Why so slow?


XS400 New Member
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I have 2 xs400's a U.S custom 1980 model and a "standard" road style 1981 model? why can my U.S custom only manage 80mph or so whereas the road style bike will pull on to over 100mph? both bikes are in good mechanical order so whats the difference?
What's the compression like on the '80?

What are the front and rear sprocket tooth counts on both? Is the '80 revving higher for less speed?
20 mph is a huge difference. two reasons,
1. Are both engines running equally well?
2. What does the tach read on the 100 mph bike when going 80 and what does the tach read on the 80 mph bike when going 80?
2.5 What is the number of teeth on each of the sprockets respectively?

Even a few teeth in final drive ratios would not account for such a large difference in top speed. I's think it a power issue between the two engines. The tach readings should bear this out.
and you've all forgotten, the custom you are riding in the wind, standard you stick out less so less drag