Low revs mis-fire, bike unridable

[MikeN]

Hi Everyone

After a bit of help again with same problem, still not fixed! I had CCTs done(in May, stopper mod). Rode away and bike was great, better than ever. After about 10-15 miles I pulled in a garage (Shell) and filled up with normal unleaded.
I rode on up the road about a mile and developed a horrendous misfire at low revs. Bike still sings at high revs but on tick-over and low revs it is missing badly. Bike bucks about somuch I had to lurch it on corners to avoid being unseated!
That day the carbs were stripped down and cleaned and the hoses etc all checked and all fine. Have checked plugs for obvious signs of problems and seem fine(1998 storm with only 4500 miles on clock).
Have since drained tank of fuel(fuel was a slight yellow colour for some reason) and re-filled with fresh unleaded and run through, to no avail, problem still seems as bad.
If anybody has any pointers where best to start checking next I would be so grateful as feeling a bit dejected now!! :-(
A mechanic friend of mine has had a listen to bike on tickover and has suggested that one cylinder seems to stop firing and suggested maybe an electrical fault(coils??)

Any advice appreciated

Mike

[VTRDark]

I would start with making sure the vacuum hose has been connected in the right place on the fuel tank http://www.vtr1000.org/phpBB3/viewtopic ... se#p218127 It's a common mistake that can cause these problems and costs nothing to check and rule out.

(:-})

[MikeN]

Checked that, mine seems to have a modified part without the bottom nipple??

Thanks for checking tho

Mike

[MacV2]

I would start buy letting us all know whereabouts in this fine country of ours you reside, then maybe someone who is local can have a look & listen, may be even swaps some bits over to see if you can isolate the fault.

[tony.mon]

The clue might be that it's only got 4500 miles on it.
I'd think about rechecking the carbs, petrol tap diaphragm, carb diaphragms and of course all of the jets.

What do the plugs look like?
The colour is often a good indicator.

[MikeN]

Hi Tony, yes it's me again, forgot old password so had to re-join with new ID.

For info I'm based on Isle of Sheppy in Kent.

Spark Plugs checked by mechanic friend and deemed in good nick( as we established before I'm not particularly mechanically minded!)

So strip down/clean of carbs would be best bet again on where to start now?? I presume you suggest this in case old fuel/muck from tank still in there??

Sorry if dumb question

Mike

[VTRDark]

Before you go stripping the carbs out, lets make sure your vacuum is all connected properly.

mine seems to have a modified part without the bottom nipple??

Have you had a later model tank fitted Can you get a pic of the tank connections? I suspect something has not been connected back up correctly after the carbs where put back on.

(:-})

[MikeN]

Hi Cybercarl, have checked it again earlier this evening to be certain and looked at the pics on other threads and all is well.
The pipe work was checked by tony.mon so I'm very confident it is okay.

Will try carbs etc again as this has not been done since fuel was drained and run through.

Thanks for the suggestions so far.…

Mike

[tony.mon]

AH, I know who you are now...

Yes, this was an odd occurrence.
The stopper mod was fine, and the bike ran perfectly.
After riding halfway home, I got a call saying it was misfiring following a fuel refill.
I rode out and met Mike at his dad's place and spent a couple of hours checking what had occurred, rode it myself and it was definitely misfiring, but couldn't find anything wrong with the pipework, connections, jets, stripped the carbs right down, etc etc.
All we had left to try was to run a fresh tank of fuel through it, in case it was contaminated.

So I left Mike to do that, and this is the first I've heard from him
I can't remember now which cylinder it was, or both....

I'd suggest trying swapping over the coils, swap plugs, and if that doesn't cure it, swap over the ECU and igniter boxes.

But the pipework is definitely ok, and in the right places.

[MikeN]

Hi Tony

Yes it's me!! Had a nightmare work schedule so have lost the summer(what there was of it) and only just started looking at it again.
As I said at the time I can't thank you enough for your efforts on the day, you came miles out of your way to help me and I really appreciated that as we knew the problem was unrelated to the work you had done.
Do you think In this case I should skip the carb clean then and check out the electrical possibilities?
Mechanic friend suggested that one cylinder only was miss firing - worth trying coils next?? Perhaps swap to see if other one miss fires?

Mike

[tony.mon]

Just carefully put your hand near the exhaust pipes form a cold start, and see which one gets warm and which one stays cold.
But as I recall they both got warm.

Try swapping coils, or borrowing another set from someone.

And it's not unrideable, you wuss!
It just misfires a bit.

[MikeN]

It is for a part timer like me!!

If you stand at back of bike, exhaust on left comes from miss firing cylinder I'm being told??

Mike

[tony.mon]

Doesn't as the exhausts join together in the middle section.
They don't run separately from one cylinder to one can.

The left one always runs with condensation for longer, and has a harder pulse of gas coming out.
They all do that, Sir!

[MikeN]

That foils that plan then!! Told you I was useless with mechanics!!

Will see if can figure out if it is just one that is miss firing and then try coils first, watch this space!!

Mike

[tony.mon]

You can't just swap the coils over, as the leads are different lengths. But you can bolt them to a nearby useful bolt, a frame one is best, and just fit them temporarily.

But the favourite is to borrow a spare set of coils from someone who has fitted stick coils.....