Jkson

You are welcome! Few days ago I repeated official and mine way. Just to be sure, one more time. It is definitely smoother and bike has more torque on low rpm, with #3 and 4# more vacuum.

Yeah, most of us read it as dropped down, less vacuum. And it is very common issue with VFR 800 any generations - hesitations, surging, jerky on small throttle opening. Many, many topics about it. When vacuum is ajusted lower or even flat, 3rd and 4th cylinders have lean mixture. Its a reason why PAIR blocking helps a bit. Because PAIR allow to intake a bit fresh air into cylinders from exhaust port. When you block it, you make your mixture reacher on idle and low revs.

Hi there! I know, its a bit strange to find incorrect procedure in workshop manual 22 years later. But no one did it, and I want to share my story now. According to 5th gen manual, 3rd cylinder vacuum pressure should be dropped to 20mm compare to 1st. Most of us read it as dropped DOWN, and translated manuals have it mentioned as LESS vacuum for 3rd and 4th. When I got my bike, it had flat sync for all cylinders. I did full maintenance some time later, through workshop manual, include starter valves synchronization. In very first day after, I noticed some surging when low throttle, it was a bit twitchy during city riding. Very uncomfortable to keep some speed at low throttle opening. Most of internet discussions about nervous VFR had tips about PAIR blocking and other redneck mods. Some of them suggested to always keep revs over 4k, because VFR doesn't love low revs... That's true, but I had very smooth bike before maintenance, even on very low RPM. First - I adjusted flat sync back. It helped me a lot, motorcycle became very friendly again. Then I did it opposite to manual. It means 3rd cylinder adjusted to 20mm MORE vacuum than 1st, and 4th 10mm more than 1st. And the bike is smooth as butter. Even better than flat, and MUCH smoother than official way. From here I want to explain why it helped. In service manual for 5th gen, they showed fuel injection diagrams. It has independent maps for each cylinder. On these graphs you can see - 3rd cylinder get lowest fuel portion, 4th a bit more, and 1+2 even more. I checked it with injector opening time frames. Diagrams are true, 3rd cylinder has less fuel than 1st on idle. For same mix ratio, fuel/air, we should feed less air into 3rd cylinder. It means we need close starter valve a bit, as result we will have MORE vacuum. It looks like they forgot to explain, what means "dropped". If your vacuum gauge has movement from right (0) to left, more vacuum will drop indicator down... If it is gravity meter, less vacuum will drop level down. There is no right description, more or less vacuum you should set with word "dropped". I'm pretty sure, they had some problems with that description, and maybe complains about flat is working better than described way. And finally they removed it from manual for next generations... P.S. I installed ABS brake system to my 5th gen VFR, with very minor modifications. If it would be interested - let me know)