Hello William.Hows things going??My xplorer 400 you worked on needs help.I recently went to an atv pull around here.I was in the 400 modified class.Darn pipe puts me there everytime.Any how I was allowed 1350 lb total quad weight.Thats exactly what I ended up weighing.I hooked to the sled and gave her heck.At about the 75-80 foot line,the 400 starts to run doggy.Kinda sounded like it was getting ready to foul a plug.I know youve heard the noise before.She felt a little flat also when this happened.I kept on it and it came out of it at around 135 foot.The sled was pulling pretty heavy by now and all of a sudden she backfired once.Then it commenced to pulling again until I lost traction.Ended up at 176 foot on a 200 foot track.The same place is having another atv pull in two weeks and I wanna rejet to run better.Am I rich or lean???Also what about clutching?I was running S55 with blue/green (factory) spring.Would the white spring run better.If you need Ill get my jetting specs for you.Ive changed them so many times that Ive forgot whats in there now.Thanks alot.Scott Sanger.

 

Hey Scott, when it comes to pulling weight like that we need to rethink the clutching. You normally set up a clutch to run with a minor load (everyday riding, hills,etc.). That will all change with pulling. You most definitely will need to change the primary spring. Go ahead and start with the white. You need to double check the secondary settings also. It's been quite some time since I talked to you so I dont remember if you have changed the secondary spring or not. If you havent, then buy an HPD violet secondary spring and set it to the 2-2 setting. If you have any other spring like the stock red or black then I would go ahead and change it out for sure. Those 2 clutch changes will make a world of difference.
Here's what is happening to you: The blue/green spring is a stocker with a low engagement and low shift out (I know that's what you wanted). On the start the bike takes off fine and starts pulling fine. As you get down the track a bit the clutch has shifted out some and is in the middle of shiftout where it is very sensitive to load. Since it doesnt have enough spring probably coupled with a lighter secondary setting or spring it wont backshift correctly or it is not load sensing like it should. Basically you end up shifting too fast and not pulling like it should, so the motor starts to bog instead of holding or backshifting. There is also rhe possibility that you might have to go with a s-53 weight to keep the motor from pulling down with all the weight your trying to pull, but I would do the others first and see what happens. But it sounds like the clutch shifts too fast, bogs the motor a little, then finally backshifts some and then continues on with the plan.
Other things to check just for maintenence would be the reeds, coil connections, and especially the plug cap. Clean it well and also change to a BR8EGV plug as it takes less ignition to fire. They cost a little more but are worth the money. After a full run you should be able to kill it immediately and take a plug reading. Remember to look more at the base section of the pocelain to get the reading instead of right at the tip. I would do clutching first and check reeds, then try it out and see what happens. You should have a fairly good line on the jetting now, so i would check that last. Hope this helps,Bubba