hi i have a 1982 xj750 iam having problems starting when cold it has air pods / filters and straight through pipes i have 134 main jets and 43 pilots will start with easy start when cold and starts ok when it has been running a while have cleaned carbs as you said also do keihin or mikuni jets fit many thanks
Hard starting when cold can have a variety of causes. It can be clogged up choke or idle circuits – but if it runs well when warm the idle isn’t part of it. It can also be jetting related, again – on the idle circuit. First, check your choke circuit and operation.
Next is valves. People tend to let the valves on the Yamaha XJ motors go without adjustment for a long time due to needing a bucket holder tool to check them properly. It’s super easy to do, but many just let it go and go and go and the valves get way out of whack. Check them.
Carb synchronization – sync them. If they’re way off it can cause a host of problems, like hard starting.
Weak spark. Check your plugs – make sure the spark is bright blue. If it’s yellow, orange, redish then it’s weak. A cold engine needs a nice strong spark – this could have tons of causes.
Finally – engine problems. Check your compression. Weak compression will obviously make a motor hard to start – then once the piston expands and oil flows, compression goes up and it’ll run ok.
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