mcman56

300s tend to be more slow reving than 250s so are stronger but a bit slower on response so can be easier to ride. However, if the throttle gets away from you and you end up at higher rpms they put out a lot of power that could get you in trouble. So, I think the answer depends on your throttle control.

I pulled out the parts. The smallest was thin and 1.3" ID. That must be the one I remember. The tapered part fits in the pipe. See picture. Send me a PM with your address, I can should be able to mail it. I have no use for it now.

I just looked it up. The outside of the spacer was shaped just like the exhaust flange with the two holes. The ID was 1.42" but I don't remember where that came from, probably some percent of the unrestricted area. It was 1/4" thick aluminum. I'll look for the actual part.

Front and back lighting wires simply unplug but the front plug is a bit difficult. If it is like the 2T, the ignition advance (sunshine/ mud) simply unplugs also. To go further seems to require cutting the harness.

I spent quite a bit of time experimenting with a 250 Rev3. (It is surprising what some people will do for entertainment.) - Instead of welding a washer in the inlet of the exhaust pipe, I made a spacer with smaller ID that fit between cylinder and pipe so it was removable. The pipe still cleared the fender but did not slide into the muffler quite so far. It softened the power quite a bit but also made it bog proof. You could use large amounts of throttle at low RPM and it would just chug along. If you are interested I may still have this spacer. I don't remember if I changed jetting. - In the US, Betas come without flywheel weights so adding one would soften power. - I made a carb spacer with small boost bottle. If you run the Mikuni manifold with a Keihin carb, you pick up an extra 1/2" to insert a spacer with port for boost bottle. IIRC this produced the same bog proof low end chug power but did not soften the overall power much. - A 26 mm OKO carb ran the same as a 28 mm Keihin but the response was just a tiny bit softer. - The expensive option is a 200 top end. The Beta 200 is a small bore 250 instead of a big bore 125 like most other brands. - Thicker base gaskets raise the ports to push the power band up in the rpm range. This would soften the low rpm power where most trials riding is done. It also drops the compression so would be easier to start. The 300 super Smooth runs low compression and is surprisingly easy to kick for a 300.

Water in gas can cause weird intermittent lean issues and be difficult to get out of system. I once pulled a carb and found a drop of water stuck in the main jet. Still, I can't see how that would cause a backfire.

Beta 4t engine maintenance schedule is based on hours so it is very useful.

Thanks for the input. I have heard that dealers do not like to sell identical bikes to two friends because one will always be slower than the other and they get complaints. I did not mean to imply that I put a lot of pressure on the tensioner. The only thing I did different was rotate the engine. The manual does not include a rotation. Assuming there are tight and loose places on the chain like a rear wheel chain, static adjustment would be random. With rotation it may adjust at the loosest point.

I put in a new tensioner today. First it was noisier so I manually pressed on the plunger while rotating the engine a few times. I reinstalled the spring and let it warm up. I think it is OK but as you listen to noises in an engine you can start to hear (imagine?) all sorts of things and I don't have another to listen to.. I made another video with the microphone not as close and out of an echo area. That specific noise is still there but it seems more in line with the other noises. Even when it was louder it went away or blended in as the rpms were bought ut to mid range. The tensioner is a ratchet design and tightens in steps. It seems logical it would get noisier as the chain wears but then quieter as the chain loosened enough for the tensioner to get out one more tooth. That could explain the difference between two bikes. The video is kind of vague because all you need to to to make it sound bad is turn up the volume.

Clearances were spot on. I rotated and looked at all parts of cam chain and it looked ok so I’m down to suspecting the cam chain tensioner. I hear the tap/ sound at idle but when I bring rpms up slowly to mid range, the sound is less noticeable or goes away.

I appreciate all of the input. I did notice it oddly hard to kick over at least once. I pulled the valve cover and see nothing obvious. The decompressor spring does not look broken and the decompressor is free to rotate. Surface finish of the decompressor shaft is not that great and looks like it was worked on with a file. If it was stuck, I guess it is possible it got unstuck during disassembly. The spring force is very very weak but it is a tiny spring. Locked in the TDC position, it feels like the weight of the lever looking part provides the force for returning. I can't rotate the cam so assume that means the cam chain is tight. Looking down from the top I can see red guides are there but no detail. Cam sprocket feels bolted tight to gear. Rocker arms have some end play but otherwise feel tight. Rollers that run on cam feel OK as does the little pieces that meet the valve stems. I did not check clearances before pulling the valve cover but, by feel, nothing was grossly loose. There were a couple of very tiny flakes on the magnetic drain plug. Oil looked good. Nothing was in the two plastic oil filters. Any other suggestions? I'll look again but all I can think of is to loctite the gear to sprocket bolts, set the clearances and see what it sounds like before going deeper.

I pulled the tensioner out. Teeth look ok and spring has enough tension to push out the plunger when off the bike. When it was out, I tried pushing on the red guide. It felt solid but I don’t know what it should feel like. It does sound much like a klx250 with bad tensioner I heard recently

I have a 2016 300 4T with maybe 75 hours on it, almost 35 since valve adjustment. It runs fine and starts easy. On the last few rides, I noticed that the top end seems to be noisier than before. Nothing sounds horrible but there is some "clitter clatter". Probing the head area with a mechanics stethoscope, it seems a little louder at the cam chain tensioner. Is this normal? See the video. It does seem to sound worse in the video than in person. The deep sound that comes and goes is it quieting down a little when pulling in the clutch. The engine was cold but I think it sounds the same hot. If not normal, any ideas? https://youtu.be/gk9x64aulWQ

I go up to 100 psi with tire lube

It sounds like the throttle is barely opening. Could it be too much play or some kind of binding. You could pull the carb boot off to verify full opening or even pull the slide out to verify. Other issues should have different symptoms.

I may have had it easy. It was a 6 volt points controlled ignition that was already 25 years old at the time. The coil had 2 leads that fired two plugs at the same time. Modern ignitions must have a lot more zap.

Comedy Central - I was once riding a V twin motorcycle with no insulation at the spark plug cap while wearing shorts. I lost my balance at a stop, planted my foot on the ground and the bike laid against my leg. Continuous high voltage shocks zapped my leg while I fought to regain balance and get the bike off of my leg. So, I can say from experience you would know. (This was prior to Youtube.)

I had a similar issue with a fantic 80. I had to use a hydraulic press to press the axle out. It took a surprising amount of force but did not damage anything. They are called shop presses here but seem like one of those things that may have another name elsewhere. Something like this. https://www.harborfreight.com/20-ton-h-frame-industrial-heavy-duty-floor-shop-press-60603.html

My 4t usually has a very steady idle but sometimes it will step down about 200 rpm and stay there. The idle does not wander like a lean 2t. It may not do it for a couple of rides and then do it consistently. Otherwise runs fine. I fiddle with the mixture screw and it does not seem to help. I do ride at different temperatures and when it started today, it was maybe 20 degrees cooler than it has been. 25 pilot, screw 2 turns out, needle one step rich from mid, 125 main. The plug is black but does anyone get a tan plug on any beta? Beta seems to run cold plugs and I never got a tan plug on a Beta 2T either. Can a blackish plug in itself cause idling issues?

Does the 130 produce any black smoke when full reved up in neutral? I have a 125 in mine and get just a hint of black smoke at full throttle in neutral. I don't know if it does that under load.

From my understanding, a common failure of CDIs is that the advance function fails. They could get stuck in a retarded mode or advanced mode that could explain crappy running but not really a dying engine. If you have a flywheel puller, you could try fully advancing the timing to see what happens. That is assuming your model has an advance curve. I checked a 97 techno that had about 20 or 25 degrees of advance from idle to full scream. I have a 2008 REV 3 that only has about 6 degrees of advance through that range. 6 degrees is likely due to higher voltages making things happen a little sooner rather than an actually designed in curve. Beta must do something different with the port timing for engines with and without advance. I wish I understood what.

Are the available rings compatible with Nikasil? I thought rings were developed for specific bore materials.

I had a rev 3 that acted like that as the stator failed. It seemed exactly like a carb issue. Possibly it did not produce enough voltage as the compression pressure went up. It started out intermittent and got worse.

This does nto really answer your question but I ran bultaco leading axle forks with the Bultaco yolks on a BSA C15 and it turned quite nicely.

Have you tried starting with the throttle fully open?