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Help Solve My Stuttering............


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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.

Any ideas?

Thanks

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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.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_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.

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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.

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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.

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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.

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sorry about that i had a looooooonnngg day..
and posted at 1 am after being up for 40 hours..

i will pm a link.. check your vacuum lines or remove them as the link shows..

check the wires to the coil and just change your spark plugs for the hell of it..

on sat did a bike that had 4 hand tight plugs.. :mellow:

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  • 3 weeks later...

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.

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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..

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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 .

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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.

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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.

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New boots are around $10 a piece. A small price to pay..............

Also found a vacuum hose on the right front cylinder that's at it's end. Almost collapsing on itself.

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New boots are around $10 a piece. A small price to pay..............

Also found a vacuum hose on the right front cylinder that's at it's end. Almost collapsing on itself.

dude dude dude!! :mellow:

did you not read the PM i sent you?

it shows you how to remove all that crap with a vacuum lines and pair system.. :beer:

re read it and trash the pair system before you buy new boots. .

http://www.vfrdiscussion.com/forum/index.php/topic/62756-how-to-busted-stud-removal/

follow the wiring part is further down the thread, it WILL save your ass. i pasted it to this one as Miquels purge wiped out tons of tips.

also check your bike HOW TO REMOVE THE PAIR SYSTEM..aka the emission control that makes the exhaust pop..

same thread!

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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.

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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:

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