an 01 Rev3 270 with almost zero wear on the original tires. Power was very sharp right off the bottom with the initial crack of the throttle. It was much much sharper than my 2014 Evo 300 2t Factory off the bottom. (The 300 Factory sort of took off mid range.) I added a full millimeter of base gasket for a total of 1.5 mm. Then I installed the heaviest flywheel weight I could find. It was something from a Techno marked Ducati. Power delivery is much smoother and it is easier to kick. I would think anyone who likes vintage bikes like a TY250 would like flywheel weights on modern bikes. I also find that going down a tooth on the front sprocket helps. The clutch out speed is slower so it makes clutch use easier in slow tight turns. (I'm no clutch master.) But, based on your injury description, you may have been going pretty fast. A smaller front sprocket also reduces the tendency to build speed with a series of obstacles to clear like log-log-log. If the throttle does get away from you, the bike will also run out of RPMs quicker with a smaller front sprocket so you can't get in as much trouble. I have tried 2 teeth lower but find it reduces the ability to get up and over things in first gear. A smaller front sprocket does reduce top speed if that is important.

This issue continues. I was deflating and reinflating tube to get it centered every couple of rides. I also increased pressure to 5 psi. In other bikes I use 4 psi. I stopped the deflation/ inflation step and developed a leak at the valve stem in a maybe 5 short rides. I installed a 4:25/ 4:50 tube and ripped the stem off in only a few miles of dirt with no rocks. There was no impact. I just came around a turn on a flat road, gave it a good bit of throttle and could feel it go flat all at once. The tire remained seated on the rim. I rode the bike about 1/4 mile with the flat and the tire was still firmly seated on the rim. The bike has a DID 2.15 x 18 rim. This is really odd. I'm not sure if I should try an IRC tire or maybe the tubliss system. Does anyone run Tubliss on a trials bike?

I run an FMF universal muffler on a TY175 and it really quieted the bike down. On that bike, I was able to just cut off the OEM muffler and clamp the new muffler on. I used the smaller FMF universal but did need a reducing collar to fit the TY. I can't picture how thick a the TY mono muffler is but the FMF is a bit wider than modern trials mufflers so you have to make sure you have clearance. Beta 4t (at least some years) had no external stinger to clamp on so the spainsh fly spark arrestor came with a short piece of tubing you had to weld on the back of the muffler to accept the spark arrestor.

A friend runs a Fisch on the standard muffler. It has the official markings. https://fischmoto.com/products/fisch-moto-spark-arrestor There are also these. https://spanishflyracing.com/collections/usfs-approved-trials-spark-arrestors?page=1 These types come in different sizes. They have the correct screen size but I don't think they have the official words. They do pass inspection at the CA off road parks I go to. https://www.ebay.com/itm/144812387857?epid=2036443760&hash=item21b77dae11:g:mG4AAOSwxuRdAQGy&amdata=enc%3AAQAIAAAA8Bo2BHlkCXTg7Kn4Te3UWlLpEySMWS40xxfzj%2FIPPL2TFnH2VPCNU46qnjf7EB5GOrl1o4kc2alPDjZ%2FnilZCPKIR%2FNud4bYtPC3hYB%2BSb2kcQW4LXx2eFxF8KcFBnBjOA2oYscMNuivkbPhg639mMsZ5AQWd%2BlqY4MlQ%2BfgkpdMETL1LWf8NwzsD6PICnbPnezD7hqwVOqbFOj%2F%2FMaEtgurY69G833xzp4VqzFCCQIyPXUq6954mLEZyZVpvpMd%2FDHDC3eBb%2FTSBdr%2BrhFxUidY9PXW2KfKrwiEtVFmOKFNfL6qoRLblcY%2BQlbKuSAA%2Bg%3D%3D|tkp%3ABk9SR-jQoIXVYg Another https://www.speedandsport.com/product/spark-arrestor-screen-universal/

The O5 in a circle sounds like a casting date. Things like this would be cast in large lot sizes. Then there is machining and painting plus transit times. I have spent a little time looking at casting dates on Beta cylinders. A cylinder with 05 casting date would likely be found on a 2006 or even a 2007.

I was able to reduce shock through the handlebars on my TY175 by using a fat bar and rubber mounts from a mid 2000 CRF250. See picture. I was already using risers to put the bars in that position so there was no ergonomic change. At rest, I can flex the bars a bit but notice no negatives while riding. Rox Risers sell something that looks similar. I don't see a good way to squeeze these into a modern bike without a big change in bar position but have found it is quite easy to change the valving in a modern Beta's forks. https://ibb.co/GWLwwMB

Can someone clarify how to install the front sprocket retention hardware for a TL250?. There is a flat washer with cut outs to slide on the spline. There is a second washer with similar cutouts which also has some horizontal protrusions that will mate with the first washer. However, I don't see how these two washers can mate once on the spline. Then there is an e ring that fits but is not a tight fit in the groove on the spline.

I have used KBS with good result on an aluminium and a steel tank. https://www.kbs-coatings.com/cycle-tank-sealer-kit.html

2016 Beta 125 also has sealed main bearings.

I did notice that quite a few 15 mm spacers are sold for car wheels. Could any of them be small enough to modify? You could probably use something much less robust than what I did. IIRC the TL250 sprocket mounting studs are 10 mm. Modern trials bikes use 6 mm.

The drawing is not to GD&T standards but implies a circular hole pattern with a 1.771" radius and holes every 90 degrees to match the stud locations....if that makes sense. You could probably make a simpler spacer but I tend to over design. The sprocket got thin at the groove area and I wanted to support it well. If the groove was faced away from the hub, a simple flat spacer would work but you would need washers or something similar in that groove. I'm really curious what the groove is for on the 125. Could Honda sell some kind of lock washer part that fits in there? I got the chain and sprocket kit from TY Trials. Pricing was quite good but for some reason was shipped 2 day to the US which almost doubled the price. TR216 60 428 was the rear. TG314 12T (428) was the front. From what I can tell the front was a special order because that P/N is normally a 520 chain. They show a spacer as unavailable on their web site. Speed and Sport in the US also showed a spacer listed as unavailable. If I were to do it again, I would consider a 520 chain. I saw at least one sprocket company on line that still sells 12T sprockets for the 1976 XL250. They could probably supply a rear sprocket with the correct number of teeth that would be flat so the groove would not have to be considered. I'm guessing they do spacers also. sprocket with groove https://www.tytrials.com/trailandtrialsuk/prod_49834-Rear-Sprocket-TL125-60t.html

I made one out of aluminium. The sprocket was a Talon supposedly for a TL125. It was not totally flat so had sort of a groove on one side. I'm really curious what that groove is for on the 125. A drawing is attached. I did add a 45 degree chamfer on the hub side. A custom sprocket company may also be able to help. https://sprocketspecialists.com/product/rear-sprocket/ sprocket spacer.pdf

I have found that Forma is taller.

I used something similar on a DT175 with 12 volts. It came without any kind of regulator and would blow up bulbs. This basic type regulator cured that issue. We had some kind of variable AC voltage generator at work so I hooked it up to see how it worked. It did nothing until about 13.5 volts and then interacted to hold the voltage down. I guess the diode "opened" at 13.5 volts and sent excess power to the resistor that dissipated it as heat.

If I am following this correctly, the diode plus resistor you mention make what is a basic voltage regulator as used on various small motorcycles. Its purpose is to limit voltage to the lights so they do not fail. Something like this: https://www.rexs-speedshop.com/product/universal-6-volt-ac-regulator/

I already had some PB blaster on the threads overnight. With some heat form a MAP torch, they came out OK without a lot of fuss. I was surprised.

I bought a new chain and sprocket kit for for my TL250 but no spacer was available for the rear sprocket. I can make one but am seeing only two ways, neither of which is highly desirable. See picture 1. -If I mount spacer to hub and then sprocket to spacer, I will have to open up holes in the freshly anodized sprocket for nut clearance for the spacer to hub attachment. -IF I could find longer studs, I could use them and basically sandwich a spacer between sprocket and hub. However, I suspect that studs that have been in place for 1/2 century will not come out easily. What have others done? Pictures? The sprocket is supposed to be a TL125 sprocket but has an undercut on the back side. Does anyone know what that is for? Sprocket at required spacing https://ibb.co/tXpwXfJ Back side of sprocket https://ibb.co/FgMt0nQ

I don't remember the Techno but there was a CDI/ coil combo replacement for the 2008 Rev3. I bought one as a spare and still have it but have no idea if it would work on a techno. The 2008 Beta came with separate CDI and coil. https://www.hpi.be/item.php?item=CD13201

I'm not sure if this helps but I had a Techno and it was likely a 1997. I once put a timing light on it and got 6 degrees at idle, 20 at mid range and 25 to 30 at full scream. If the CDI advance stuck at full advance it may kick back. In contrast a 2008 Rev3 200 had 15 degrees BTDC at idle and revved up got 20 degrees I'm not an EE but from my understanding, an ignition with no designed in advance will give you about 5 degrees due to higher generated voltages at higher RPMs making things happen a little quicker.