GazW Posted April 12, 2011 Share Posted April 12, 2011 Since I swapped my engine on the CG for a newer model and blanked off the EGR valve, the bike will only run (well) on half choke. It will work with the choke off, but struggles with any variation of the throttle. So I could quite easily maintain a speed with a constant throtte. If I was to accelerate the the bike just burbles and loses power, like its going to die untill I back off the throttle. However it runs well enough on half choke, (only 50MPH max) but it is not something I want to make a habit of.I am using the correct carb for the year. The one with the carb heater on it. So far I have stripped the carb, cleaned the main, pilot and needle jets out. I have stripped the accelerator pump from its housing and cleaned the diaphragm and checked the needle for straightness, then put back together according to the haynes manual. I have also checked the float height and it all seems to be in order. (I have played about with the pilot screw but that only deals with the idle to 1st 1/4 of throttle according to the manual, and this is not where its having problems, Its probably from 1/3 throttle up)So here is where I am at, I have come to the conclusion that the carb itself is in perfect working order, I just think that A) My airbox/filter (I have put an '05 Engine in a '94 frame due to the job seeming simple enough, just had to swap the loom) is not as efficient as the one off the newer model and is drawing too much air in. B) The main jet is too small for the correct fuel and air mixture and I am really struggling to find jets for the Keihin. To rectify this I was thinking of buying a Mikuni VM22 Carburettor, (intended for pitbikes I think, but if it works...) That should bolt straight on, and doesn't have an accelerator pump so it is essentially less complicated, with a load of different jets and just play with it untill I get it working. Can anyone think of any reason why this is a bad idea? I think the accelerator pump is to add fuel if you crack the throttle wide open from closed. So I can't see it making much of a difference on a 125 anyway. Also theoretically if I get the engine running right with the right mixture, it shouldn't matter what carburettor is feeding it should it? Quote Link to comment Share on other sites More sharing options...
cypek Posted April 12, 2011 Share Posted April 12, 2011 I had exactly same problem with my CBR125 copy. It had exact copy of CG125 engine. All I did was adjusted mixture on carb and replaced spark plug as one fitted was wrong type with incorrect gap. After that bike was running spot on Thats all I can say Quote Link to comment Share on other sites More sharing options...
Fozzie Posted April 13, 2011 Share Posted April 13, 2011 Start easy, check the plug! Put a new one in there, preferably an iridium one. Quote Link to comment Share on other sites More sharing options...
polecat Posted April 13, 2011 Share Posted April 13, 2011 Start easy, check the plug! Put a new one in there, preferably an iridium one.I thought my cb250 engine was mashed as it was only running on one cylinder but it was incorrect gap that caused the problem ! sometimes it is simple things (and when it was running before it had same symptoms as OP's bike Btw) Quote Link to comment Share on other sites More sharing options...
GazW Posted April 14, 2011 Author Share Posted April 14, 2011 Should have mentioned, its running on a new plug. I bought one before I swapped the engine, I suppose I could swap the spark plug cap and see what happens. I'll try that before I try the carb. Would an iridium plug be benificial on a 125 single? Quote Link to comment Share on other sites More sharing options...
Fozzie Posted April 14, 2011 Share Posted April 14, 2011 I noticed my 125 4-stroke singles would work more smoothly and with a bit more throttle responce when I fitted an iridium. This is sounding like a wrong gap! Quote Link to comment Share on other sites More sharing options...
GazW Posted April 21, 2011 Author Share Posted April 21, 2011 Update on the situation, I tried setting the plug gap, even went and bought a new plug to be sure, all to no avail. So I bit the bullet, bought the carb, fitted it and it has made the world of difference! The bike pulls a million times better, it just has a bit of a hole in the middle of the rev range, so I may lift the needle a notch, and go up one size on the pilot jet, (although it idles Ok) and two sizes on the main. Fingers crossed I can get it running even better Quote Link to comment Share on other sites More sharing options...
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