Fuel pump issues '93 750ss? - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 130 (permalink) Old Apr 16th, 2019, 10:43 pm Thread Starter
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Fuel pump issues '93 750ss?

After a few minutes on the highway I bog out and have to pull off as it dies. Its acts exactly like Im out of gas, but Im not. After shutting it off, it runs fine for a while then it does this over again. Im hearing a clicking sound from the tank possibly. I am getting a lot of backfire when this happens.

I have been able to ride around the city with no issues, as soon as I hit the highway this happens.

It is not draining the battery or acting funny at the gauges or headlight. The bike has a new regulator and spark plugs.

It has the 2-1 DND exhaust conversion which runs great, so far without jetting, at all RPMs.

I recently purchased my bike from its original owner with 14,500 miles. It is a near mint, all original bike. The only mods are the 2-1 exhaust.


Im hoping Ducvet or anyone can help...thanks guys!

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550
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post #2 of 130 (permalink) Old Apr 16th, 2019, 10:59 pm
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On the supersports the fuel pump is on full time, see if you hear it cutting out. unlike a injected bike this pump is on 100% when running.
make sure the tank is getting air to replace the fuel used or it will not get fuel, this happens when the air line into the tank is pinched off, possibly a check valve installed backwards. make sure you can blow air into the tank but not out.

Check that you do not have a clogged fuel filter inside the tank or that the gas tank was sealed with a coating like por-15 or kreeme. If something is plugging the fuel exit then you will starve the bike under steady full acceleration. go after the fuel starvation first and if nothing shows up look at spark which is less likely.
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post #3 of 130 (permalink) Old Apr 16th, 2019, 11:48 pm Thread Starter
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Originally Posted by ducvet View Post
On the supersports the fuel pump is on full time, see if you hear it cutting out. unlike a injected bike this pump is on 100% when running.
make sure the tank is getting air to replace the fuel used or it will not get fuel, this happens when the air line into the tank is pinched off, possibly a check valve installed backwards. make sure you can blow air into the tank but not out.

Check that you do not have a clogged fuel filter inside the tank or that the gas tank was sealed with a coating like por-15 or kreeme. If something is plugging the fuel exit then you will starve the bike under steady full acceleration. go after the fuel starvation first and if nothing shows up look at spark which is less likely.
Thank you Ducvet! I really appreciate your help. That's good to know about the fuel pump. Ill start by checking these things and let you know what I find.

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550
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post #4 of 130 (permalink) Old Apr 17th, 2019, 12:00 am Thread Starter
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Quote:
Originally Posted by ducvet View Post
On the supersports the fuel pump is on full time, see if you hear it cutting out. unlike a injected bike this pump is on 100% when running.
make sure the tank is getting air to replace the fuel used or it will not get fuel, this happens when the air line into the tank is pinched off, possibly a check valve installed backwards. make sure you can blow air into the tank but not out.

Check that you do not have a clogged fuel filter inside the tank or that the gas tank was sealed with a coating like por-15 or kreeme. If something is plugging the fuel exit then you will starve the bike under steady full acceleration. go after the fuel starvation first and if nothing shows up look at spark which is less likely.

Before I bought the bike the carbs needed work...it was leaking fuel from the carbs the first day I looked at it. A mechanic from a local bike shop added an external fuel filter with new lines and cleaned out the carbs, then it drove fine and is not leaking fuel at all.

I have driven this bike for a hundred miles before this started happening. Ive had it near 100mph once with no issues. I have driven it on the highway a couple of times prior to this happening and Ive done some twisties at a park for extended periods with no issues.

Heres what I found so far:

+++I am hearing a lot of clicking from the tank area or under it, when it bogs out. Im also hearing a click when I first drive off that Im not sure Ive ever heard before. It sounded like an old school clock ticking once per second, at a stop light today.

When I blow air into the tank, through the check valve, I can hear air going into the tank and I can hear it coming back out of the cap/carrier at the same time. When I put my hand over the cap it quiets the tiny amount of escaping air.

(I restored the entire fuel cap weeks ago, it had sludge inside the lock mechanism. Since that cleaning it closes flush and functions much better. I have not checked the green carrier gasket yet, but I will soon. This is the tank that leaks when propped up that we talked about).

When I blow back into the check valve, I can blow air out of the tank. I can hear air coming out of the other end of the tube at the ground if I cover it with my finger then remove it...then I can hear it releasing. I have to blow hard for a tiny amount of air to come out.

When I turn the key on, the fuel pump stays running, I gave it about 30 seconds a couple of times and it didn't change in pitch or stop. It did start with a higher pitch the first time, then it settled and ran steady. Is there a way to check this as Im stalling out? Do they click when they go out?

I was afraid to look, but I took a flashlight to the tank. It is slightly discolored in spots with very small amounts of rust around the fittings. Overall not as bad as I thought. Im not seeing debris.

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550

Last edited by ifly65; Apr 17th, 2019 at 2:01 am.
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post #5 of 130 (permalink) Old Apr 17th, 2019, 3:06 am
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Yes, it does sound like a clogged fuel filter and probably pick up screen. Fuel pump is working hard, better open it up.

1991 900SS
1995 900SS SP #746
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post #6 of 130 (permalink) Old Apr 17th, 2019, 7:58 am
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And if your mechanic added a external fuel filter you now have 2 fuel filters, it is possible the added restriction is not helping. If you are not getting anything in the external filter remove it temporarily and see if it improves. You can decide later which one you want to keep but I will tell you that carby fuel pumps are low pressure and I do not change the oem filter often at all maybe once in 20,000-30,000 miles where a fuel injected filter gets changed every 7,000-12,000.

I would chase the clicking to see if it is in the tank (pump) or under the tank. First make sure both battery terminals are tight at the battery, look for signs of arcing. The noise could be the pump working hard as RockAz said other than that there should be nothing making that noise. Check for exhaust leaks at the heads, make sure the head nuts do not spin with your fingers. Listen carefully to the alternator cover, flywheels did fall off/come loose in this era so make sure you do not see the flywheel wobbling in the timing window.
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post #7 of 130 (permalink) Old Apr 17th, 2019, 11:07 am
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I once chased a similar problem on my bike, it turned out the ring terminal on the positive battery lead for the harness [under the red cap] had fractured and was making intermittant contact. The clicking was the pump relay turning on and off. You may also want to check/substitute the relay and if it has the original fuse in it, I've seen the fuse wire break inside and only with really close inspection could you tell it was broken.
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post #8 of 130 (permalink) Old Apr 17th, 2019, 12:05 pm Thread Starter
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Yes, it does sound like a clogged fuel filter and probably pick up screen. Fuel pump is working hard, better open it up.
Thanks RockAZ! Ive seen a post on here somewhere showing the filter removal...that can be done from the top correct? Where is the pick up screen? Im not seeing it in my tank pic in the work manual.

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550
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post #9 of 130 (permalink) Old Apr 17th, 2019, 12:06 pm Thread Starter
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Originally Posted by wdietz186 View Post
I once chased a similar problem on my bike, it turned out the ring terminal on the positive battery lead for the harness [under the red cap] had fractured and was making intermittant contact. The clicking was the pump relay turning on and off. You may also want to check/substitute the relay and if it has the original fuse in it, I've seen the fuse wire break inside and only with really close inspection could you tell it was broken.
Thanks wdietz! Ill check these things for sure. Is the pump relay under the tank?

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550

Last edited by ifly65; Apr 17th, 2019 at 12:22 pm.
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post #10 of 130 (permalink) Old Apr 17th, 2019, 12:13 pm Thread Starter
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And if your mechanic added a external fuel filter you now have 2 fuel filters, it is possible the added restriction is not helping. If you are not getting anything in the external filter remove it temporarily and see if it improves. You can decide later which one you want to keep but I will tell you that carby fuel pumps are low pressure and I do not change the oem filter often at all maybe once in 20,000-30,000 miles where a fuel injected filter gets changed every 7,000-12,000.

I would chase the clicking to see if it is in the tank (pump) or under the tank. First make sure both battery terminals are tight at the battery, look for signs of arcing. The noise could be the pump working hard as RockAz said other than that there should be nothing making that noise. Check for exhaust leaks at the heads, make sure the head nuts do not spin with your fingers. Listen carefully to the alternator cover, flywheels did fall off/come loose in this era so make sure you do not see the flywheel wobbling in the timing window.

Thanks again Ducvet and all of you guys! I cant tell you how much I appreciate this help on this forum. Im pretty sure my connections are good but Ill check again. The clicking really sounded like it was coming from the inside of the tank...which I think was the pump. It didn't sound like it was coming from the engine or alternator flywheel but that is also great to know and Ill check both that and my exhaust. I forgot to look at the new filter for debris and I will try removing it.

Ducati 1993 750ss/cr
The past: Honda 1000RR Fireblade F2 Yamaha R6 xj700 xs400 Suzuki GSXR600 Kaw 750 550
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