Misfire - Fuel filter - Airlock ?

[Gerrit]

I was doing a carb balance today, in my ongoing quest to cure the misfire.

All went well, idled smoothly, the levels were even, and all of a sudden she started idling very rough.

I killed the motor, and then noticed that the right side filter was dry (rear cylinder).

I sucked on the vacuum hose, and as the filter filled up again I noticed airbubbles in the filter, like a (fizzy drink) coming from the carb side into the filter.....very strange.

Can it be that the use of inline filters can cause an airlock?

Or are the bubbles heat generated, the carburettor bowls soak up a lot of heat from the engine, and that the airbubbles is actually heatsoak?

Perhaps when on the move it is not so severe, but with the engine running stationary in the garage, the heat build up is more severe.

However, why would the filter have run dry in the firts place, as that is probably why I get the misfire at 8-9K rpm.

Any thoughts on this?

Gerrit

[benny hedges]

what about the breather on the carb.... is it ok and not kinked from when you put the airbox back on?
if the breather is blocked, no fuel can get in...

[Gerrit]

The breather is fine, I had the carbs off on Thursday, carbs are 100%

Gerrit

[tony.mon]

You should have positive pressure down the line from the tank due to gravity, this should maintained in the line by the float needles shutting fuel flow off when the float is high enough.

Assuming your float and needle is ok on that carb (you could try swapping them over to see if the problem moves to the other carb, but for the cost of a float needle it's probably easier just to replace it) then for some reason there isn't enough fuel running down that line to keep the float bowl filled.
Possibilities are:
Partial blockage in fuel tap
Fuel tap not allowing enough fuel to flow to one outlet
Partial blockage in fuel line
Float problem in that carb- sticking? wrong float level?

Do you ever see particle in the filters? They look pretty clean from your photo.

You could try a fuel flow comparison- remove the floats from both carbs, hook them back up to the tank, and measure how much fuel flows out of the overflows on each carb.
If the front flows more than the rear, there's a good clue that something is not right. (best not have a fag while thinking about it, though!)

But beyond that you've got me.
It might just be simpler to replace all of the pipework, tee both outlets from the tank into a fuel pump, then tee them off into each carb again. Pump needs to be on a switched live, i.e. comes on with the ignition, of course.
A cheap car fuel pump will do fine.

[Gerrit]

Thanks for the advice Tony, I will work thru your list....

Phoned Honda this morn', for needle 'n seats, & floats etc, but they do not carry stock.

The reality with biking in SA, is that as long as you have a current/popular model you are OK with spares and accesories. CBR - GSX - R1 - ZX, no problem.

I have in the past called just about every Honda dealer in SA, to talk to an experience Honda technician about my bike, "sorry sir we can assist you with current generation bikes only" obviously the PC is doing the diagnostics and the technician does basics such as oil & filter change. It really sucks, whereas you can walk into a car dealer and speak to a 60yr old mechanic, that has worked on generations of cars, the same does not apply in the biking world.

Anyway, I will source the needle & seats & floats online, even though my floats are plastic, and non adjustable, and it baffles me how the float levels could possible be incorrect, but I will replace them nontheless.

gerrit

[firestorm27]

Hi Fella hope this is of some use to you I had a similar problem she would run nice when driving sensible( thats rare for a storm rider) once you started to ride about 65-75mph it would hold back misfire and run like shite. i balanced the carbs changed the plugs and even stripped the plug caps down and measured the readings for the resistors in the caps. with no joy. i Spoke to a guy in a breakers shop in Aberdeen told him the symptoms and he said the diaphragm in the fuel tap may be split if you have a prime setting on the tap, turn it to that and that should be it if not you can bypass the vacum valve, I done that and she goes like a rocket once more. it's worth a look.
Good luck

[benny hedges]

Anyway, I will source the needle & seats & floats online, even though my floats are plastic, and non adjustable, and it baffles me how the float levels could possible be incorrect, but I will replace them nontheless.

gerrit

tbh you will wait ages and spend a fortune and probably still have the misfire - not dissing what tony suggests, just it will be cheaper to get a used set of carbs off ebay than buy individual components from honda.
it's more than likely fuel starvation as the lads suggest, check the vac lines arent perished or split, no air leaks around the carb rubbers which will decrease vacuum and affect the fuel tap diaphragm.
you can remove the diaphragm and piston inside the fuel tap but you will need to cap off the vac inlet on the tap or fuel will leak out of it.
or fit a fuel valve off a 19L tank which has no vac valve.

i had similar issues with mine, only when i ragged it, and it turned out to be the fuel pipes were twisted from where id rested the tank on the seat by turning it 180 degrees, then instead of turning it back, i turned it another 180 when i refitted it, putting a twist in the hoses.

i since changed the fuel lines from 8mm hoses to 12mm and havent had problems since.

also check the air filter isn't choked with dead flies... mine was lol, banged it out on the top of my bin and there was a pile of dead insects and shite in there... probably isnt affecting it until you demand a lot of air

[Gerrit]

Thanks for all the advice giys, way better than the zero response from Honda SA.

I worked thru Tony's list, and all is in order.

I found some additional things, the cable that bolrts onto the starter motor was totally rusted onto the bolt, I sorted this with new, lotsa voltage lost here I suppose.

I then removed the ignition switch, opened the bottom, where the wiring goes in, jeez what a mess, rusted dirty gunk, and one almost loose wire, cleaned up the lot, and I am sure more voltage save

I did however, replace the Honda Supressor caps on the spark plugs with a NGK derivative, and wow, gone is the low-end stutter, etc, It pulls from way low, in 1st -2nd 3rd ..absolutely awesome.

Went for some sunny rides this weekend...When I gently roll-on the misfire only comes in around 8,5 to 9,, however, if I just yank it open the misfire is evident as low as 7k.

I think I will open the fuel tap and and discard with the diapram, and see what happens.

Regards,
Gerrit

[tony.mon]

Getting there.......
Now, before you butcher your fuel tap, try this first:

Take any old plastic bottle, with a drinking teat on it. Energy drink sort of thing.
Rig up a piece of fuel line from this via a tee into both carbs.
Tape the bottle to the top of the tank with gaffer (duck) tape, and go for a ride.
Bear in mind that the engine will pull a vacuum form the bottle quite quickly, so you'll need to make a couple of pinholes in the topmost point to let air in.

If your misfire's gone, then butcher that fuel tap!