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Garage built 400ex summer project


400ex
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So after my 400ex pep up (High comp piston, stage 2 hot cam, and some others), There was a malfunction with the rocker arm jam-nut; guess it wasn't torqued to spec. The rocker arm nut caused the lash to become too out of clearance and I bent a valve on a test rip high in the rpm range. There was no damage to the piston but only that valve, a couple dents in the head, and a completely destroyed valve guide. So I decided to take it upon myself (after watching kenoconnors race porting instructions and reading up on this subject) to port my cylinder head significantly. I had the head decked, cylinder honed and smoothed/polished the dome/exhaust port (intake wasn't polished but dimpled slightly to ensure fuel atomization). So after porting, decking the head, I had all valves and guides replaced/reamed, 5 angle valve job, and recut seats, then I installed xr400 gaskets (for higher compression), carb jets; 42 pilot, 175 or 6 main not sure, dynojet needle, k and n filter with no lid, enlarging of header ports and big gun eco slip on exhaust for a 450r, trx 250r coil (adds 1000+ rpm to limiter), 11:1 85mm piston, stg 2 hc with springs and retainers replaced, and polished rocker arms. I then replaced both sprockets one down in front and stock in rear, o ring chain, and 18in tires. There is a larger list of mods but these were the only ones affecting acceleration/performance. On the dyno, this quad put down 42rwhp and was estimated at 46 to the flywheel. Once again this was 42 to the wheel on the stock bore/carb size/header. All this was done at 16 yrs old. You may not be able to see it in the picture but peak whp was 42 on a mustang dyno.

21430483_800483270111046_536164941926463227_n.jpg

400ex dyno.png

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Dream Car Giveaway
  • 2 weeks later...

Cool. I'm rebuilding my 03 400EX engine with a Pro-X piston kit and quadboss gaskets with Maxxis RAZR's(22 inch) in the rear and RAZR's in the front. It's got a Lexx full exaust system and renthal handlebars. I installed a 05 400EX carb and I find it gives it a bit more HP. I also have a question to whoever can answer: The front right wheel of my 400EX is leaning in towards the frame causing extra tire ware on that wheel. I'm pretty sure it's not the bearings because the wheel still rolls like new. Any help would be appreciated.😃

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