750 fuel pumps

[Maico88]

I took my 750 sport to Daytona this weekend. I really like to ride it. However, the fuel pump stopped pumping fuel 3 times over the weekend. Each time I was able to get it to start pumping by tapping lightly on th pump. All of the electrical circuits check out ok. I am considering removing the pump, cutting off the fuel line close to the bottom of the tank and letting gravity be the pump. The bike has 36 phf dellortos. Does anyone have thoughts on the advisabilty of the mods I am considering?

[ducinthebay]

I thought the same thing, but it won't work unless you do some further modifications to the inside of the tank. I tried doing the same thing a few years back. If you simply remove the fuel pump, filter and hoses in the tank, the pickup in the tank is half way up the tank, and you will "run out of gas" with a half a tank of gas still in the tank. In my bike, the steel lines are brazed into the tank. Knowing Ducati at the time, there may be quite a bit of differences between bikes, so your bike may be different.

That being said, you may want to check out everything in the tank. There is a filter, and if its clogged, the fuel pump may be working too hard and shutting down. Fuel pumps are generally thermally protected, for obvious reasons. You may have just reset it when you stopped and went to tap on the pump. The wires to the pump may be intermittent, or loose. They are held on with very small nuts, I think 3 or 4mm as I remember. The hoses also have some problems as they degrade over time, and may be sending small pieces into your fuel pump. Bits of rust will also create problems in your pump. Make sure the prefilter sock is still good. When replacing your tubing, always buy tubing for fuel injection, and use F.I clamps, as it is a higher standard tubing and less prone to degradation while sitting in fuel all its life, and the clamps offer better distribution of force without chewing up your tubing. If you use gasahol, be aware that the alcohol will disolve any spare paint in the tank, and that too will clog your pump or filter. ( voice of experience here). Also check your electrical connections to the tank. As with all bikes, clean all the connectors and put some silicone dielectric grease on the connectors.

ST's have had problems with the tubing just degrading to the point that it won't hold pressure anymore, and the bike dies. $1.00 worth of good tubing, and your are back on the road.

Another thing to check is that huge petcock. If that has some obstruction, then the fuel pump may be working too hard. I removed my petcock and replaced it with a banjo bolt and fitting. Its a 10mmx 1.0 thread into the tank. I didn't see the need for a petcock with a fuel pump in the system. I will be adding a vacuum petcock from a Monster just for my peace of mind, but I've never flooded the bike in the past 5 years.

Of course, there is always the possiblity that your pump has just flat died.

If you can get into the tank to cut off the steel lines, then gravity will easily do its job to feed your Dells. Be careful of sparks, even after you rinse it with water and thoroughly dry it. I couldn't find a graceful way to do this, so I just rebuilt what I had, and everything worked out just fine.

Cheers,

[samandkimberly]

I just brazed a 1/8 pipe thread fitting into the back underside of my tank; there are any variety of fittings that will screw into that. The fitting is available in any hardware store, anyone with basic welding skills can put it in, and you can locate it in far enough that you don' thave to worry about the hear distorting the paint. For that matter, you could probably use a bulkhead fitting instead and seal it with epoxy. Plus, you can go back to the old system this way if you want to. Welding tanks is generally not nearly as dangerous as some people make it out to be. drain it, wash it out with soapy water (including the steel lines) and it will weld perfectly safely.

Don't forget to add a fuel filter.


Sam

[Maico88]

Thanks for the ideas. I replaced the in-tank filter, oil and oil filter, and the timing belts shortly after I bought the bike since I really had no idea when those had been changed. I also replaced the spark plugs (to Champions). I intend to check all connections (especially ground connections) that have any thing to do with the fuel pump circuit. If I am able to rebuild or replace the fuel pump I probably will. I asked about removal of the pump because I don't understand why a carbureted bike with the tank higher than the carbs needs a fuel pump.

[samandkimberly]

I asked about removal of the pump because I don't understand why a carbureted bike with the tank higher than the carbs needs a fuel pump.

Because the float bowl on the OE Weber carb is much higher up!

Sam

[ducinthebay]

Yeah, I haven't figured out why the Sport had a fuel pump either, but then again, I don't have the stock carb setup either (36 Dells). Its more of mystery why they kept that antique petcock after they added a fuel pump. It seems that there were a bunch of junior engineers working on it, and they didn't talk to eachother, or their managers were feuding. Did the F1 have a fuel pump?

One of the reasons to run a fuel pump is to overcome any restriction that a good fuel filter (or dirty one) may pose. It also delivers constant pressure no matter what level of fuel you have.

One of the other oddities of the Sport is the grab strap on the seat. That is a complete relic of the 60's and 70's. What that is doing on a sport bike from 1990 is just baffling.


Cheers,