HELP - only firing on 3 Cylinders! [vf500]

Hi All!

Ive been riding my VF500 for a good three years now, not a problem.

Winter has arrived and I decided to give her a full service:

Work I did sofar:

Cleaned Sump
Replaced Oil and Filter
Replaced Clutch and Break Fluid

Work I still need to do:

Replace fuel filter
Adjust Front and Rear shocks (pump up)
Replace Rear Tyre

My problem has now developed suddenly that its only firing on three cylinders!

The way i found this out was that I first realised that power was low (had to put choke full on for it idle proper), and it sounded almost like a harley
So i checked that spark leads one by one, then i got to the Rear Right cylinder, took the lead off while its idling, and noticed no difference in power, therefore that cylinder isnt firing.

I dont think its the carb, i think the CDI/Coil pack is faulty, does anyone have any two cents to add to this, any similar experiences?

Thanks in advance,

Seb.

 

You could test the coil windings, both low and hv output with a multimeter, then check the pulse generator resistance. If they're all good, the CDI box is suspect or that carb is clogged.

FSM will tell you that pulling off a plug wire while engine is running could damage a CDI, i think.

 

When I got my 700 it was running on 3. Changed the plugs and that took care of it. You didn't say if you had changed them or not.

 

I swapped the rear plugs around, didnt make a differrence. They must be at least 3 years old.

I did a second inspection: and realiseed that the "third" cyliner is firing, but it seems like the timing is off, so my bike will idle with almost full choke position. When she runs, the petrol smell is very strong.

 

Timing won't go off on one cylinder only. Inspect all 4 plugs; if one is black, probably a leaky float needle

Runs best on choke means your carbs need a proper cleaning.

 

both the rear plugs are black, i know for a fact that if i leave the fluel switch ON, then the engine floods and requires a complete oil change. Would this be due to leaky carb?

1. I have two spare carbs, should i investigate these?

2. And I have run it with and without rear mufflers to check the backpressure. But since then I have applied exhaust sealer on all pipes going into the 4-to-2 box. (will check the idling now)

3. silly me ran the engine with socks in the carbs, not sure if that will screw the carb up.

 

just posted a youtube video: VF500 idling problem

[video=youtube;WK_iMaA5IYo]http://www.youtube.com/watch?v=WK_iMaA5IYo[/video]

 

Once again I will mention fitting a fuel shutoff solonoid at least then it won't flood the motor regardless of the needles not shutting off the fuel flow

 

Thanks NormK

 

With an electric fuel pump, no fuel can flow while the engine isn't running, so no need for shutoff valve.

 

Regardless of wether fuel should or shoudn't flow through the fuel pump it obviously can because it has been the case with many motors hydrolocking or filling the sump with fuel. Can't get there anyother way than through the pump

 

Update:
I didn't do anything for the last week. Now she splutterd back to life! She has started running much smoother now, seems to be [mostly] firing on all fours and revs much better now.

New problem thou:
1. the front right exhaust pipe is ALOT cooler than the front left.
I have a feeling the spark plug is problematic, will check both front ones out this eve and update tomorrow.

 

Helps alot when wrestling with running problems to have at least one new, never used plug to substitute. Deposits that cause plugs to misfire can't be seen by eye.