Vtech Behaviour

Sorry, I am new here and scrolled the topics for a while.

I bought a 2006 model and experienced yesterday:

-after cruising 4-5000RPM and once rev. it up the power is cut off for a sec. at 6800 RPM

- 2. 3. trial, no problem, no changes in power output

-after cruising again, the previous power loss will come again

How is the bike normal behaviour? how the vetec should change? What RPM?

Or is it a seious issue, and should I go to the dealer?

The only thing I can offer with the limited information is that on an 06 6800 rpm is right at the VTEC engagement point. Seems like the transition is not going smoothly since there is a jump in power but no interruption.

You mean, I should feel some jump in the torque at 6800?

I know it is the transition point for the model till 2005.

The newer version should switch at 6500??

but anyway, my bike makes there a full interruption for a sec. Luckily I made it on the straight and alone.

Yea, unfortunately with the 6th gen right at vtec engagement there is actually a dip in both torque and power. If you roll through the engagement rpm slowly (partial throttle) it can actually seem like a noticeable interruption to power. I love my 08 but this is the one thing I dislike, you can't smoothly and slowly rev high into the range without this interruption. Ive learned to shift before this point unless Im at a large throttle opening. Here's a dyno chart of the 08 that clearly illustrates this. 

[image: Honda_VFR_Dyno_Chart.jpg]

Check to see if the O2 sensors are plugged in in the wrong order, back to front so to speak...

And  are you  anticipating  the  VTEC  and rolling  off of   the throttle.

No issues like those described on my '08 Vtec.

Vtec in at 6800rpm-ish, out at 6400rpm-ish is the norm for 06+ models. Are you sure yours is an 06+ and not an older model year with the Vtec in/out at the same revs (6800-ish)? Hovering around that rpm can cause some lagging/surging, hence they changed it on the 06+ model.

Yes, my model is 2006-so updated06+.

I made this accelerating test from 4000RPM-in 4.gear at least with 50% throttle. So it was not that smooth-slow change.

But the torque drop was complete for a sec. Luckily I was on the straight and did not fall down.

The difference: when I let the rev. down only till 5000RPM, I could not feel and hesitating, no interuption, just smooth acceleration till 7000RPM.

I will also look the O2 sensors. But it is not that easy  to see

Yes, my model is 2006-so updated06+.

I made this accelerating test from 4000RPM-in 4.gear at least with 50% throttle. So it was not that smooth-slow change.

But the torque drop was complete for a sec. Luckily I was on the straight and did not fall down.

The difference: when I let the rev. down only till 5000RPM, I could not feel and hesitating, no interuption, just smooth acceleration till 7000RPM.

I will also look the O2 sensors. But it is not that easy  to see

In that case, I'm struggling for an answer. It certainly does not happen on my Vtec, which is beautifully smooth throughout virtually the whole rev range.

Hopefully there will be someone more knowledgeable along soon to help you.

I think I had this for a while.  If memory serves, I had a bad vacuum line. Therefor, my suggestion is the usual supects, spark plugs, starter valve sync, injectors out and profesionally cleaned. Definitely check each and every vacuum line. It looks daunting under the airbox at firat, but if you spend a little time tracing each line with your finger, you should be able to get a grasp on where everything is routed. Also, check your PAIR valves and your flapper valve. Definitely check your vacuum lines. That is what handled it for me.

Yes, my model is 2006-so updated06+.

I made this accelerating test from 4000RPM-in 4.gear at least with 50% throttle. So it was not that smooth-slow change.

But the torque drop was complete for a sec. Luckily I was on the straight and did not fall down.

The difference: when I let the rev. down only till 5000RPM, I could not feel and hesitating, no interuption, just smooth acceleration till 7000RPM.

I will also look the O2 sensors. But it is not that easy  to see

For the most part, that transition is totally seamless on many bikes. I saw some harsh engagement when my 06 was new, in the first couple thousand miles. Not always but hard enough to hurt my hands, a few times it hit so hard. One time Sub 3000 miles , I was in 29 degree weather and had been riding for 25 miles or so. Accelerated hard in first to get up to speed on the highway, and the bike hit so hard , it could have broken a motor mount, I mean hard, but after about 4,000 miles, those occasional episodes disappeared. IMO never adjust the vtecs(valves) if you want to touch the standard valves okay, but avoid the vtecs., I think that's the reason mine stopped doing that after a few thousand miles.

But any fueling deficiencies can also bring out issues in that area, and an 06 with low mieage has been sitting way too much for its own longterm health with fueling.

Any 06 should have well over 100,000 miles   , you might also try disconnecting the battery so the bike recalibrates

Thanks for the hints. Today, I checked again how it is working. I accelerated below 4000rpm up to 7000rpm in each gears from 2-5. When I let the rev. down and accelerated with 50+% throttle, I could feel some change at 6800 each time. It was not that big interruption like last week, a a bit different al the time. In 2-3. gears only some chenges, in 4-5. gears some torque drop. Maybe at 75+% throttle comes some interruption.

And I have a high freq. vibration from the engine from 4000rpm+ . Above this 6800rpm, the vibration gets more.

Yes, might be aslo somehere the exhaust, I should check. But not that easy. I should remove the blastic budy w/o breaking the clips.

How can I check the vacuum lines? They can have cracks or breaks or loose connections???

How to check the PAIR and flapper valves? Do I need OBD reader (Honda)?

You do not need to remove the palstic to remove the exhaust.  Simply pull your seat and you can access the bolts holding it on with a ratchet and socket as well as a hex key.  Hex key on the bolt head outside, ratchet and socket to hold the nut still in the space under the seat.  To check the vacuum lines, you would lift and brace your tank, then remove the airbox cover, then the airbox base, via the two screws holding each venturi down.  Get a small flashlight and trace them all down and check each vacuum line end to see if there is any cracking or if any of them are loose.  The Pair valve is connected to the back of the airbox, download the service manual to see where.  The flapper valve is on top of the airbox, with a vacuum line running down to the right side of the airbox.

Go here to download the service manual: http://www.vfrdiscus...-new-cover-ocr/