mattya Posted March 21, 2009 Report Share Posted March 21, 2009 got a gas gas 125 with a very flat bottom end not reponding at all at botom end but runs fine other than this also does anydoby not the fuel mixture it should be run on. it isent been used in trials yet just playing about at moment. matty Quote Link to comment Share on other sites More sharing options...
16000rpm Posted March 22, 2009 Report Share Posted March 22, 2009 Hi Matty Fuel to oil ratio depends very much on oil quality and the oil companys recomendations,i use a good quality synthetic and run 35:1 . Chris Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 22, 2009 Report Share Posted March 22, 2009 Hi MattyFuel to oil ratio depends very much on oil quality and the oil companys recomendations,i use a good quality synthetic and run 35:1 . Chris 35:1 in a GG125?? I would say 80:1 to 100:1 The little GG isnt known for gobs of low end, but sounds like you may need to sort the jetting and air screw. Quote Link to comment Share on other sites More sharing options...
16000rpm Posted March 22, 2009 Report Share Posted March 22, 2009 (edited) 35:1 in a GG125?? I would say 80:1 to 100:1 The little GG isnt known for gobs of low end, but sounds like you may need to sort the jetting and air screw. 100:1 Could this be the reason my engines seem to last forever when other riders are fitting new mains/pistons and cylinder re plates on a regular basis ? my background is road racing and i must ask the question why such low powered trials engines need such regular service and repair? oil ratio perhaps Edited March 22, 2009 by 16000rpm Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 22, 2009 Report Share Posted March 22, 2009 100:1 Could this be the reason my engines seem to last forever when other riders are fitting new mains/pistons and cylinder re plates on a regular basis ? my background is road racing and i must ask the question why such low powered trials engines need such regular service and repair? oil ratio perhaps I can see where you may want that extra film of protection at 16000 rpm, but not needed for trials bikes that operate at 1/2 that rpm and infrequently at that. The crank bearings on the GG are lubed via the tranny fluid, so the lean mix wont hurt them at all. All of my GG lasts for years w/o replates- but my bike never sees the main jet for that matter...so I personally worry more about splooge buildup in the midbox/silencer ect...There is a poll on here somewhere where most people use 80:1 and almost no one under 50:1 so I think its fairly well proven. Quote Link to comment Share on other sites More sharing options...
16000rpm Posted March 23, 2009 Report Share Posted March 23, 2009 I can see where you may want that extra film of protection at 16000 rpm, but not needed for trials bikes that operate at 1/2 that rpm and infrequently at that. The crank bearings on the GG are lubed via the tranny fluid, so the lean mix wont hurt them at all. All of my GG lasts for years w/o replates- but my bike never sees the main jet for that matter...so I personally worry more about splooge buildup in the midbox/silencer ect...There is a poll on here somewhere where most people use 80:1 and almost no one under 50:1 so I think its fairly well proven. Looks like its 100:1 then and best of luck but i will stick with my 35:1 ,the 16000rpm relates to my race bikes and not my 350 gas gas Quote Link to comment Share on other sites More sharing options...
dan williams Posted March 23, 2009 Report Share Posted March 23, 2009 (edited) 70:1 - 100:1 with a full synthetic is typical on a trials engine. Anything more and you'll be replacing muffler packing every few months and having to rev the motor before each climb to clean the goo out. Maybe 50:1 if you plan on running an enduro flat out on the thing. After 20 years of running at between 80:1-100:1 I've never had an engine failure. After about three years I'll change rings but that's pretty much it. Every time I've opened a trials engine I'm amazed at how little wear there is on the top end. I also notice, even when run at 100:1, there's always residual oil on the bottom of the crank. I've run Spectro, Mobil 2T, Belray MC1, Melray HR1, IPONE. So far the bikes just don't really care as long as the jetting is correct. I think compared to a road race engine there's a lot of time for the oil to stick to the parts so the mixture can be a lot less saturated. At 35:1 you'll be the guy with the smokey bad running bike. People will think you've blown a seal. Edited March 23, 2009 by Dan Williams Quote Link to comment Share on other sites More sharing options...
jse Posted March 23, 2009 Report Share Posted March 23, 2009 Looks like its 100:1 then and best of luck but i will stick with my 35:1 ,the 16000rpm relates to my race bikes and not my 350 gas gas Generally speaking, most of us tend to use a full-synthetic premix oil at around the 80:1 ratio (I use 70:1 in my Pro 280 and 50:1 in my air-cooled 85" TY350 Mono) due to the unusual demands we put on the engines (compared to other forms of competition). Richer oil mixtures tend to cause carbon buildup in the front of the headpipe and sometimes oil buildup in the mid and final mufflers due to the on/off/trailing throttle applications (as well as a concern for the possibility of fuel/oil fouling plug problems) and the heat/cool cycles normal in Trials use. Trials carbs (any carbs for that matter) have a hard time providing effective metering in the off-idle area (where the multiple "circuits" overlap--idle/fuel mixture, pilot, slide cutaway, needle profile/height) where we spend most of our time, so our engines tend towards the rich end of the carburation spectrum. The "benefit" (if you could call it that) of this rich mixture and the low/staggered RPM range is that we don't need to demand as much from our premix ratios, hense the unusually low ratios. I'm assuming your bike is a mid-90's JT35 model, for which the factory recommendation was a 80:1 premix ratio. I think you should run whatever ratio you are comfortable with (I'm more comfortable with the "richer" 70:1 ratio myself), I just thought it might be helpful if you had an idea of why other riders opt for the seeming insane lean ratios. I understand how you feel as I come from a background of building high-performance race engines (including TZ, RS, Formula-S etc roadracers) and I thought these guys were nuts to run those ratios, but from my experience in Trials since 1971, engine failure/damage from a lean premix oil ratio cause is extremely rare (I actually can't think of one). They almost always are caused by an "outside" condition such as an airfilter installed incorrectly, low-octane fuel or incorrect jetting. Jon Quote Link to comment Share on other sites More sharing options...
manx2day Posted March 23, 2009 Report Share Posted March 23, 2009 I've alwasy run my bikes at 50:1 and never had any engine problems. Never had to replace/replate anything. Quote Link to comment Share on other sites More sharing options...
cdn280 Posted March 23, 2009 Report Share Posted March 23, 2009 See the poll in >> http://www.trialscentral.com/forums/index....showtopic=17883 Nothing richer than 50:1 listed... For a few yrs now, I've been using 70-80:1 for straight trials work and 50-60:1 for trail riding where I can actually use 5th or 6th gear Quote Link to comment Share on other sites More sharing options...
jse Posted March 23, 2009 Report Share Posted March 23, 2009 I've alwasy run my bikes at 50:1 and never had any engine problems. Never had to replace/replate anything. I think that's fine. I see that on the GasGas Spain website they usually recommend a "2%" mix, which is, of course, a 50:1 ratio. With the new full-synthetics that burn much cleaner (not a "synthetic blend" type) than the mineral bases, a rider has a lot more leeway to run whatever mix ratio that they are comfortable with. I've rarely seen an engine damaged by more than the recommended ratio of the correct oil. Maybe a little more carbon buildup or ooze, but not actual damage. Jon Quote Link to comment Share on other sites More sharing options...
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