jimsshed Posted January 5, 2006 Report Share Posted January 5, 2006 (edited) Hi, My son has a new 2006 50cc mini trial and it wont idle properly. When riding, it idles high, but after 15~20 seconds it will idle right down then stop. * Have re-cleaned the carb with compressed air * Checked the inlet manifold for leaks. Checked bolts. * Confirmed that slide closes and opens fully and that steering movement does not interfere. * Needle and seat looks new (as it should). The fuel tap runs freely, but have noticed that fuel line constantly has a long air bubble inside it after the bike has ran for a few minutes (fuel pipe is clear tubing). I don't know why. Stalling problem interferes with his riding as we noticed it always does it when he rides down a slope with the throttle backed off. Motor will remain running if you work the throttle whilst on the slope. After seeing this in action, I can replicate the problem and make it immediately idle down and stall simply by lifting the back wheel 6 inches in the air. Motor otherwise starts easy (hot or cold), runs clean, and produces good power even with me on it. Does anyone have any ideas or experience with this problem ? Cheers, Jim Edited January 5, 2006 by JimsShed Quote Link to comment Share on other sites More sharing options...
lineaway Posted January 5, 2006 Report Share Posted January 5, 2006 Maybe try the vent on the fuel cap?!? Quote Link to comment Share on other sites More sharing options...
ruffrider Posted January 5, 2006 Report Share Posted January 5, 2006 As the problem seems to be with the angle of the bike, have you checked that there is no dirt or water in the bottom of the fuel tank that's getting through when the back wheel is raised? What about similar in the air box ? Quote Link to comment Share on other sites More sharing options...
charliechitlins Posted January 5, 2006 Report Share Posted January 5, 2006 I don't know if this helps, but I recently came across the only defective carburetor that I've seen...some sort of machining error. It was on a different brand, but the result was the bike would stall when the rear wheel got high. Drove me NUTS. Quote Link to comment Share on other sites More sharing options...
bikespace Posted January 5, 2006 Report Share Posted January 5, 2006 (edited) Easy test to make sure which one of the two areas the problem is coming from. Take the tank off and hold it level along side the bike while you lift the rear wheel. You can narrow down whether it's the fuel feed from the tank or if it's carburation problems at least. Not seen much of the mini. Just a thought - if it has a reserve, is it the same on reserve? Maybe has the same cheapish in-line tap as my lads rev50 in which case, not relevant. If it's a normal tap, possibility that the standpipe thet protrudes in to the tank is too long? Worth looking at it maybe if the first test above shows a fuel feed problem. Edited January 5, 2006 by bikespace Quote Link to comment Share on other sites More sharing options...
ktmsprocket Posted January 5, 2006 Report Share Posted January 5, 2006 My thoughts/questions are: Easyish stuff... 1. If the odd idling is after a LONG run down hill, then I'd be looking at the float and its free movement or setting. ie. temporary starvation? 2. Does it matter if the bike is hot/cold. If hot, you may find temporary vapour locks in the fuel line if the fuel line runs close to the barrel (it does in the KTM Mini Adventure which shares that engine - and this is common issue). 3. Are the jets tight? 4. Enough fuel in the tank? (exposing the fuel inlet tube) 5. Rubbish in the tank (it wouldn't be the first time a new bike came with crap in the tank!!!) 6. Inline filter a problem? 7. Water in tank? Slightly trickier stuff... 1. Wiring chaffing or pinched somewhere? 2. Plug cap secure and HT lead correctly fitted to cap? 3. Crankcase fuel of fuel from lying on side at some point? IT HAPPENS! 4. Water/Condensation under stator cover and/or stator with faulty wiring? There is a test for this you can run with the multimeter. let me know... Tricky... 1. Air leak on engine side of carb? (Ignition side crankcase seal has failed? Crank case centre gasket failed? Reed block or carb not air tight) Unlikely to be these though on a new bike... When engine is warm and bike on level, does the bike idle nicely and not idle up and down whole sitting there? Good luck J. Quote Link to comment Share on other sites More sharing options...
jimsshed Posted January 6, 2006 Author Report Share Posted January 6, 2006 (edited) Thanks everyone for your suggestions. * I've checked the fuel cap. * No water or dirt in fuel tank. * Air box is clean (btw the only air filter is a metal gauze wtf!!! but I'll deal with that next). * charliechitlins: interesting...what brand, bike or carb?. This carb is a Dellorto SHA 15/15...cheapest carb I've ever seen: No pilot jet, no air screw, plastic slide. * Fuel flows freely thru tap even when rear is up. * KTMSprocket: Odd idling occurs straight away when the rear is up. Problem occurs most noticably when hot. I changed the fuel pipe to a shorter one yesterday and the problem appears diminished a little in that the idle speed still goes down when the rear is up, but not as quickly. Could this be related to vapour lock?. I will investigate your fuel in the crankcase theory; the crate it arrived in had been on it's side somewhere in transit as all the gearbox oil had leaked out into the cardboard. Bike is not blowing smoke as I would expect in this case though, and I feel he's already ridden it enough to consume any residue that might have been there. Will also check the stator. Lastly, if you leave the bike idling on flat ground, it will eventually idle right down then stall in about 30 seconds. It's a journey... Cheers, Jim Edited January 6, 2006 by JimsShed Quote Link to comment Share on other sites More sharing options...
ktmsprocket Posted January 6, 2006 Report Share Posted January 6, 2006 I just need to double check something. Is this the Beta Minitrial with the engine now used in the small KTMs? do you have a pic you can post?.....you got me thinking when you mentioned the crappy carb....they run a 12mm delorto in the little ktms and in general, its ok for those bikes. sometimes with say a loose main jet or something, the crank case ends up with buckets of fuel in it...causes the weirdest problems. i had a non-start issue that came out of nowhere....checked everything under the sun.....then left the bike for two weeks with the plug out (it was off-season so didnt matter). came back...squirted fuel in (didnt connect the tank) and kicked it...it fired and ran momentarily. pulled the bowl off the carb and the main jet was sitting in the bottom. ie. the bike flooded with fuel flowing straight from tank into the chambers!!!! you also mention oil all over the place? was it lube from the clutch out of the breather? or is this bike injected....confused now as you can tell!!!!!! Quote Link to comment Share on other sites More sharing options...
jimsshed Posted January 6, 2006 Author Report Share Posted January 6, 2006 I'm not sure about the KTM ad I've never see one, although one of my trials buddies told me the engine is used in a KTM. The engine sidecovers have the words "MX Racing" on them. Auto clutch. Single speed, but noisy/whiny transmission. Carb is definitely SHA 15/15 as stated in the owner's manual..and I measured it to confirm. Main jet is definitely intact. Bike has no injection and runs on premix. We assume the gearbox oil ran out thru the breather. Cheers, Jim Quote Link to comment Share on other sites More sharing options...
29r Posted January 6, 2006 Report Share Posted January 6, 2006 Thinkin' maybe the crank seal/ primary side . Lifting the rear is moving the oil to the seal . Justa thought . Quote Link to comment Share on other sites More sharing options...
brian r Posted January 6, 2006 Report Share Posted January 6, 2006 Float level? Richening up when the back is raised eventually flooding it out? Quote Link to comment Share on other sites More sharing options...
ktmsprocket Posted January 8, 2006 Report Share Posted January 8, 2006 That engine is the one used in KTMs (altough I think originally it was used designed and built by Beta). Anyway...I tend to think this is a carb issue...as a coupl of us have mentioned, float does sound likely. If the dealer is close, get them to swap the carb for a new one and see what happens (pain in rs i know).??? BTW. The oild that was spilled was probably the clutch oil used in the clutch oil bath (there isn't a 'gearbox' as such). That whine is normal - sometimes at high speed in MX configuration it sounds like a Turbo whine!!! I'm not familiar with that carb. The 12mm is used in low power air cooled Mini Adventure and a 19mm is used in the high power, liquid cooled, SX Pro Senior. That same 19mm is used in our Beta engined Beta Rev 50. I'd be surprised if oil movement was causing such an immediate problem when lifted. If that much oil was getting through, it would be smokier than a brothel on a saturday night all the time. J. Quote Link to comment Share on other sites More sharing options...
jimsshed Posted January 8, 2006 Author Report Share Posted January 8, 2006 KTMSprocket, yes I agree with you on all points. I did the tank removal thing on Saturday to eliminate anything in that area. It all points to the carb, and the next logical step is to swap it out. I had entertained thoughts of puting our Rev-50 carb on it to try it out, but as you too probably know, it uses a different style of inlet manifold. Does anybody else following this forum actually have a Beta 50 Mini-trial, and if so, how does your engine behave?. What do you use for an air cleaner?. What other issues am I likely to face with this bike?. Thanks, Jim Quote Link to comment Share on other sites More sharing options...
ktmsprocket Posted January 9, 2006 Report Share Posted January 9, 2006 Hmmm...I had a dig around the web. That carb seems popular on mopeds. If you don't have an airbox on that Minitial, then I imagine they went that way for space saving etc and chose that carb as a result. Hence, a stupid metal gauze. That KTM motor runs a 12mm or 14mm dell carb on it, but they use an airbox. I'll ask some guys on a KTM forum if anybody has fiddled with you setup and maybe even converted to a diff carb (NOT THAT U WANT TO WITH A BRAND NEW BIKE!!!) J Quote Link to comment Share on other sites More sharing options...
ktmsprocket Posted January 10, 2006 Report Share Posted January 10, 2006 I tried - but nobody offered up anything. Quote Link to comment Share on other sites More sharing options...
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