ST1100 fuel problem

The problem was when we went for a ride the other day the bike ran fine till it got down to about 1/4 of a tank right on 300k's, (Been that low before), it started to loose power then onto 2 cylinders so pulled over and turned it off opened the petrol cap and after a few min's tried to start it but rough and on 2 so sat there for about 15 min's then pushed it to top of the hill (not far thank heavens) rolling down I clutched it and onto 2 for a bit then onto 4 and never missed a beat till we got to town 60k's away filled up been fine since, it was a very hot hot day.
Any ideas on what the problem maybe and how to fix it, I've only had to bike for a few months so I've ordered fuel & air filters.
Wayne

Hard to diagnose remotely, the usual suspects would be a punctured diaphragm in the auto fuel-valve/pet-cock and/or the fuel pump going frizz...

Sounds like a heat problem with the fuel pump.

Check this out.

If it's the pump , you may want to replace it with a LOW PRESSURE auto fuel pump off an early Honda car with a carburetor. I did that.

Try a bypass of the vac. operated fuel valve. It is free, quick and easy. Can be easily restored if it isn't the problem.

Instructions are some where on this site I'm sure.

Thanks very much for the info I like the car fuel pump idea was thinking of putting in an inline external pump but it's all fuel for thought,
Thank you. Wayne

Have you tried the vac. valve bypass? It's free and easy. Your problems sounded just like mine did. 2 hose clamps and plugging a vac. line. Go ride. The valve is by your right knee under the tank cover. Could save you some money and time.

https://www.st-owners.com/forums/showthread.php?89040-ST1100-Fuel-Pump-Replacement/page13 sounds like hot fuel pump syndrome look at these posts an easy fuel pump change without welding all kinds of brackets, uses vent hose and the original pressure regulator from the old pump. Some have not used the vent hose or the original pressure regulator and have not have any problems.

another "Check the vacuum petcock" vote here, then if not bad, look at the pump. Once apart, it is rater easy to see when the diaphragm is bad, and normally you can pull the spring, flip it to seal the fuel seat area, put it back together, and plug the vacuum line and go until a better fix is done (or like my Black 91, until the heat death of the universe .. nearly 60,000 miles on that bypass )
Neither bike of mine has had a fuel pump issue.

yet.

don't jinx me!

ST1100Y said:

Hard to diagnose remotely, the usual suspects would be a punctured diaphragm in the auto fuel-valve/pet-cock and/or the fuel pump going frizz...

Click to expand...

a punctured or cracked diaphragm will have fuel leaking into the vacuum line. If the hose is soft of any traces of fuel suspect the vacuum cut off valve. It also can be gummed up internally, its simple to take apart to check. When I thought my valve was sticking(on a desolate road 60 miles to the nearest town) I just took the spring out so it would stay open.

Al st1100 said:

a punctured or cracked diaphragm will have fuel leaking into the vacuum line.

Click to expand...

Actually not, vac diaphragm and fuel ways are hermetically separated... (the fuel valve itself would need to break to create a leak...)

Thanks for all the replies, it's given me a lot to look at when the fuel and air filters arrive I'll start work and hope its one of the easy fixes and not the very costly fuel pump, can only hope. Thanks once again to all.
Wayne

Your problems sounds exactly like my own three years ago...high ambiant temps coupled with low fuel levels. Pump problems, my friend. When I did a bit of research on a substitute, I read thru the threads. At the time NO ONE was happy with the experiment after about a year of use.(do the fuel shut off bypass as others have suggested as a first step). The replacement pump is expensive, but only hurts once

An auto LOW PRESSURE fuel pump ( for a carbed engine ) like I installed on my ST1100 are a heck of a lot cheaper than the OEM pump and probably more trouble free. I bought a close-out Delphi pump from Rock Auto for $16. In fact, I bought two and carry one as a spare- just in case. That way I will never need it.

They don't have any of those left, but you can get another make from Rock Auto for a good price. Look for a pump for an '86 Honda Accord WITH a carburetor, not F.I. I just looked at what they stock, and I would get the Valeo 347256. it has a pressure rating of 0.1 Bar which is about 1.5 psi. That would be a very good choice. They are $36 .

ST1100Y said:

Actually not, vac diaphragm and fuel ways are hermetically separated... (the fuel valve itself would need to break to create a leak...)

Click to expand...

fuel on one side of the diaphragm, vacuum on the other side.. pull the diaphragm off and look at the holes to the fuel lines,, there are no o rings on valve itself to stop or seal fuel from being on the diaphragm side

the_gr8t_waldo said:

Your problems sounds exactly like my own three years ago...high ambiant temps coupled with low fuel levels. Pump problems, my friend. When I did a bit of research on a substitute, I read thru the threads. At the time NO ONE was happy with the experiment after about a year of use.(do the fuel shut off bypass as others have suggested as a first step). The replacement pump is expensive, but only hurts once

Click to expand...

$15 ouch http://www.ebay.com/itm/New-LIFETIME-Warranty-In-Tank-offset-Inlet-Fuel-Pump-and-Kit-01-/231316730377?fits=Year:1997|Make:Honda&hash=item35db8d3209:g:QU8AAOSwyZ5Umk6E&vxp=mtr

Al st1100 said:

$15 ouch http://www.ebay.com/itm/New-LIFETIME-Warranty-In-Tank-offset-Inlet-Fuel-Pump-and-Kit-01-/231316730377?fits=Year:1997|Make:Honda&hash=item35db8d3209:g:QU8AAOSwyZ5Umk6E&vxp=mtr

Click to expand...

Wrong Pump !! That's a 300 KPascal pump ( 43 psi ) . You need a LOW PRESSURE pump for a carb, not F.I.

Al st1100 said:

fuel on one side of the diaphragm, vacuum on the other side...

Click to expand...

I suggest to take one apart, examine it and report back...

Jim Van said:

Wrong Pump !! That's a 300 KPascal pump ( 43 psi ) . You need a LOW PRESSURE pump for a carb, not F.I.

Click to expand...

My bad , too much in a hurry, $22 http://www.ebay.com/itm/Airtex-E8371-Electric-Fuel-Pump-/251958904286?hash=item3aa9ebc5de:g:C00AAOxyXDhSiCSW&vxp=mtr 2-4 psi... look in fuel pump articles easy

I was looking at the Airtex on Ebay from the link you sent Al and I notice it's 2-4 psi and the standard pump is 1-2 psi I was wondering if I have to run a fuel regulator in the line so as not to put to much pressure on the carby floats and flood the motor or is it a straight change over, also does it come with filter and which is the best to get if it don't
Wayne

Good question, but I think the carb float needle valve in the ST1100 carbs can handle a few extra psi without a problem. The ST1100 float needle valves look similar to the needle valves used in an auto carb. The Delphi pump I have been using for the last several years has worked fine.

If the Airtex doesn't come with a sock type filter , you can get one at any auto parts store. They will have a number of different styles available. I got mine at my local auto parts store. It will snap into the fuel inlet on the pump.