Hesitation, Stumbling, And Occasional Surging - What Are We Missing?

[Laney]

Maybe my memory's fading, but I remember my '02 VFR being fairly smooth throughout the throttle range. And he had ALL the electrical gremlins that were associated with the harness recall!

Now I I have an '09 VFR - new to me in April - with (only!) 7200 miles on it. It starts quickly and runs pretty smoothly a lot of the time. Does the 40 mile round trip to work and back daily. But - when accelerating from a stop, or opening the throttle back up after it's closed, it often hesitates, then surges when it catches. Parking lot speeds just suck. At times, when I start it, I have to give it gas very gradually or it stalls, and this is more noticeable in the afternoon leaving work in 80+ degree weather than in the morning when it's cooler.

We've sync'd the starter valves (and rechecked), marbled the pair valve, and replaced the plugs. The plugs had only 5800 miles of use, but looked like they had over 30k on them. Adjusted the wax motor, then returned it to the original setting when that made no change. Air cleaner looks great, battery is a brand new Shorai. It's had Sea Foam run through it for two tanks of gas in a row. The throttle cables were lubed with Dri-Slide. The previous owner didn't ride it much, but it was garaged and well cared for -

When we sync'd the starter valves the first time, the vacuum line to #3 was not connected - at the time, the bike had 5500 miles on it. When we went through the starter valve sync, and the bike still had the air cleaner off, etc., the throttle was awesomely smooth, both times, and again today when we took it all back apart to see if we'd left something loose or disconnected. After everything's reassembled, the bike briefly runs really well, but then degrades. The hesitation, stumble, and surge come back.

So - what are we missing? Maybe it just likes its tank in the air and the air box removed?

[vfrurknee]

Laney,

Have you completely drained the gas tank? I got some bad gas on a road trip several years ago and it took a long time and several tanks of ethanol free gas to clear up the issues. Also might be a thermostat issue or MAP sensor. Is the "running" temp normal? Like 175-195 when moving? And what kind of gas mileage are you getting?

[zRoYz]

Fuelling issues can be very intermittent at times, I don't have a solution as you seem to have already started a process of elimination doing the basics first. As your problem tends to come & go but come off throttle back on throttle low rpm I would inspect the 02 sensors just do the resistor trick & remove them from the system as a test, your cat could also for some reason be overly restricted which will also effect 02 sensors which really only effect low rpm which is your problem area. You may even need to remove the injectors & have them flow tested.

[Laney]

Laney,

Have you completely drained the gas tank? I got some bad gas on a road trip several years ago and it took a long time and several tanks of ethanol free gas to clear up the issues. Also might be a thermostat issue or MAP sensor. Is the "running" temp normal? Like 175-195 when moving? And what kind of gas mileage are you getting?

Good questions - I haven't drained the tank, but there's been almost 2k miles since I started riding it and realized the problem wasn't me not adjusting to a "new" bike. Since then, I've run two full tanks with Sea Foam, and at least 32 gallons more after, all Premium (91 octane in CA). Could bad gas still be a problem? I see temps in that range, a little lower in the early mornings, and a little higher on the streets on hotter days. I get an average around 40 mpg - which seems lower than I remember getting with the '02 I had, but it's 7 years later, and in CA they're probably putting more crap in the gas now than they were back then.

Fuelling issues can be very intermittent at times, I don't have a solution as you seem to have already started a process of elimination doing the basics first. As your problem tends to come & go but come off throttle back on throttle low rpm I would inspect the 02 sensors just do the resistor trick & remove them from the system as a test, your cat could also for some reason be overly restricted which will also effect 02 sensors which really only effect low rpm which is your problem area. You may even need to remove the injectors & have them flow tested.

II think bypassing the 02 sensors with resistors is next, but in reading different posts on the effects of doing that, there seems to be some that say it affects low speed and others who say it will only affect freeway speeds. It can't hurt to try either way, I just need to dig out the 330 ohm resistors from wherever I put them in the garage. And take some plastic off... :smile2:

[Dedofnite]

Hi Laney,

Sounds a lot like the thermostat. Not sure what you meant by plugs looking like 30,000 miles. Were the electrodes eroded, or did the plugs look black and sooty? The thermo is a cheap and easy fix. If it's bad, your bike will take longer to warm up on cold starts, and stall or run rough on warm starts because the FI is confused and runs it too rich, also decreasing your gas mileage. A new one wouldn't hurt after 5 years anyway, and you eliminate one possibility.

Ded

[Laney]

Hi Laney,

Sounds a lot like the thermostat. Not sure what you meant by plugs looking like 30,000 miles. Were the electrodes eroded, or did the plugs look black and sooty? The thermo is a cheap and easy fix. If it's bad, your bike will take longer to warm up on cold starts, and stall or run rough on warm starts because the FI is confused and runs it too rich, also decreasing your gas mileage. A new one wouldn't hurt after 5 years anyway, and you eliminate one possibility.

Ded

Replacing the thermostat sounds painful but worthwhile. We're installing new tires this weekend (truthfully: he is installing, I clean wheels and balance ) and I guess the following weekend will be the thermostat. It'll be worthwhile to take the time to check everything else as we go along. And I'll probably take the time to install some "real" horns so I can share my opinion of cagers who can't see motorcycles and try to take my lane while I'm in it.

Oddly enough, on the way home from work today he ran flawlessly. He probably heard me say I was going to ride the other bike starting tomorrow until the new tires showed up! :laugh2:

[vfrurknee]

Save yourself some money and run the 86-87 octane fuel, best if you can find ethanol free. Hope you get it sorted out soon.

[Cogswell]

Since you've covered many of the bases already, I'm going to go out on a limb a little bit. The EPA is mandating fuel mixtures very close to a 'perfect' 14.7:1 to keep emissions in check. An injector(s) that are not delivering the calibrated amount of fuel when commanded by the ECU can result in a lean condition. The holes in the injectors are incredibly small and it doesn't take much to alter what they can flow. Since the mixture is already on the "ragged edge" of being lean, any change in flow ends up being noticed, especially at lower RPM's coming off light throttle settings. I have had a PCIII installed with O2 elim's on my '08 since new and was at times was still having the same issue you are. At about 10,000 miles I pulled all 4 injectors and sent them to RC Engineering to have them professionally cleaned and bench flowed. The report I got back showed that prior to cleaning 3 had "good" flow patterns and 1 "fair". After cleaning all 4 were "excellent". I was surprised that I would have 1 with only "fair" with just 10,000 miles on the clock. I talked to their tech support - they said that's not uncommon, even on very new injectors with even fewer miles. Bikes sit a lot (mine sat at the dealer for 2 years before I bought it) which gives them a lot of time for gas to degrade and create issues. Ever since my stumbling / surging issues have completely disappeared. Like you, I had run Seafoam and all sorts of cleaner through the tank to no effect. IMO there's no substitute for having injectors in pristine operating condition. My guess is that many of these types of issues end up being blamed on all sorts of things when at the heart of it is partially or even slightly impaired fuel delivery.

That may or may not be the issue you're experiencing, but it's still good maintenance, and it's not all that difficult a job - it may sound intimidating, but it's just "plug and play". I disconnected the fuel line at the tank so I could set it aside, but you really don't even need to do that - just flip the tank over and set it on something. If you do remove the tank, you can siphon virtually all the fuel out by propping it up first. Getting the airbox off is probably the worst part of the job - once that's done the injectors are removed very easily on a 6th gen - just follow the manual. Be sure to stuff rags in the intake runners once the air cleaner is removed so you don't get debris down in to the engine. The O-rings need a small amount of light oil on them when re-installing the injectors. The cost was $25 per injector - IMO a bargain considering how nicely it runs now.

YMMV.

Cheers

[Duc2V4]

Gogswell, RC Engineering is located here in So Cal, correct? Torrance I think.

[1TallTXn]

I found your thread searching for solutions for my '02 doing much the same thing.

I've put 4+ thermostats in mine. It still runs a little cooler than I remember it, but at least it's mostly staying at operating temp.

If yours is getting to ~170F in <5min of idling after a cold start, you're probably fine on the T-stat.

I just pulled up RC Engineerings website and I don't see anything about an injector service listed. Is that something i need to call them for?
http://www.rceng.com/

[Willy]

Their cleaning service is listed on the left side of their home page. It's $24 per injector with 1 day turn around time.

I think I'm going to try this. My 6th gen has about 20K miles on it now. I have a PCV and Autotune. It runs excellent - only minor surging. Stock was a handful at low speed and in throttle transition in turns. The PCV and Autotune did the trick, but I'm due for starter valves synch and other maintenance. While in there I think I'll pull the injectors and send them In - their service sounds thorough and does not cost a fortune.

Laney that snatching to some degree seems inherent. I highly recommend a PCV.

Ernie

[Duc2V4]

Laney, I have a PCV that I have not installed yet, if you want to try it before you buy one, just to make sure it fixes the issue(s), just send me a PM. I'd be happy to loan it to you for a while.

[Cogswell]

Gogswell, RC Engineering is located here in So Cal, correct? Torrance I think.

Yes, that's it.

[Laney]

That may or may not be the issue you're experiencing, but it's still good maintenance,

YMMV.

Cheers

I agree, and thanks for describing the process! It doesn't sound like it's adding much to the process of replacing the thermostat. Since the prior owner was in Denver, this bike did sit idle over 5 winters, and only averaged 1100 miles a year before I brought it home.

Laney, I have a PCV that I have not installed yet, if you want to try it before you buy one, just to make sure it fixes the issue(s), just send me a PM. I'd be happy to loan it to you for a while.

Thank you, that's really a great offer, and I'd love to try it, but - reality is that you'll probably have it installed before we get the disassembly/injector cleaning/thermostat install/reassembly finished. There's also two tires to be installed, and an oil change on the list. I'd guess it'll be a few weekends before we wrap everything up. On the bright side, the bike's been really well maintained and is extremely clean, so there's less chance of surprises in taking things apart.

If you're tied up for a while and really don't get to install it... I'll post when this is over and you can jump in if the offer's still there. :smile2:

Anybody tried the G2 Throttle Tamer? I'm curious - but definitely going to invest in cleaning injectors before anything else gets added -

[Duc2V4]

Laney, I have a PCV that I have not installed yet, if you want to try it before you buy one, just to make sure it fixes the issue(s), just send me a PM. I'd be happy to loan it to you for a while.

Thank you, that's really a great offer, and I'd love to try it, but - reality is that you'll probably have it installed before we get the disassembly/injector cleaning/thermostat install/reassembly finished. There's also two tires to be installed, and an oil change on the list. I'd guess it'll be a few weekends before we wrap everything up. On the bright side, the bike's been really well maintained and is extremely clean, so there's less chance of surprises in taking things apart.

If you're tied up for a while and really don't get to install it... I'll post when this is over and you can jump in if the offer's still there. :smile2:

Anybody tried the G2 Throttle Tamer? I'm curious - but definitely going to invest in cleaning injectors before anything else gets added -

To be honest, you'll be done well before I get this installed. It is intended for my 5 Gen but I wasn't going to be installing it until I changed the headers & exhaust. Which won't be happening any time real soon as I'll be waiting to see how the HiPerform headers turn out. So just let me know...

Cheers!

[Cogswell]

That may or may not be the issue you're experiencing, but it's still good maintenance,

YMMV.

Cheers

I agree, and thanks for describing the process! It doesn't sound like it's adding much to the process of replacing the thermostat. Since the prior owner was in Denver, this bike did sit idle over 5 winters, and only averaged 1100 miles a year before I brought it home.

Laney, I have a PCV that I have not installed yet, if you want to try it before you buy one, just to make sure it fixes the issue(s), just send me a PM. I'd be happy to loan it to you for a while.

Thank you, that's really a great offer, and I'd love to try it, but - reality is that you'll probably have it installed before we get the disassembly/injector cleaning/thermostat install/reassembly finished. There's also two tires to be installed, and an oil change on the list. I'd guess it'll be a few weekends before we wrap everything up. On the bright side, the bike's been really well maintained and is extremely clean, so there's less chance of surprises in taking things apart.

If you're tied up for a while and really don't get to install it... I'll post when this is over and you can jump in if the offer's still there. :smile2:

Anybody tried the G2 Throttle Tamer? I'm curious - but definitely going to invest in cleaning injectors before anything else gets added -

For sure - if you've got the thermostat out, you already have the airbox removed, so removing the injectors is just 4 small bolts securing the fuel rail to the manifold and lifting it off - piece of cake. RC will replace 2 of the 3 O-rings on the injectors. I kept the ones with me that have square edges and cushion the injector against the fuel rail - they said they didn't have those, and I did not want to lose them. RC will replace the 2 with round edges so don't worry about those. I highly recommend taking a good number of photographs and labeling where all the hoses on the airbox go and how everything is configured - makes re-assembly much easier. Also, the air horns each have their own position and that should be noted for each - I used some tape to keep them in place and oriented correctly. If you do decide to remove the tank, there is a crush washer sealing the banjo bolt to the tank on the high pressure hose. Be sure to replace it and follow the torque spec for it - it's sealing in fuel pressurized to at least 35 psi right beneath the rider's crotch and on top of the rear headers - not an ideal place for a leak! While you're in there, if you were going to remove the PAIR system, this would be the ideal time to do it.

You still may find that you want a Power Commander even after doing this - as I mentioned, I've been running a PC III since new, so I don't have a direct comparison as to how it ran without it, clean injectors or not. It may be a combination of both - but it can't hurt to try one at a time until you get the desired result. Best of luck on it and tell us how it comes out!

Cheers

[Rush2112]

That may or may not be the issue you're experiencing, but it's still good maintenance,

YMMV.

Cheers

I agree, and thanks for describing the process! It doesn't sound like it's adding much to the process of replacing the thermostat. Since the prior owner was in Denver, this bike did sit idle over 5 winters, and only averaged 1100 miles a year before I brought it home.

Laney, I have a PCV that I have not installed yet, if you want to try it before you buy one, just to make sure it fixes the issue(s), just send me a PM. I'd be happy to loan it to you for a while.

Thank you, that's really a great offer, and I'd love to try it, but - reality is that you'll probably have it installed before we get the disassembly/injector cleaning/thermostat install/reassembly finished. There's also two tires to be installed, and an oil change on the list. I'd guess it'll be a few weekends before we wrap everything up. On the bright side, the bike's been really well maintained and is extremely clean, so there's less chance of surprises in taking things apart.

If you're tied up for a while and really don't get to install it... I'll post when this is over and you can jump in if the offer's still there. :smile2:

Anybody tried the G2 Throttle Tamer? I'm curious - but definitely going to invest in cleaning injectors before anything else gets added -

Hi Laney,

I have the G2 throttle tamer on my 5th gen and really like it. I have a screw in my right wrist and and the G2 made small adjustments at partial throttle openings much smoother for me...

[Laney]

Hi Laney,

I have the G2 throttle tamer on my 5th gen and really like it. I have a screw in my right wrist and and the G2 made small adjustments at partial throttle openings much smoother for me...

The Throttle Tamer's on the backup list if the thermostat and injector cleaning don't make much of a difference. I'm kind of optimistic that the injector cleaning is likely to make the most noticeable change, and I'm ready to get the wrenches out and get started. :smile2:

It won't really get started until the weekend after this one though.

[zRoYz]

Thermostat problem very easy to diagnose without having to pull your bike apart, the only parts to remove are one side fairing so you have access to one radiator. Start your bike from cold & fell the radiator it wont start feeling warm till your temp gauge is around 70-80C (don't feel neck at filler cap that will warm up) if you can get access to a laser thermometer for an exact reading all the better. The radiators bypass when thermostat closed reason they should stay cold till temp gauge is in range above, if they start to feel warm before that range you have coolant flowing past thermostat.

My bike doesn't get great fuel economy & motor operating bellow above range can cause that but my thermostat is operating perfectly, I also don't have fuel leaking pressure reg which is other cause. I do use high rpm when I ride because don't commute bike is for fun & don't really mind low fuel mileage it's just friends bikes seem to do allot better with same motor mods. I run a PC with dyno map but even with zero map using default ECU mapping my mileage is no better. It is the main reason I haven't fitted the Torro charger sitting in my garage because I don't want to be stopping large amounts of times on long trips filling up with petrol as my ride buddies would get annoyed.

The thing is my bike runs & goes very well (pulls like a train) & the only thing I have left to see if there can be an improvement is have the injectors flow & spray pattern tested, so the meaning of all this none relevant information is each VFR can have it's own idiosyncrasies.

I would put money on a fix for your bikes problem but not legal for emissions & that is remove the cat, my bike every now & then had hesitation & surging on/off throttle, fitted Motad headers & haven't experienced that problem since. Without hesitation I would say out of every mod my bike has except suspension the cat removal changed the bike the most for the better, doing pair valve block off plates, flapper mod, 02 eliminators, after market cans, pc with dyno did nothing to fix the problem like removing the cat did. The other mods helped in small ways to limit the problem but removing the cat fixed the problem completely.

[spud786]

Yeah, before you go to the trouble of replacing the thermostat, is the one in there behaving right? Typically bikes take a long time to warm fully, and fail to hold a normalized temperature. You should be at full temp within a mile and a half off a cold start , and even in sub freezing temps it should not drop below 160 degrees (ever).

[spud786]

On a side note my chevy Colorado, at 125,000 miles, at times idle would fluctuate and almost stall, and would stumble sometimes taking off from idle. I had firestone do their injector cleaning, where they take a wire brush and scrub the carbon out of the throttle bodies, and I assume the injectors are scrubbed also, but It was well worth the money, no more issue. I was very happy, enough to also get my wifes rav 4 done also.

Now on the vfr they have a brown moly coating on the throttle body plates, so you don't want to damage that, but if pulling the throttle body, id look in there to see if carbon build up. around the injector areas, and the venturies.

[Antics72]

Laney, I've just finished reading your troubleshooting process. I believe you are on the right track, except for the thermostat. The thermostat has absolutely nothing to with your problem, and is an absolute pita. The thermo will not effect fuelling in any way whatsoever. It is purely to do with warmup time and running temps, save yourself a lot of hassle and forget about the thermo.

Fwiw I would definitely go down the injector cleaning path, not additives, physical cleaning by a reputable expert.

As has been previously mentioned, the thermo is very easy to check. Start the bike, switch to engine temp, and watch. As it reaches around 65-70ish © watch closely and you should see the temp decrease by about 6-10 degrees, then slowly climb, then drop, and so on. This is signifying the thermostat opening or cycling to get to, and maintain the optimum temp.

Hope this is of some help/explanation.

Ant.

[klrtovfr]

you can try the 99 blackbird fpr from the other thread. It will make it run richer getting rid of that surge.

[joemaniaci]

I have the same issue down in low RPMs on a 2004 that doesn't even have 10,000 miles on it. Going to do the flapper, pair and snorkel mod as seen here tomorrow.

[joemaniaci]

Did all three to my bike, and like others, it is a completely new bike. Louder, smoother, throatier, more fun. There is still a little bit of hesitation down low, but mostly gone.