trialmarc Posted September 25, 2017 Report Share Posted September 25, 2017 Hello! The bike is 2000 Rev3 2T 250 2T which was living at 5800ft (1750 meter) elevation and it ran just fine during test ride at that elevation. The bike now lives at sea level, and it was running fine as-is for about 4 rides. Now the bike is hard to start, so I took a look the spark plug -- it was wet, dark and the bike refuses to start many times. If I clean the spark plug thoroughly, bike starts fine and the issue repeats after few rides. Being new to trials bikes and two strokes, I may be facing a jetting issue that I am hoping someone can help me with. Few forum searches say recommended pilot jet is 30 or 27.5. The carb is Mikuni and I am not sure of the current pilot size. I will be taking out the carb soon, and if you have recommendation on mainjet/pilotjet/airscrew for a newbie like me, I would really appreciate it. 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 25, 2017 Report Share Posted September 25, 2017 145 main and the 27.5 pilot Quote Link to comment Share on other sites More sharing options...
copemech Posted September 25, 2017 Report Share Posted September 25, 2017 nd a NEW plug! They are inexpensive. Quote Link to comment Share on other sites More sharing options...
trialmarc Posted September 25, 2017 Author Report Share Posted September 25, 2017 @lineaway thanks. Are the Mikuni jets model specific? i see some listings on Ebay but was wondering if I need to be aware of the Mikuni carb model that the bike uses which I could not find upon cursory look at the bike. @copemech: sure will do, thanks. Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 25, 2017 Report Share Posted September 25, 2017 It`s a short hex used in many bikes over the years. You can remove yours just from the bottom of the carb, 6mm wrench. Quote Link to comment Share on other sites More sharing options...
trialmarc Posted September 25, 2017 Author Report Share Posted September 25, 2017 @lineaway, apologies, I should have been clearer in my request. If have to buy new pilot and main jet, should i worry about fitment to a specific Mikuni carburetor model? Is there a Mikuni model number for 2000 Beta rev3 2T? I did not find in manuals and I didn't see it on the carb. Cheers. Quote Link to comment Share on other sites More sharing options...
klonheadd Posted September 25, 2017 Report Share Posted September 25, 2017 (edited) It's Mikuni VM26 carb. I have found pilot and main jets for that carb here: https://trialstribulations.net/ . Just use search box on their website and look for: mikuni vm26 jets Edited September 25, 2017 by klonheadd Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 25, 2017 Report Share Posted September 25, 2017 (edited) Lineaway is correct. Also what oil/fuel mixture are you using? If you are like most new trials guys you are throwing far too much oil in. Modern water-cooled, plated-cylinder bikes are quite happy at 80:1 and a lot of real plonkers (riders who don’t race between sections) are fine at 100:1. I think the injected bikes run even higher ratios. It’s been many years since I’ve seen an oil related failure in a trials engine. Carb is VM26-208 to be specific but that’s an OEM number so the generic VM26 will get you to the right place. There is a Mikuni thread pinned to the Beta forum chock full of good info. Despite what some say it is a good card that provided years of good performance on my many Betas. Edited September 25, 2017 by dan williams Quote Link to comment Share on other sites More sharing options...
trialmarc Posted September 27, 2017 Author Report Share Posted September 27, 2017 Thank you @klonheadd and @danwilliams. I have already ordered the 27.5 pilot! On 9/25/2017 at 2:54 PM, dan williams said: Also what oil/fuel mixture are you using? If you are like most new trials guys you are throwing far too much oil in. Modern water-cooled, plated-cylinder bikes are quite happy at 80:1 Initially it was 65:1 which i based it on the Beta manual. Per recommendation from fellow riders, I am currently at 80:1. Since I also do some single tracks and ride along fire roads to access those single tracks, I will stick to 80:1. On 9/25/2017 at 2:54 PM, dan williams said: Carb is VM26-208 to be specific but that’s an OEM number so the generic VM26 will get you to the right place. Out of curiosity, how does one get to know the carb model? With dirt bikes, things were pretty simple - the manual would say the carb model I do miss the attention to details of Honda manuals. Currently I have to stick with 2002 or prior models so I can ride year round (green/red sticker BS from Socialist Republic of California) On 9/25/2017 at 2:54 PM, dan williams said: There is a Mikuni thread pinned to the Beta forum chock full of good info. Ok will do. Quote Link to comment Share on other sites More sharing options...
lineaway Posted September 27, 2017 Report Share Posted September 27, 2017 Knowing the carb model does nothing for your search. You could of taken your existing jets to any motorcycle shop and either they would have them or could order them. Googling Mikuni short hex takes about 10 seconds. By the way did you replace the plug yet as that might have been your real problem. Info at http://www.betausa.com/content/support Quote Link to comment Share on other sites More sharing options...
billyt Posted September 27, 2017 Report Share Posted September 27, 2017 All the jets are stock Mikuni jets with the exception of the needle (5DP) it is a needle machined by Beta for the bike. 1 Quote Link to comment Share on other sites More sharing options...
trialmarc Posted September 27, 2017 Author Report Share Posted September 27, 2017 7 hours ago, lineaway said: By the way did you replace the plug yet as that might have been your real problem Yes, I have already replaced it with BR7ES and bike starts fine, and that should do till I get the pilot jet in next few days. Thanks for the help guys! Quote Link to comment Share on other sites More sharing options...
dan williams Posted September 27, 2017 Report Share Posted September 27, 2017 Old bikes came jetted rich for break-in and new bikes come jetted so lean for emissions they barely run. 27.5 pilot makes a big difference in how the bike pulls off bottom. You’ll be pleased. Quote Link to comment Share on other sites More sharing options...
trialmarc Posted October 10, 2017 Author Report Share Posted October 10, 2017 Hello folks! The main jet is 145 and pilot is 27.5 now. Do I need to worry about the jet needle clip position? The needle has 5C23 stamped on it, and clip is currently at 2nd groove from top. Thank you! Quote Link to comment Share on other sites More sharing options...
dan williams Posted October 10, 2017 Report Share Posted October 10, 2017 I’m all for fine tuning but at some point you just have to ride the damn thing. You should be pretty close at this point. You have all the baseline stuff. Any fine tuning from here on is ride, tweak, ride, tweak.... only you can say the bike is tuned properly for you. On my ‘13 I spent many hours fettling with the carb and eventually went back to stock on the pilot and one size down on the main. On the older bikes 27.5 pilot always worked and the main depended on the nature of the bike as Beta tuning is variable year to year. Go out and play for a bit. Quote Link to comment Share on other sites More sharing options...
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