Tacho Fast and Serious Lack of Power

[louisb]

My VT250 is doing bad things.

The Tacho is reading about twice the actual rpm... which i think is indicative of a more serious problem. lack of power and seems to die if i gun it.

I've had problems before with a major lack of power, and ive fixed it by blasting carby/throttle body cleaner through the carbs and draining the bowls.

Does anyone know what could cause this...? i'm suspecting either the pulse generator or the spark unit.

[onearmedbandit]

I had one a few years back, first bike after my accident. Fueling was a problem on mine, and as you've had similar problems, I'd be looking there. Can't offer much more help though, as I fluked my repair by removing and re-installing the petcock assembly.

[louisb]

Yeah, I removed the petcock right after i bought it. It still dosent work properly, the off position does nothing!

[onearmedbandit]

I'd be definately checking over the fuel system then, from what you've said so far it would be my first approach.

[louisb]

But what's with the tacho reading crazy? it's only just started doing it. the fuel system has been problematic all along.

[ZorsT]

the tacho reads crazy on mine when the battery is flat, could be a coincidence?

[louisb]

Nah...maybe... the battery seems fine. starts no worries. sit's there with the 100w lowbeam on while engine isn't running for ages.

It's gotta be one of those really expensive electronic black boxes

Or an bad earth somewhere...

[onearmedbandit]

No expensive black boxes on your bike. Tacho would be pulse driven, very simple. I would disconnect the rev counter if it's concerning you, and sort the fueling out first.

[louisb]

After cleaning out the carbs again i took it for a ride.

It's actually worse than ever. it's back firing while going downhill...which to me means that it's getting enough fuel it's just not burning it. it'll only just get up our hill and you've got to rev the shit out of it.

It's got to be the spark unit, pulse generator or the coils.

[F5 Dave]

When I first red tacho showing loads of revs & slow I first thought I wonder if the clutch is slipping, but most people would work that out.

For a start the simple stuff as you may have more than one problem. I’d change the plugs & measure the resistance of the plug caps &/or just change them. A cheap meter from Dick Smith will run you ~$20. While you are at it check the charging voltage & see that with the lights on & revving the voltage doesn’t sag below 12.5V yet also doesn’t exceed 15V.

Funnily enough I followed a backfiring VT250 down the Rimatukas yesterday afternoon. Though it was an older model, please tell me it wasn’t you. This guy was keen on rubbing himself out with idiotic overtaking way over his head & tailgating a 748 & several cars stupidly close.

As your written thread is quite articulate I’m sure it can’t be you.

[vifferman]

I have a suspicion that the tacho runs off the ignition, so that would fit in with the backfiring and general misbehaving.

[louisb]

When I first red tacho showing loads of revs & slow I first thought I wonder if the clutch is slipping, but most people would work that out.

For a start the simple stuff as you may have more than one problem. I’d change the plugs & measure the resistance of the plug caps &/or just change them. A cheap meter from Dick Smith will run you ~$20. While you are at it check the charging voltage & see that with the lights on & revving the voltage doesn’t sag below 12.5V yet also doesn’t exceed 15V.

Funnily enough I followed a backfiring VT250 down the Rimatukas yesterday afternoon. Though it was an older model, please tell me it wasn’t you. This guy was keen on rubbing himself out with idiotic overtaking way over his head & tailgating a 748 & several cars stupidly close.

As your written thread is quite articulate I’m sure it can’t be you.

Hey Dave... Nope that wasn't me. I don't think the spada would have made it UP the takas yesterday.

I've got the manual and have tested the resistance of the leads and the coils and they are pretty close to specs... It's hard to detect if the coils are breaking down under load but that's what it feels like, It'll start and run just fine but as soon as you load it up it just dies.

Still it could be the CDI ('spark unit' says Honda) or the pulse generators.

I'm getting sick of walking everwhere.

[louisb]

I have a suspicion that the tacho runs off the ignition, so that would fit in with the backfiring and general misbehaving.

Yes your right.. it's conected to the coils and the spark unit.

i just hope it's one problem not two.

[F5 Dave]

It is always hard to say in these situations as it could be several things. But vibration & heat do affect coils like the pulse coils which determine when the spark is timed. My old CBX pulse coils failed immediately with a big ‘bang’! Going fine one second, stopped at side of road the next.

But intermittent is possible. You have checked the battery voltage under load yes? If it was falling low that would cause bad running. You could try running the bike at night to see if the HT leads or caps were tracking. Does one cylinder pipe stay colder than the other indicating one side is a prob?

But ignition coils could be an issue as well. You haven't replaced the HT leads with silicone car types or anything?

[louisb]

I've tested the charging voltage. it sits at about 15.3v at about 3000rpm with headlight on (100w halogen). and dosen't go up when reved higher than that.

It has the original HT leads...i think.

Ok. I'll start it up tonight and see if there is any spark earthing. It dosen't seem like it's missing.