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MX, SX & Off-Road Discussions
Dirt Bike Mods & Maintenance
weak spark
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[QUOTE="FenryHonda, post: 280997, member: 25819"] Service manuals are VERY available for this bike. They are on E-Bay constantly, plus Dennis Kirk (800-328-9280) has them for around $28.00. I just picked up a '77 YZ 400 last month, and had the same problem as you. I found the problems to be: a) deteriorated air filter- luckily the local Yamaha dealer had a NOS filter b) plugged silencer- some moron had welded the silencer to the pipe so it was a good excuse to buy a DG National pipe and Type II silencer. The pipe was dented and the silencer was not the right one anyway. c) very dirty, shellac filled carb- cleaned the carb and replaced all the jets, had stock jets and needed leaning out anyway, added Boyesen reeds also At kicking speed, my YZ has a weak spark, but fires on the 1st or 2nd kick when cold, 1st every time when hot. My advice would be to try these steps before you start disassembling the ignition system. ;) [/QUOTE]
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MX, SX & Off-Road Discussions
Dirt Bike Mods & Maintenance
weak spark
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