Well it finally happened , my brother blew up the old 86' Honda TRX 350 Foreman 4x4 while drag racing our nefew's 98' Yamaha 350 Wolverine 4x4 ; both where fulltime 4WD quad's ! I owned the Honda from Feb. 1989 when it had less than or a little over 20hrs when i bought it from the original owner , they were racing on 2 lane blacktop when he blew it ; he said he beat the wolverine all the way to less than a quarter mile from his house and it was a about a mile and a half race before it blew ! And it kept running wihile it was runing at high speed , only bgging down when he would try to go to full throddle ; and he had his wife push his the rest of the way home ! And he said it was still running when he stopped , but when he tried to give it throddle it stalled out and wouldn't start backup ; it would fire but only backfire when he turned over the engine ! He said he put a post on the forums describing what happened , and someone told the timing chain jump time a full 180% on the timing ; he plans to rebuild it and keep it as a spare for friend's to ride with him when they went riding together ! What thought's do everyone think he will need to rebuild it , i told him i would look at it when we tear it down to see what all the damage is done ; i've never replaced a timing chain and i would like to know if it's just the timimng chain and gear set does it requare splitting the case's on the bottom end ? I had done a lot of work on it before i sold it to him in Nov. 2005 and he didn't keep up the service of the quad like i did when i owned it , i think he only changed the oil and oil filter once since right after i sold it to him ; and i kept telling him to keep the air filter cleaned and reoiled properly ! But i don't think he ever got around to cleaning it the whole time since i sold it to him , because the last time i rode with him it was running to rich a fuel misture , because it would blow black smoke when he would first start it up ; and everytime he changed the spark plug it would be black as the ace of spades ! So i know it was running to rich and needed a complete servicing and rejetting the carb , but he kept saying i'll do it tomorrow ; any advice will be great ! .............

 

The first thing to do is check compression. If the compression is down, it probably did slip a tooth on the timing chain or swallowed a valve. The only way you'll know is by pulling the head. Good luck.