Shudder Off Idle Releasing the Clutch

Hi guys,

I bought my 99 vfr last May, and with your collective help repaired the brakes and got it back on the road. Since then, my brother rode it on our Lake Superior circle trip, approximately 2000 miles and it did great!

But we both noticed something annoying about it. When releasing the clutch to accelerate from a stop or near stop, the bike will shudder. It kinda feels like when you lug an engine, that shudder/studder just before it stalls. But it doesn't stall, it does the shake thing then continues on as normal. I’ve started revving it up more and riding the clutch to get past that. Even so, it will still studder a little bit.

I’ve done the usual tune up, oil change, air filter, spark plugs. It’s currently got about 25,000 miles. I haven’t cracked into the engine to check the valves and have no real plans to. Aside from this odd issue it runs great! When I bought it, the previous owner told me it had a big bore kit. I have no way to confirm or deny that, but it does not have a tuner (Power Commander etc.).

I’m wondering, would the big bore kit without a tune cause this off idle stumble?

If so, would the simplest solution be to install a tuner?

I should add, the bike is plenty fast! I’m not looking for an excuse to slap on a Power Commander. I’m wanting to solve this specific rideability problem and hoping for an “off the self” solution.

Thanks for your input!

 

Have you considered that you might just need a new clutch, possibly including the steel plates?

 

Should take it to a tuner, rolling road dyno of some sort. Sure there is someone around your neck of the woods, you in FL? Other point, after you get into 4, 5 and get up into triple digits, does it hold or does it slip?

 

Captain, I know I'm talking WAY out of my knowledge base here but, isn't that the purpose of the "Jutter Spring"? If that "Gen" even has one.
If not... What is the purpose of the jutter spring??

 

Honestly no, the thought never crossed my mind. But you're right its the obvious place to start!
The shaking does kinda feel like when I had a burned up and warped flywheel in my old F150.

I'm in Southwest Michigan, I don't know of any tuners local.
I've never noticed any clutch slip, I'll pay more attention as I ride it this weekend.

 

When you eliminate the judder spring installing an aftermarket clutch kit it doesn't mean you're then gonna get shuddering when releasing the clutch lever. It was something Honda did to try and get a little more refinement out of the clutch action.

A clutch the shudders pretty bad when engaging doesn't automatically mean it's a clutch that is slipping.

If you don't know the whole history of the bike, how how it's been ridden or if the clutch has ever been replaced, it's the first place I would start. Have to eliminate the kinda-on-the-nose, easiest and cheapest candidate first. And if that's not it, it probably wasn't a terrible thing to do on a new-to-you bike anyway.

 

On my high mileage 91 750, I replaced all the components, steels, fibres and springs, all OEM stuff. At 120 mph, I could feel maybe a difference, barely. There are measurements in the bible but by the time you remove all the kit, your better off just replacing all the stuff. I want to say, at 120 up to 140 or so, I did feel a difference but this was a number of years ago.

I don't know how you could have a big bore kit on a nikel-cilled cylinder any way, I know they bore them and re-coat them, but you need to reflash the ECU etc. In your case, I don't even know if your black box could be reflashed, I am still an analog guy. Just food for thought.

 

So... you're saying your off idle shudder was slightly better at 120 mph?

 

No, That would make your name Captain Obvious, (pun intended) What I was trying to explain was a clutch where I myself decided to replace the clutch pack with new parts and did not notice a discernible difference.

On my particular bike, I had no judder or shudder, I really had no issues but since I got parts at 10% above dealer cost, I did it. What I found out was that the only difference was at uber high speeds, remember I am married to this bike and know when it farts wrong. I never measured the old parts btw, I have another bikes where switching to heavier springs helped the over all feel of the clutch lever, but never had a judder on that bike either. I do have a judder on my Kia Soul with the 6 speed on occasions.

I got a new OEM fuel line for one of my gen3 bikes a while back, I was surprised that I could in fact get one, sent a message to you and never heard back, good to see your alive and well. Cheers.

 

Sorry I failed to repsond to your message, it must have slipped thru with some other messages. Pretty sure I don't have a record of not responding.

And I sincerely apologize for what was supposed to be a friendly jab that came across as a smart ass dis. And I see why. Poor judgement.

Cheers to you too.

 

Thanks guys!

I'm planning on doing a bunch of work to it this winter anyway. I'll add new clutch to the list.

 

how about checking the master cylinder and clutch slave? clean master and use new DOT 4, etc. Simpler than doing the whole tuner thing, do the simple things first right?

 

Didn't say so in the first post, but I rebuild both the clutch slave and master cylinders this spring. I put on a 6th clutch master hoping to have more control over the shuddering and not stall as often. It works ok, the pull is much lighter and it gives a much bigger friction zone. But the clutch bites right at the bar, so its still a little touchy.

This part should probably be a separate thread, but I also NEED new tires. Does anyone have experience running a 180/60 on the rear? Is there any reason not to do it?

 

Now everything goes out the window.

 

If it were a particular kind of "big bore kit", I'd make you an offer for the bike and fix the judder myself, lol.

Pardon a short thread hijack to explain why...

There were two big bore kits available for this bike way back in the late '90s/early '00s, both offered in North America by Brian Law of Dynamo Humm in Canada. The simpler one was just a set of larger JE pistons/rings/pins, originally commissioned by TTS in the UK and re-sold by Brian. I have one of these kits, which I have never installed:





(The used piston in these photos is from my '93 VFR750FP, but it is very similar to the OEM VFR800Fi piston.)

IINM, these pistons could be installed in a re-bored RC46 engine case, but they didn't increase the engine's displacement very much--only up to 837cc--the same as they did in my VFR750. Not really worth the cost and effort to install, especially given the alleged difficulty in finding any machine shops able to properly re-bore the VFR engine cases. (Brian used to mention that many "regular" automotive machine shops had messed up the job, but I never understood exactly why it was supposed to have been so challenging.) Living in the UK at the time, I had Richard Albans at TTS install big bore kits in both my VFR750 and VFR400--simply because I could.

Which brings us to the other kind of VFR800 big bore kit! Brian developed his own big bore kit (also using JE pistons), but in order to get any meaningful displacement increase he had to use sleeves and re-bore the engine case to accommodate them. This was the legendary 870cc Dynamo Humm big bore kit. I don't know how many he sold, but there used to be a few running around the US and Canada. Also not a huge jump in power, but with tuning it should have at least been noticeable.

The only other VFR big bore "kit" I'm aware of was developed by someone in New Zealand, using CBR900RR pistons, IIRC. It was detailed on VFRD a while ago, and I don't know how successful he was. I suppose, given that the various versions of the Fireblade used pistons ranging from 70mm to 75mm in diameter (OEM VFR800 pistons were 72mm in diameter), and Honda's penchant for using interchangeable parts, that would mean that there are OEM "big bore" pistons theoretically available from Honda. That the pistons from a CBR could be used in a modified VFR engine wouldn't surprise me. I believe the NC30 and NC29 (VFR400R and CBR400RR) shared their OEM pistons, for example.

Unfortunately, it wouldn't be very easy to tell if your engine had one of these big bore kits or not, without taking a head off. A borescope could tell you if you had JE pistons or OEM, but not which ones. Good luck with your clutch!

Ciao,

JZH

 

Nice write up, I talked to the doode from Dynamo-humm back aboot 30 years ago I guess. Oh, the good old days.