Question about 2005 Suzuki RM-Z 450
Well, without physically hearing the noise it's a bit of a guessing game. However based on your description and past experience (all of which is from my past life as an auto tech of 23 years) it sounds to me like it may be a fuel problem, probably lean; generally a spark related misfire will occur more under load than steady state and a rich fuel condition will typically lead to bogging, while a lean condition is likely to cause misfires. I don't know if your bike is fuel injected or carbureted but judging by the vintage I'd guess it was carbureted. I'll assume that the engine runs fine under full load acceleration. You may have a carburetion problem (do you have single or multi carbs?) possibly a weak fuel pump although that would tend to show up more under heavy load than steady cruise or even over advanced timing causing detonation. I'm not sure of the specific systems on your bike so I can't offer any advice on how to check timing or examine the carb(s), but I can offer general procedures that may be helpful. Assuming again that you have carbs and a manual choke system, you could try putting a little choke on when the problem occurs to see if the problem goes away, if so this would prove the theory that the engine is running lean. One other thing I would do is to look at the plugs that came out of it (hopefully you saved and numbered them) and then pull the new ones back out and examine and compare them. Perhaps you could take some good pics and post them for us to look at and offer opinions on their condition and cause? Can you duplicate the problem in neutral? Is it only occuring at one particular road or engine speed or any steady speed? Does ambient temperature have any effect?
Posted on Nov 20, 2008
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