When I went down to the Celtic Warriors rally last week. My bike started running rough. A couple of times at low rev corners, I thought it was going to stall on me and chuck me off. On a steady throttle at higher revs, it seems to be okay. It was a bit worrying, when you're 400 miles away from home. :verysad:

When I stopped at traffic lights, it seemed to be heating up hell of a quick as well and I had to give the bike an extra few revs to get away cleanly.

I'll need to try and have a look at it this weekend but does anyone have any suggestions on where I should start looking.

Yeah, check out the engine.

No, cant help much really.  Heating up? did it start low rev crapness when it got hot or was it before?   Have you been messing with the carbs?  Stuck valves or only partially opening exhaust valves?

god there must be someone here who has a clue!

Somebody will know something. It runs reasonable well, when just started but is as rough as a badger after a couple of minutes.

Do the basics 1st Davie,

we checked the water level, but do you know if the fan works?Run it till it gets nice & hot & see if the fan kicks in.
also find the bleed valve (if fitted) & give it a bleed.
we discussed air locks, so if all else fails run it with the rad cap off & squeeze the hoses to see if any trapped air escapes.

Are the plug HT leads the OE ones? at that age they might be breaking down & shorting.
Plugs, I know they are a bastard to get at but it could just be a duff plug.

Carbs, floats ok?take the  bowls off & check for pinholes in the floats.
If all that fails then lets put our heads together & see what else we can come up with.

I'll probably try and pick up a new set of plugs at the weekend. I won't go wrong with a new set anyway. I might as well do the valve clearances as well. The front cylinders usually get neglected on the vfrs because they're the hardest one to change the plugs on. While I've got everything off to do the plugs, I'm as well doing the valves. I need a new set of feeler gauges though cos mine are crap.

It probably is the original HT leads, although I'm guessing at that.

So that's new plugs, feeler gauges and possibly HT leads. Looks like I will be working that OT at the weekend.  :cry:

Anything else to add to the list.

It could be the one of the coils dave The bike'll start ok from cold but as it heats up it'll start to run choppy my cm 125 did this on me and i must admit i just got a new coil from the breakers.
I'm not sure exactly how to check for this i'm well rusty on my leccy stuff.

That's a good shout, Rick.

Who knows how to check a coil?

Dave, from memory this...  :blush: Timing being out can cause overheating (the combustion occurring before top dead centre or some such) and that's also worth a check.

Check the coil? Take the lead that comes from the coil. Remove the end that's in the distributor cap. Hold it about 4 mm from earth (frame, possibly as I don't know a lot about bikes really) and then spin the engine. If you get lovely blue clickety flashes that are good 'n strong the coils alright.

You could also check the capacitance of it But I haven't the faintest idea what that means

Err, hang on. The VFR is PGM F-i isn't it? Or is that the 800 Dave?

I think that's on the later models. I haven't good it on mine. I don't know what capacitance is either but it sounds good.

I think its time for Zomb or ff to give a brief explanation of electrical circuits. Right guys, who was it, that posted the info on cricuits a while back.

And how do I can the timing. You need a strobe gun to do that or am I wrang? It has been known.  :blush:

Dave Be careful with this coil thing mate.
As I remember the ht lead must be attached to a plug or it can kack up the cdi also if you try holding a ht lead with you bare fingers you're gonna get a hell of a belt.
Be careful.

So what you're saying is, 'Get the wife to give me a hand'.  :eyebrow:  :O

No mate what i'm saying is get some pliers with well insulated handles and hold the ht leads firmly but not enough to cut through the insulation.
Alternatively if you can rest the plug on the top of the engine and still see the electrode while you're cranking the starter
Then thats even better.
I'm not kidding about this voltage thing if you get a belt it feels like you've been hit with a hammer.