Paso SOS!!

[jklnhyde]

I'll try to make this as short as possible. First, I need to thank higgy for all the help in sorting out the jetting in my Weber--I can finally ride without hiccups and bucking!
Unfortunately, I can only ride less than a mile before the bike just quits!!
While I sorted out the jetting issue on the Weber, I replaced the factory fuel pump with a CB Performance rotary fuel pump. The pump works at 3.5 lbs of pressure (I checked it) and fit almost like it came from the factory. I am getting great flow and excellent throttle response; the idle is smooth, and I can rev the engine effortlessly. In my garage the bike runs fine and offers no indication that it could starve for fuel.

I took it for a test ride down a long country road just yards from my house and she ran amazingly for a few minutes, then the bike coughed once and acted like it had run out of fuel. The throttle went dead and she slowly coasted to the side of the road less than 1/2 mile from my garage. I waited (and listened for the fuel pump) before restarting. I got back on the road, but less than 100 feet later she coughed and stopped running again.
I got smart and turned her around only to have the same exact thing happen 5 more times before I got home.
I looked over the entire fuel system and found the fuel filter dry of fuel--barely a drop!
I had a FULL tank of fuel, the tap was ON, the tank has no debris in it and the fuel pump is running; what is going on??!!
By the way, I test-rode the bike 3 other times on different days and the bike stalled out at the EXACT LOCATION EVERY SINGLE TIME!!Could the fuel pump be cycling itself off for some reason??

Rick

[higgy]

Sounds like you have a problem with the fuel tank,either you have the breather tube and the return tube backwards or the breather tube is blocked up somehow. Something somewhere is preventing the free flow of fuel to the pump.
Where did you finally end up with your jetting?
One more rider turned into a tuner, it is the way of the ducati

[jklnhyde]

You may be right, but on several occasions I undid the fuel cap and left it loose--it made no difference. I had the tubes under the tank labeled properly so I'm 99% sure, unless they've been marked wrong since 1988!!

Rick

[88WhitePaso750]

I had a similar issue with my 750 paso with mikuni 38s on it. Check the fuel filter. Mine was installed backwards by a not so smart dealer, outside element looked good but all debris was on inside. This issue will present as the bike running all day long at idle, but when you are moving at normal speeds you will empty the bowls and the refill rate is hampered by the dirty filter causing it to act like it is out of gas. If it sits for a while then restarts, this may be your gremlin. Mine happened if I had a sustained speed over 60mph.

[jklnhyde]

I did think that a dirty filter could be causing my problem, but I have 2 filters on the Paso. A clear one immediately after the fuel tap (to be able to see any contamination) followed by a factory-type metal cannister filter before the pump. It's the clear one that I look at and see dry of fuel.
I have the fuel return line tee'd off after the pump; could too much fuel be diverted back to the tank? This problem only started after replacing the stock pump with the rotary.
What about the small metering jet in the tee? I removed it thinking routing excess fuel pressure would keep it below the 3.5 lbs threshold...

Rick

[englishstiv]

Hi Rick you say the pump runs dry? Are you sure that the pump is not actually stopping as on my 907ie I had a similiar problem that was caused by a faulty wire within the main connector block. The one you disconnect to take off the tank. The pins inside had corroded. I am assuming the connections/set up are the same for both bikes?
The only difference to your problem was that mine occured as I leaned into the same corners on the same route. The whole engine just spluttered and died. I'd stop wait a second or two press the start button and ride off again until the next bend when it would do the same.

Took a while to find out and suss the problem but an easy fix.

maybe (hopefully) you have the same?

[Mc tool]

This is a long shot but .... are you sure the pump is pumping FROM the tank to the carb and not the other way ? .If the tank was FULL , as you say then the fuel could gravity feed backwards thru the pump to the carb while the pump wasnt running , soon as you turn the key on the pump clears the line ( empty filter ) leaving some fuel in the float bowl. The first run would be a long one as the float bowl would be full , subcequent runs would be shorter as the only chance fuel would have to get to the carb is while your sitting on the side of the road wondering what the phuck is going on

[jklnhyde]

The replacement pump is wired to the stock pump connectors; as far as I can tell the wiring is fine and has never been an issue. I suppose the pump could be shutting off, but I'm not convinced. It has idled in my driveway for 15-20 minutes while I adjusted the idle, mixture screws and air bypass screws. It should have starved for fuel at least once during that time, but never did.
As for the direction of flow, I'm 100% certain it's facing in the correct direction!!

Rick

[Tamburinifan]

What about ignition?
Do you have spark when it stops?

[jklnhyde]

Hard to tell. The bike putt-putts slower and slower until it stops. I can roll on the throttle and hear the carb throat gasping for air. It would be hard to tell if I have lost spark at that moment.
Rick

[Mc tool]

my next trick ( assuming that the new pump has its own relief valve set at 3.5 psi ) would be to plug the return line , and check the strainer at the carb ( part of the carb )

[paso750]

...filter could be causing my problem, but I have 2 filters on the Paso. A clear one immediately after the fuel tap (to be able to see any contamination) followed by a factory-type metal cannister filter before the pump. It's the clear one that I look at and see dry of fuel.

Actually you have 3 filters as there`s another one on the inner side of the fuel tap. It`s a fine mesh filter. If the clear filter is directly connected to the fuel tab and there`s no fuel coming out (when the tab is open) the tap or its filter may be clogged if there`s rust or other dirt in the tank.

G.

[88WhitePaso750]

This must be fuel starvation. I would try removing the output line of the pump and put a piece of scrap fuel line on. Put the open end of that line into a can or old gas can and turn the key on. My bet is you see a trickle instead of a stream. This trickle is enough to run the bike at idle forever, but a couple good whacks on the throttle under load can easily deplete the bowls and cause starvation. It has to be bad pump or plugged input to pump (fuel filter, petcock, internal tank sludge).

Good Luck,

[higgy]

This must be fuel starvation. I would try removing the output line of the pump and put a piece of scrap fuel line on. Put the open end of that line into a can or old gas can and turn the key on.

Very good idea Flow is just as important as pressure,something somewhere has an issue,could even be an air leak somewhere on the carb body

[jklnhyde]

I agree on the fuel starvation. My plan is to plug the fuel return line and test ride. If it runs without stalling then I might put the restrictor jet on the tee and test again with the line back in place. I'm also suspecting that 4 fuel filters could be affecting flow as well, so the clear filter will have to go too. I'll report back with my findings in a few days.
Thanks for all the advice!!!
Rick