htrdoug Posted March 5, 2013 Report Share Posted March 5, 2013 (edited) I think what makes them occasionally rich without a airbox is that at certain rpm a resonance sets up that blows the charge back out through the carb backwards,then is sucked right back through the carb again,each time the charge passes through the carb it picks up more fuel,thus almost triple charging the mixture(probably doesn't pick up as much fuel in each successive pass as the air gets heavy with fuel and doesn't draw that much again) having a airbox breaks up this resonance so the air just makes one pass through the carb. Very common issue with "pod" air filters too,impossible to jet out due to specific rpm resonances rather than throttle position determining richness. Edited March 5, 2013 by htrdoug Quote Link to comment Share on other sites More sharing options...
coop650 Posted March 5, 2013 Report Share Posted March 5, 2013 I'm sorry but I disagree completely with the "no air filter making it run rich" logic. It will certainly run lean. A dirty filter causes a bike to run rich because it can't get the air it needs, no air filter= too much air. Example: If you swap your air filter with something more flowing like a K&N "performance" filter the company even tells you the bike pulls more air and will run lean and needs rejetted. I worked in a shop as a mechanic for several years, I am not a know-it-all but I am not a noob either. That bog you are hearing is a lean bog. Obviously that's just my opinion. Quote Link to comment Share on other sites More sharing options...
coop650 Posted March 5, 2013 Report Share Posted March 5, 2013 And congrats on getting it running! Quote Link to comment Share on other sites More sharing options...
duffers Posted March 5, 2013 Report Share Posted March 5, 2013 Seems to me your worrying about something which need not be an issue. you clearly will be putting the air filter on when you find it and would not be using the bike without it, so only when you've got it on is the time to fault find and set up the carb. Two turns out is a good place to start with the fuel screw and adjust from there as needed. Glad you got it running it makes all your previous frustration worthwhile. Quote Link to comment Share on other sites More sharing options...
thats_a_five Posted March 6, 2013 Report Share Posted March 6, 2013 That is awesome that you got her running again! I think your bike has the Delorto carb. Remember that the "air screw" is actually a fuel screw so turning it out will give more fuel, not more air. Black, wet and sooty plug and piston indicate too rich to me. The bogging I heard in the video does sound like fuel starvation. It could be super rich at idle and starving as you open the throttle and let in more air. Check the float height and needle height as well as the proper jets and fuel screw settings. What fuel - oil mix are you using? Remember that more oil makes the mixture leaner - the opposite of what some people think. I found a spec sheet for the '93 model and have pasted it here. I hope it helps. Keep your chin up. You are so close! 1993 GT25T: THE STOCK JETTING DELIVERED IS GOOD FOR SOME BIKES, BUT OTHERS ARE RICH AND REQUIRE REJETTING. THE FOLLOWING INFORMATION WAS SUPPLIED BY Gas Gas R&D IN SPAIN. STOCK ALTERNATIVE JIM SNELL'S SETTINGS MAIN 95 95 95 (92 OK) PILOT 33 38 38 (36 OK) NEEDLE 2ND CLIP FROM TOP 2ND CLIP FROM TOP TOP CLIP NEEDLE SIZE D36 D36 D36 NEEDLE JET 270 270 268 SLIDE #40 #40 (CUT 2MM) #50 SEE BELOW FLOAT HEIGHT 24MM 27MM 27MM FUEL SCREW 4 TURNS OUT 4 TURNS OUT On Jim's settings NOTE: If you wish to run unleaded Premium gasoline rather than race gas use #95, the #92 main may cause spark knock. TO MODIFY THE 93 GT25T JETTING: (NOTE:GT25T BIKES BUILT AFTER JULY 1993 HAVE THE SLIDE MODIFIED AT THE FACTORY. IF THE #40 STAMPED ON THE INSIDE OF THE SLIDE HAS BEEN DRILLED OUT, THIS IS A FACTORY MODIFIED SLIDE. IF YOU SEE THE #40 STAMPING YOU HAVE THE UNMODIFIED ONE.) CHANGE THE PILOT FROM A #33 TO A #38 OR #36, AND FILE 2mm FROM THE CUTAWAY ON THE AIRBOX SIDE OF THE SLIDE. (OR REPLACE WITH A No.50 SLIDE). BE SURE TO CHAMFER THE EDGES TO PREVENT THE SLIDE FROM STICKING IN THE BARREL OF THE CARBURETOR. SET THE FLOAT HEIGHT TO 27mm (STOCK IS 24mm) TURN THE FUEL SCREW TO 3.5 TO 4 TURNS FROM THE INMOST POSITION. MAKE SURE THAT THE NEEDLE CLIP IS IN THE SECOND SLOT FROM THE TOP. TAKE 2cm FROM THE INSIDE OPENING OF THE AIR BOX LID. (THIS IS TO ALLOW A FREE FLOW OF AIR TO THE CARB) GT25T USED BY Gas Gas UK IN ENGLAND, NOT TESTED BY Gas Gas USA: MAIN: 95 PILOT: 35 NEEDLE: 2ND OR 3RD NEEDLE SIZE: D31 NEEDLE JET: 268 SLIDE: 40 FLOAT HEIGHT: 25mm FUEL SCREW: 3.25 TURNS Quote Link to comment Share on other sites More sharing options...
thats_a_five Posted March 6, 2013 Report Share Posted March 6, 2013 (edited) Ah, it looks like the formatting of the table got lost when I posted the spec sheet. I hope you can understand the logic: the first number listed in each of the categories is the stock setting. the second number is an alternative and the third is Jim Snells recommendation. Also note that Jim Snell is in USA where the highest octane pump gas we can get is 92. Edited March 6, 2013 by thats_a_five Quote Link to comment Share on other sites More sharing options...
duffers Posted March 6, 2013 Report Share Posted March 6, 2013 (edited) j13me, don,t allow yourself to complicate things. This is not a new bike to you. When you put it away 8 years ago it ran fine! Therefore you know the jets in the carb worked. Assuming the shed mice in Great Yarmouth don't know how how to change Dellorto jets and the Norfolk area hasn't changed altitude overnight, these should be correct. If they are all clean then don't change them, at best replace them with new parts of the same size!! Assemble the bike as it is intended to be run(with the air filter fitted) and adjust the fuel screw as previously described. Be patient and keep it simple. Correct setting of the fuel screw will be achieved when you open the throttle fast from a slow tickover and it revs up freely without bogging. Hope this helps. Edited March 6, 2013 by duffers 1 Quote Link to comment Share on other sites More sharing options...
j13me Posted March 6, 2013 Author Report Share Posted March 6, 2013 Cheers for all the input as always guys! Massively appreciate it! The spec sheet says 4 turns out on fuel? That seems a MASSIVE amount? I suppose I could try it, hopefully finishing work early today so will have a play later! Any ideas why it only starts with a hot plug? (Hot not warm, I can barely touch it when it goes in) warm wont start Quote Link to comment Share on other sites More sharing options...
coop650 Posted March 6, 2013 Report Share Posted March 6, 2013 I suspect your head gasket may be bad from taking it apart. That could cause the need for the hot plug. Quote Link to comment Share on other sites More sharing options...
j13me Posted March 6, 2013 Author Report Share Posted March 6, 2013 Update, with the fuel screw 4 turns out it starts 2 or 3rd kick idle is high and very hard to adjust with screw, either raises or cuts out! I do have a gasket gone I think, frothy coolant in tank, grey colour gearbox oil? Quote Link to comment Share on other sites More sharing options...
shipdamite Posted March 6, 2013 Report Share Posted March 6, 2013 or is that a waterpump seal failure?? Quote Link to comment Share on other sites More sharing options...
j13me Posted March 6, 2013 Author Report Share Posted March 6, 2013 Can I check this simply? Just pop it off or is it more in depth? Cheers Quote Link to comment Share on other sites More sharing options...
thats_a_five Posted March 6, 2013 Report Share Posted March 6, 2013 Milky transmission oil is almosdt always due to water pump seal failure. Agree completely with Duffers about jetting etc. Jets don't change themselves, but they can get plugged if fuel or water are allowed to sit in them for too long. I recall your pics of lots of gunk in the carb. Check the float height again. Too high will cause flooding. Not sure why a heated plug will help the bike start but i suspect it is helping to atomize the fuel mixture so it will ignite. My thinking is there are 2 problems: 1) flooding at idle due to float height or excess fuel leaking through the choke passage. 2) fuel starvation when opening the throlle due to plugged jets or passages inside the carb. But of course i could be wrong - wouldn't be the first time! Cheers! Quote Link to comment Share on other sites More sharing options...
j13me Posted March 7, 2013 Author Report Share Posted March 7, 2013 Forgot too add, with the fuel screw 4 turns out she revs perfect! No bogging at all! Its just the idle I'm struggling with, when I rev it a bit the engine takes a while to drop back down too. I'm thinking maybe a small air leak but visably all seems ok Quote Link to comment Share on other sites More sharing options...
coop650 Posted March 7, 2013 Report Share Posted March 7, 2013 That could be due to no air filter (unless you put it back in). That oil/coolant issue is more than likely the water pump. http://www.youtube.com/watch?v=GmSkJCII0fY Quote Link to comment Share on other sites More sharing options...
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