maximokmo Posted July 21, 2021 Share Posted July 21, 2021 On my DT 125 MX (1981), whenever I go WOT and a reach higher revs in each gear the engine starts stuttering rapidly and won't rev/accelerate any higher. This is annoying because it happens just as I get into the powerband. If I change the spark plug, the bike runs pretty sweet and can rev much higher but then after a few rides it goes back to the stuttering problem. Any suggestions to fix this? Cheers Link to comment Share on other sites More sharing options...
Moderator Snakebite68 Posted July 21, 2021 Moderator Share Posted July 21, 2021 What colour are your spark plugs when you take them out? Pictures would be good... Link to comment Share on other sites More sharing options...
blackhat250 Posted July 21, 2021 Share Posted July 21, 2021 Sounds like its 4 Stroking ,,[ rich],, whats the plug colour look like,,,, have the jets been tampered with ,? Air filter ? you looked ? Link to comment Share on other sites More sharing options...
maximokmo Posted July 22, 2021 Author Share Posted July 22, 2021 Hi, thanks for the swift responses. I am away for the weekend but will upload some photos next week of spark plug colours and other details etc next week. last time I looked the spark plug was a brown colour so thought that was fine. Have changed air filter few months ago too. Im not sure whether the carb is the stock carb for the engine, also not sure if the jetting is definitely correct - it’s a mikuni 4J300? I lowered the needle jet by two notches, it didnt seem to make much difference. it also is difficult to start - if its running rich is that the plugs being fouled? Link to comment Share on other sites More sharing options...
blackhat250 Posted July 25, 2021 Share Posted July 25, 2021 Rich = dark plug colour, [ or black] starting > is it with choke or better without,,? ,and if dropping the needle did nowt , it maybe the main jet too big, Link to comment Share on other sites More sharing options...
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