mcman56

In addition to the diaphragm for the slide, the carb has a diaphragm with spring on the side. On a CV carb diagram for a different bike, I see something similar identified as a coasting enricher. I think I have also seen something called an anti backfire valve on other carb diagrams. Could that be the culprit? Is the purpose of such valves to prevent a pop? The bike runs well so I'm reluctant to change jetting. MK-BSR33-79-Detail-Sheet-copy.pdf

This is their rule book. https://www.ahrma.org/ahrma-handbook/ I'm no expert but the few AHRMA events I have seen even have a class that allows modern bikes so you should be able to find a class for anything. IIRC, otter frames are not legal for their pre 65 class. I have seen TY175s with extended swing-arms and lay down shocks competing but I don't think they meet the letter of the rules. Based on absolutely nothing, I wonder if no one is too picky about the rules unless you are going for a championship.

Plug color is a bit uneven but doesn't look too bad. It doesn't smoke. I am running much leaner than stock jetting. When I got it in 2018, it had the factory jetting of 27.5 pilot and 120 main but ran poorly. The advice was to go richer but when I went that way it was worse so I went the other way. It kept running better the leaner it got so I ended up with 17.5 and 115 which is much leaner than all recommendations. The engine is getting up near 300 run hours so I wonder if it has slightly less vacuum and is less tolerant of lean jetting.

I have a 2016 300 4T standard model. It has started to produce a little pop in the exhaust when closing the throttle from small to moderate openings. The pop is not loud but sort of echos in the exhaust. It starts, idles and runs well but has become cold blooded so needs to run for several minutes before it will take any throttle when cold started. I checked valve clearances and cleaned the carb with no affect. This is with California pump gas. Has anyone experienced this? I'm not sure if I should go up on the pilot size or raise the needle. Carb access is not great on this bike.

I was curious so looked at the manual. It looks like the minimum piston clearance for the 250 is 0.050 and the maximum is 0.080. What is the 0.100 "Assembly" number?

It definitely should do much better than that. Could someone have geared it way up?

You may be missing the hit or "coming on the pipe" of other type two strokes. Trials bikes mostly have very smooth torque curves so don't tend to do that. IIRC, that particular model does not run to high RPMs so if you are trying to lift the wheel when you are already up in the RPM range, it may not happen. However, It should be able to lift the front wheel. What happens if you are rolling along at a slow walking speed in first or second gear and quickly open the throttle most of the way?

I used a hand pump to pull the gas out. When leaning left on the stand some gas leaked when removing the petcock but not a large amount. I was then able to lean it right to get most of the gas into a funnel. The back part of the little black plastic lever had broken so was non functional. The parts list just shows the entire petcock assembly which is not cheap. Is the little lever available somewhere, maybe in a rebuild kit? This would be a really annoying failure mode to happen if you show up to a trial and need to manually get gas to the carb.

I have a 2016 Evo with the electronic petcock. I am getting no flow when turning the manual override lever. When I try kicking nothing dribbles out either. I need to pull the petcock to investigate. Is there another way to get the petcock open so I can drain the tank? I could try a hand pump to siphon out the gas but suspect there will still be a lot of gas flowing out when I remove the mounting bolt. Is there a cleanish way to do this? The odd thing is that the initial symptom was hard starting when cold or hot. The bike ran fine once started but I did start to get occasional odd noises in the exhaust. I adjusted the valves and cleaned the carb but when trying to start discovered this no flow issue.

Lampkins (Beta UK) did have a complete spare parts order system on line for all years and models. The UK mail system must be very good because I could frequently get parts delivered to the US in one week which was faster than most US suppliers. In the past, shipping cost was comparable but a few years ago shipping went up 2x or more so I have not used their site lately.

With the Jitsie electric start kit, the bank angle sensor assembly is removed. I'm not sure that is a good idea but assume it was done to make space for other components. I have seen no formal description of what the sensor assembly does but it likely cuts power to the fuel pump when the bike is on its side. I guess is could cut power to the whole FI system.

I also wonder why Montesa recommends very expensive oil for the transmission. I used that for the first change but plan to look for alternatives. I ride in mostly dry conditions.

The manual shows 15 hours as the oil/ filter change interval for a 2018 300. That sounds like an MX bike. Meanwhile, the Beta 4T manual shows 40 hours. What interval are people using?

Is the tool still available? I don't see anything in the 2018 300RR parts list or service manual. Searching online, I get no clear answer. Although, I see one for a CFR250 is pretty expensive so hard to justify https://www.rockymountainatvmc.com/parts/honda-pgm-fi-setting-tool-p?srsltid=AfmBOoriVL_t6J6WD2_uqMxRoEZDE-ZnbgTGCmcIl9nImw-E11jsmHkL

My question was really related to an XT225 (Serow). The carb is a mikuni and looks similar to the Beta 4t carb so I was wondering if the Beta springs would work in the XT225 to improve response. I have made springs before so that is an option I had not thought about. Interesting comment on the 4RT. I have a 2016 Beta 4t standard model and recently got a 2018 300 4RT but find it harder to ride due to the sharp throttle response. It is difficult to get just a little bit of power and feels like it has about 1/3 of the throttle resolution compared to the Beta . Can the 4RT be tuned to respond more like the Beta? It does have the black throttle tube. I sort of remember options for early models that allowed the owners to tune or maybe load different maps. I'm not finding anything online so is anything like that still available. I know......the solution is to improve clutch control but with arthritic hands and the beginning of trigger finger in my clutch finger that is unlikely.