After driving the paso for about 30 km it starts backfiring and cutting out.

Shoulkd I start with electrics (coils breaking down?) or fuel (vapourisation, pump failure, dirt in carb)?

Anyone experience similar previously?

Start with fuel, then check electrics. Electrically start at the battery

G has a chart in the documents section

As Higgy said start with your fuel.Possibly clogged fuel filter,dirt or water in your tank.Back firing usually means lean especially on the over run so it sounds like it is starving for fuel.If you let it sit for a few minutes then ride it does it again run for a while before the same problem arises?.If so then fuel sounds like your problem.

Cheers
Andrew

P.S. also check your breather tube as that can become blocked causing a vacuum in your tank.

what igntion system does your bike have digiplex or keyosan.
does it seem that it only happens when the bike get warm (after 30 km)
and after the bike sits for 5-10 mins does it start right away but will not rev above 3-4000
without backfireing

Jeez - you had me thinkin' someone stole you ride! Whew!

I had a similar problem . . . I had an Earwig stuck in my fuel line!!! Go figure

I had a somewhat similar problem just recently: I would start the '87 750 Paso up no problem and it would idle fine and I'd ride off and it would then die. I'd pull over and it would not easily restart until maybe five minutes passed. Then I'd ride for 30 miles or so and the vertical cylinder would drop out. I'd pull over and another SF Bay Area Pasoista (Gunther) and I would fiddle with the electrics— checking connections, checking for spark, switching plugs etc. Ten minutes would pass and it would start up again fine and both cylinders would be firing. We'd ride off but after a few miles the vertical cylinder would drop out again. This happened several times over until we abandoned the idea of a long ride. As I tried to get home on the interstate highway, both cylinders died. By then, it was time to call the wife and get the truck and trailer out for a rescue. After a lengthy diagnosis (we all thought the problem was an ignition coil, bad wiring or a pick-up coil), the problem turned out to be the new fuel filter I had just installed when I replaced all the fuel lines and had the tank leak welded up and the tank cleansed of the loose rust within. I had plumbed the new fuel filter upstream from the fuel pump (as the old one was) but it seems the fuel pump just couldn't cope with the added strain of sucking the fuel through the new filter (even though I had installed it with the flow arrow pointing in the correct direction), hence starving the vertical cylinder first, then both cylinders of fuel. After removing the filter, it was apparent that there was a bit of staining from some minute rust particulate that passed through the filter in the tank at the petcock, but we could still easily blow our breath through the new inline filter. I guess the fuel pump is a sensitive old pump even though it is a very low pressure pump. Upon removal of the new fuel filter, the Paso has run perfectly under all conditions for 200+ miles. From now on, I'll just rely on the petcock filter and the filters at the fuel line banjos at each of the Dellorto PHM40's. Strange but true...

Randtcassel,
sounds as though your old fuel pump just that. Old. I think you found the limit of what it can do at this point. While I haven't taken a fuel pump apart, it does have moving parts, and they do wear out over time. I suppose the correct thing to do is to check to see what pressure it is putting out. Easy way is to just disconnect the fuel line from the bottom of the tank and direct it into a bucket and turn on the key and see what output looks like.

Do you still have the restricting jet in the fuel line? Maybe time to yank it out.

Cheers,
Phil

Hey Phil:

Thanks for your response and knowledgeable opinion. I have previously remove the restricting jet in the fuel line. I wish there was either a viable replacement for the fuel pump that was a plug and play solution or a way to eliminate the item from the circuit. But for now, I'll just ride 'till it fails. I had a great 220 mile ride yesterday mostly through the Santa Cruz Mountains:

Part 1: http://g.co/maps/4622z

Part 2: http://g.co/maps/5j3du

No problems, just temps in the nineties.

Best, Randy

I really should have been out there too. Great roads.
We should meet up at Alices for a ride some weekend.
Cheers,
Phil in Fremont.