I bought my 750 sport with the fuel pump removed. It seemed to run fine. After more time and longer trips, it started popping or cutting out, resulting in an instant power loss and flaming backfires t jg en straight back to running fine. I was thinking that the carbs started getting fouled but more i read about the fuel pump I wonder if this is the behavior of gravity fed carbs. I have dellortos. Could this be happening because I'm low in fuel and there is not enough pressure head to fuel the carbs? I bought the bike from Maico88. He had a post that makes me wonder...

Has anyone ever successfully run dellortos with no fuel pump?

Have a search through ducinthebay (Phil) posts he has been running gravity feed for a fair while with no issues I can remember being posted about, the other thing is that if it was running fine, then started acting up could be a raft of reasons as you have written, some rubbish in the tank, bad fuel, float needles, electrical, dud plug or cap, H/T leads, coils, the list does go on and on.

Good luck with it.

Cheers

Peter

Yeah ,I was thinking electrix , specially if it has a digiplex , sounds more like poor connections/volt drop to the digiplex

Actually, I do run the fuel pump, and a return line, with my dell'0rtos.
- If you haven't already, get new coils. 20 year old coils can't be trusted. Dyna Coils are nice. Stock coils don't allow you to change out the high voltage leads, and coils get flaky when they get hot.
- Of course, clean the carbs, at least pull the float bowls and see if anything is hanging in there.
- Throw in a bit of Sea Foam or other fuel treatment that will absorb water that may be lurking in your tank.
- I had intake manifolds that did not have o-rings installed, but had silicone sealing it. Modern fuels disintegrate silicone after some time, and the bike ran worse when hot, and generally just got worse over time. New intake o-rings made a HUGE difference.
- Since you don't have a fuel pump, then you need a fuel filter suitable for gravity feed. Confirm that fuel flows freely through it. A fuel filter designed for a pump, may have too much restriction for gravity feed.
- The fuel petcock is always suspect. Some crap in the tank can clog it quick, then fix it self just as quick.
- Yeah, electrics can be erratic, and create the symptoms you mention. Lots of chances for failure in the system. Check everything that feeds the coils and computer.
- If you feel that the carbs aren't getting enough fuel, you can add a vacuum operated fuel pump from a Monster or Yamaha. There's a string on it in here on the site somewhere. Cheap on e-bay.
- Balance your carbs. I use the Twin Max, and it works pretty well. Start with the Ducati Cuddle to get close. I run my rear cylinder/carb one step richer on the main.

OK, I'm just rambling on now. The on and off again nature of your problem could be a lot of different things.

Cheers,
Phil

Petcock have a small net filter inside tank... It's a cheap and fast job to clean it!

I'll start with float bowl and petcock. It seems more fuel than spark but who knows. Good excuse to buy some new Dyna coils, but I didn't think coils usually went bad. I know wires and caps do. Whatever it is, it happens for a split second then it's gone and back to running strong. It might cough a few times back t oback if I don'tease off, but, i usually back off throttle and it goes smooth again. Gotta love old bikes!

That does sound like some type of fuel starvation, my Sport would have the odd miss and cough at trackdays when the tank was getting low on fuel, even though it had the fuel pump, put it down to surge in the tank under hard braking and acceleration, and the pickup in the tank sucking air i/o fuel.

It never did it road riding though.

Be interested to read what it turns out to be.

Cheers

Peter

Testing theories now. No work done, filled tank and ran it hard on a short ride in 5 degrees. No backfires - might actually be lack of fuel pressure below half tank. Will get to float bowls and filter soon as i can, stay posted...

check out the thread on the 906 tab about vacuum fuel pumps.

Okay, I took up dirt bike racing and got a little lost on getting my 750 Sport running well again.

I bought a Mikuni dF52136 vacuum fuel pump.
mikuni pump.JPG [ 11.43 KiB | Viewed 13314 times ]
I now realize I have no idea how to install it. I have the dual DellOrtos. There is a cap screw sticking out of each of my intake manifolds (manifold going from carb to cylinder). Do I put an air nipple into each of those, run it to a T, then into the vacuum line of the pump? Will this pump work? It has 4 nipples with arrows. 2 arrows are going out of the pump, one arrow is going into the pump and one nipple has no arrows (is this the vacuum?). Any help would be greatly appreciated. I now know this may not work...

Update, is this nipple the vacuum line from the carb?
vacuum nipple.jpg [ 66.32 KiB | Viewed 13312 times ]
Each carb has this nipple, this one just has a hose that goes to the bottom of the bike like a drain. The other carb's nipple has no hose. If those are the vacuum lines, I think I can figure this out.

Can I put a nipple in this screw hole (where blue arrow is pointing at the screw) and use that as the pulse vacuum?

yes. The only thing is that you will have to remove the vacuum line for the fuel pump if you sync the carbs as that is where you would connect the sync gauge.