I have a '91 VFR with 60K miles. Went on a recent trip and everything was running fine. About 3 hours in (after filling up at a questionable station) I started getting some stuttering. While cruising at a steady speed and then giving it a bit of gas the stuttering will start. Feels like its running on 3 cylinders. If I give it plenty of gas the stuttering quickly disappears. Thought I'd gotten some bad gas but after draining the carbs multiple times and finally draining the tank and filling up with non ethanol it still happens. I've run about 7 tanks of gas thru it since it started. Weird thing though is it won't happen when the bike is cold. Only after riding for about 15 minutes. I've changed the plugs, checked on the coils and wires (one wire was out of spec and was replaced). I can feel the stuttering even while cruising although at a steady speed it's not bad. I feel it most when trying to accelerate out of a turn. It stumbles for a moment before clearing itself. It's really evident between 3K and 5K rpms. Under hard acceleration I don't feel anything wrong.
How old is your battery?
Misfires/stuttering can be caused by a battery not giving enough juice to your ignition system to produce a good spark at the plugs.....
This sounds more like a carb problem to me, maybe a float height issue? Have a look at the CV Carb Tuning notes on the FactoryPro website: http://www.factorypr...pm_engines.html.
But don't ask me why this would come on after fuelling up! Unless you got a bit of grit stuck in a float valve so it doesn't hold the level correctly.
come on now!!.. if your problem started after filling up with new gas.. DRAIN YOUR TANK!!. ALL OF IT!!
( keep it just in case its not the problem..)
add a quart of new gas.. slosh around.. and dump that too!
fill with a gallon of new gas.. go for a quick ride.. problem solved???
if yes.. fill it up!!
if no.. then you clean your carbs.
I DID drain the tank as I stated. And the carbs have been drained 5 times. I think it was just a coincidence that it happened shortly after filling up.
I was with Don right after this started, we went to my house house and drained the tank completely, drained the carbs several times before that and when we drained the tank. Filled up with 90 octane ethanol free fuel and it was still there. I rode his bike on the road and if you rode the bike hard it was less noticeable, seems like it got better for a while, then it would get worse again.
The fact that it is good for a few miles when the bike is cold, then show up makes me think electrical, but I guess it could be a cracked carb boot or the vacuum port for syncing the carbs being open.
Don rides the bike often, so I don't think it is a case of the bike sitting too long.
Finally got around to working on it a bit more. Replaced all 4 spark plugs, replaced a questionable plug cap, swapped all 4 coils for used ones. And guess what?! After 15 miles the bike got warm and the stuttering reappeared.................sigh.
ok.. run the bike till it gets warm and starts to stutter then spray some starting fluid at the intake boots.. there may be a leak that shows up after the boots get warm..
I would bet it is spark plug wires that are breaking down at part throttle openings ,have had this a lot in cars with light acceleration pain to do but replace one at a time to find the bad one or ones ,for some reason voltage is maxed out at these lean openings and will emphasize the wire break down with a stutter ,will not do it cold because of the richer mixture . Hope this helps .
I sympathise with you. This sort of problem is a real pain. I have a1990 VFR but fortunately haven't experienced this.
However, if I did, I would be trying to isolate to electrical or fueling.
To completely eliminate a bad fuel problem, can you rig up a gravity fed supply from a bottle. This may also help in doing tests while on the centrestand (I hope you have one).
Some things I would try are - (not necessarily in this order):
- disconnecting each spark plug in turn to try to find out whether it is a particular cylinder.
- check that the choke is fully off (my bike stalls if the choke is left on, particularly at low revs which is consistent with your problem occurring at low revs).
- check that the fuel pump doing its job (mine has just had to be replaced).
Others may be able to add to this list.
So, I start the bike tonight with full choke and spray carb cleaner around each carb boot. Each spray resulted in the the engine idling down. With the bike warmed up it and no choke it was nowhere near as evident but still there.
Pair has been removed but your instructions don't get into the charcoal canister, PCV and associated vacuum lines. I'd love for you to explain to me what to do with the rest.
Pair has been removed but your instructions don't get into the charcoal canister, PCV and associated vacuum lines. I'd love for you to explain to me what to do with the rest.
rip that crap off!!!
the big tubes tube are gas over flow lines.. replace them with some thin clear line and rout them down under the bike.
the thin tubes too to be vac lines. cap them off and the problem disappears
did you down load the manual for the non cali model? follow the gas line routing. very simple :fing02:
Pair has been removed but your instructions don't get into the charcoal canister, PCV and associated vacuum lines. I'd love for you to explain to me what to do with the rest.
rip that crap off!!!
the big tubes tube are gas over flow lines.. replace them with some thin clear line and rout them down under the bike.
the thin tubes too to be vac lines. cap them off and the problem disappears
did you down load the manual for the non cali model? follow the gas line routing. very simple :fing02:
Well, I ripped that crap off!! Plugged any vacuum lines. It now runs even worse. Just cruising along the bike does nothing but surge constantly loading and unloading. Medium to full acceleration is great.
you should have NO vacuum lines left!! 4 screws in the intake manifolds.. thats it.
then a tube from the gastank for over flow to behind the motor.. connects to nothing...
follow the non cali vent line pic in the manual.
did you tighten the boots ?
Had one vacuum line going to the ASV (?) behind the steering head. Blocked it off because I can't get to the end at the carbs.
What non-california vent line pic are you talking about? I don't see that in the manual.
Boots are tight. With the choke at halfway I can spray carb cleaner at the boot(s) and it definitely affects the idle. When not using the choke it's not very noticeable.
so to repeat it it one more time... remove vac ports # 1,2,3,4 in the cali pic.. replace with a screw..
detach # 6 hose to evap control. and toss it,, ditto for all evap crap and remove the remainind PAIR stuff if you havent already.. plug the or weld up the pair tubes..
I had a really bad cutout issue on my 5th gen that ended up being the kickstand kill switch. Just jump the harness side connector and see if that helps.
Hell idk haha. I never saw that on the site or heard about it when I was researching my issue. It just hit me as the possible culprit while thinking about it in the shop one day after I got my bike on the road after sitting for a few months during its build.
Well, I've finally gotten motivated to get at the problem again.
Took the carbs off and gave them a thorough cleaning. Remounted them and checked for leaks and this time there seems to be none. Took it out for a ride and still getting the same sputtering as before after it got hot. When I got home I got to thinking about it and realized I had an infrared temp gun. Got it out and the front left was at about 200 degrees and the other 3 were well over 400. Changed out that plug wire and started it back up. That cylinder didn't change but the rear right cylinder suddenly dropped to about 200 and the bike started running terribly. I could rev it up and the right rear temps would slowly come up but the front left would max out at about 250. The front right and left rear at idle hovered around 500 and would rise as the bike was revved up.
At this point I'm wondering if the ECM is having issues. Anyone with anymore guesses?
Got back to working on it today. Took the carbs back out to check float height. They were a little low but nothing terrible. Put it back together and the front left cylinder is still dead. Only about 125 degrees compared to over 600 for the other 3. Took out the spark plug and it was black. Swapped it with one of the rears which was a light grey and the same thing, front left still dead. Swapped out the coil, plug wire and cap and still no change. I even have a second ecu and pulse generators that I swapped out and no change.
Any ideas? I'm pretty convinced that one cylinder is not firing or not firing well but I can't figure out why.
I haven't re-read the whole thread... Have you tried pulling the plug wire from the bad cylinder, attach it to a spare plug, ground that plug to the frame or engine, and hit the starter and check for spark?
I haven't re-read the whole thread... Have you tried pulling the plug wire from the bad cylinder, attach it to a spare plug, ground that plug to the frame or engine, and hit the starter and check for spark
Yes, I had. Thought it looked weak so I decided to look again tonight. Looks fine. So, I'm back to thinking............carbs? Just don't know what else to check.
End of thread · 39 posts recoveredWayback Machine snapshot 18 Jul 2015
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