748 misfiring.....
 

After spending some time on an m900 and 900ss I decided to get a 748 - so I now have a misfiring 748 which is driving me nuts.

The misfire only appears to happen after I've used around 90 miles worth of fuel then the misfire kicks in - won't rev and sounds very sick. Changed the plugs, drained the tank and replaced the filter - all fuel lines look ok / no kinks, breather is clear. It starts first prod from cold and will restart even after the misfire kicks in. Refilling the tank appears to solve the problem - until the fuel level gets down to around the same point....... any ideas?

Thanks G.

Don't go below that fuel level? ;)

Sounds like you may have a split in the fuel supply hose which is getting air into the line. While the split is in fuel, it will continue to pump without problem as it will be sucking fuel in. Once the fuel level drops below the split it will be sucking in air from the tank and not fuel.

Take the pump out and check the connections to make sure they're secure and that you haven't got any splits. Worst case scenario is to buy some fuel hose off ebay and replace the lot to be sure - shouldn't cost you more than a tenner.

misfire
 

Thanks for that - yeah, I did consider just regarding the 90 mile mark as a reduced tank range. :lol:

Looks like it's out with the pump / filter assembly again this weekend. Cheers G.

Don't moan, that's more than I get from my Hyper! ;)

Make sure that you get fuel hose that can live with being submerged in petrol, some can't and degrade.

thanks - probably would have missed that!!

748 still misbehaving......
 

:mad:

OK, after another week of trying most things within my limited technical ability -

New plugs
Fuel pump out - replaced filter, checked all hoses and connnections (all sound.)
Blown through breather pipe - all clear.
Added some injector cleaner to fuel but no difference.
No rust or rubbish in the tank.

It is now misfiring sometimes with a full tank - but it is still intermittent. Go for 70 miles without a hitch then just won't rev - feels like it's suffering from a kinked fuel hose or blocked breather - but all checked and all clear.

Starts perfectly and ticks over nicely - and may start off ok, but other times starts coughing and spluttering not long after setting off....

Any other ideas welcome (or I may throw in the towel and get someone who knows what they're doing to look at it :confused: )

Could be the pump itself and it may be getting worse, one of the reasons they mount a smaller pump in the tank is the petrol acts as a coolant, so when the fuel level is low the pump could be warming up and stuggling, this warmer weather lately could rais the temp of the coolant(petrol) and cause the issue to arise earlier