ST1100 Fuel Pressure

[wingingit2]

I have a bike that that has been badly neglected. The carb slide diaphragms were melted with carb cleaner were and the fuel pump was bad. I replaced the fuel pump with a Quantum brand unit and bought a new set of carbs. It was cheaper to buy a set of carbs than to replace all the rubber parts inside.
My problem is that after going over the replacement carbs, which were in perfect condition, I had a flooding problem. All the plugs were wet. I then replaced the float valves, needle & seat & filter. The carbs are still flooding.
The fuel pump is putting out 9 psi. Is that too high?? Is it pushing past the float needle?

 

[dwalby]

There are many forum members who have replaced the fuel pump, do a search on ST1100 fuel pump replacement and you'll find plenty of info. I think the correct pressure is in the range of 1-2psi, so 9 would likely be the cause of your flooding.

 

[bdalameda]

9 is to high - also check your float level.

 

[Ron]

Pressure should be 1-2 psi.

 

[Jim Van]

There are many forum members who have replaced the fuel pump, do a search on ST1100 fuel pump replacement and you'll find plenty of info. I think the correct pressure is in the range of 1-2psi, so 9 would likely be the cause of your flooding.

Just curious, what is the spec on the Quantum replacement pump ?

 

[fnmag]

Hope you can sort out your fuel pump/carb problem.
Welcome to the forum.

 

[wingingit2]

Here is a link to the pump. https://www.highflowfuel.com/ag-1320125.1317987.1317818.1320306-motorcycle-scooter-1992-honda-st1100.html
It shows a fitment from 1990 to 2003. I don't see any specs.

 

[wingingit2]

No answer at their phone number, maybe too early in the morning. I sent an email and am waiting for a reply.

 

[Jim Van]

Quantum says it should work on a ST1100, but 9 psi is way too much pressure.

A lot of guys have used the Airtex E8371 which has a max pressure of 4 psi. I'm using a Carter low pressure pump with an inline check valve to help reduce the pressure and as a safety feature since I have removed the OEM vacuum actuated fuel shut-off valve.

 

[wingingit2]

Never heard from Quantum so I ordered an Airtex as recommend. Ill' let you know if it makes a difference.

 

[wingingit2]

I did get a reply by email waiting for another reply.

 

[wingingit2]

I used the airtex pump and everything was good. No more flooding and fouled plugs.

 

[dwalby]

I used the airtex pump and everything was good. No more flooding and fouled plugs.

 

[fnmag]

I used the airtex pump and everything was good. No more flooding and fouled plugs.

Well done on sorting out the flooding/fouled plug problem.

 

[2000st1100az]

How would fuel foul the plugs before overflowing? I'm in a similar situation and can see too much fuel coming out of the needle orifices. My understanding is that is if the float needles properly shut and prevent the fuel from coming in to the bowl the bike should not be taking in too much fuel to burn. If the bowls fill too high they will overflow and drain through the overflow tube and not go into the intake? I started at 7mm with my float levels and still have to much fuel getting in. I adjusted them again and made the floats close much sooner and still no change. I'm at a loss. Lol
I have the same quantum fuel pump as mentioned.

 

[Uncle Phil]

Buy a fuel regulator and it will probably solve the problem. I bought one like this -

Metal Adjustable Fuel Pressure Regulator for Carburetor Engines Universal W2H7 | eBay

and set it to 1.5 on the 'dial'. You probably don't need to use the 'choke'(technically a fuel enricher) when you start it up either.

 

[jrp]

How would fuel foul the plugs before overflowing? I'm in a similar situation and can see too much fuel coming out of the needle orifices. My understanding is that is if the float needles properly shut and prevent the fuel from coming in to the bowl the bike should not be taking in too much fuel to burn. If the bowls fill too high they will overflow and drain through the overflow tube and not go into the intake? I started at 7mm with my float levels and still have to much fuel getting in. I adjusted them again and made the floats close much sooner and still no change. I'm at a loss. Lol
I have the same quantum fuel pump as mentioned.

The ST1100 does not have overflow tubes. They will leak through the needle orifice down into the intake.