How to de-restrict a Suzuki VX800
Q. I have a Suzuki VX800 that pulls cleanly up to 80mph with no problem, but then seems to run into a brick wall.
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I think it could be restricted as it was brought to Britain by a merchant seaman.
How can I tell whether it is limited and if so, what can I do to free up those extra horses?
Flecherno5, MCN technical forum
A. If you look at the inlet tract you might find blanked-off portions upstream of the air-filters, cut them out to allow the air to flow freely and replace the current air-filters with original equipment filters.
You might also need to rejet the carbs. Replace the main jets with 122.5 front, 135 rear.
Check the needle heights (the clips should be on the third groove from the top).
DO NOT mix-up the needles, as front and rear are different. The jets are available through any bike shop (front is "Mikuni small round", rear is "Mikuni large round").
Then reset the mixture screws for best idle - they should be around two and a quarter turns out front, three turns out rear.
This is all assuming it's restricted that way. If not, it could have been fitted with a British-made restrictor kit, which usually involves removing the two metal washers fitted inside the inlet rubbers between the cylinder head and carbs.