Jerky at slow speeds

Hi all,

I'm Martyn from the UK. New to the forum Love all the great info.

I've not long owned a 2003 VFR800 with 11,000miles. It seems that it is very lumpy/jerky in traffic or up to about 5k RPM? I tried the PAIR and flapper mod and this improved it however feels a bit rough. Is this normal?

I also carried out a few voltage checks on the bike as it feels like its misfiring and what I noticed is that at idle I'm at 14.0v but when I rev it to 5k RPM the voltage drops to 13.8v? should the volts not go up?


Thanks.

 

The VFR is a bit rough if you lug it. Running it under 4000 rpm, the on/off throttle transition will be rough. A PCIII is supposed to help, but it also reduces MPG. I have just learned to work with the power delivery and don't see a need to install an aftermarket controller. I don't know what to make of the voltage issue. You are well above 12V, so output seems good.

Cheers.

Jose

 

Mine has done that since new when I would be just rolling along in first gear without applying any throttle in bogged down freeway traffic. I found that if I let it continue, it would really jump around so whenever it started that, I clutched and allowed room between me and the vehicle in front. Lane splitting not allowed here and would be dangerous even if it was the way the idiots drive around here with their ability to give themselves a prostate exam visually.

I don't think you are doing your bike any great favours by doing this a lot but occasionally it sure does not seem to hurt. But yes, these bikes like the higher rpms.

 

BTW. Welcome to the life!

 

I think someone suggested for you in the other forum to tune the starter valves. If the off-on throttle response is jerky, if you are cruising at 30 or 60 mph at very light throttle and the engine shakes and does not want to stay at that rpm, the problem would be the starter valves are out of synch.

Note "dogging the engine" is a different issue. The stock gearing is to enable speeds of 130 MPH. That means at the traffic light you must slip the clutch a bit. Changing sprockets can make city riding much better, but the increased RPMS lower fuel mileage and means more noise at highway speeds.

 

Welcome. As mentioned above keeping around 4k rpm helps, but also make sure your throttle is adjusted properly. Removing slack in the throttle will help with the jerkiness. My wife's VFR and my ST1300 both suffered from this jerkiness until I adjusted the throttle and removed most of the slack. This can be done at the grip so it is easy to do.

One other note practice smooth throttle control, both in rolling on and off the throttle this will go a long way to help with better riding techniques too.

 

Mine was they same way when I got my '03. Took the advice of this forum and installed a PC III, made all the difference. Keep you eyes open for a used one.

 

Thanks for all the help and advice I'll keep my eyes out for a PCIII.

 

Definitely starter valve sync, PC and hopefully a dynotune as well. The combination of these has made my '04 purr - no surges or lumps. Best money I ever spent.

 

Hi guys, I'm new to the forum having just bought an 03 VTEC and have noticed the throttle control challenges sub 4k. The PCIII seems to be highly recommended but can someone tell me what on earth it is? Cheers, Andy

 

Hi Andy, speedmerchant is a great name. People will bother you to post in the introduction forum with photos of your bike.

PC means Power Commander. This is a fuel controller from the company Dynojet. There is a specific PCIII part or PCV part for your particular, sixth generation, vehicle.

Despite the fact that many people recommend a fuel controller as a very first step, it is actually the last thing to add to the bike. It will improve response and it will increase the power in the acceleration range. However, you need to make sure the bike is running correctly first, as a well tuned bike will minimize any outstanding performance issues. I guarantee you that one or more of the following will require adjustment and will affect the performance. So perform this maintenance first:

1) Tune the starter valves

2) Adjust the throttle cable

3) A common problem on these used bikes is a stuck open thermostat, so test it and replace it if necessary. If the engine runs cool it will always run rich and not run as smoothly as it should. Start the cold bike. Put your hand on the radiator. If it slowly warms with the bike the thermostat is stuck open. Otherwise it should remain cool until the thermostat kicks in, then it should get unbearably (180°F) hot all at once. (Don't burn yourself or otherwise use an infrared thermometer.)

4) What type of riding do you do, and are you aware of which sprockets are on the bike? If you do a lot of city riding you may want to make the gearing shorter (input smaller, output larger) to get the engine RPMs up faster. The bike is geared for high speed so the stock gearing is a compromise. Now if you will be doing a great deal of high speed riding, then stock gearing may be fine for you.

5) Adjust the chain. For longevity all of the recommendations here indicate that the chain should be towards the loose end of the specification.

6) Do you know the history of the spark plugs? Old plugs can affect response dramatically.

7) You should go through the brakes thoroughly. If they are binding your on/off throttle control will be affected, in addition to having low mileage and overheated, ineffective brakes.

8) Thoroughly inspect all of the vacuum hoses for loose hoses or physical damage.

Guys if I missed anything from all of your recommendations please chime in.

You may know that when doing slow speed maneuvers it helps particularly to drag the rear brake slightly. This takes up the slack in the drivetrain.

When this standard maintenance is all done you will have minimized any jerkiness. You can then buy a PCIII or PCV, load a stock map that matches your exhaust, or get a map from someone here who has dynoe'd a bike with a similar setup, and that will perfect the performance. There is a user on this and vfrdiscussion who promotes the Rapid Bike system as having more capability. More people have the PC which makes it easy to swap maps, but it is not necessarily better. It is the most common fuel controller so people tend to be comfortable with it where they speak the same language in supporting each other.

 

Knight Great write up. I always do this general maintenance prior to spending any money. This also will give you an introduction to your bike and how to do things your self.

Also on the topic of dragging the rear brake a slow speed. This is trail braking and should be done in-conjunction with using the friction zone on the clutch and throttle control. Sometimes this is referred to as the slow race. When you get this mastered a rider should be able to go 3 to 5 mph in traffic without feet down and without any jerkiness.

 

It is not often we see two newbies make their first post in the same thread - so welcome to Pymzola and Speedmerchant. :welcome:


When you get time please swing by the "introductions" forum and say hi to the rest of the folks on here - and add a photo of your VFR if you don't want folks raggin on you.

:focus:

I am not entirely convinced there is anything actually wrong with your bike! I note that both of you own early versions of the vtec models, so I am not entirely surprised by the Jerky behaviour which you describe. This nervous power output was precisely why Honda basically tweeked the vtec engagement/disengagement points for the later 2006+ vtec models to give far better manners especially in busy traffic.

Honda realised that because the extra valves on the early vtecs engage/disengage at 6,800 RPM this could result in rather on-off power output if the revs selected by the rider were at or very close to the engagement threshold. Depending on the riders choice of gear this on-off behaviour could occur unexpectedly when riding in heavy traffic and even a tiny move on the throttle might result in a rider being caught out if the RPM crossed the vtec engagement threshold resulting in the bike making a sudden lunge at the vehicle in front.

On the 2006+ VFRs the extra valves engage at 6,400 rpm and disengage at 6,100 rpm. That 300 rpm change may not sound much but is enough to ensure the power output for the bike was more predictable.

So some suggestions:

1 - when riding in traffic leave a bigger gap in front of you - at least until you get more familiar with your VFR.

2 - when riding in traffic choose a gear which will ensure you remain either well above or below the vtec threshold. Personally I would choose to drop down enough gears to keep the bike well above the vtec engagement point, that way you will hear the v4 howl and have full power available whenever an opportunity to overtake appears.

3 - get out and ride the bike. The more you ride the sooner you will become accustomed to its power delivery and know precisely when the bike is going to launch towards the horizon.

:vtr2:

Have fun and take care.




SkiMad

 

Welcome aboard.

I didn't see that anyone commented on your Voltage issue. While you may not have issues, here is a link to the standard testing procedure, specifically post #9. It is odd that your volts are going down when RPMs are going up.

http://vfrworld.com/forums/showthread.php/39277-How-to-fix-common-regulator-Stator-failures

 

No, you actually just described the operational indication of a perfectly healthy Rectifier/Regulator.

At idle the bike's rotor-stator AC power production is relatively low so the Regulator part of the R/R isn't having to work that hard (or even at all). But as the RPMs increase and the stator's power production rises the Regulator has to begin shunting the excess voltage to ground. The old R/Rs used thyristors to shunt excess to ground while the new R/Rs use the more efficient/accurate MOSFET technology.

Your VFR's R/R is doing a good job, holding voltage to 13.8. This is the system voltage level that insures the longest battery life.

When the old thyristor type R/Rs begin to fail it's the ability to shunt the excess off to ground that is lost. As this failure mode progresses the bike's system voltage rises to a point were the battery gets chronically overcharged and ruined.

 

Regarding your complaint about the bike being "jerky" at low speed:

Could it be that the feeling you're getting is purely driveline related? Could it be that there's excessive "lash" in the driveline?

Like most chain driven motorcycles the VFR has a cush-drive in the rear hub. As the bike ages the rubber pieces of the cush-drive shrink/deform leaving more room than the manufacturer intended. If your VFR has a loosened up cush drive plus a chain that's even slightly out of adjustment toward the loose side you could have a lot of jerkiness in off-and-on throttle situations.

With other bikes I've owned it's commonplace to "shim the cush-drive" with pieces of thin, hard plastic material (I used pieces of a thin, roll-up cutting board).







Shimming the cush-drive and insuring the chain is properly adjusted will rule out a purely driveline-related cause for your "jerkiness".

 

Now that is an interesting shim device. Never seen that one done before.

 

Greg thank you for putting this on my radar! New knowledge. I read up and see recommendations to replace this rubber at 10-year intervals (Comments? Does the rubber/internal hub heat up dramatically?). These pieces are still available for many of these bikes. In that case just use OEM parts right? Your shim is for when parts are N/A right?

 

On one of my bikes, a 2005 Kawasaki EX250, the owner community has discovered that ordering the OEM replacement cush-drive rubber pieces gives bad results. We don't know if the OEM replacement cush-drives are badly reproduced parts or if they've aged-out while sitting in shelf stock or whatever, but guys with loose cush-drives were replacing with new OEM cush-drives and getting no improvement. So we've settled on shimming them up as a solution, and I can tell you that shimming is very effective.

Also, the old rubber pieces of the cush-drive usually don't show any wear or look bad or messed up, they simply seem to shrink or deform a bit over time which introduces "lash" or jerkiness into the driveline.

So it's a case of the OEM replacement part still being available but it doesn't fix the problem.

 

A worn out drive chain that has a series of loose-then-tight spots can contribute to a jerky feeling.

If you adjust the chain you need to find the tightest spot and set proper tension there.