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I give up. The XR has me beat...

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My 03 XR400 lost all compression after getting some grit in the cylinder from a spark plug change, taking the head off I found a piece of grit sticking an intake valve open a tiny bit. Took the intakes out and cleaned the ports, put the valves back in and with the exhaust looking clear vacuumed the grit off the piston and put it back together. Little more compression but not much. Leakdown tester shows exhaust is leaking so off with it's head again and out with the exhaust valves. No grit this time but the same black buildup around the backside of the valvehead and the seat area that was on the intake. Almost like 2 stroke splooge but the bike doesn't use any oil (only 480 miles on it). Has a Yosh pipe, twin air filter, air box snorkle removed, and jetted 58/160, started and ran great. Never seemed to be running rich at all. Anyway, filled the combustion chamber with laquer thinner and no leaks so on with its head, more gaskets. Had good compression but after three kicks and an almost start it lost a little of it's comp. again so it's almost start but not quite. I'm tired of foolin' with it so to the shop it goes. Need to clean the splooge in the solvent tank I guess. Had some on the top of the piston but I scraped and vacuumed it off. Question is, what's the splooge crap and how to keep it fron reappearing. Was using Conoco 93 octane back in the heat of the early and middle summer. Any thoughts? 😢

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My bet is leaky valves. Lap the valves/seats. Could be valve seals. It aint no biggy, dont give up yet!

Get the Denso Iridium plug, mines been in for 3 1/2 yrs.

Robert 😢

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Prior to ever pulling my Plug on my XR I use my Blow Tip on my Compressor to blow about 150psi around the Plug to make sure nothing is left to fall in the hole once plug is pulled.

This assures there is NOTHING left to cause that problem.

Yep, you can bet I will too next time. 😢 Seems that a lot of the problem is that layer of sticky black junk in and around the valve pocket. Works like fly paper and when I took the exhaust valves out this time there wasn't any grit to be found, just a buildup of the black crap. Part of why I'm going to bail and take it to a shop is to figure out if I need to jet it leaner or just change gas. 😢

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