Article [11] ST1100 - Fuel Pump Replacement

Re: ST1100 - Fuel Pump revisited

:confused:There are a lot of opinions about the st1100 fuel pump. After my 2nd stall, I verified no fuel pressure. Once it cooled down it I had pressure but not what it should be. Bought an Airtec pump to install but I read on a post that some didn't last that long. So I decided to dismantle the oe pump. The oe pump has a check valve and a fuel pressure regulator built into the black cap that the hoses connect to. If you cut the screen, take the cap assemble and if you into the inlet port(from fuel pump)you will find it takes quite a bit of pressure to open the check valve (to get fuel thu). Now if you block the outlet port it take a lot more pressure to get air thu, as it does (sound like a horn) the pressure is released thu a pressure valve, small brass plate located next to the inlet port. In my opinion it take too much pressure to get fuel by the check valve. Why it has a check valve is beyond me, there is a vacuum shut off already. I wanted to use the old pressure regulator with the Airtec pump so I pryed the clips back, to open the regulator cap. The I gently pryed out the check valve, back side of inlet port, threaded inlet port 1/8 pipe and installed a 90 deg ,5/16 hose fitting. snapped cap back together making sure 2 o rings are in place. I installed the regulator inline a shown in the last picture. Cut the vent hose to fit. 800 miles currently... #1 shows inside of cap with ck valve removed Pic #2 shows threaded fittingIMG_0480.jpgIMG_0473.jpgIMG_0473.jpgView attachment 153784IMG_0485.jpg next to pressure regulator valve. Pic # 4 shows regulator reassembled Pic #5 shows final assembly. I feel with out the check valve even a week pump will get the gas to the carbs (no restrictions) and the fuel needs somewhere to go when its no needed, Idle or long down hill. I'm planning on putting on a lot of miles ... will keep posted
 
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Interesting. Curious what the fuel pressure is coming out of the tank in this configuration. I ended up with an external regulator in the location of the vacuum cut off.
Without it the bike was running a bit rich, went from an average of 45mpg to 35.
Didn't need to use the choke at all. With the regulator I'm back to 42.
 
Put a pressure gauge on today had 1.5 to 2 psi-- had good flow/ about 8 oz with two key on cycles--- I don't think it needs much pressure after all how much pressure is there on a gravity feed system
 
Sounds about right.
Before I added the pressure regulator mine read 4-5 psi.
Haven't checked again with the regulator because I broke the gauge when I dropped it.
 
The other day I was riding down the interstate and the bike lost power, coasted over to the shoulder and waited about 15 min and she started back up. So I read these posts and ordered an Airtex and a Pressure Regulator. I removed the vacuum shutoff, added the pressure regulator and backed out the pressure screw. I am reading 0 psi on the gauge (with the OEM pump). The tank hose is connected to the bottom inlet of the regulator and the carbs connected to the middle outlet, as is the pressure gauge on a second port of the regulator. Is that the correct use of the pressure regulator? Am I just not getting any pressure from the OEM pump? I haven't installed the airtex yet, I am a little hesitant to do so.
photo.jpg
 
regulator should have a flow direction , if it's on right you have o pressure. should be running or read pressure when the key is first turned on -- always check flow, straight hose into a container. When the key is turned on the pump will energize for a second or two. should then stay on when running, and verify power to pump with a test light
 
Al st1100 said:
regulator should have a flow direction , if it's on right you have o pressure. should be running or read pressure when the key is first turned on -- always check flow, straight hose into a container. When the key is turned on the pump will energize for a second or two. should then stay on when running, and verify power to pump with a test light
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Thanks for the reply. All of the electrics are working, one for time period at key on then on all the time after start. I have flow coming through the regulator with the regulator backed all the way out. I think the problem is the regulator, I bought the wrong one. It has an adjustable range of 0-150 psi, too much. I believe if I order the OEM pump it will come with the entire assembly, I may go ahead and bite that bullet then rebuild this one as a backup unit and find a 1-4 psi regulator. Anyone need a high pressure regulator?
 
Changing my fuel pump out today, it just stop pumping?? Bike wouldn't run but at full choke and at idle only, give it any throttle and it dies. Disconnected the fuel filter to check pump flow, turned key on flow was only for 1-sec then nothing... Hope all goes well
 
WillySt1100 said:
Changing my fuel pump out today, it just stop pumping?? Bike wouldn't run but at full choke and at idle only, give it any throttle and it dies. Disconnected the fuel filter to check pump flow, turned key on flow was only for 1-sec then nothing... Hope all goes well
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Well good luck with this repair, have you removed or replaced your diaphragm in the fuel tank? Those can cause some problems with fuel delivery also.
 
Having the same problem now with new pump???? Checked power to pump, 12v only for that 1-sec when turning key on then nothing, never powers up again even with engine running..
 
I have also just completed this fuel pump replacement. I left the pressure regulator portion of the OEM unit pretty much untouched. The ?check valve? as mentioned in post #123 is actually the part that regulates the fuel pressure. Removing it sends full pump output to the carbs. I can verify AL?s function of the regulator. By applying pressure at the inlet, you can hear air moving through the regulator body and out the output fitting. By blocking the outlet it takes more pressure to open the bypass valve and it does sound like a horn. This is as it should be. I verified function of the unit by actually setting up the fuel pump in a gas tank mock-up and running gas through the system. The flow at the outlet had a good volume at a low pressure. Clamping off the outlet allowed fuel to flow out of the bypass valve on the black cap unit. I did not re-connect the vent hose. In this configuration, it doesn?t do anything.
Kreemed Tank6X8.jpg
I ran the bike at about 4000 RPM on the highway for about a 15 mile run. Fuel flow to the carbs was sufficient at this speed. There was no fuel starvation so there is sufficient flow and pressure with this set up. It?s still pretty cool here so I won?t get many miles on the new system for a few weeks. Time will tell how long the pump lasts but it should work well.
 
Eagle59 said:
I have also just completed this fuel pump replacement. I left the pressure regulator portion of the OEM unit pretty much untouched. The ?check valve? as mentioned in post #123 is actually the part that regulates the fuel pressure. Removing it sends full pump output to the carbs. I can verify AL?s function of the regulator. By applying pressure at the inlet, you can hear air moving through the regulator body and out the output fitting. By blocking the outlet it takes more pressure to open the bypass valve and it does sound like a horn. This is as it should be. I verified function of the unit by actually setting up the fuel pump in a gas tank mock-up and running gas through the system. The flow at the outlet had a good volume at a low pressure. Clamping off the outlet allowed fuel to flow out of the bypass valve on the black cap unit. I did not re-connect the vent hose. In this configuration, it doesn?t do anything.
Kreemed Tank6X8.jpg
I ran the bike at about 4000 RPM on the highway for about a 15 mile run. Fuel flow to the carbs was sufficient at this speed. There was no fuel starvation so there is sufficient flow and pressure with this set up. It?s still pretty cool here so I won?t get many miles on the new system for a few weeks. Time will tell how long the pump lasts but it should work well.
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Eagle59, just inquisitive, did you check the flow rate with this set-up? I have a Airtex unit in my 97 and did a 3500 mile ride last year with no problems but did not do this set-up. I still have the old pump that runs but not consistent so I removed it. Might be inclined to try this system out. My Airtex is running over the 600cc per minute rate but not by much.

thanks, best, Ed
 
Eagle59 said:
I have also just completed this fuel pump replacement. I left the pressure regulator portion of the OEM unit pretty much untouched. The “check valve” as mentioned in post #123 is actually the part that regulates the fuel pressure. Removing it sends full pump output to the carbs. I can verify AL’s function of the regulator. By applying pressure at the inlet, you can hear air moving through the regulator body and out the output fitting. By blocking the outlet it takes more pressure to open the bypass valve and it does sound like a horn. This is as it should be. I verified function of the unit by actually setting up the fuel pump in a gas tank mock-up and running gas through the system. The flow at the outlet had a good volume at a low pressure. Clamping off the outlet allowed fuel to flow out of the bypass valve on the black cap unit. I did not re-connect the vent hose. In this configuration, it doesn’t do anything.
Kreemed Tank6X8.jpg
I ran the bike at about 4000 RPM on the highway for about a 15 mile run. Fuel flow to the carbs was sufficient at this speed. There was no fuel starvation so there is sufficient flow and pressure with this set up. It’s still pretty cool here so I won’t get many miles on the new system for a few weeks. Time will tell how long the pump lasts but it should work well.
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Did you replace the OEM with an Airtex? Also - tips on best way to remove the pressure regulator you took off the OEM? I'm having a tough time getting it to pop off the rest of the assembly.
 
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EJ
I did not perform a flow rate check but the volume was definitely good. I've only put about 300 miles on the ST so far this spring. I did a short 15 minute run at highway speeds and the the pump kept up with carb demand. The main reason I wanted to incorporate the regulator was to keep fuel coming to the carb bank in as close to factory conditions as possible. I know there are many posters here that have connected the Airtex directly into the fuel supply to the carb bank with no issues. Simpler is better and I hope I have not created an issue for myself later with the path I took. Time will tell I guess.
 
Eagle59 said:
EJ
I did not perform a flow rate check but the volume was definitely good. I've only put about 300 miles on the ST so far this spring. I did a short 15 minute run at highway speeds and the the pump kept up with carb demand. The main reason I wanted to incorporate the regulator was to keep fuel coming to the carb bank in as close to factory conditions as possible. I know there are many posters here that have connected the Airtex directly into the fuel supply to the carb bank with no issues. Simpler is better and I hope I have not created an issue for myself later with the path I took. Time will tell I guess.
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Yea, I ended up pulling my Airtex, when I got back from CA last year it sounded like it was a little louder than the initial install, pulled the line to do a flow check a few months back and it was way over 600cc per minute flow. Moved to a Quantum pump and added the same set up as you. Flow check with the newer pump were better by far and much quitter design and they have a life time return on their pumps. Results are still out for long trips but the last several hundred miles to include twistes' have been just fine. So we're good to go.............;)

The only problem I had was negotiating the tank hole with the way the clamps and hoses lined up....:eek::

Best, Ed
 
I am now having a fuel issue with my 94', bike died when hot. With all the posts and opinions here, is there a "best" after market pump option utilizing wiring already in place? Thanks .............Rod
 
Eagle59 said:
EJ
I did not perform a flow rate check but the volume was definitely good. I've only put about 300 miles on the ST so far this spring. I did a short 15 minute run at highway speeds and the the pump kept up with carb demand. The main reason I wanted to incorporate the regulator was to keep fuel coming to the carb bank in as close to factory conditions as possible. I know there are many posters here that have connected the Airtex directly into the fuel supply to the carb bank with no issues. Simpler is better and I hope I have not created an issue for myself later with the path I took. Time will tell I guess.
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Did over 6k in the last year with no problems with fact regulator and airtec pump/ when changing something that factory engineers designed it may work but at some point there may be a unintended consequence. I ask if it doesn't need it why would the put it in? After all don't they try to pinch every penny in production? ..... Al
 
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