Drinking like a fish

[smegballs]

Hi guys i just restricted my dow to 33bhp so i can ride it on my license. At the dyno readout is 24bhp at 8000 revs so obviously it is a quite a bit under 33. The restrictors are homemade washers in the inlet manifold and i might well file a bit more out of them. Anyway i have not rejetted of adjusted the carbs at all and i put a fiver of petrol in and the next day i was back on reserve after only about 35 miles. When my dad had the bike without restrictors he got about 60 mpg no problems. Is there any carb fiddling i should do and does anyone know of a cheap yet good set of vacum gauges for carb balancing.

[Ichy]

errr, did you check the power output before you started messing? I thought the XS put out less than 30bhp in perfect condition, probably closer to 25bhp?

When you say inlet manifold do you mean before or after the carbs?

Before the carbs you are restricting the airflow, after you are seriously messing with the combustible mixture. Either way you will need to tune to get the best performance.


There are plenty of sites on the 'net that explain how to make your own balancer. The cheap ones on ebay, while not accurate, are ok if you calibrate them to each other first. Balancing the carbs will not sort out the low MPG.

[smegballs]

my haynes told me that the was putting out aqround 39 bhp but then agen it is quite old so i doubt that it its making that. Well with my restrictors in (after the carbs, before cylinders) its only making 23.5 bhp @ 8000 rpm. I think i overdid it a bit so will probably have a go with the files later on ...

[Ichy]

https://www.bikez.com/motorcycles/yamaha_xs_400_1982.php

27hp @7000rpm

The Seca XS400 does put out about 38hp since it has a different engine. so which one you got? The seca is more angular while the standard is more cruisery.

Personally I would take out the restrictors and ride as is. The extra couple of HP, if they exist, will not make much difference.

[.Chris.]

You could always use the old 'hosepipes to ears' method to balance the carbs if you don't have a vacuum gauge.
____________________
Chris
1985 Kawasaki Z550F

[smegballs]