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.

[F5 Dave]

Golly 15.3 seems pretty high, I guess if it is kept no higher than that with the light off then the regulator must still be working. What about with light off? No higher I would hope.

It used to be they were reigned in at about 13.7 & if they went higher then they were kafunk. I was surprised my RF sits at 14.5, so maybe they have bumped them to 15.3 but I’d expect the battery to get a hard time at that voltage & the occasional bulb to blow. Incidentally the high wattage bulb in a bike with a relatively puny alternator is a bit tasking on the system. On an 80s Suzuki that would prove certain doom to the alternator which would take the battery & rectifier with it, with the rectifier gone the voltage would spike up high enough to kill the ignition. Oh joy.

[Motu]

That charge voltage sounds way too high,turn the lights out and see what it's putting in - 14.75v is the max you want to see.I'd say your rec/reg has failed,the excess voltage may have killed one or two CDI units.The rev counter will be triggered by one cyls ign pulse...sounds like it's firing erraticaly,which makes the rev counter leap up and down.

[edit] oops,too slow on the typing again..still,two similar diagnosis may be confirmation?

[louisb]

The manual say 14.5 - 15.5 volts at 3000rpm. Which does sound pretty high...

[thepilot]

I had a similar problem with my ZXR250C last week, it had the same power loss when you gave it any revs and the tacho was going bezerk. Funnily enough when the brakes were engaged it fixed the problem, as it was generating a new earth to the chassis. Hence i rewired the earth lead from the batt to the engine block and had the battery load tested and charged and it runs like new. So i suggest at least testing to make sure you have a good earth to the frame, and get the battery tested. Not running, the battery should read above 12.5V with a standard digital multimeter.

NB: the Ninja charging voltage is 14 ~ 15V.

[vifferman]

Golly 15.3 seems pretty high, I guess if it is kept no higher than that with the light off then the regulator must still be working. What about with light off? No higher I would hope.

It used to be they were reigned in at about 13.7 & if they went higher then they were kafunk. I was surprised my RF sits at 14.5, so maybe they have bumped them to 15.3 but I’d expect the battery to get a hard time at that voltage & the occasional bulb to blow. Incidentally the high wattage bulb in a bike with a relatively puny alternator is a bit tasking on the system. On an 80s Suzuki that would prove certain doom to the alternator which would take the battery & rectifier with it, with the rectifier gone the voltage would spike up high enough to kill the ignition. Oh joy.
While it sounds like a lot, it's not uncommon. My VFR with a new battery and brand-new, rewired heavy-duty R/R put out that much. And the high-wattage bulbs make things better, as they suck current that the R/R doesn't have to bleed off as heat (through the resistors). Just make sure the connectors to the bulb are good, and that it's using a relay, as any corrosion in connectors, thin wires in the circuit etc. will cause too much heat due to the current flow, and things could melt and/or burn.

thepilot's suggestion about checking the earth(s) is a very good one, anda not uncommon source of electrical problems.

[Devil]

I had similar problems a while ago and they were centered around the starter solenoid. Bad connections made the tacho read way too high, then made the bike gurgle and eventually die. Check out the connections around there, assuming thats where your main fuse is.

[F5 Dave]

High wattage bulbs in a bike that has a grunty alternator ok. In a small bike I would be concerned.

On my RF it was losing ~ 0.8V between the battery & the (std wattage but 50% brighter type) bulb. With a relay it got the whole lot.

[vifferman]

High wattage bulbs in a bike that has a grunty alternator ok. In a small bike I would be concerned.

On my RF it was losing ~ 0.8V between the battery & the (std wattage but 50% brighter type) bulb. With a relay it got the whole lot.
True - I forgot it was a 250.
However, I ran a 130/90W headlamp in my VF500 (not a huge alternator, I bet) for several years, and had no electrical problems (apart from some idiot leaving the ignition in "P" instead of "OFF"). I had the same battery in it from July 1994 to when I sold it (early 2000?) But like you, I ran a relay, with large gauge wires to the battery. Incidentally, using a realy for the horn(s) makes a HUGE difference to their effectiveness. Bikes have wiring that is way too light.

[louisb]

Ok. current situation. Last night i tested everything i could find. pulse generators, alternator, regulator, charging voltage, coil and spark lead resistance... I even re-soldered all joints in the CDI!

Still going like a dog, and seems to be missing now!

Next thing to do is change the headlight back to the original and try and find all earth points, clean and retighten...

I was going to buy a replacement CDI but at $150 i am a little reluctant as it could be anything.

[louisb]

After re-checking everything on the bike again, including reconnecting and checking the earths, i've decided that it can either be the CDI or the coils.

So does anyone know where i can get a replacement CDI for the spada?

Buckets n Bits (welly) are not answering there phone.

[F5 Dave]

Try after lunch, sometimes goes out in mornings.

[louisb]

Thanks Dave.

[louisb]

After replacing the CDI unit $150 later... Still exactly the same.

Only just idles and when you rev it it takes ages to speed up and has virtually only enough power to move the bike while reving the shit out of it and riding the clutch.

Next thing to replace is the coils... this could get expensive. :(

If anyone has any other ideas... i'll take em.

[F5 Dave]

So do both pipes get hot at the same time from cold, or does one take longer to get hot?

[Motu]

Throwing parts at it is not a good diagnostic proceedure - find the fault and fix that,much cheaper.

[cantridetosavemylife]

check the rear tyre pressure and make sure that the seat is dry, i have never owned one of these but that would be my guess :woohoo:

[louisb]

Who's this Joker...

Anyway back to the problem at hand. I've booked the bike into TSS... Hopefully they find the problem and it isn't too expensive.

Anyone wanna buy a perfectly good CDI unit... :(

[FROSTY]

Dude Im sorry I diddnt see this sooner--I have the same bike and had the EXACT same problem.
Short version--you have blocked filters INSIDE your carbs -blowing air into em aint gonna fix it

Long version
Remove the carbs -pain in the ass jobe but not overly complicated
Tank off top of airbox off -6 screws-2 semi hidden at front of airbox. unscrew bottom of airbox from carb set. -4 screws.
loosen off 2 top hoseclips on carb inlet rubbers.
Pull the carbs up and slightly back
Turn carbs upside down.
DO THIS 1 CARB AT A TIME
undo 3 screws hold float bowls on.
remove float bowl -
you will find a float like a loo cistern inside pivoting off of a 2cmx3mm pin
knock the pin out sideways and GENTLY remove the float and needle jet
using a 10mm socket remove the jet seat under it.
Be carefull not to loose the washer on the bottom of it.
When you remove this you will see a mesh filter on the end of it which will be all gunged up with shite. You can pull this off of the end of the jet. Blow it out with compressed air. and possibly a liuttle bit of petrol
Whilst in there remove the 2 jets--the pilot u remove with a screwdriver the main youll need a 8mm socket. Down the sides of these are tiny little holes you should at the correct angle be able to see light through all these holes.
If not clean em out.
I would blow compressed air all through all the orifices I can see in the carbs especially down the inlet tract.
Once youve done this put the whole plot back together making sure the inlet needle is in place
Ill put a heap of mooolah on the table that this fixes ya problem

[louisb]

Thanks Frosty, it bloody worked!!

There was heaps of crap... bits of rust from the rusty tank. Exactly as frosy said.

Now it goes like a beauty.

I'm riding again. woohoo.

[FROSTY]

Thatll cost ya a beer young fella

[louisb]

Yep. no worries. Definately saved me some money.