VVC Not Working?

[fast al gordo]

Hi Guys

Just in the middle of a full service of a recent ebay purchase.

Whilst riding around for a few days after picking her up I noticed the following issues. She wouldn't idle below 2K RPM till really warm, there was a huge flat spot around 4K RPM and the top end was really tappity.

I've read in the manual that a tappity top end could be indicative of the engine being in HI Cam mode, unfortunantley I haven't had the opportunity to get the bike above 9k RPM so can't really tell if the VVC is working.

I've done the inlet valve clearances, which are mostly spot on, cyl 4 is a bit on the tight side though.

My question is has anyone had any experience with the VVC being in HI Mode? If so how loud was the top end and will there be a detrimental effect on the engine?

I'm hoping the exhaust clearances are just as good as the inlet side and this combined with a carb clean, new set of o-rings and balance will help with the noise and flat spot issue.

[Squishy]

I don't think it being stuck in high cam mode will damage the engine much, but it won't have good torque below the VVC range.

From your story it sounds like it's not getting enough fuel or it's running on 3 cylinders.
Start it up and (carefully) touch the exhaust pipes to be sure it's running on all 4.
If it's running on all 4, it could be a dirty jet/carb or bad spark plug.

I'm not sure what the symptoms on stuck HI mode would be on lower RPM, mine is regular model.
You can test whether VVC  is working without riding, see the manual.

Ps. are you sure you are checking against VVC valve clearances? The procedure (and clearances) are a bit different compared to regular.

[Gouraami]

I find it a lot less painful using a spray bottle with water in to see if a cylinder is down.

If you do want to touch the headers make sure to do it as quickly as possible, a slight tap.

I also don't have a VC model, so can't help you there

[fast al gordo]

I don't think it being stuck in high cam mode will damage the engine much, but it won't have good torque below the VVC range.

From your story it sounds like it's not getting enough fuel or it's running on 3 cylinders.
Start it up and (carefully) touch the exhaust pipes to be sure it's running on all 4.
If it's running on all 4, it could be a dirty jet/carb or bad spark plug.

I'm not sure what the symptoms on stuck HI mode would be on lower RPM, mine is regular model.
You can test whether VVC  is working without riding, see the manual.

Ps. are you sure you are checking against VVC valve clearances? The procedure (and clearances) are a bit different compared to regular.

Yeah, I checked the exhaust pipes after I picked it up, 40 mile trip on mostly motorways. They were all hot. However I did check them again after a short 5 mile journey and at least 1 was noticeable cooler than the others. I will look into again once everything is back together.

I was using the GSF400 manual found I on carlsalter.com and followed the guide for the 97 Variable Valve engine to do the intake clearances. I think the spec is 0.1-0.2mm and both valves need to be within 0.05mm of each other. Haven't got round to doing the exhausts yet.

[Squishy]

Yeah, on page 11-17 of that same manual you can see how to check the VVC mechanism

[fast al gordo]

Just to clarify...

Where is the right place to measure the clearances?

The pictures in the manual aren't the clearest. I get that the LO position clearance is taken between the end of the valve stem and the rocker arm and the subrocker arm clearance is taken, at well, the sub rocker arm. These are both taken when the rocker arm shaft is in the LO position?

Is the HI Position clearance taken at the same place as the subrocker arm clearance, except with rocker arm shaft set in the HI Position?

Also when doing the exhaust clearances, is the rocker arm turned in the the opposite ditections for the LO and HI positions?