CB900FZ DOHC smoking and spitting...

[SteveD CB500K0]

My blue FZ was running perfectly before I ran out of petrol the other day. I knocked on the door of the nearest cottage and a little old lady said "My late husband had a Triumph" (I was wearing my Triumph jacket) "we went all over Europe on it in the 30's"...

She gave me (wouldn't accept any payment) a gallon of unleaded from her lawnmower can and I started it up and rode it home. I added more fuel from my lawnmower can.

One week later it has proved impossible to start. Not even firing.

Removed all the plugs. All black and wet so cleaned them all and it struggled into life on 3 cylinders.
Number 1 chimes in every now and then but smokes heavily and backfires through the exhaust.

Any ideas?

[Spitfire]

Empty the tank, refill with clean stuff straight from the filling station in a clean can, and give it another go.

Cheers

Den

[SteveD CB500K0]

Could crap fuel really have that effect?

Works OK in the mower...   

[Bryanj]

Yeh steve but a mower isnt dohc and might even have been a 2 stroke at one point

[matthewmosse]

my thoughts exactly, sounds like your on borrowed 2 stroke oil perhaps.

[florence]

..Warning, putting two stroke mixed petrol into a four stroke can cause serious overheating because the ratio of petrol to air is greatly reduced causing the engine to run very hot.

I seized my four stroke lawn mower by running it on my chain saw petrol.  It's a 40 min round trip to get petrol here and I thought it would be ok just once to finish off the grass cutting.  I wrongly assumed it would just smoke a bit.  Luckily, once it cooled down it was ok.  I wouldn't like to treat my bike like that though.

[SteveD CB500K0]

I have a big lawn and a gallon of unleaded doesn't last long. I've certainly never put two-stroke in it!

However, who knows what the LOL (little old lady) put in her lawnmower...

[K2-K6]

This may explain it, I thought that "stale" petrol was a load of rubbish but read a really good explanation about it recently and it went something along these lines:- the aromatic part that you can smell when filling up is very volatile to aid starting etc and the base fuel that gives a lot of the energy to make power is much more resistant to firing and more stable during combustion hence a blend of the various components to give a complete fuel. When it's kept for long an an aerated container the good volatile starting component simply evaporates but if your engine was hot it should have little trouble and probably wouldn't again if you could get it running. So I doubt if any damage but just empty it and put fresh/new in to get back to where you were. The fact that the plugs are getting wet shows it's getting in there but the plugs fail to ignite it. The old fuel usually has a much heavier smell to it, more toward diesel.

Hope this helps to explain it (someone has already suggested new fuel)

[Spitfire]

Hi Steve, as suggested, the LOL could have given you either a two stroke mix, or leaded fuel, or old fuel. As also mentioned you have to remember that gasolene is not a straight run product, it is a blend of componants, light and heavy, with time the light more volatile componants will evaporate. These give you the easy starting, in fact butane can also be added to aid starting and as you can imagine this will disappear quite fast.

Cheers

Den

[SteveD CB500K0]

Thanks guys.

I was always aware of the "stale fuel" problem - but more to do with trying to start the bike once per year for an MOT and finding the carbs bunged up!

I take it this could happen in mere days?

[Spitfire]

Hi Steve, don't think it could happen that quickly (days) contained in a vehicle's fuel tank, I know that my bike gets left alone for 4-5 months and all is OK gum wise. However I do make sure that the tank is full before I lay it up, this leaves a small air/fuel interface, hopefully this reduces the evaporation and corrossion rate.

Cheers

Den

[Bryanj]

The 750/900 was the first i remember that if it stood for 2 weeks had to drain the carbs and let fresh tank fuel in but dont remember ever having to drain the tank

[notobikeparkingtax]

Just a thought, but if you ran out of petrol surely you would have sucked the mucky dregs in the tank down into the carbs ?

I realise there's a filter in the fuel tap but if it's split it would have let the carp through,,or, it might now be blocked.