crazy ignition problem; misfires - VF1000F

crazy ignition problem; misfires - VF1000F SOLVED

Hi!

New user here. Hello! Excuse my bad english......

I bought my VF1000F 84´ 8 years ago. Since then it rests in my garage. Has 12k miles on the clock.

I decided to bring the bike back to the road last year (december). Because it´s in good condition, I thought its an easy job; unfortunately not.

Last year I checked everything; changed all wear parts, compression, checked valve timing and lash, the wiring harness for bad connections (alternator plug was lighty grilled), cleaned the carbs and the tank. So, it starts right on first try at the time and runs good. That was five month ago......

So, yesterday I filled the tank, installed the new, fully charged battery and..... nothing except a very weak starter turning the engine very slow. WTH?
Ok, I had an RC36 starter siting around, easy enough to change; 15 minutes later a push on the starter turns the engine now fast enough. Jobs done - not.

One ear-shredering BOOM! Massive exhaust misfire.

Roughly 1 sec after releasing the starter-buttom, it misfires in to the exhaust; There is no signs of combustion while cranking. I can smell fuel out of the exhaust. Only misfires as describded after releasing the starter buttom.

I pulled the plugs, checked for spark. There is spark on all cylinders. And it sparks once at the same time on all cylinders short after releasing the starter buttom and the fuel pump turns for one ignition event.

I don´t think thats correct. I pulled the clutch cover and all looks good. Ignition pickups are in place with correct gap and wiring should be ok. Wiring to the ignition-units are fine. Grounds are ok and cleaned.

I have done nothing to the bike in these five month...mysterious.


What can that be?

Thanks!

 

The sparks you see are fat, blue, and crackely, right, not weak and orange. Remember that plugs may spark OK out of the bike but fail under cylinder compression.

Could be a battery problem (anything much less than about 12.6v), not sufficient voltage. Check it with a meter and check the charging system output too. Some batteries can show good voltage but not have enough cranking amps to power both the high-draw starter and the ignition system too. Coils may have rusted, dirty ground contacts. A STARTING BOOM MAY WORK ITSELF OUT AFTER SOME MILES OF RIDING. If you let the bike sit for 5 months with fuel in the carbs, you could have some idle jet clogging, one cause of a starting BOOM.

 

Yes, has a strong visible spark. Tested with the stock battery and a big car battery.

But "not sufficient voltage during cranking" sounds good. Will check wiring harness again ......:mad-new:

 

short the fuel pump relay so the carbs are full then try again.

 

Always a good idea if the bike hasn't been started for awhile, yes. :smile-new:

 

Carbs are connected directly to a external fuel tank bypassing the fuel pump.

 

ReSeat all connectors involved (Pickups, Coils and Ignition Boxes). They corrode after 30 years.
Its unclear if your bike actually "ran". I had a IGN Box fail (rear cylinders) and it still started, but ran real rough.
Couldn't belive it would run on 2 front cylinders.
I repair'd the IGN box by opening it up (need hair dryer to soften the glue, pull on heat sink with pliers) and re-soldered the Wire Pins;

Also found one IGN box had water in it, still worked.
Good Luck

 

Hi all!

Ok, done some work on the bike today.
Again, checked voltage drop on all connectors while cranking. OK. All connectors looking good; found no corrosion.

@VF1000fe

Yes, bike rans fine last year and (smile) 8 years ago. On all cylinders with good idle, no smoke etc.
I will check the TCI-boxes.

 

Ok, both TCI-units are open, only one shown. Re-soldered the wire pins, looked around the components - but none of them had cold solder points.

 

While you have it open, it wouldn't hurt to Flow the solder on the 3 FET pins.
The FET is always Heating up/Cooling down.
The solder cracks are hard to see, must use a magnifier.
If in doubt just solder it.
ReSeat all Fuses. ReSeat all Connectors under Dash.

 

Ok, will do this tommorow.

 

Update:

All connectors behind the dash, near the coolant cap and around the front cylinders are in good shape. Pickup wiring and resistance of the pickups matches the workshop-manual.

Another try to start the engine today - funny enough BOOM! Not a single sign of combustion during cranking. And the starter spins the engine fast enough.

The engine gets fuel; and I tried spraying brake cleaner right in to the carbs. Works on all (one more lol) of my bikes after sitting a good time.

BTW, I drained the fuel out of the carbs 5 months ago, so there was no old fuel in the carbs.

Summary:


- bike starts last year (december) immediately
- no misfire
- original starter turns the engine like it should

and now, sitting 5 month in a dry garage without doing anything on it:

- original starter turns the engine very slow
- does not start
- misfires 1-2 secs after relasing the starter buttom in to the exhaust plus sparks on all four cylinders
at the same time and fuel pump starts for a second (with and without spark plugs in place)

I have changed or exchanged or checked the following parts in dec 2015:

- new carb rubbers and carbs ultrasonic cleaned and fuel level inspection plus a carb sync
- oil, spark plugs, brakes, new battery, tires etc.
- valve lash and timing
- compression - like new

I have changed or exchanged or checked the following parts this week:

- new (ugly red) non-resistance ignition wire with NGK 5k ohm spark plug caps. 23k ohm between the secondary coil windings with spark plug caps in place. Primary igintion coil resistance 3,2 ohm.
- RC36 starter
- ground connections - OK
- starter relay - OK
- starter cable - OK
- all connectors checked for resistance - OK
- TCI units resolder
- checked fuse holder for corossion - OK



IMHO, even with bad valve timing, wrong ignition timing etc, it should not fire once after the engine is turned off.

I will do a ignition timing test with a timing light tonight.
If everything comes out ok, I try a "push start" tommorow. If the engine fires instantly, there is some sort of BIG resistance - big voltage drop somewhere or these TCI are faulty - or I have gremlin lodgers in my house.

And next time I wear ear-plugs. What did you say? :wink:

 

I´m back :wink:

During my ignition timing test and while cranking, something starts to smell.

And I found this:



Spark plugs were grounded correct while testing timing.

 

The problem is electrical, this is indicated by the BOOM as you release the start button, increased voltage going into the coils for a split second. One way to test would be using 2 batteries one directly to the starter and the other one to the ignition, bit of messing around to set it up but you seem capable enough to get that sorted. It won't tell you where the problem is but will point you in a direction

 

Looks like power was ON the Coil all the time, cooked it.
That would happen if the FET is shorted. Best way to test the FET is to Ohm it after removal from the board.
I've replaced a few of those FETs, think I might have a spare.
If not available, equivalents are beefier and they are cheap.

Bad Grounds also cause Weird Problems. Check for Corroded GND at Frame Ground near rear of Gas Tank (2 Green Wires).
A Coil builds a magnetic field when power goes thru it, when power stops, the magnetic field collapses (12 times faster than when building) and that's when the spark happens.
Makes sense that you get the spark when Key Off.

 

Hi all!

Problem solved.

I desoldered both D1113, open circuit between C-E; should be ok. Hmm. Something else on BOTH circuit boards must be faulty.

Anyway, two "new" TCI-units and two coils later, engine started immediately. Funny, both old blown coils meassure still ok.
No idea why it starts glorious in dec 2015, and month later both TCI-units are grilled... Maybe a voltage-spike? Bad ground? My fault?

Hopefully old lady is on the road in two weeks or so. I am really eager :smug:

BTW, I cleaned the rims with soapy water yesterday. They have ugly blueish stains. :confusion: What's this?

Thanks for the help folks!

 

Good Deal, so it was the TCI box(s).
Reactive Loads (Inductive, Capacitive) are hard on Solid States.
A solder crack will damage them, can be so small ya can't see'em.
Wouldn't hurt to "flow" the solder on your "new" boxes FETs and Wire Pins, just to keep ahead of it.
I had a box "fail" over winter, worked when I put it away, was dead in the Spring,,..
+12V and GND are common to both boxes, maybe trace those wires, could still be a fault somewhere.
Reseating the boxes connectors may have been a fix.
You can examine and test the old boxes now, get them working as spares.