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400ex

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400ex last won the day on December 21 2017

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About 400ex

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  • Location Perrysburg, OH, United States

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  1. 400ex

    Post your mods...

    400ex high comp piston, titanium valves, bronze valve guides, fully ported head with port matching done to intake/ exhaust, decked head, enlarged header opening, big gun eco for 450r, 45pilot 175 main, stage 2 hot cam, polished rockers, 5 angle valve job, k and n with outerwears, 14 tooth front sprocket, stock rear, 18 in rear tires - stock front - cst ambush, red o ring chain, wheel spacers with extended studs, trx250r rev box, dg nerf bars, ac bars, moose racing grips and clutch perch, new throttle/clutch cables, 450r axle nut, new starter, and much more.
  2. 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.

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